Patent Publication Number: US-11394578-B2

Title: Supporting multicast over a network domain

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/024,084, filed on Jun. 29, 2018, entitled SUPPORTING MULTICAST OVER A NETWORK DOMAIN, which is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to communication networks and, more particularly but not exclusively, to supporting multicast in communication networks. 
     BACKGROUND 
     Multicast is used in many types of communication networks to deliver various types of information. 
     SUMMARY 
     Various example embodiments relate generally to supporting Multiprotocol Label Switching (MPLS)-based multicast via a Bit Index Explicit Replication (BIER) domain. 
     In at least some example embodiments, an apparatus is provided. In at least some example embodiments, the apparatus includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least receive, by a BIER border router (BBR) of a BIER domain from an MPLS domain, MPLS signaling information associated with a point-to-multipoint (P2MP) label switched path (LSP) and send, by the BBR toward a device configured to assign a BIER tree label (BTL) identifying the P2MP LSP within the BIER domain, the MPLS signaling information associated with the P2MP LSP. In at least some example embodiments, the MPLS signaling information is received as Multiprotocol Label Distribution Protocol (mLDP) signaling. In at least some example embodiments, the MPLS signaling information includes a forwarding equivalence class (FEC) and an action. In at least some example embodiments, the MPLS signaling information is sent in a BIER signaling packet. In at least some example embodiments, the device configured to assign the BTL identifying the P2MP LSP within the BIER domain is a controller of the BIER domain or an egress BBR (EBBR) of the BIER domain. In at least some example embodiments, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least determine, by the BBR, whether the root of the P2MP LSP is located across the BIER domain from the BBR. In at least some example embodiments, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least receive, by the BBR from the device configured to assign the BTL identifying the P2MP LSP within the BIER domain, the BTL identifying the P2MP LSP within the BIER domain and configure, by the BBR based on the BTL identifying the P2MP LSP within the BIER domain, an entry indicative of handling of packets of the P2MP LSP within the MPLS domain. In at least some example embodiments, the entry indicative of handling of packets of the P2MP LSP within the MPLS domain includes an indication of an MPLS label identifying the P2MP LSP within the MPLS domain. In at least some example embodiments, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least receive, by the BBR via the BIER domain, a packet of the P2MP LSP that includes the BTL identifying the P2MP LSP within the BIER domain, modify, by the BBR, the packet of the P2MP LSP to replace the BTL identifying the P2MP LSP within the BIER domain with an MPLS label identifying the P2MP LSP within the MPLS domain to provide a modified packet, and send, by the BBR via the MPLS domain, the modified packet. In at least some example embodiments, an apparatus includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least receive, by a border router of a multicast explicit replication domain from a multicast label switching domain, multicast signaling information associated with a multicast label switched path and send, by the border router toward a device configured to assign a tree label identifying the multicast label switched path within the multicast explicit replication domain, the multicast signaling information associated with the multicast label switched path. 
     In at least some example embodiments, a method is provided. In at least some example embodiments, the method includes receiving, by a BIER border router (BBR) of a BIER domain from an MPLS domain, MPLS signaling information associated with a point-to-multipoint (P2MP) label switched path (LSP) and sending, by the BBR toward a device configured to assign a BIER tree label (BTL) identifying the P2MP LSP within the BIER domain, the MPLS signaling information associated with the P2MP LSP. In at least some example embodiments, the MPLS signaling information is received as Multiprotocol Label Distribution Protocol (mLDP) signaling. In at least some example embodiments, the MPLS signaling information includes a forwarding equivalence class (FEC) and an action. In at least some example embodiments, the MPLS signaling information is sent in a BIER signaling packet. In at least some example embodiments, the device configured to assign the BTL identifying the P2MP LSP within the BIER domain is a controller of the BIER domain or an egress BBR (EBBR) of the BIER domain. In at least some example embodiments, the method includes determining, by the BBR, whether the root of the P2MP LSP is located across the BIER domain from the BBR. In at least some example embodiments, the method includes receiving, by the BBR from the device configured to assign the BTL identifying the P2MP LSP within the BIER domain, the BTL identifying the P2MP LSP within the BIER domain and configuring, by the BBR based on the BTL identifying the P2MP LSP within the BIER domain, an entry indicative of handling of packets of the P2MP LSP within the MPLS domain. In at least some example embodiments, the entry indicative of handling of packets of the P2MP LSP within the MPLS domain includes an indication of an MPLS label identifying the P2MP LSP within the MPLS domain. In at least some example embodiments, the method includes receiving, by the BBR via the BIER domain, a packet of the P2MP LSP that includes the BTL identifying the P2MP LSP within the BIER domain, modifying, by the BBR, the packet of the P2MP LSP to replace the BTL identifying the P2MP LSP within the BIER domain with an MPLS label identifying the P2MP LSP within the MPLS domain to provide a modified packet, and sending, by the BBR via the MPLS domain, the modified packet. In at least some example embodiments, a method includes receiving, by a border router of a multicast explicit replication domain from a multicast label switching domain, multicast signaling information associated with a multicast label switched path and sending, by the border router toward a device configured to assign a tree label identifying the multicast label switched path within the multicast explicit replication domain, the multicast signaling information associated with the multicast label switched path. 
     In at least some example embodiments, a non-transitory computer readable medium is provided. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing an apparatus to at least receive, by a BIER border router (BBR) of a BIER domain from an MPLS domain, MPLS signaling information associated with a point-to-multipoint (P2MP) label switched path (LSP) and send, by the BBR toward a device configured to assign a BIER tree label (BTL) identifying the P2MP LSP within the BIER domain, the MPLS signaling information associated with the P2MP LSP. In at least some example embodiments, the MPLS signaling information is received as Multiprotocol Label Distribution Protocol (mLDP) signaling. In at least some example embodiments, the MPLS signaling information includes a forwarding equivalence class (FEC) and an action. In at least some example embodiments, the MPLS signaling information is sent in a BIER signaling packet. In at least some example embodiments, the device configured to assign the BTL identifying the P2MP LSP within the BIER domain is a controller of the BIER domain or an egress BBR (EBBR) of the BIER domain. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least determine, by the BBR, whether the root of the P2MP LSP is located across the BIER domain from the BBR. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least receive, by the BBR from the device configured to assign the BTL identifying the P2MP LSP within the BIER domain, the BTL identifying the P2MP LSP within the BIER domain and configure, by the BBR based on the BTL identifying the P2MP LSP within the BIER domain, an entry indicative of handling of packets of the P2MP LSP within the MPLS domain. In at least some example embodiments, the entry indicative of handling of packets of the P2MP LSP within the MPLS domain includes an indication of an MPLS label identifying the P2MP LSP within the MPLS domain. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least receive, by the BBR via the BIER domain, a packet of the P2MP LSP that includes the BTL identifying the P2MP LSP within the BIER domain, modify, by the BBR, the packet of the P2MP LSP to replace the BTL identifying the P2MP LSP within the BIER domain with an MPLS label identifying the P2MP LSP within the MPLS domain to provide a modified packet, and send, by the BBR via the MPLS domain, the modified packet. In a non-transitory computer-readable medium includes program instructions for causing an apparatus to at least receive, by a border router of a multicast explicit replication domain from a multicast label switching domain, multicast signaling information associated with a multicast label switched path and send, by the border router toward a device configured to assign a tree label identifying the multicast label switched path within the multicast explicit replication domain, the multicast signaling information associated with the multicast label switched path. 
     In at least some example embodiments, an apparatus is provided. In at least some example embodiments, the apparatus includes means for receiving, by a BIER border router (BBR) of a BIER domain from an MPLS domain, MPLS signaling information associated with a point-to-multipoint (P2MP) label switched path (LSP) and means for sending, by the BBR toward a device configured to assign a BIER tree label (BTL) identifying the P2MP LSP within the BIER domain, the MPLS signaling information associated with the P2MP LSP. In at least some example embodiments, the MPLS signaling information is received as Multiprotocol Label Distribution Protocol (mLDP) signaling. In at least some example embodiments, the MPLS signaling information includes a forwarding equivalence class (FEC) and an action. In at least some example embodiments, the MPLS signaling information is sent in a BIER signaling packet. In at least some example embodiments, the device configured to assign the BTL identifying the P2MP LSP within the BIER domain is a controller of the BIER domain or an egress BBR (EBBR) of the BIER domain. In at least some example embodiments, the apparatus includes means for determining, by the BBR, whether the root of the P2MP LSP is located across the BIER domain from the BBR. In at least some example embodiments, the apparatus includes means for receiving, by the BBR from the device configured to assign the BTL identifying the P2MP LSP within the BIER domain, the BTL identifying the P2MP LSP within the BIER domain and means for configuring, by the BBR based on the BTL identifying the P2MP LSP within the BIER domain, an entry indicative of handling of packets of the P2MP LSP within the MPLS domain. In at least some example embodiments, the entry indicative of handling of packets of the P2MP LSP within the MPLS domain includes an indication of an MPLS label identifying the P2MP LSP within the MPLS domain. In at least some example embodiments, the apparatus includes means for receiving, by the BBR via the BIER domain, a packet of the P2MP LSP that includes the BTL identifying the P2MP LSP within the BIER domain, means for modifying, by the BBR, the packet of the P2MP LSP to replace the BTL identifying the P2MP LSP within the BIER domain with an MPLS label identifying the P2MP LSP within the MPLS domain to provide a modified packet, and means for sending, by the BBR via the MPLS domain, the modified packet. In at least some example embodiments, an apparatus includes means for receiving, by a border router of a multicast explicit replication domain from a multicast label switching domain, multicast signaling information associated with a multicast label switched path and means for sending, by the border router toward a device configured to assign a tree label identifying the multicast label switched path within the multicast explicit replication domain, the multicast signaling information associated with the multicast label switched path. 
     In at least some example embodiments, an apparatus is provided. In at least some example embodiments, the apparatus includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least receive, by a device associated with a BIER domain, MPLS signaling information associated with a point-to-multipoint (P2MP) label switched path (LSP) and assign, by the device based on the MPLS signaling information associated with the P2MP LSP, a BIER tree label (BTL) identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the MPLS signaling information is received from an ingress BIER border router (IBBR) of the BIER domain. In at least some example embodiments, the MPLS signaling information is received in a BIER signaling packet. In at least some example embodiments, the MPLS signaling information includes a forwarding equivalence class (FEC) and an action. In at least some example embodiments, the device associated with the BIER domain is a controller of the BIER domain or an egress BIER border router (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the device associated with the BIER domain is a controller of the BIER domain. In at least some example embodiments, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least send, from the device toward one or more BIER border routers (BBRs) interested in the P2MP LSP, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the one or more BBRs interested in the P2MP LSP include an ingress BBR (IBBR) from which the MPLS signaling information is received and an egress BBR (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the device associated with the BIER domain is an egress BIER border router (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least send, from the device toward a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least assign, by the device, an MPLS label identifying the P2MP LSP within an MPLS domain and send, by the device toward a root of the P2MP LSP via the MPLS domain, the MPLS label identifying the P2MP LSP within the MPLS domain. In at least some example embodiments, an apparatus includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least receive, by a device associated with a multicast explicit replication domain, multicast signaling information associated with a multicast label switched path and assign, by the device based on the multicast signaling information associated with the multicast label switched path, a tree label identifying the multicast label switched path within the multicast explicit replication domain. 
     In at least some example embodiments, a method is provided. In at least some example embodiments, the method includes receiving, by a device associated with a BIER domain, MPLS signaling information associated with a point-to-multipoint (P2MP) label switched path (LSP) and assigning, by the device based on the MPLS signaling information associated with the P2MP LSP, a BIER tree label (BTL) identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the MPLS signaling information is received from an ingress BIER border router (IBBR) of the BIER domain. In at least some example embodiments, the MPLS signaling information is received in a BIER signaling packet. In at least some example embodiments, the MPLS signaling information includes a forwarding equivalence class (FEC) and an action. In at least some example embodiments, the device associated with the BIER domain is a controller of the BIER domain or an egress BIER border router (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the device associated with the BIER domain is a controller of the BIER domain. In at least some example embodiments, the method includes sending, from the device toward one or more BIER border routers (BBRs) interested in the P2MP LSP, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the one or more BBRs interested in the P2MP LSP include an ingress BBR (IBBR) from which the MPLS signaling information is received and an egress BBR (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the device associated with the BIER domain is an egress BIER border router (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the method includes sending, from the device toward a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the method includes assigning, by the device, an MPLS label identifying the P2MP LSP within an MPLS domain and sending, by the device toward a root of the P2MP LSP via the MPLS domain, the MPLS label identifying the P2MP LSP within the MPLS domain. In at least some example embodiments, a method includes receiving, by a device associated with a multicast explicit replication domain, multicast signaling information associated with a multicast label switched path and assigning, by the device based on the multicast signaling information associated with the multicast label switched path, a tree label identifying the multicast label switched path within the multicast explicit replication domain. 
     In at least some example embodiments, a non-transitory computer readable medium is provided. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing an apparatus to at least receive, by a device associated with a BIER domain, MPLS signaling information associated with a point-to-multipoint (P2MP) label switched path (LSP) and assign, by the device based on the MPLS signaling information associated with the P2MP LSP, a BIER tree label (BTL) identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the MPLS signaling information is received from an ingress BIER border router (IBBR) of the BIER domain. In at least some example embodiments, the MPLS signaling information is received in a BIER signaling packet. In at least some example embodiments, the MPLS signaling information includes a forwarding equivalence class (FEC) and an action. In at least some example embodiments, the device associated with the BIER domain is a controller of the BIER domain or an egress BIER border router (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the device associated with the BIER domain is a controller of the BIER domain. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least send, from the device toward one or more BIER border routers (BBRs) interested in the P2MP LSP, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the one or more BBRs interested in the P2MP LSP include an ingress BBR (IBBR) from which the MPLS signaling information is received and an egress BBR (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the device associated with the BIER domain is an egress BIER border router (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least send, from the device toward a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least assign, by the device, an MPLS label identifying the P2MP LSP within an MPLS domain and send, by the device toward a root of the P2MP LSP via the MPLS domain, the MPLS label identifying the P2MP LSP within the MPLS domain. In at least some example embodiments, a non-transitory computer-readable medium includes program instructions for causing an apparatus to at least receive, by a device associated with a multicast explicit replication domain, multicast signaling information associated with a multicast label switched path and assign, by the device based on the multicast signaling information associated with the multicast label switched path, a tree label identifying the multicast label switched path within the multicast explicit replication domain. 
     In at least some example embodiments, an apparatus is provided. In at least some example embodiments, the apparatus includes means for receiving, by a device associated with a BIER domain, MPLS signaling information associated with a point-to-multipoint (P2MP) label switched path (LSP) and means for assigning, by the device based on the MPLS signaling information associated with the P2MP LSP, a BIER tree label (BTL) identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the MPLS signaling information is received from an ingress BIER border router (IBBR) of the BIER domain. In at least some example embodiments, the MPLS signaling information is received in a BIER signaling packet. In at least some example embodiments, the MPLS signaling information includes a forwarding equivalence class (FEC) and an action. In at least some example embodiments, the device associated with the BIER domain is a controller of the BIER domain or an egress BIER border router (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the device associated with the BIER domain is a controller of the BIER domain. In at least some example embodiments, the apparatus includes means for sending, from the device toward one or more BIER border routers (BBRs) interested in the P2MP LSP, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the one or more BBRs interested in the P2MP LSP include an ingress BBR (IBBR) from which the MPLS signaling information is received and an egress BBR (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the device associated with the BIER domain is an egress BIER border router (EBBR) of the BIER domain for the P2MP LSP. In at least some example embodiments, the apparatus includes means for sending, from the device toward a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the apparatus includes means for assigning, by the device, an MPLS label identifying the P2MP LSP within an MPLS domain and means for sending, by the device toward a root of the P2MP LSP via the MPLS domain, the MPLS label identifying the P2MP LSP within the MPLS domain. In at least some example embodiments, an apparatus includes means for receiving, by a device associated with a multicast explicit replication domain, multicast signaling information associated with a multicast label switched path and means for assigning, by the device based on the multicast signaling information associated with the multicast label switched path, a tree label identifying the multicast label switched path within the multicast explicit replication domain. 
     In at least some example embodiments, an apparatus is provided. In at least some example embodiments, the apparatus includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least obtain, by a BIER border router (BBR) of a BIER domain, a BIER tree label (BTL) identifying a point-to-multipoint (P2MP) label switched path (LSP) within the BIER domain. In at least some example embodiments, to obtain BTL identifying the P2MP LSP within the BIER domain, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least receive, by the device from a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, to obtain the BTL identifying the P2MP LSP within the BIER domain, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least receive, by the device from an ingress BBR of the BIER domain, MPLS signaling information including a forwarding equivalence class (FEC) associated with the P2MP LSP and assign, by the device based on the FEC associated with the P2MP LSP, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the FEC associated with the P2MP LSP is received in a BIER signaling packet. In at least some example embodiments, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least send, by the device toward a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least send, by the device toward the IBBR of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the BTL identifying the P2MP LSP within the BIER domain is sent based on at least one of a Multiprotocol-Border Gateway Protocol (MP-BGP) adjacency, a BGP Multicast Virtual Private Network (MVPN), or Segment Routing-Traffic Engineering (SR-TE). In at least some example embodiments, an apparatus includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to at least obtain, by a border router of a multicast explicit replication domain, a tree label identifying a multicast label switched path within the multicast explicit replication domain. 
     In at least some example embodiments, a method is provided. In at least some example embodiments, the method includes obtaining, by a BIER border router (BBR) of a BIER domain, a BIER tree label (BTL) identifying a point-to-multipoint (P2MP) label switched path (LSP) within the BIER domain. In at least some example embodiments, obtaining the BTL identifying the P2MP LSP within the BIER domain includes receiving, by the device from a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, obtaining the BTL identifying the P2MP LSP within the BIER domain includes receiving, by the device from an ingress BBR of the BIER domain, MPLS signaling information including a forwarding equivalence class (FEC) associated with the P2MP LSP and assigning, by the device based on the FEC associated with the P2MP LSP, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the FEC associated with the P2MP LSP is received in a BIER signaling packet. In at least some example embodiments, the method includes sending, by the device toward a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the method includes sending, by the device toward the IBBR of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the BTL identifying the P2MP LSP within the BIER domain is sent based on at least one of a Multiprotocol-Border Gateway Protocol (MP-BGP) adjacency, a BGP Multicast Virtual Private Network (MVPN), or Segment Routing-Traffic Engineering (SR-TE). In at least some example embodiments, a method includes obtaining, by a border router of a multicast explicit replication domain, a tree label identifying a multicast label switched path within the multicast explicit replication domain. 
     In at least some example embodiments, a non-transitory computer readable medium is provided. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing an apparatus to at least obtain, by a BIER border router (BBR) of a BIER domain, a BIER tree label (BTL) identifying a point-to-multipoint (P2MP) label switched path (LSP) within the BIER domain. In at least some example embodiments, to obtain BTL identifying the P2MP LSP within the BIER domain, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least receive, by the device from a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, to obtain the BTL identifying the P2MP LSP within the BIER domain, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least receive, by the device from an ingress BBR of the BIER domain, MPLS signaling information including a forwarding equivalence class (FEC) associated with the P2MP LSP and assign, by the device based on the FEC associated with the P2MP LSP, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the FEC associated with the P2MP LSP is received in a BIER signaling packet. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least send, by the device toward a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the non-transitory computer-readable medium includes program instructions for causing the apparatus to at least send, by the device toward the IBBR of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the BTL identifying the P2MP LSP within the BIER domain is sent based on at least one of a Multiprotocol-Border Gateway Protocol (MP-BGP) adjacency, a BGP Multicast Virtual Private Network (MVPN), or Segment Routing-Traffic Engineering (SR-TE). In at least some example embodiments, a non-transitory computer-readable medium includes program instructions for causing an apparatus to at least obtain, by a border router of a multicast explicit replication domain, a tree label identifying a multicast label switched path within the multicast explicit replication domain. 
     In at least some example embodiments, an apparatus is provided. In at least some example embodiments, the apparatus includes means for obtaining, by a BIER border router (BBR) of a BIER domain, a BIER tree label (BTL) identifying a point-to-multipoint (P2MP) label switched path (LSP) within the BIER domain. In at least some example embodiments, the means for obtaining the BTL identifying the P2MP LSP within the BIER domain includes means for receiving, by the device from a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the means for obtaining the BTL identifying the P2MP LSP within the BIER domain includes means for receiving, by the device from an ingress BBR of the BIER domain, MPLS signaling information including a forwarding equivalence class (FEC) associated with the P2MP LSP and means for assigning, by the device based on the FEC associated with the P2MP LSP, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the FEC associated with the P2MP LSP is received in a BIER signaling packet. In at least some example embodiments, the apparatus includes means for sending, by the device toward a controller of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the apparatus includes means for sending, by the device toward the IBBR of the BIER domain, the BTL identifying the P2MP LSP within the BIER domain. In at least some example embodiments, the BTL identifying the P2MP LSP within the BIER domain is sent based on at least one of a Multiprotocol-Border Gateway Protocol (MP-BGP) adjacency, a BGP Multicast Virtual Private Network (MVPN), or Segment Routing-Traffic Engineering (SR-TE). In at least some example embodiments, an apparatus includes means for obtaining, by a border router of a multicast explicit replication domain, a tree label identifying a multicast label switched path within the multicast explicit replication domain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings herein can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  depicts a communication system configured to support a P2MP LSP via a BIER domain based on assignment of a label in the BIER domain that uniquely identifies P2MP LSP within the BIER domain; 
         FIG. 2  depicts a communication system for illustrating assignment of a label to a P2MP LSP, for uniquely identifying the P2MP LSP within the BIER domain, by a controller of the BIER domain; 
         FIG. 3  depicts a communication system for illustrating assignment of a label to a P2MP LSP, for uniquely identifying the P2MP LSP within the BIER domain, by a BIER border router (BBR) of the BIER domain; 
         FIG. 4  depicts a communication system for illustrating assignment of a label to a P2MP LSP, for uniquely identifying the P2MP LSP within the BIER domain, by a BIER border router (BBR) of the BIER domain; 
         FIG. 5  depicts a communication system for illustrating transport of MPLS packets of a P2MP LSP across a BIER domain based on assignment of a label to the P2MP LSP for uniquely identifying the P2MP LSP within the BIER domain; 
         FIG. 6  depicts an example embodiment of a method for use by an IBBR for supporting assignment of a label to a P2MP LSP within a BIER domain for uniquely identifying the P2MP LSP within the BIER domain; 
         FIG. 7  depicts an example embodiment of a method for use by a BTL assigning node for supporting assignment of a label to a P2MP LSP within a BIER domain for uniquely identifying the P2MP LSP within the BIER domain; 
         FIG. 8  depicts an example embodiment of a method for use by an EBBR for supporting assignment of a label to a P2MP LSP within a BIER domain for uniquely identifying the P2MP LSP within the BIER domain; 
         FIG. 9  depicts an example embodiment of a method for use by border router of a multicast explicit replication domain for supporting assignment of a label to a multicast label switched path within the multicast explicit replication domain for uniquely identifying the multicast label switched path within the multicast explicit replication domain; 
         FIG. 10  depicts an example embodiment of a method for use by an assigning node of a multicast explicit replication domain for supporting assignment of a label to a multicast label switched path within the multicast explicit replication domain for uniquely identifying the multicast label switched path within the multicast explicit replication domain; 
         FIG. 11  depicts an example embodiment of a method for use by a border router of a multicast explicit replication domain for supporting assignment of a label to a multicast label switched path within the multicast explicit replication domain for uniquely identifying the multicast label switched path within the multicast explicit replication domain; and 
         FIG. 12  depicts a high-level block diagram of a computer suitable for use in performing various functions presented herein. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     Various example embodiments relate generally to supporting Multiprotocol Label Switching (MPLS)-based multicast over a Bit Index Explicit Replication (BIER) domain. Various example embodiments for supporting MPLS-based multicast over a BIER domain may be configured to support MPLS point-to-multipoint (P2MP) label switched paths (LSPs) over a BIER domain. Various example embodiments for supporting MPLS-based multicast over a BIER domain may be configured to support establishment and transport of P2MP LSPs over a BIER domain (e.g., signaling MPLS via the BIER domain, stitching the MPLS datapath to the BIER domain based on identification of P2MP LSPs within the BIER domain, and so forth). Various example embodiments for supporting MPLS-based multicast over a BIER domain may be configured to support signaling of MPLS via the BIER domain based on termination of MPLS signaling at the edge of the BIER domain and forwarding of MPLS signaling information from the MPLS signaling within the BIER domain (e.g., Multicast Label Distribution Protocol (mLDP) signaling). Various example embodiments for supporting MPLS-based multicast over a BIER domain may be configured to support stitching the MPLS datapath to the BIER domain based on identification of P2MP LSPs within the BIER domain using BIER tree labels (BTLs) that uniquely identify the P2MP LSPs (and, thus, are associated with the forwarding equivalence classes (FECs) for the P2MP LSPs) within the BIER domain, respectively. Various example embodiments for supporting MPLS-based multicast over a BIER domain may be configured to support assignment of a BTL for a P2MP LSP within the BIER domain, which uniquely identifies the P2MP LSP within the BIER domain, by a controller of the associated BIER domain (e.g., a Software Defined Networking (SDN) controller or other suitable type of controller), by a BIER border router of the associated BIER domain (e.g., a BIER border router on the P2MP LSP, such as by a BIER border router that is an ingress point into the BIER domain for multicast data traffic of the P2MP LSP), or the like, as well as various combinations thereof. It will be appreciated that these and various other embodiments and potential advantages for supporting stitching of P2MP LSPs via a BIER domain may be further understood by way of reference to the example communication system of  FIG. 1 . 
       FIG. 1  depicts a communication system configured to support a P2MP LSP via a BIER domain based on assignment of a label in the BIER domain that uniquely identifies P2MP LSP within the BIER domain. 
     The communication system  100  includes a communication network (CN)  110  that is configured to support multicasting of traffic to a multicast host (MH)  120  from a multicast source (MS)  130 . 
     The communication system  100  illustrates an arrangement in which multicast control traffic is propagated from right to left on the page (e.g., from the MH  120  toward the MS  130 , via the CN  110 , for enabling the MH  120  to join and leave multicast services) and in which multicast traffic is propagated from left to right on the page (e.g., from the MS  130  toward the MH  120 , via the CN  110 , for enabling the MH  120  to receive multicast data traffic). 
     The CN  110  is composed of an Interior Gateway Protocol (IGP) area (which, illustratively, may be IGP area  111 -A or IGP area  111 -S), a pair of MPLS domains  112 - 1  and  112 - 2  (collectively, MPLS domains  112 ), and a BIER domain  113 . In at least some embodiments, the IGP area and the BIER domain  113  are commensurate in scope as the entire IGP area is implemented using BIER (illustrated in  FIG. 1  using the IGP area  111 -A indicator). In at least some embodiments, the IGP area and the BIER domain  113  are not commensurate in scope as only a portion of the IGP area is implemented using BIER (illustrated in  FIG. 1  using the IGP area  111 -S indicator, which illustrates that the BIER domain  113  is actually a BIER sub-domain that is only part of the IGP area  111 -S). It will be appreciated that certain aspects of supporting multicast within the CN  110  may vary depending on whether the BIER domain  113  forms all or part of the IGP area. 
     The CN  110  includes a set of MPLS routers  114 - 1 - 114 - 4  (collectively, MPLS routers  114 ) operating within the MPLS domains  112  and a set of BIER routers  115  operating within the BIER domain  113 . The set of BIER routers  115  includes a set of BIER border routers (BBRs)  115 -B 1 - 115 -B 4  (collectively, BBRs  115 -B) and a BIER core router (BCR)  115 -C. The MPLS routers  114 - 1  and  114 - 2  (operating in the MPLS domain  112 - 1 ) are each connected to the BBRs  115 -B 1  and  115 -B 3  and the MPLS routers  114 - 3  and  114 - 4  (operating in the MPLS domain  112 - 2 ) are each connected to the BBRs  115 -B 2  and  115 -B 4 . The BBRs  115 -B are each connected to the BCR  115 -C. The MH  120  is communicatively connected to MPLS router  114 - 4  via an access network  121  and the MS  130  is communicatively connected to the MPLS router  114 - 2  via an access network  131 . 
     The MPLS routers  114  are configured to facilitate communication between multicast endpoints (e.g., MS  130  and MH  120 ) and the BBRs  115 -B of the BIER domain  113 . The MPLS routers  114  are configured to support communication of multicast control traffic in the control traffic direction based on multicast control protocols and communication of multicast data traffic in the data traffic direction based on multicast data protocols. 
     The MPLS routers  114  are configured to support communications with multicast endpoints, including multicast hosts (e.g., the MH  120 ) and multicast sources (e.g., the MS  130 ). The MPLS routers  114  are configured to support multicast control communications with multicast hosts and multicast sources using various multicast control protocols (e.g., Label Distribution Protocol (LDP), Multicast LDP (mLDP), or the like). For example, MPLS router  114 - 4  may receive multicast control protocol signaling from the MH  120  for enabling the MH  120  to join or leave a multicast group supported by MS  130  and, similarly, MS  130  may receive multicast control protocol signaling from the MPLS router  114 - 2  for enabling the MH  120  to join or leave a multicast group supported by MS  130 . The MPLS routers  114  are configured to support multicast data communications with multicast sources and multicast sources using various data transport protocols (e.g., MPLS or the like). For example, MPLS router  114 - 2  may receive multicast data traffic from the MS  130  and MPLS router  114 - 4  may send multicast data traffic to the MH  120 . The MPLS routers  114  may be configured to support multicast control and data communications with multicast hosts and multicast sources based on various other types of protocols. 
     The MPLS routers  114  are configured to support communications with BBRs  115 -B. The MPLS routers  114  are configured to support multicast control communications with BBRs  115 -B using various multicast control protocols (e.g., LDP, mLDP, or the like). For example, MPLS router  114 - 4  may send multicast control protocol signaling received from the MH  120  (e.g., for enabling the MH  120  to join or leave a multicast group supported by MS  130 ) to BBR  115 -B 2  or BBR  115 -B 4  and, similarly, MPLS router  114 - 2  may receive multicast control protocol signal intended for MS  130  (e.g., for enabling the MH  120  to join or leave a multicast group supported by MS  130 ) from BBR  115 - 1  or BBR  115 - 3 . The MPLS routers  114  are configured to support multicast data communications with BBRs  115 -B using various multicast data protocols (e.g., MPLS or the like). For example, the MPLS router  114 - 2  may receive multicast data traffic from the MS  130  and send the multicast data to BBR  115 -B 1  or BBR  115 -B 3  and, similarly, MPLS router  114 - 4  may receive multicast data traffic from BBR  115 -B 2  or BBR  115 -B 4  and send the multicast data to the MH  120 . The communication of multicast data traffic between the MPLS routers  114  and the BBRs  115 -B may be based on MPLS P2MP LSPs or other types of multicast data communication mechanisms. The MPLS routers  114  may be configured to support various other types of communications with BBRs  115 -B. 
     The BIER routers  115  are configured to support BIER, an architecture that, in general, provides multicast forwarding through a BIER domain (illustratively, BIER domain  113 ) without requiring intermediate routers to maintain multicast-related per-flow state and without requiring use of an explicit tree-building protocol. In the BIER architecture for a BIER domain, a multicast data packet enters the BIER domain at a Bit-Forwarding Ingress Router (BFIR) and leaves the BIER domain at one or more Bit-Forwarding Egress Routers (BFERs) based on use of a BIER packet header that includes a Bit-String in which each bit represents one BFER (namely, the bits of the Bit-String are set in a manner indicating the one or more BFERs to which the multicast data packet is to be provided). In general, in the BIER architecture for a BIER domain, the BIER domain may be identified by a unique BIER domain identifier and can support multiple Bit-String Lengths. In the BIER architecture for a BIER domain, the BIER routers of the BIER domain also may be referred to herein as Bit Forwarding Routers (BFRs), which are routers that participate in Bit Index Multipoint Forwarding. In the BIER architecture for a BIER domain, each BFR of the BIER domain may be configured with a BFR-ID, a BFR-Prefix that uniquely identifies the BFR in the BIER domain, a Bit String Length (BSL), a Sub-Domain (SD), a Set-Id (SI), and other parameters as defined in the BIER architecture documents. Various other aspects of the BIER architecture will be understood from the BIER architecture documents. 
     The BBRs  115 -B may be configured to operate as ingress border routers of the BIER domain  113  and as egress border routers of the BIER domain  113 , where the mode of operation being used may vary depending on the locations of the BBRs  115 -B relative to the multicast hosts and the multicast sources, the type of communications being supported (e.g., multicast control traffic versus multicast data traffic), or the like, as well as various combinations thereof. 
     Herein, unless indicated otherwise, the terms Bit-Forwarding Ingress Router (BFIR) and Bit-Forwarding Egress Router (BFER) are used in conjunction with handling of the multicast data traffic in the data traffic direction from the MS  130  toward the MH  120 . In general, the BFIR and the BFER support datapath stitching for forwarding of multicast data traffic (e.g., MPLS packets) via the BIER domain  113 . In general, the BFIR and the BFER may support datapath stitching for forwarding of multicast data traffic via the BIER domain  113  based on stitching of the multicast protocol used outside of the BIER domain  113  (e.g., MPLS) to the BIER datapath within the BIER domain  113  (e.g., using BIER packets based on BIER packet headers) on the ingress and egress sides of the BIER domain  113 , respectively. In general, a BFIR is the ingress border router that supports datapath stitching for forwarding of multicast data traffic based on receipt of the multicast data traffic based on MPLS, identification of a stitching forwarding entry, label handling (e.g., based on the MPLS label for the P2MP LSP within the MPLS domain  112 - 1  and based on the BTL of the associated P2MP LSP within the BIER domain  113 ), and generation of a BIER packet including setting of the BIER header fields. In general, a BFER is an egress border that is a leaf of the multicast tree and that supports datapath stitching for forwarding of multicast data traffic based on processing of the BIER header, removal of the multicast data traffic from the BIER packet, label handling (e.g., based on the BTL of the associated P2MP LSP within the BIER domain  113  and based on the MPLS label for the P2MP LSP within the MPLS domain  112 - 2 ), and forwarding of the multicast data traffic based on MPLS. In other words, the BFIR and the BFER are the BBRs from the multicast data traffic point of view. For example, in the example of  FIG. 1 , BBR  115 -B 3  would be a BFIR and BBR  115 -B 4  would be a BFER. 
     Herein, unless indicated otherwise, the terms Ingress BBR (IBBR) and Egress BBR (EBBR) are used in conjunction with handling of the multicast control messages in the control traffic direction from the MH  120  toward the MS  130 . In general, an IBBR is an ingress boundary router between a MPLS domain (e.g., MPLS domain  112 - 2 ) and a BIER domain (e.g., BIER domain  113 ) that receives MPLS signaling including MPLS signaling information, terminates the MPLS signaling, and forwards MPLS signaling information from the MPLS signaling within the BIER domain for enabling assignment of the BTL to identify the associated P2MP LSP within the BIER domain and to enable delivery of the MPLS signaling information from the MPLS signaling to the multicast source (e.g., MS  130 ). In general, an EBBR is an egress boundary router between a BIER domain (e.g., BIER domain  113 ) and a MPLS domain (e.g., MPLS domain  112 - 1 ) that receives MPLS signaling information from the MPLS signaling terminated by an IBBR and generates corresponding MPLS signaling including the MPLS signaling information for delivery to the multicast source (e.g., MS  130 ) via the MPLS domain. It will be appreciated that the MPLS signaling information may include a combination of a forwarding equivalence class (FEC) and an associated action (e.g., label mapping, label withdraw, or the like) which may be denoted as &lt;FEC, Action&gt;. In other words, the IBBR and the EBBR are the BBRs from the control signaling point of view. For example, in the example of  FIG. 1 , BBR  115 -B 4  would be an IBBR and BBR  115 -B 3  would be an EBBR. 
     The BBRs  115 -B, as discussed above, may be configured to operate as ingress border routers and as egress border routers under various conditions. As discussed above, a BFIR would be an EBBR of the control plane traffic (e.g., BBR  115 -B 3 ) and a BFER would be an IBBR of the control plane traffic (e.g., BBR  115 -B 4 ). Similarly, as discussed above, an IBBR would be a BFER of the multicast data traffic (e.g., BBR  115 -B 4 ) and an EBBR would be a BFIR of the multicast data traffic (e.g., BBR  115 -B 3 ). In other words, each of the BBRs  115 -B may be configured to operate in multiple roles, for supporting control plane traffic and data traffic, under various conditions. 
     The BBRs  115 -B, given that the BIER domain  113  is an IGP area (which corresponds to the case of IGP area  111 -A) or a portion of an IGP area (which corresponds to the case of IGP area  111 -S), may be area border routers (ABRs) or autonomous system border routers (ASBRs) that are connected to the edge network (e.g., MPLS routers  114 ) via an appropriate protocol (e.g., an IGP, a Border Gateway Protocol (BGP), or the like), provider (P) routers that are selected to operate as BIER border routers in the BIER domain  113 , or the like, as well as various combinations thereof. 
     The BBRs  115 -B, as discussed above, are configured to support datapath stitching for supporting forwarding of multicast data traffic of a multicast label switched path (e.g., MPLS packets of an LSP, such as a P2MP LSP) via the BIER domain  113 . The stitching of the datapath for forwarding of multicast data traffic of a P2MP LSP via the BIER domain  113  may be based on use of a BTL to uniquely identify the P2MP LSP within the BIER domain  113 . For example, the BTL may be an MPLS label that uniquely identifies a P2MP LSP within the BIER domain  113 . The BTL may be assigned within the BIER domain  113  by a controller of the BIER domain  113  (an embodiment of which is presented with respect to  FIG. 2 ), by a BBR  115 -B of the BIER domain  113  (embodiments of which are presented with respect to  FIG. 3  and  FIG. 4 ), or the like, as well as various combinations thereof. 
     It will be appreciated that communication system  100 , although primarily presented as having a specific arrangement (e.g., specific types, numbers, and arrangements of domains, routers, multicast end devices, control plane protocols, datapath protocols, and the like), may have various other arrangements (e.g., other types, numbers, or arrangements of domains, routers, multicast end devices, control plane protocols, datapath protocols, or the like, as well as various combinations thereof). 
       FIG. 2  depicts a communication system for illustrating assignment of a label to a P2MP LSP, for uniquely identifying the P2MP LSP within the BIER domain, by a controller of the BIER domain. 
     The communication system  200  of  FIG. 2  is similar to the communication system  100  of  FIG. 1 , with the exception that the BEIR domain  113  is controlled by a BIER domain controller  201  (although it will be appreciated that such a BIER domain controller also may be used within the context of communication system  100  of  FIG. 1 ). The BIER domain controller  201  may be an SDN controller or other suitable type of controller. In communication system  200 , the BIER domain controller  201  is responsible for assigning the BTL that uniquely identifies a P2MP LSP within the BIER domain  113 . A description of a process for enabling the BIER domain controller  201  to assign the BTL that uniquely identifies an MPLS P2MP LSP within the BIER domain  113  follows. 
     The MPLS router (illustratively, MPLS router  114 - 4 ) associated with the multicast host (illustratively, MH  120 ) that is requesting to join the multicast group (S,G) of the P2MP LSP, sends MPLS signaling information to an IBBR of the BIER domain (illustratively, IBBR  115 -B 4  of BIER domain  113 ) using MPLS signaling in the MPLS domain (illustratively, MPLS domain  112 - 2 ). The MPLS signaling may be an mLDP control packet or other suitable control packet. The MPLS signaling information may be a combination of a FEC and an associated action (e.g., label mapping, label withdraw, or the like) which may be denoted as &lt;FEC, Action&gt; for the P2MP LSP. It will be appreciated that the FEC may be a basic opaque FEC (e.g., for a single IGP area) or may be a recursive opaque FEC (e.g., for seamless MPLS). In  FIG. 2 , the sending of the MPLS signaling information to the IBBR of the BIER domain is indicated by message  210 . For example, the message  210  may include mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 ), mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 ), or the like. 
     The IBBR (illustratively, the BBR  115 -B 4 ) receives the mLDP signaling packet including MPLS signaling information. The IBBR terminates the MPLS signaling and sends the MPLS signaling information of the MPLS signaling to the BIER domain controller  201 . The IBBR includes its own BFR-Prefix and BFR-ID when sending the MPLS signaling information to the BIER domain controller  201 . In  FIG. 2 , the sending of the MPLS signaling information and the BFR-Prefix of the IBBR from the IBBR to the BIER domain controller  201  is indicated by message  220 . For example, the message  220  may include mLDP FEC (root, opaque&lt;lspID 1 &gt;) where message  210  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, mLDP FEC (root, opaque&lt;lspID 2 &gt;) where message  210  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     The BIER domain controller  201  receives the MPLS signaling information and the BFR-Prefix of the IBBR from the IBBR. 
     The BIER domain controller  201  identifies the EBBR (illustratively, BBR  115 -B 3 ) for which the MPLS signaling was intended. The BIER domain controller  201  may identify the EBBR based on the root address of the FEC from the MPLS signaling information. In the case of a basic opaque (Type  1 ) FEC, the root is the root of &lt;root, opaque&lt;id&gt;&gt;. In the case of a recursive opaque FEC, the root is the outer root of &lt;root, opaque&lt;inner-root, opaque&lt;id&gt;&gt;. The BIER domain controller  201  may identify the EBBR based on procedures defined in the draft-ietf-bier-pim-signaling document. 
     The BIER domain controller  201  assigns a BTL for the FEC (and, thus, for the associated P2MP LSP) from the MPLS signaling information. The BTL that is assigned may be used to uniquely identify the associated P2MP LSP within the BIER domain  113  for supporting stitching of the P2MP LSP to the BIER datapath in the BIER domain  113 . The BIER domain controller  201  may assign the BTL from an overall label pool for the BIER domain  113 , from an &lt;EBBR,SD&gt; label pool associated with the EBBR for which the MPLS signaling was intended (e.g., where the BIER domain controller  201  maintains a label pool per &lt;EBBR,SD&gt;, which may be used for better scalability or for other purposes), or the like. 
     The BIER domain controller  201  tracks each of the IBBRs of the BIER domain  113  that are receiving this FEC on the MPLS domain and would like to join this specific P2MP LSP. The BIER domain controller  201  may track the IBBRs of the BIER domain  113  that are receiving this FEC on the MPLS domain and would like to join this specific P2MP LSP by tracking the BFR-Prefixes and BFR-IDs of the IBBRs. As an example, each IBBR that receives the FEC and sends the FEC (along with its BFR-Prefix and BFR-ID) to the BIER domain controller  201  will be tracked by the BIER domain controller  201 . This tracking enables the EBBR to build the correct BIER header and set the bits (in the BIER header) for all the IBBRs that are interested in the traffic from this specific P2MP LSP. 
     The BIER domain controller  201  updates the relevant BBRs of the BIER domain with the BTL identifying the P2MP LSP within the BIER domain  113 . The relevant BBRs may include the IBBRs and the EBBR that are interested in the P2MP LSP. For example, the relevant EBBR may be the EBBR that is closest to the root node of the P2MP LSP (illustratively, BBR  115 -B 3 ) and the relevant IBBRs may include any IBBRs that have terminated the MPLS domain and extracted the FEC to the BIER domain controller  201  for the P2MP LSP (illustratively, BBR  115 -B 4 ). The BIER domain controller  201  updates the relevant BBRs with the BTL identifying the P2MP LSP by sending the MPLS signaling information and the BTL identifying the P2MP LSP to the relevant BBRs. The sending of the MPLS signaling information and the BTL identifying the P2MP LSP may be denoted as &lt;EBBR (BFR-Prefix), SD&gt; (BTL), &lt;IBBR (BFR-Prefix), FEC, Action&gt;&gt;. The BIER domain controller  201  may send the MPLS signaling information and the BTL identifying the P2MP LSP to the relevant BBRs via downloading into the relevant BBRs. In  FIG. 2 , the sending of the MPLS signaling information and the BTL identifying the P2MP LSP from the BIER domain controller  201  to relevant BBRs is indicated by messages  230 . For example, the messages  230  may include [&lt;EBBR BFR-Prefix, SD&gt; (BTL- 1 ), &lt;IBBR BFR-Prefix, mLDP FEC (root, opaque&lt;lspID 1 &gt;, Action&gt;] where message  210  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, [&lt;EBBR Prefix, SD&gt; (BTL- 2 ), &lt;IBBR BFR-Prefix, mLDP FEC (root, opaque&lt;lspID 2 &gt;, Action&gt;] where message  210  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     The relevant EBBR (illustratively, BBR  115 -B 3 ) receives the MPLS signaling information and the BDT identifying the P2MP LSP from the BIER domain controller  201 . The relevant EBBR, based on the MPLS signaling information, assigns a new outgoing label toward the root node (illustratively, MPLS router  114 - 2 ) for MPLS signaling within the MPLS domain (illustratively, MPLS domain  112 - 1 ). The relevant EBBR reconstitutes MPLS signaling and sends the MPLS signaling information to the root node using MPLS signaling. In  FIG. 2 , the sending of the MPLS signaling information from the relevant EBBR to the root node is indicated by message  240 . For example, the message  240  may include &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 3 )&gt; where message  210  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 4 )&gt; where message  210  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     The relevant EBBR (illustratively, BBR  115 -B 3 ) receives the MPLS signaling information and the BDT identifying the P2MP LSP from the BIER domain controller  201 . The relevant EBBR (illustratively, BBR  115 -B 3 ), based on the IBBR BFR-Prefix of the IBBR (illustratively, BBR  115 -B 4 ) which received the MPLS signaling information for the P2MP LSP, configures a stitched label forwarding entry on the relevant EBBR for the IBBR indicated by the IBBR BFR-Prefix. The stitched label forwarding entry is configured to stitch the incoming MPLS domain label for the P2MP LSP to the outgoing BTL which was uniquely assigned for the P2MP LSP by the BIER domain controller  201 , with the outgoing interfaces (OIFs) being each of the IBBRs interested in the P2MP LSP (at least including the IBBR indicated by the IBBR BFR-Prefix received from the BIER domain controller  201 ). On the dataplane, as discussed further below, the relevant EBBR will use the BFR-Prefixes, of the IBBRs interested in the P2MP LSP in the corresponding SD, as the OIFs in order to find the corresponding BIER header bit index for each IBBR in its OIF list. 
     The relevant IBBR (illustratively, BBR  115 -B 4 ) receives the MPLS signaling information and the BDT identifying the P2MP LSP from the BIER domain controller  201 . The relevant IBBR (illustratively, BBR  115 -B 4 ), based on the EBBR BFR-Prefix of the relevant EBBR (illustratively, BBR  115 -B 3 ) that is received, configures a stitched label forwarding entry on the relevant IBBR for the EBBR indicated by the EBBR BFR-Prefix. The stitched label forwarding entry is configured to stitch the incoming EBBR BFR-Prefix (BTL) for the P2MP LSP to the outgoing MPLS domain label for the P2MP LSP in the corresponding SD. On the dataplane, as discussed further below, the relevant IBBR will (1) use the BIER header to determine that the BIER payload is an MPLS packet and (2) remove the BIER header and use the BTL pushed by the EBBR to do a lookup in the ILM for the EBBR BFR-Prefix (BTL) for determining handling of the packet in the MPLS domain (illustratively, MPLS domain  112 - 2 ). 
     It will be appreciated that, while primarily presented in  FIG. 2  within the context of handling of a specific type of action for the multicast tree (namely, a label mapping action in which the MPLS router  114  is joining the multicast tree), various embodiments of  FIG. 2  may be adapted for use in handling other types of actions (e.g., a label withdraw action in which the MPLS router  114  is leaving the multicast tree or the like). 
     It will be appreciated that, while primarily presented in  FIG. 2  within the context of embodiments in which the multicast datapath is provided using MPLS and the multicast control signaling is based on mLDP, various embodiments may adapted for use with other multicast datapath protocols, other multicast control signaling protocols, or the like, as well as various combinations thereof. 
       FIG. 3  depicts a communication system for illustrating assignment of a label to a P2MP LSP, for uniquely identifying the P2MP LSP within the BIER domain, by a BBR of the BIER domain. 
     The communication system  300  of  FIG. 3  is similar to the communication system  100  of  FIG. 1 , with the exception that the BEIR domain  113  is controlled by a BIER domain controller  301  (although it will be appreciated that such a BIER domain controller also may be used within the context of communication system  100  of  FIG. 1 ). The BIER domain controller  301  may be an SDN controller or other suitable type of controller. In communication system  300 , an EBBR (illustratively, BBR  115 -B 3 ) is responsible for assigning the BTL that uniquely identifies a P2MP LSP within the BIER domain  113  and the BIER domain controller  301  is responsible for distributing the BTL that uniquely identifies the P2MP LSP within the BIER domain  113 . A description of a process for enabling the EBBR to assign the BTL that uniquely identifies a P2MP LSP within the BIER domain  113  and for enabling the BIER domain controller  301  to distribute the BTL that uniquely identifies the P2MP LSP within the BIER domain  113  follows. The MPLS router (illustratively, MPLS router  114 - 4 ) associated with the multicast host (illustratively, MH  120 ) that is requesting to join the multicast group (S,G) of the P2MP LSP, sends MPLS signaling information to an IBBR of the BIER domain (illustratively, IBBR  115 -B 4  of BIER domain  113 ) using MPLS signaling in the MPLS domain (illustratively, MPLS domain  112 - 2 ). The MPLS signaling may be an mLDP signaling packet or other suitable signaling packet. The MPLS signaling information may be a combination of a FEC and an associated action (e.g., label mapping, label withdraw, or the like) which may be denoted as &lt;FEC, Action&gt; for the P2MP LSP. It will be appreciated that the FEC may be a basic opaque FEC (e.g., for a single IGP area) or may be a recursive opaque FEC (e.g., for seamless MPLS). In  FIG. 3 , the sending of the MPLS signaling information to the IBBR of the BIER domain is indicated by message  310 . For example, the message  310  may be an mLDP label mapping message including mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 ), mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 ), or the like. 
     The IBBR (illustratively, the BBR  115 -B 4 ) receives the MPLS signaling including MPLS signaling information. The IBBR terminates the MPLS signaling, identifies the EBBR (illustratively, BBR  115 -B 3 ) for which the MPLS signaling was intended, and sends the MPLS signaling information of the MPLS signaling to the EBBR for which the MPLS signaling was intended. 
     The IBBR identifies the EBBR (illustratively, BBR  115 -B 3 ) for which the MPLS signaling was intended. The IBBR may identify the EBBR based on the root address of the FEC from the MPLS signaling information. In the case of a basic opaque (Type  1 ) FEC, the root is the root of &lt;root, opaque&lt;id&gt;&gt;. In the case of a recursive opaque FEC, the root is the outer root of &lt;root, opaque&lt;inner-root, opaque&lt;id&gt;&gt;. The IBBR may identify the EBBR based on procedures defined in the draft-ietf-bier-pim-signaling document. 
     The IBBR sends the MPLS signaling information of the MPLS signaling to the EBBR for which the MPLS signaling was intended using BIER signaling. The IBBR sends the MPLS signaling information of the MPLS signaling to the EBBR for which the MPLS signaling was intended by encapsulating the MPLS signaling information of the MPLS signaling within a BIER packet, setting the BIER header to indicate routing of the BIER packet to the EBBR for which the MPLS signaling was intended (e.g., by setting the BIER header bit corresponding to the EBBR for which the MPLS signaling was intended), and forwarding the BIER packet into the BIER domain for delivery to the EBBR for which the MPLS signaling was intended. The MPLS signaling information may be encapsulated within the BIER packet by encapsulating the MPLS signaling packet (including the MPLS signaling information) within the BIER packet or by only encapsulating the MPLS signaling information (rather than the entire MPLS signaling packet) within the BIER packet. It is noted that, here, the BIER domain does not create mLDP adjacency between the two disjoint mLDP domains; rather, the BIER domain merely uses the mLDP packet for signaling purposes. In  FIG. 3 , the sending of the MPLS signaling information from the IBBR to the EBBR is indicated by message  320 . For example, the message  320  may include mLDP FEC (root, opaque&lt;lspID 1 &gt;) where message  310  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, mLDP FEC (root, opaque&lt;lspID 2 &gt;) where message  310  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     The EBBR receives the BIER packet including the MPLS signaling information from the IBBR. The EBBR removes the MPLS signaling information from the BIER packet and processes the MPLS signaling information. 
     The EBBR, based on a determination that this is the first IBBR that has forwarded the FEC to the EBBR, assigns a BTL for the FEC (and, thus, for the associated P2MP LSP) from the MPLS signaling information. The BTL that is assigned may be used to uniquely identify the associated P2MP LSP within the BIER domain  113  for supporting stitching of the P2MP LSP to the BIER datapath in the BIER domain  113 . The EBBR may assign the BTL from an overall label pool for the BIER domain  113 , from an &lt;EBBR,SD&gt; label pool associated with the EBBR (e.g., where the BIER domain controller  301  maintains a label pool per &lt;EBBR,SD&gt;, which may be used for better scalability or for other purposes, and distributes the per-EBBR label pools to the EBBRs, respectively), or the like. It is noted that the EBBR, based on a determination that this is not the first IBBR that has forwarded the FEC to the EBBR (but, rather, is a subsequent IBBR interested in the P2MP LSP), will add the IBBR BFR-Prefix to the OIF list of the FEC (since the EBBR will have already assigned the BTL for the FEC, as described above, when the FEC was received from the first IBBR interested in the P2MP LSP). 
     The EBBR sends the MPLS signaling information and the BTL identifying the P2MP LSP to the BIER domain controller  301  such that the BIER domain controller  301  may further distribute the MPLS signaling information and the BTL identifying the P2MP LSP. For example, the EBBR may create a message &lt;&lt;EBBR, SD&gt; BTL, &lt;IBBR, &lt;FEC, Action&gt;&gt;, where EBBR and IBBR are the BFR-Prefixes and BFR-IDs of the EBBR and the IBBR, respectively. In  FIG. 3 , the sending of the MPLS signaling information and the BTL identifying the P2MP LSP from the EBBR to the BIER domain controller  301  is indicated by message  330 . For example, the message  330  may include [&lt;EBBR BFR-Prefix, BFR-ID, SD&gt; (BTL- 1 ), &lt;IBBR BFR-Prefix, BFR-ID, mLDP FEC (root, opaque&lt;lspID 1 &gt;, Action&gt;] where message  310  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, [&lt;EBBR BFR-Prefix, BFR-ID, SD&gt; (BTL- 2 ), &lt;IBBR BFR-Prefix, BFR-ID, mLDP FEC (root, opaque&lt;lspID 2 &gt;&gt;] where message  310  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     The BIER domain controller  301  receives the MPLS signaling information and the BTL identifying the P2MP LSP from the EBBR (illustratively, BBR  115 -B 3 ). The BIER domain controller  301  sends the MPLS signaling information and the BTL identifying the P2MP LSP to IBBRs of the BIER domain  113 , which may include all of the IBBRs of the BIER domain  113  or IBBRs of the BIER domain  113  that are relevant to the P2MP LSP. The relevant IBBRs may include any IBBRs that have terminated the MPLS domain and extracted the FEC to the BIER domain controller  301  for the P2MP LSP (illustratively, BBR  115 -B 4 ). The sending of the MPLS signaling information and the BTL identifying the P2MP LSP may be denoted as &lt;EBBR (BFR-Prefix, BFR-ID), SD&gt; (BTL), &lt;IBBR (BFR-Prefix, BFR-ID), FEC, Action&gt;&gt;. The BIER domain controller  301  may send the MPLS signaling information and the BTL identifying the P2MP LSP to IBBRs via downloading into the IBBRs. In  FIG. 3 , the sending of the MPLS signaling information and the BTL identifying the P2MP LSP from the BIER domain controller  301  to relevant IBBRs is indicated by message  340 . For example, the message  340  may include [&lt;EBBR BFR-Prefix, BFR-ID, SD&gt; (BTL- 1 ), &lt;IBBR BFR-Prefix, BFR-ID, mLDP FEC (root, opaque&lt;lspID 1 &gt;, Action&gt;] where message  310  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, [&lt;EBBR BFR-Prefix, SD&gt; (BTL- 2 ), &lt;IBBR BFR-Prefix, mLDP FEC (root, opaque&lt;lspID 2 &gt;&gt;] where message  310  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     The relevant IBBR (illustratively, BBR  115 -B 4 ) receives the MPLS signaling information and the BDT identifying the P2MP LSP from the BIER domain controller  301 . The relevant IBBR (illustratively, BBR  115 -B 4 ), based on the EBBR BFR-Prefix of the relevant EBBR (illustratively, BBR  115 -B 3 ) that is received, configures a stitched label forwarding entry on the relevant IBBR for the EBBR indicated by the EBBR BFR-Prefix. The stitched label forwarding entry is configured to stitch the incoming EBBR BFR-Prefix (BTL) for the P2MP LSP to the outgoing MPLS domain label for the P2MP LSP. On the dataplane, as discussed further below, the relevant IBBR will look at the BIER header protocol and, if the BIER header protocol is MPLS, will remove the BIER header and use the BTL under the BIER header to do a lookup in ILM for the EBBR BFR-Prefix (BTL) for determining handling of the packet in the MPLS domain (illustratively, MPLS domain  112 - 2 ). 
     The EBBR (illustratively, BBR  115 -B 3 ), in addition to assigning the BTL for the FEC from the MPLS signaling information, uses the IBBR BFR-Prefix, of the IBBR (illustratively, BBR  115 -B 4 ) which received the MPLS signaling information for the P2MP LSP, to configure a new stitched label forwarding entry on the EBBR, where the stitched label forwarding entry is configured to stitch the incoming MPLS domain label for the P2MP LSP to the outgoing BTL for the P2MP LSP, with the output interfaces (OIFs) being each of the IBBRs interested in the P2MP LSP. On the dataplane, as discussed further below, the EBBR will use the BFR-Prefixes of the IBBRs interested in the P2MP LSP as the OIFs in order to find the corresponding BIER header bit index for each IBBR in its OIF list. 
     The EBBR (illustratively, BBR  115 -B 3 ), in addition to assigning the BTL for the FEC from the MPLS signaling information, assigns a new outgoing label toward the root node (illustratively, MPLS router  114 - 2 ) for MPLS signaling within the MPLS domain (illustratively, MPLS domain  112 - 1 ). The EBBR reconstitutes MPLS signaling and sends the MPLS signaling information to the root node using MPLS signaling. In  FIG. 3 , the sending of the MPLS signaling information from the EBBR to the root node is indicated by message  350 . For example, the message  350  may include &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 3 )&gt; where message  310  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 4 )&gt; where message  310  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     It will be appreciated that, while primarily presented in  FIG. 3  within the context of handling of a specific type of action for the multicast tree (namely, a label mapping action in which the MPLS router  114  is joining the multicast tree), various embodiments of  FIG. 3  may be adapted for use in handling other types of actions (e.g., a label withdraw action in which the MPLS router  114  is leaving the multicast tree or the like). 
     It will be appreciated that, while primarily presented in  FIG. 3  within the context of embodiments in which the multicast datapath is provided using MPLS and the multicast control signaling is based on mLDP, various embodiments may adapted for use with other multicast datapath protocols, other multicast control signaling protocols, or the like, as well as various combinations thereof. 
       FIG. 4  depicts a communication system for illustrating assignment of a label to a P2MP LSP, for uniquely identifying the P2MP LSP within the BIER domain, by a BBR of the BIER domain. 
     The communication system  400  of  FIG. 4  is similar to the communication system  100  of  FIG. 1 . It will be appreciated that, although omitted for purposes of clarity, the communication system  400  may include a BIER domain controller configured to control elements of the BIER domain  113  (e.g., an SDN controller or other suitable type of controller. In communication system  400 , an EBBR (illustratively, BBR  115 -B 3 ) is responsible for assigning the BTL that uniquely identifies a P2MP LSP within the BIER domain  113  and for distributing the BTL that uniquely identifies the P2MP LSP within the BIER domain  113 . A description of a process for enabling the EBBR to assign the BTL that uniquely identifies a P2MP LSP within the BIER domain  113  and for enabling the EBBR to distribute the BTL that uniquely identifies the P2MP LSP within the BIER domain  113  follows. 
     The MPLS router (illustratively, MPLS router  114 - 4 ) associated with the multicast host (illustratively, MH  120 ) that is requesting to join the multicast group (S,G) of the P2MP LSP, sends MPLS signaling information to an IBBR of the BIER domain (illustratively, IBBR  115 -B 4  of BIER domain  113 ) using MPLS signaling in the MPLS domain (illustratively, MPLS domain  112 - 2 ). The MPLS signaling may be mLDP signaling packet or other suitable signaling packet. The MPLS signaling information may be a combination of a FEC and an associated action (e.g., label mapping, label withdraw, or the like) which may be denoted as &lt;FEC, Action&gt; for the P2MP LSP. It will be appreciated that the FEC may be a basic opaque FEC (e.g., for a single IGP area) or may be a recursive opaque FEC (e.g., for seamless MPLS). In  FIG. 4 , the sending of the MPLS signaling information to the IBBR of the BIER domain is indicated by message  410 . For example, the message  310  may include mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 ), mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 ), or the like. 
     The IBBR (illustratively, the BBR  115 -B 4 ) receives the MPLS signaling including MPLS signaling information. The IBBR terminates the MPLS signaling, identifies the EBBR (illustratively, BBR  115 -B 3 ) for which the MPLS signaling was intended, and sends the MPLS signaling information of the MPLS signaling to the EBBR for which the MPLS signaling was intended. 
     The IBBR identifies the EBBR (illustratively, BBR  115 -B 3 ) for which the MPLS signaling was intended. The IBBR may identify the EBBR based on the root address of the FEC from the MPLS signaling information. In the case of a basic opaque (Type  1 ) FEC, the root is the root of &lt;root, opaque&lt;id&gt;&gt;. In the case of a recursive opaque FEC, the root is the outer root of &lt;root, opaque&lt;inner-root, opaque&lt;id&gt;&gt;. The IBBR may identify the EBBR based on procedures defined in the draft-ietf-bier-pim-signaling document. 
     The IBBR sends the MPLS signaling information of the MPLS signaling to the EBBR for which the MPLS signaling was intended using BIER signaling. The IBBR sends the MPLS signaling information of the MPLS signaling to the EBBR for which the MPLS signaling was intended by encapsulating the MPLS signaling information of the MPLS signaling within a BIER packet, setting the BIER header to indicate routing of the BIER packet to the EBBR for which the MPLS signaling was intended (e.g., by setting the BIER header bit corresponding to the EBBR for which the MPLS signaling was intended), and forwarding the BIER packet into the BIER domain for delivery to the EBBR for which the MPLS signaling was intended. The MPLS signaling information may be encapsulated within the BIER packet by encapsulating the MPLS signaling packet (including the MPLS signaling information) within the BIER packet or by only encapsulating the MPLS signaling information (rather than the entire MPLS signaling packet) within the BIER packet. It is noted that, here, the BIER domain does not create mLDP adjacency between the two disjoint mLDP domains; rather, the BIER domain merely uses the mLDP packet for signaling purposes. In  FIG. 4 , the sending of the MPLS signaling information from the IBBR to the EBBR is indicated by message  420 . For example, the message  420  may include mLDP FEC (root, opaque&lt;lspID 1 &gt;) where message  410  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, mLDP FEC (root, opaque&lt;lspID 2 &gt;) where message  410  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     The EBBR receives the BIER packet including the MPLS signaling information from the IBBR. The EBBR removes the MPLS signaling information from the BIER packet and processes the MPLS signaling information. 
     The EBBR, based on a determination that this is the first IBBR that has forwarded the FEC to the EBBR, assigns a BTL for the FEC (and, thus, for the associated P2MP LSP) from the MPLS signaling information. The BTL that is assigned may be used to uniquely identify the associated P2MP LSP within the BIER domain  113  for supporting stitching of the P2MP LSP to the BIER datapath in the BIER domain  113 . The EBBR may assign the BTL from an overall label pool for the BIER domain  113 , from an &lt;EBBR,SD&gt; label pool associated with the EBBR (e.g., where the BIER domain controller  301  maintains a label pool per &lt;EBBR,SD&gt;, which may be used for better scalability or for other purposes, and distributes the per-EBBR label pools to the EBBRs, respectively), or the like. It is noted that the EBBR, based on a determination that this is not the first IBBR that has forwarded the FEC to the EBBR (but, rather, is a subsequent IBBR interested in the P2MP LSP), will add the IBBR BFR-Prefix to the OIF list of the FEC (since the EBBR will have already assigned the BTL for the FEC, as described above, when the FEC was received from the first IBBR interested in the P2MP LSP). 
     The EBBR sends the MPLS signaling information and the BTL identifying the P2MP LSP to the IBBR from which the MPLS signaling information was received (namely, BBR  115 -B 4 ). The EBBR may send the MPLS signaling information and the BTL identifying the P2MP LSP to the IBBR from which the MPLS signaling information was received based on a Multiprotocol-Border Gateway Protocol (MP-BGP) adjacency to the IBBR from which the MPLS signaling information was received (e.g., based on a P-Multicast Service Interface (PMSI) Tunnel Attribute (PTA) and Network Layer Reachability Information (NLRI)). The EBBR may send the MPLS signaling information and the BTL identifying the P2MP LSP to the IBBR from which the MPLS signaling information was received based on a BGP Multicast Virtual Private Network (MVPN). The EBBR may send the MPLS signaling information and the BTL identifying the P2MP LSP to the IBBR from which the MPLS signaling information was received based on Segment Routing-Traffic Engineering (SR-TE). In  FIG. 4 , the sending of the MPLS signaling information and the BTL identifying the P2MP LSP from the EBBR to the IBBR from which the MPLS signaling information was received is indicated by message  430 . For example, the message  430  may include [&lt;EBBR BFR-Prefix, SD&gt; (BTL- 1 ), &lt;IBBR BFR-Prefix, mLDP FEC (root, opaque&lt;lspID 1 &gt;&gt;] where message  410  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, [&lt;EBBR BFR-Prefix, SD&gt; (BTL- 2 ), &lt;IBBR BFR-Prefix, mLDP FEC (root, opaque&lt;lspID 2 &gt;&gt;] where message  410  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     The relevant IBBR (illustratively, BBR  115 -B 4 ) receives the MPLS signaling information and the BDT identifying the P2MP LSP from the EBBR. The relevant IBBR (illustratively, BBR  115 -B 4 ), based on the EBBR BFR-Prefix of the relevant EBBR (illustratively, BBR  115 -B 3 ) that is received, configures a stitched label forwarding entry on the relevant IBBR for the EBBR indicated by the EBBR BFR-Prefix. The stitched label forwarding entry is configured to stitch the incoming EBBR BFR-Prefix (BTL) for the P2MP LSP to the outgoing MPLS domain label for the P2MP LSP. On the dataplane, as discussed further below, the relevant IBBR will look at the BIER header protocol and, if the BIER header protocol is MPLS, will perform a lookup in the ILM for the EBBR BFR-Prefix (BTL) for determining handling of the packet in the MPLS domain (illustratively, MPLS domain  112 - 2 ). 
     The EBBR (illustratively, BBR  115 -B 3 ), in addition to assigning the BTL for the FEC from the MPLS signaling information, uses the IBBR BFR-Prefix, of the IBBR (illustratively, BBR  115 -B 4 ) which received the MPLS signaling information for the P2MP LSP, to configure a new stitched label forwarding entry on the EBBR, where the stitched label forwarding entry is configured to stitch the incoming MPLS domain label for the P2MP LSP to the outgoing BTL for the P2MP LSP, with the output interfaces (OIFs) being each of the IBBRs interested in the P2MP LSP. On the dataplane, as discussed further below, the EBBR will use the BFR-Prefixes of the IBBRs interested in the P2MP LSP as the OIFs in order to find the corresponding BIER header bit index for each IBBR in its OIF list. 
     The EBBR (illustratively, BBR  115 -B 3 ), in addition to assigning the BTL for the FEC from the MPLS signaling information, assigns a new outgoing label toward the root node (illustratively, MPLS router  114 - 2 ) for MPLS signaling within the MPLS domain (illustratively, MPLS domain  112 - 1 ). The EBBR reconstitutes MPLS signaling and sends the MPLS signaling information to the root node using MPLS signaling. In  FIG. 4 , the sending of the MPLS signaling information from the EBBR to the root node is indicated by message  440 . For example, the message  440  may include &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 3 )&gt; where message  410  includes &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 1 )&gt;, &lt;mLDP FEC (root, opaque&lt;lspID 1 &gt;, label 4 )&gt; where message  410  includes &lt;mLDP FEC (root, opaque&lt;lspID 2 &gt;, label 2 )&gt;, or the like. 
     It will be appreciated that, while primarily presented in  FIG. 4  within the context of handling of a specific type of action for the multicast tree (namely, a label mapping action in which the MPLS router  114  is joining the multicast tree), various embodiments of  FIG. 4  may be adapted for use in handling other types of actions (e.g., a label withdraw action in which the MPLS router  114  is leaving the multicast tree or the like). 
     It will be appreciated that, while primarily presented in  FIG. 4  within the context of embodiments in which the multicast datapath is provided using MPLS and the multicast control signaling is based on mLDP, various embodiments may adapted for use with other multicast datapath protocols, other multicast control signaling protocols, or the like, as well as various combinations thereof. 
       FIG. 5  depicts a communication system for illustrating transport of MPLS packets of a P2MP LSP across a BIER domain based on assignment of a label to the P2MP LSP for uniquely identifying the P2MP LSP within the BIER domain. 
     The communication system  500  of  FIG. 5  is similar to the communication system  100  of  FIG. 1 . In communication system  500 , a BTL has been assigned to a P2MP LSP for uniquely identifying the P2MP LSP within the BIER domain  113 . A description of a process for routing a multicast packet via the P2MP LSP across the BIER domain  113  based on the BTL assigned to the P2MP LSP (e.g., assigned as presented with respect to any of  FIGS. 2-4 ) follows. In this example, for purposes of clarity, it is assumed that only the MH  120  is part of the multicast group. 
     The multicast source (illustratively, MS  130 ) sends an MPLS packet to a multicast group (e.g., multicast group (S, G)) that includes a multicast host (illustratively, MH  120 ). It will be appreciated that the multicast group may include other multicast hosts; however, for purposes of clarity, routing of the MPLS packet to MH  120  is presented. The multicast source provides the MPLS packet to its associated MPLS router (illustratively, MPLS router  114 - 2  communicatively connected to MS  130  via access network  131 ). 
     The MPLS router (illustratively, MPLS router  114 - 2 ) associated with the multicast source (illustratively, MS  130 ) receives the MPLS packet from the multicast source and sends the MPLS packet to the associated BFIR of the multicast tree for the multicast group (illustratively, BBR  115 -B 3 ) via the associated MPLS domain (illustratively, MPLS domain  112 - 1 ). The MPLS packet is routed via the MPLS domain based on an MPLS label for the P2MP LSP within the MPLS domain. 
     The BFIR of the multicast tree for the multicast group (illustratively, BBR  115 -B 3 ) receives the MPLS packet via the associated MPLS domain (illustratively, MPLS domain  112 - 1 ). 
     The BFIR performs a lookup based on the MPLS label of the MPLS packet to identify the BTL for the P2MP LSP within the BIER domain. The BFIR may perform the lookup to identify the BTL for the P2MP LSP within the BIER domain in the ILM table of the BFIR. 
     The BFIR replaces the MPLS label for the P2MP LSP within the MPLS domain with the BTL for the P2MP LSP within the BIER domain (e.g., by swapping the MPLS label with the BTL, by popping the MPLS label and pushing the BTL, or the like). 
     The BFIR encapsulates the MPLS packet within a BIER header to form a BIER packet and forwards the BIER packet into the BIER domain. The BFIR identifies IBBRs of the BIER domain that belong to the multicast group and, thus, are interested in the P2MP LSP for the multicast group. The BFIR may identify IBBRs of the BIER domain that belong to the multicast group by checking the outgoing interface list of the BTL for the P2MP LSP (which includes a list of the BFR-Prefixes and BFR-IDs of the IBBRs that belong to the multicast group for the P2MP LSP). The BFIR sets the BIER Bit Index of the BIER header in a manner that indicates each of the BBRs of the BIER domain identified as belonging to the multicast group. The BFIR sets the BIER Header Protocol field in a manner that indicates the protocol of the packet being transported by the BIER packet in the BIER domain (e.g., BIERHeader.Proto=MPLS since the packet is an MPLS packet entering the BIER domain  113  from MPLS domain  112 - 1 ). The BFIR may set other fields of the BIER header. The BFIR forwards the BIER packet into the BIER domain within the corresponding SD for transporting the MPLS packet across the SD based on stitching of the MPLS P2MP LSP and the BIER datapath. 
     The BIER domain uses BIER forwarding procedures (e.g., based on RFC 8279) to provide the BIER packet to each of the IBBRs that belong to the multicast group (illustratively, BBR  115 -B 4 , which is the IBBR for the multicast group). 
     The IBBRs of the BIER domain that correspond to the same SD and that are interested in the P2MP LSP (illustratively, BBR  115 -B 4  which is the EBBR for MH  120 ) receive the BIER packet. The IBBR that is identified is the BFER of the BIER datapath for the P2MP LSP. The BFER that receives the BIER packet checks the protocol of the BIER header (in this example, BIERHeader.Proto=MPLS). The BFER that receives the BIER packet performs a lookup based on the BFR-ID of the BIER packet to identify the EBBR label pool base for the BIER packet. The BFER that receives the BIER packet removes the BIER header of the BIER packet and performs a lookup based on the EBBR BFR-Prefix (BTL) to identify the MPLS label for the P2MP LSP within the MPLS domain (illustratively, MPLS domain  112 - 2 ). The BFER may perform the lookup to identify the MPLS label for the P2MP LSP within the MPLS domain in the ILM table (e.g., the ILM table for the EBBR BFR-Prefix (BTL)) of the BFER. 
     The BFER replaces the BTL for the P2MP LSP within the BIER domain with the MPLS label for the P2MP LSP within the MPLS domain (e.g., by swapping the BTL with the MPLS label, by popping the BTL and pushing the MPLS label, or the like). 
     The BFER forwards the MPLS packet to each of the MPLS OIFs on the BFER such that the MPLS packet is delivered to each of the MPLS routers serving multicast hosts that belong to the multicast group (illustratively, for delivery to MPLS router  114 - 4  that serves MH  120 ). 
     The MPLS router that serves the multicast host belonging to the multicast group (illustratively, MPLS router  114 - 4  that serves MH  120 ) receives the MPLS and forwards the MPLS packet toward the multicast host (illustratively, toward MH  120  via associate access network  121 ). 
     It will be appreciated that, while primarily presented in  FIG. 5  within the context of embodiments in which the multicast datapath is provided using MPLS, various embodiments may adapted for use with other multicast datapath protocols. 
       FIG. 6  depicts an example embodiment of a method for use by an IBBR for supporting assignment of a label to a P2MP LSP within a BIER domain for uniquely identifying the P2MP LSP within the BIER domain. It will be appreciated that, although primarily presented herein as being performed serially, at least a portion of the functions of method  600  may be performed contemporaneously or in a different order than as presented in  FIG. 6 . At block  601 , method  600  begins. At block  610 , receive, by a BBR of a BIER domain from an MPLS domain, MPLS signaling information associated with a P2MP LSP. At block  620 , send, by the BBR toward a device configured to assign a BTL identifying the P2MP LSP within the BIER domain, the MPLS signaling information associated with the P2MP LSP. At block  699 , method  600  ends. It will be appreciated that various other functions presented herein as being supported by IBBRs (e.g., as presented in  FIGS. 1-5 ) may be performed within the context of method  600  of  FIG. 6  or using one or more other methods which may be performed in conjunction with or independent of method  600  of  FIG. 6 . 
       FIG. 7  depicts an example embodiment of a method for use by a BTL assigning node for supporting assignment of a label to a P2MP LSP within a BIER domain for uniquely identifying the P2MP LSP within the BIER domain. It will be appreciated that, although primarily presented herein as being performed serially, at least a portion of the functions of method  700  may be performed contemporaneously or in a different order than as presented in  FIG. 7 . At block  701 , method  700  begins. At block  710 , receive, by a device associated with a BIER domain, MPLS signaling information associated with a P2MP LSP. At block  720 , assign, by the device based on the MPLS signaling information associated with the P2MP LSP, a BTL identifying the P2MP LSP within the BIER domain. At block  799 , method  700  ends. It will be appreciated that various other functions presented herein as being supported by BDT assigning entities (e.g., as presented in  FIGS. 1-5 ) may be performed within the context of method  700  of  FIG. 7  or using one or more other methods which may be performed in conjunction with or independent of method  700  of  FIG. 7 . 
       FIG. 8  depicts an example embodiment of a method for use by an EBBR for supporting assignment of a label to a P2MP LSP within a BIER domain for uniquely identifying the P2MP LSP within the BIER domain. It will be appreciated that, although primarily presented herein as being performed serially, at least a portion of the functions of method  800  may be performed contemporaneously or in a different order than as presented in  FIG. 8 . At block  801 , method  800  begins. At block  810 , obtain, by a BBR of a BIER domain, a BTL identifying a P2MP LSP within the BIER domain. The BTL identifying a P2MP LSP within the BIER domain may be obtained by receiving the BTL identifying a P2MP LSP within the BIER domain, assigning the BTL identifying a P2MP LSP within the BIER domain, or the like. At block  899 , method  800  ends. It will be appreciated that various other functions presented herein as being supported by EBBRs (e.g., as presented in  FIGS. 1-5 ) may be performed within the context of method  800  of  FIG. 8  or using one or more other methods which may be performed in conjunction with or independent of method  800  of  FIG. 8 . 
     It will be appreciated that, although embodiments for supporting MPLS-based multicast via a BIER domain are primarily presented herein within the context of a specific type of multicast explicit replication domain (e.g., BIER), specific types of multicast protocols (e.g., MPLS) supporting specific types of multicast label switched paths (e.g., P2MP LSPs) based on specific types of multicast signaling protocols (e.g., mLDP), various embodiments for supporting MPLS-based multicast via a BIER domain may be provided in conjunction with other types of multicast explicit replication domains, other types of multicast protocols, other types of multicast label switched paths, other types of multicast signaling protocols, or the like, as well as various combinations thereof. 
       FIG. 9  depicts an example embodiment of a method for use by border router of a multicast explicit replication domain for supporting assignment of a label to a multicast label switched path within the multicast explicit replication domain for uniquely identifying the multicast label switched path within the multicast explicit replication domain. It will be appreciated that, although primarily presented herein as being performed serially, at least a portion of the functions of method  900  may be performed contemporaneously or in a different order than as presented in  FIG. 9 . At block  901 , method  900  begins. At block  910 , receive, by a border router of a multicast explicit replication domain from a multicast label switching domain, multicast signaling information associated with a multicast label switched path. At block  920 , send, by the border router toward a device configured to assign a tree label identifying the multicast label switched path within the multicast explicit replication domain, the multicast signaling information associated with the multicast label switched path. At block  999 , method  900  ends. It will be appreciated that method  600  of  FIG. 6  may correspond to an embodiment of method  900  of  FIG. 9  in which the multicast explicit replication domain is a BIER domain, the multicast label switching domain is an MPLS domain, the multicast signaling information is MPLS signaling information, the multicast label switched path is a P2MP LSP, and the tree label is a BDT for the P2MP LSP within the BIER domain. 
       FIG. 10  depicts an example embodiment of a method for use by an assigning node of a multicast explicit replication domain for supporting assignment of a label to a multicast label switched path within the multicast explicit replication domain for uniquely identifying the multicast label switched path within the multicast explicit replication domain. It will be appreciated that, although primarily presented herein as being performed serially, at least a portion of the functions of method  1000  may be performed contemporaneously or in a different order than as presented in  FIG. 10 . At block  1001 , method  1000  begins. At block  1010 , receive, by a device associated with a multicast explicit replication domain, multicast signaling information associated with a multicast label switched path. At block  1020 , assign, by the device based on the multicast signaling information associated with the multicast label switched path, a tree label identifying the multicast label switched path within the multicast explicit replication domain. At block  1099 , method  1000  ends. It will be appreciated that method  700  of  FIG. 7  may correspond to an embodiment of method  1000  of  FIG. 10  in which the multicast explicit replication domain is a BIER domain, the multicast signaling information is MPLS signaling information, the multicast label switched path is a P2MP LSP, and the tree label is a BDT for the P2MP LSP within the BIER domain. 
       FIG. 11  depicts an example embodiment of a method for use by a border router of a multicast explicit replication domain for supporting assignment of a label to a multicast label switched path within the multicast explicit replication domain for uniquely identifying the multicast label switched path within the multicast explicit replication domain. It will be appreciated that, although primarily presented herein as being performed serially, at least a portion of the functions of method  1100  may be performed contemporaneously or in a different order than as presented in  FIG. 11 . At block  1101 , method  1100  begins. At block  1110 , obtain, by a border router of a multicast explicit replication domain, a tree label identifying a multicast label switched path within the multicast explicit replication domain. At block  1199 , method  1100  ends. It will be appreciated that method  800  of  FIG. 8  may correspond to an embodiment of method  1100  of  FIG. 11  in which the multicast explicit replication domain is a BIER domain, the multicast label switched path is a P2MP LSP, and the tree label is a BDT for the P2MP LSP within the BIER domain. 
     Various embodiments for supporting MPLS-based multicast via a BIER domain may provide various advantages or potential advantages. Various embodiments for supporting MPLS-based multicast via a BIER domain may be configured to enable a network provider to deploy BIER in some segments of the network while retaining legacy multicast technology in other segments of the network. Various embodiments for supporting MPLS-based multicast via a BIER domain may provide various other advantages or potential advantages. 
       FIG. 12  depicts a high-level block diagram of a computer suitable for use in performing various functions described herein. 
     The computer  1200  includes a processor  1202  (e.g., a central processing unit (CPU), a processor having a set of one or more processor cores, or the like) and a memory  1204  (e.g., a random access memory (RAM), a read only memory (ROM), or the like). The processor  1202  and the memory  1204  are communicatively connected. 
     The computer  1200  also may include a cooperating element  1205 . The cooperating element  1205  may be a hardware device. The cooperating element  1205  may be a process that can be loaded into the memory  1204  and executed by the processor  1202  to implement functions as discussed herein (in which case, for example, the cooperating element  1205  (including associated data structures) can be stored on a non-transitory computer-readable storage medium, such as a storage device or other storage element (e.g., a magnetic drive, an optical drive, or the like)). 
     The computer  1200  also may include one or more input/output devices  1206 . The input/output devices  1206  may include one or more of a user input device (e.g., a keyboard, a keypad, a mouse, a microphone, a camera, or the like), a user output device (e.g., a display, a speaker, or the like), one or more network communication devices or elements (e.g., an input port, an output port, a receiver, a transmitter, a transceiver, or the like), one or more storage devices or elements (e.g., a tape drive, a floppy drive, a hard disk drive, a compact disk drive, or the like), or the like, as well as various combinations thereof. 
     It will be appreciated that computer  1200  of  FIG. 12  may represent a general architecture and functionality suitable for implementing functional elements described herein, portions of functional elements described herein, or the like, as well as various combinations thereof. For example, computer  1200  may provide a general architecture and functionality that is suitable for implementing one or more of an MPLS router  114 , a BIER router  115 , MH  120 , MS  130 , BIER domain controller  201 , BIER domain controller  301 , or the like, as well as various combinations thereof. 
     It will be appreciated that various functions presented herein may be implemented in software (e.g., via implementation of software on one or more processors, for executing on a general purpose computer (e.g., via execution by one or more processors) so as to provide a special purpose computer, and the like) and/or may be implemented in hardware (e.g., using a general purpose computer, one or more application specific integrated circuits (ASIC), and/or any other hardware equivalents). 
     It will be appreciated that various functions presented herein may be implemented within hardware, for example, as circuitry that cooperates with the processor to perform various functions. Portions of the functions/elements described herein may be implemented as a computer program product wherein computer instructions, when processed by a computer, adapt the operation of the computer such that the methods and/or techniques described herein are invoked or otherwise provided. Instructions for invoking the various methods may be stored in fixed or removable media (e.g., non-transitory computer-readable media), transmitted via a data stream in a broadcast or other signal bearing medium, and/or stored within a memory within a computing device operating according to the instructions. 
     It will be appreciated that the term “or” as used herein refers to a non-exclusive “or” unless otherwise indicated (e.g., use of “or else” or “or in the alternative”). 
     It will be appreciated that, although various embodiments which incorporate the teachings presented herein have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.