Traffic black holing avoidance and fast convergence for active-active PBB-EVPN redundancy

In one example, a method includes configuring a first provider edge (PE) router of a Provider Backbone Bridging (PBB) Ethernet Virtual Private Network (EVPN) to join an Ethernet Segment in active-active mode with at least a second PE router that is operating as a designated forwarder for the Ethernet Segment; receiving, by the first PE router from a remote PE router and prior to the first PE router performing Media Access Control (MAC) learning of a customer-MAC (C-MAC) address that is reachable via a backbone-MAC (B-MAC) address associated with the Ethernet Segment, a network packet that includes the C-MAC address; and in response to determining that the C-MAC address has not been learned by the first PE router and the B-MAC address included in the network packet is associated with the Ethernet Segment, forwarding, by the first PE router, the network packet to a destination identified by the C-MAC address.

TECHNICAL FIELD

The invention relates to computer networks and, more specifically, to forwarding network traffic within computer networks.

BACKGROUND

An Ethernet Virtual Private Network (EVPN) may be used to extend two or more remote layer two (L2) customer networks through an intermediate layer three (L3) network (usually referred to as a provider network), in a transparent manner, i.e., as if the intermediate L3 network does not exist. In particular, the EVPN transports L2 communications, such as Ethernet packets or “frames,” between customer networks via the intermediate network. In a typical configuration, provider edge (PE) network devices (e.g., routers and/or switches) coupled to the customer edge (CE) network devices of the customer networks define label switched paths (LSPs) (also referred to as pseudowires) within the provider network to carry encapsulated L2 communications as if these customer networks were directly attached to the same local area network (LAN). In some configurations, the PE network devices may also be connected by an Internet Protocol (IP) infrastructure in which case IP/Generic Routing Encapsulation (GRE) tunneling or other IP tunneling can be used between the network devices.

EVPN may be combined with Provider Backbone Bridging (PBB) defined in accordance with IEEE standard 802.1ah. PBB defines an architecture and bridging protocols in which a Provider Backbone Bridged Network (PBBN) provides L2 connectivity between multiple provider bridge networks (PBNs) of one or more different network service providers. Such large area L2 network connectivity may be deployed, for example, in metropolitan area networks. Each PBN provides one or more service virtual LANs (“S-VLANS”) to service and isolate L2 traffic from customer networks. Access switches for the PBBN typically include a set of Backbone Edge Bridges (BEBs) that interconnect some or all of the S-VLANs supported by multiple PBNs. Each BEB provides interfaces that further encapsulate L2 frames for transport through the PBBN. The VLANs used to encapsulate L2 frames from the PBNs and transport the L2 traffic through the PBBN are known as backbone VLANs (B-VLANs), and the resources that support those VLANs are usually considered to be part of the PBBN. In this way, the PBBN may be referred to as a Virtual Bridged Local Area Network under the administrative control of a backbone provider. PBB-EVPN combines functionality of an EVPN and PBB BEB bridge, such that Multi-Protocol Label Switching (MPLS) LSPs defined in an EVPN are mapped to PBB encapsulated traffic.

In a PBB-EVPN, a set of PE routers may operate in a common Ethernet Segment in active-active mode with all PE routers forwarding network traffic in the Ethernet Segment. One of the PE routers in the Ethernet Segment may operate as a designated forwarder (DF) to forward Broadcast, Unknown Unicast, and Multicast (BUM) traffic while the other PE routers in the Ethernet Segment drop BUM traffic. The Ethernet Segment may also be associated with a Backbone Media Access Control (B-MAC) address, which is used by remote PE routers to forward network traffic through a service provider network to the set of PE routers included in the common Ethernet Segment. In some examples, a remote PE router may forward a known unicast packet to a particular non-DF PE router that is associated with the B-MAC address. Although the remote PE router may have already learned the destination Customer-MAC (C-MAC) thereby causing the remote PE router to send the network packet as known unicast traffic, the particular PE router may not have yet learned the C-MAC address. As such, although the particular PE router may include a path via the Ethernet Segment to forward the network packet to its destination, the particular PE router may treat the known unicast traffic as BUM traffic (i.e., drop the traffic) because the particular PE router does not recognize the C-MAC address and the particular PE router is not the DF.

SUMMARY

The techniques described herein enable a particular PE router included in an Ethernet Segment of a PBB-EVPN to forward known unicast traffic from a service provider network to a customer network, although the PE router has not previously learned the destination C-MAC address and the particular PE router is not the designated forwarder (DF) for the Ethernet Segment. For instance, the PBB-EVPN may initially include a set of PE routers operating in active-active mode, in which one of the set of PE routers operates as a DF for forwarding BUM traffic. The set of PE routers may forward network traffic to a remote PE router, which performs MAC learning on source C-MAC addresses included in the network traffic. As part of the MAC learning, the remote PE router may store associations between source C-MAC addresses and a source B-MAC address that corresponds to the Ethernet Segment from which the network packets were sent to the remote PE router. At a later time, a particular PE router may join the Ethernet Segment as a non-DF router and advertise its reachability to the remote PE based on a B-MAC address associated with the Ethernet Segment.

If the remote PE router receives a network packet which includes a destination C-MAC address that it previously learned, the remote PE router may forward the network packet to any of the PE routers associated with the B-MAC for the Ethernet Segment. If the remote PE router forwards the network packet to the particular PE router that joined the Ethernet Segment, the particular PE router will perform a lookup in its C-MAC table for the destination C-MAC address included in the network packet. If the particular PE router did not previously learn the destination C-MAC address, the particular PE router would conventionally drop the network packet as BUM traffic because the particular PE router is not the DF for the Ethernet Segment associated with the destination B-MAC included in the network packet. Rather than drop the network packet, the PE router is configured to perform an additional lookup in accordance with techniques of the disclosure to determine whether the destination B-MAC of the network packet matches a B-MAC included in the B-MAC table of the particular PE router. If a match exists, the particular PE router determines an egress interface of the Ethernet Segment that corresponds to the matching B-MAC, and forwards the network packet using the egress interface. Because the destination for the network packet is reachable via the Ethernet Segment, the particular PE router can still forward the network packet to the destination, although the particular PE router has neither previously learned the destination C-MAC address, nor is the particular PE router the DF for the Ethernet Segment. By allowing a PE router to perform an additional lookup on the B-MAC table when forwarding network traffic from the service provider network to a customer network, techniques of the disclosure enable the PE router to avoid dropping network packets when a path to the destination exists at the particular PE router.

In one example, a method includes configuring a first provider edge (PE) router of a Provider Backbone Bridging (PBB) Ethernet Virtual Private Network (EVPN) to join an Ethernet Segment in active-active mode with at least a second PE router that is operating as a designated forwarder for the Ethernet Segment, receiving, by the first PE router from a remote PE router and prior to the first PE router performing Media Access Control (MAC) learning of a customer-MAC (C-MAC) address that is reachable via a backbone-MAC (B-MAC) address associated with the Ethernet Segment, a network packet that includes the C-MAC address, and in response to determining that the C-MAC address has not been learned by the first PE router and that the B-MAC address included in the network packet is associated with the Ethernet Segment, forwarding, by the first PE router, the network packet to a destination identified by the C-MAC address.

In another example, a first provider edge (PE) router of a Provider Backbone Bridging (PBB) Ethernet Virtual Private Network (EVPN), includes a control unit having at least one processor coupled to a memory, wherein the control unit executes software configured to: join an Ethernet Segment in active-active mode with at least a second PE router that is operating as a designated forwarder for the Ethernet Segment; receive, from a remote PE router and prior to the first PE router performing Media Access Control (MAC) learning of a customer-MAC (C-MAC) address that is reachable via a backbone-MAC (B-MAC) address associated with the Ethernet Segment, a network packet that includes the C-MAC address; and in response to determining that the C-MAC address has not been learned by the first PE router and that the B-MAC address included in the network packet is associated with the Ethernet Segment, forward the network packet to a destination identified by the C-MAC address.

In a further example, a computer-readable medium includes instructions for causing at least one programmable processor of a first (PE) router to: join an Ethernet Segment in active-active mode with at least a second PE router that is operating as a designated forwarder for the Ethernet Segment; receive, from a remote PE router and prior to the first PE router performing Media Access Control (MAC) learning of a customer-MAC (C-MAC) address that is reachable via a backbone-MAC (B-MAC) address associated with the Ethernet Segment, a network packet that includes the C-MAC address; and in response to determining that the C-MAC address has not been learned by the first PE router and that the B-MAC address included in the network packet is associated with the Ethernet Segment, forward the network packet to a destination identified by the C-MAC address.

DETAILED DESCRIPTION

FIG. 1is a block diagram illustrating an example system2, in accordance with techniques of the disclosure. In the example ofFIG. 1, PE routers10A-10E (“PE routers10”) provide customer equipment4A-4F (“customer equipment4”) associated with customer networks6A-6C (“customer networks6”) with access to service provider network12via CE routers8A-8C (“CE routers8”). Communication links16A-16L may be Ethernet connections, Asynchronous Transfer Mode (ATM) connections or any other suitable network connections.

PE routers10and CE routers8are illustrated as routers in the example ofFIG. 1. However, techniques of the disclosure may be implemented using switches or other suitable network devices that participate in a layer two (L2) virtual private network service, such as an Ethernet Virtual Private Network (EVPN) or Provider Backbone Bridging (PBB)-EVPN. Customer networks6may be networks for geographically separated sites of an enterprise. Each of customer networks6may include additional customer equipment4A-4F, such as, one or more non-edge switches, routers, hubs, gateways, security devices such as firewalls, intrusion detection, and/or intrusion prevention devices, servers, computer terminals, laptops, printers, databases, wireless mobile devices such as cellular phones or personal digital assistants, wireless access points, bridges, cable modems, application accelerators, or other network devices. The configuration of network2illustrated inFIG. 1is merely an example. For example, an enterprise may include any number of customer networks6. Nonetheless, for ease of description, only customer networks6A-6C are illustrated inFIG. 1.

Service provider network12represents a publicly accessible computer network that is owned and operated by a service provider, which is usually large telecommunications entity or corporation. Service provider network12is usually a large layer three (L3) computer network, where reference to a layer followed by a number refers to a corresponding layer in the Open Systems Interconnection (OSI) model. Service provider network12is a L3 network in the sense that it natively supports L3 operations as described in the OSI model. Common L3 operations include those performed in accordance with L3 protocols, such as the Internet protocol (IP). L3 is also known as a “network layer” in the OSI model and the term L3 may be used interchangeably with the phrase “network layer” throughout this disclosure.

Although not illustrated, service provider network12may be coupled to one or more networks administered by other providers, and may thus form part of a large-scale public network infrastructure, e.g., the Internet. Consequently, customer networks6may be viewed as edge networks of the Internet. Service provider network12may provide computing devices within customer networks6with access to the Internet, and may allow the computing devices within the customer networks to communicate with each other.

Although additional network devices are not shown for ease of explanation, it should be understood that system2may comprise additional network and/or computing devices such as, for example, one or more additional switches, routers, hubs, gateways, security devices such as firewalls, intrusion detection, and/or intrusion prevention devices, servers, computer terminals, laptops, printers, databases, wireless mobile devices such as cellular phones or personal digital assistants, wireless access points, bridges, cable modems, application accelerators, or other network devices. Moreover, although the elements of system2are illustrated as being directly coupled, it should be understood that one or more additional network elements may be included along any of network links16, such that the network elements of system2are not directly coupled.

Service provider network12typically provides a number of residential and business services, including residential and business class data services (which are often referred to as “Internet services” in that these data services permit access to the collection of publically accessible networks referred to as the Internet), residential and business class telephone and/or voice services, and residential and business class television services. One such business class data service offered by service provider network12includes L2 EVPN service. For example, an EVPN is a service that provides a form of L2 connectivity across an intermediate L3 network, such as service provider network12, to interconnect two L2 customer networks, such as L2 customer networks6, that are usually located in two different geographic areas. Often, EVPN is transparent to the customer networks in that these customer networks are not aware of the intervening intermediate service provider network and instead act and operate as if these two customer networks were directly connected and formed a single L2 network. In a way, EVPN enables a form of a transparent LAN connection between two geographically distant customer sites that each operates a L2 network and, for this reason, EVPN may also be referred to as a “transparent LAN service.”

To configure an EVPN, a network operator of the service provider configures various devices included within service provider network12that interface with L2 customer networks6. The EVPN configuration may include an EVPN instance (EVI), which consists of one or more broadcast domains. Generally, an EVI may refer to a routing and forwarding instance on a PE router, such as PE routers10A-10B and10E. Consequently, multiple EVIs may be configured on PE routers10for Ethernet segment14A, as further described herein, each providing a separate, logical layer two (L2) forwarding domain. In this way, multiple EVIs may be configured that each includes one or more of PE routers10A-10B and10E of Ethernet segment14A. In some examples, Ethernet Tags are then used to identify a particular broadcast domain, e.g., a VLAN, in an EVI. A PE router may advertise a unique EVPN label per <ESI, Ethernet Tag> combination. This label assignment methodology is referred to as a per <ESI, Ethernet Tag> label assignment. Alternatively, a PE router may advertise a unique EVPN label per MAC address. In still another example, a PE router may advertise the same single EVPN label for all MAC addresses in a given EVI. This label assignment methodology is referred to as a per EVI label assignment.

FIG. 1illustrates a PBB-EVPN environment that includes Ethernet Segments14A and14B. In typical operation, PE routers10communicate using the Border Gateway Protocol (BGP). PE routers10may interoperate using BGP in accordance with the techniques described in Provider Backbone Bridging Combined with Ethernet VPN (PBB-EVPN), draft-ietf-l2vpn-pbb-evpn-10, Nov. 14, 2015, the entire contents of which are incorporated herein by reference. PBB-EVPN enables one or more routers to operate in single-active redundancy mode or all-active (e.g., active-active) redundancy mode. In single-active redundancy mode, only a single PE router, among a group of PE routers attached to an Ethernet segment, is allowed to forward traffic to/from that Ethernet Segment, then the Ethernet segment is defined to be operating in Single-Active redundancy mode. For instance, PE router10B may be allowed to forward traffic to and from Ethernet Segment14A. In all-active redundancy mode, all PE routers attached to an Ethernet Segment are allowed to forward traffic to/from that Ethernet Segment. For instance, in all-active redundancy mode, each of PE routers10A,10B, and10E are allowed to forward traffic to and from Ethernet Segment14A. As further described in this disclosure, when operating in all-active redundancy mode, one of PE routers10A,10B, or10E in Ethernet Segment14A may be elected as the designated forwarder (DF) to forward Broadcast, Unknown Unicast, and Multicast (BUM) traffic to and from Ethernet Segment14A, while non-designated forwarders will drop such BUM traffic for Ethernet Segment14A.

In an EVPN that does not utilize PBB, a PE router performs MAC learning of customer/client MAC (C-MAC) addresses and advertises the C-MACs in BGP MAC Advertisement Routes to other PE routers in the EVPN. Such BGP MAC Advertisement Routes indicate the reachability of the C-MACs via the PE router that advertised the BGP MAC Advertisement Routes. Therefore, in EVPN, all the PE nodes participating in the same EVPN instance are exposed to all the C-MAC addresses learnt by any one of these PE routers because a C-MAC learned by one of the PE routers is advertised to other PE routers in that EVPN instance.

To reduce the number of BGP MAC Advertisement routes and the size of C-MAC tables, PBB-EVPN relies on a MAC summarization scheme, as is provided by PBB. In the MAC summarization scheme, network packets are forwarded through service provider network12by encapsulating network packets with source and destination Backbone MAC (B-MAC) addresses. PBB-EVPN defines a B-MAC address space of B-MAC addresses that are independent of a C-MAC address space, and aggregates C-MAC addresses via a single B-MAC address.

Each PE router may maintain a B-MAC table and a C-MAC table for the respective address spaces. A PE router may build a B-MAC table that includes associations between B-MAC addresses and respective sets of PE router IP addresses that are associated with a particular Ethernet Segment. For instance, an entry or row in a B-MAC table of a PE router may include a B-MAC address and a set of identifiers (e.g., MAC or IP addresses) of PE routers in a particular Ethernet Segment, where the PE router has configured the B-MAC address to correspond to the particular Ethernet Segment. Each PE router may be associated with an MPLS label that uniquely identifies the respective PE router, and the MPLS label may be associated with the respective identifier or entry in B-MAC table for respective PE router.

PE routers may be initially configured to associate a B-MAC with a particular Ethernet Segment. For instance, PE routers10A,10B, and10E may each be configured in the Ethernet Segment14A. To perform this configuration, PE routers10A,10B, and10E may each store a mapping that represents an association between an identifier of Ethernet Segment14A and a common B-MAC address (e.g., B-MAC1). As such, PE routers10A,10B, and10E may encapsulate egress traffic forwarded into the service provider network12with B-MAC1 as the source B-MAC address.

In PBB-EVPN, PE routers learn remote C-MAC to B-MAC bindings in the data plane for traffic received from the core per-PBB bridging operation. For instance, PE routers initially advertise local B-MAC address reachability information in BGP to all other PE routers in the same set of service instances, but perform C-MAC learning in the data plane. When advertising reachability, each PE router may advertise an MPLS label that identifies the respective PE router. As an example, if PE router10A receives a network packet from customer network6C, PE router10A may perform C-MAC learning to store an association, in the C-MAC table of PE router10A, between B-MAC1 and the source C-MAC of the network packet. PE router10A may encapsulate the packet with B-MAC1 as the source B-MAC and B-MAC2 as the destination B-MAC, where B-MAC2 is associated with PE router10C. PE router10C, upon receiving the network packet may perform MAC learning based on the source C-MAC included in the packet. If PE router10C does not include an entry in its C-MAC table for the source C-MAC, then PE router10C may store an entry that includes an association between the source C-MAC and B-MAC1.

At a later time, if PE router10C receives a network packet from customer network6A, PE router10C may determine the destination C-MAC for the packet matches the previously learned C-MAC stored in C-MAC table of PE router10A that is associated with B-MAC1. PE router10A may encapsulate the packet with B-MAC2 as the source B-MAC and B-MAC1 as the destination B-MAC. To forward the network packet to Ethernet Segment14A that corresponds to B-MAC1, PE router10C performs a lookup in its B-MAC table. PE router10C identifies an entry with B-MAC1 and selects the IP address of one of PE routers10A,10B, or10E, which are each associated with B-MAC1 in the B-MAC table. If PE router10C selects PE router10A as PE router to forward the network packet to customer network6C, PE router10C includes the MPLS label for PE router10A as part of the network packet header and forwards the network packet using its egress interface for PE router10A. PE router10A, upon receiving the network packet, performs a lookup in the C-MAC table based on the destination C-MAC included in the network packet. Because PE router10A previously learned the C-MAC address, PE router10A forwards the network packet to customer network6C using the interface for link16D.

At configuration and startup, a PE router, such as PE router10A performs a number of operations. For instance, PE router10A discovers all remote PE routers for a PBB I-SID in which PE router10A is included. PE router10A, at configuration and startup, distributes B-MACs to other PE routers in the PBB I-SID, so as to indicate PE router10A is reachable via the B-MACs, which may be associated with respective Ethernet Segments. PE router10A, at configuration and startup, may also discover other PE routers in the same Ethernet Segment (e.g., PE routers10B and10E in Ethernet Segment14A) and perform a designated forwarder (DF) election that is responsible for forwarding Broadcast, Unidentified Unicast or Multicast traffic (BUM) traffic for a given PBB B-MAC, and/or Ethernet Segment. In the example ofFIG. 1, PE router10A is elected the DF and PE routers10B and10E are elected non-DFs or backup-DFs. As such, PE router10A will forward BUM traffic from service provider network12for BMAC-1, while PE routers10B and10E will not.

As shown inFIG. 1, CE routers8may be multi-homed and/or singly-homed to one or more of PE routers10. In EVPN, a CE router may be said to be multi-homed when it is coupled to two physically different PE routers on the same EVI when the PE routers are resident on the same physical Ethernet Segment. As one example, CE router8C is coupled to PE routers10A,10B, and10E via links16D-16F, respectively, where10A,10B, and10E are capable of providing access to EVPN for L2 customer network6C via CE router8C. In instances where a given customer network (such as customer network6C) may couple to service provider network12via two different and, to a certain extent, redundant links, the customer network may be referred to as being “multi-homed.” In this example, CE router8C may be multi-homed to PE routers10A,10B, and10E because CE router8C is coupled to two different PE routers PE routers10A,10B, and10E via separate and, to a certain extent, redundant links16D-16F where PE routers10A,10B, and10E are each capable of providing access to EVPN for L2 customer network6C. Multi-homed networks are often employed by network operators so as to improve access to EVPN provided by service provider network12should a failure in one of links16D,16E, and16F occur. In a typical EVPN configuration, only the multi-homing PEs10A,10B, and10E participate in DF election for each ESI. CE router8B is single-homed to PE router10A via communication link16C.

An EVPN, such as illustrated inFIG. 1, may operate over a Multi-Protocol Label Switching (MPLS)-configured network and use MPLS labels to forward network traffic accordingly. MPLS is a mechanism used to engineer traffic patterns within Internet Protocol (IP) networks according to the routing information maintained by the routers in the networks. By utilizing MPLS protocols, such as the Label Distribution protocol (LDP) or the Resource Reservation Protocol with Traffic Engineering extensions (RSVP-TE), a source device can request a path through a network to a destination device, i.e., a Label Switched Path (LSP). An LSP defines a distinct path through the network to carry MPLS packets from the source device to a destination device. Using a MPLS protocol, each router along an LSP allocates a label and propagates the label to the closest upstream router along the path. Routers along the path add or remote the labels and perform other MPLS operations to forward the MPLS packets along the established path.

As shown in the example ofFIG. 1, PE routers10A-10E and provider router18may provide an MPLS core for sending network packets from customer network6A to and from customer network6C. Each of PE routers10A-10E implement the MPLS protocol and apply one or more MPLS labels, i.e., a label stack, to network packets in accordance with routing and forwarding information configured at each respective PE router. As described above, PE router10C may attach an MPLS label advertised by PE router10A to a packet that PE router10C is forwarding to PE router10A, such that the packet is forwarded through service provider network12to PE router10C.

In system2ofFIG. 1, PE routers10A and10B operate in all-active redundancy mode for B-MAC1 and Ethernet Segment14A, while PE router10E is initially not configured for B-MAC1 and Ethernet Segment14A. If, as described above, PE router10A sends a network packet to PE router10C with a C-MAC that PE router10C has not previously learned, PE router10C will learn the C-MAC by storing the C-MAC in the C-MAC table of PE router10C. After PE router10C has learned the C-MAC, PE router10E may come online and be configured for B-MAC1 and Ethernet Segment14A. Like PE router10A, at initial configuration and startup, PE router10E discovers all remote PE routers for a PBB I-SID in which PE router10E is included. PE router10E, at configuration and startup, distributes B-MACs to other PE routers in the PBB I-SID, so as to indicate PE router10E is reachable via the B-MACs, which may be associated with respective Ethernet Segments. For instance, PE router10C may receive a BGP messages from PE router10E that indicates B-MAC1is reachable via PE router10E. PE router10E, at configuration and startup, may also discover other PE routers in the same Ethernet Segment (e.g., PE routers10A and10B in Ethernet Segment14A) and perform a designated forwarder (DF) election.

PE router10C may later receive a network packet destined for customer network6after PE router10C has configured its B-MAC table to include an association between B-MAC1 and an identifier of PE router10E. PE router10C may determine that the network packet includes the previously learned C-MAC by performing a lookup in the C-MAC table that includes an association between the C-MAC and B-MAC1. Based on the association between the C-MAC and B-MAC1, PE router10C may perform a lookup in its B-MAC table which includes B-MAC1 associated with identifiers of PE routers10A,10B, and10E. Using one or more load-balancing operations, PE router10C may use the identifier of PE router10E to forward the network packet to PE router10E. For instance, PE router10C may encapsulate the packet with B-MAC2 as the source B-MAC, B-MAC1 as the destination B-MAC, and attach and MPLS label previously advertised by PE router10E that identifies PE router10E the PBB-EVPN. PE router10C may then forward the encapsulated packet as known unicast traffic to PE router10E using a logical interface of PE router10C that corresponds to PE router10E. Notably, source and destination C-MACs may be included in the encapsulated network packet as it is sent to provider network12.

PE router10E may receive the encapsulated packet and perform a lookup in the C-MAC table for an entry that includes the destination C-MAC of the encapsulated packet. Conventionally, if PE router10E had not previously learned the C-MAC address (e.g., the C-MAC address is not included in the C-MAC table), then PE router10E would have dropped the encapsulated network packet because PE router10E is not the DF for Ethernet Segment14A that is associated with B-MAC1. Rather than dropping the encapsulated network packet, PE router10E is configured to, in accordance with techniques of the disclosure determine whether PE router10E is included in an Ethernet Segment that corresponds to the destination B-MAC, i.e., B-MAC1. To perform this determination, PE router10E determines whether the destination B-MAC, i.e., B-MAC1, is included in the B-MAC table of PE router10E. If PE router10E determines that B-MAC1 is included in the B-MAC table, then PE router10E determines the egress interface for Ethernet Segment14A based on an association between B-MAC1 and an identifier of Ethernet Segment14A. PE router10E removes at least the destination and source B-MACs and the MPLS labels used for forwarding the encapsulated network through service provider network12, and forwards the network packet to CE router8C via communication link16F that corresponds to the egress interface.

As described above in accordance with techniques of the disclosure, PE router10E may avoid dropping known unicast traffic from remote PE routers for B-MAC1, although PE router10E has not yet learned the C-MAC address in such known unicast traffic and although PE router10E is not the designated forwarder for Ethernet Segment14A. As such, rather than dropping known unicast traffic destined for customer network6C, PE router10E may forward the network traffic, thereby reducing or eliminating the need for PE router10C to re-send known unicast packets that would otherwise have been dropped. Accordingly, techniques of the disclosure may prevent PE router10E from treating known unicast traffic as BUM traffic when PE router10E has not yet learned the C-MAC in the known unicast traffic. This can reduce or avoid dropped traffic (an effect sometimes referred to as “traffic black holing”), and may also improve a speed of network convergence in active-active PBB-EVPN redundancy systems.

FIG. 2is a block diagram illustrating an example PE router10E capable of performing the disclosed techniques. In general, PE router10E may operate substantially similar to PE router10E ofFIG. 1. In this example, PE router10E includes interface cards88A-88N (“IFCs88”) that receive packets via incoming links90A-90N (“incoming links90”) and send packets via outbound links92A-92N (“outbound links92”). IFCs88are typically coupled to links90,92via a number of interface interfaces. PE router10E also includes a control unit82that determines routes of received packets and forwards the packets accordingly via IFCs88.

Control unit82may comprise a routing engine84and a packet forwarding engine86(or “forwarding unit”). Routing engine84operates as the control plane for provider router18and includes an operating system that provides a multi-tasking operating environment for execution of a number of concurrent processes. Routing engine84, for example, execute software instructions to implement one or more control plane networking protocols97. For example, protocols97may include one or more routing protocols, such as Border Gateway Protocol (BGP)99for exchanging routing information with other routing devices and for updating routing information94. Protocols97may also include Multiprotocol Label Switching Protocol (MPLS)95for tunneling packets within service provider network12.

Routing protocol daemon (RPD)99may use protocols97to exchange routing information, stored in routing information94, with other routers. Routing information94may include information defining a topology of a network. RPD99may resolve the topology defined by routing information in routing information94to select or determine one or more routes through the network. RPD99may then generate forwarding information106and update forwarding plane86with routes from forwarding information106.

Routing information94may describe a topology of the computer network in which provider router18resides, and may also include routes through the shared trees in the computer network. Routing information94describes various routes within the computer network, and the appropriate next hops for each route, i.e., the neighboring routing devices along each of the routes. Routing engine84analyzes stored routing information94and generates forwarding information106for forwarding engine86. Forwarding information106may associate, for example, network destinations for certain multicast groups with specific next hops and corresponding IFCs88and physical output interfaces for output links92. Forwarding information106may be a radix tree programmed into dedicated forwarding chips, a series of tables, a complex database, a link list, a radix tree, a database, a flat file, or various other data structures.

In addition, routing engine84executes EVPN protocol87, which operates to communicate with other routers to establish and maintain an EVPN, such as the EVPN ofFIG. 1, for transporting L2 communications through an intermediate network so as to logically extend an Ethernet network through the intermediate network. EVPN protocol87may, for example, communicate with EVPN protocols executing on remote routers. EVPN protocol87may operate in accordance with techniques described in “BGP MPLS-Based Ethernet VPN,” RFC 7432, February 2015, the entire contents of which are incorporated herein by reference.

Routing engine84executes PBB protocol101in accordance with IEEE 802.1ah-2008, Provider Backbone Bridges, June 2008, the entire contents of which are incorporated herein by reference. PBB protocol101provides for the exchange of control plane messages that include PBB configuration information, such as announcing B-MAC addresses. PBB protocol101is also used by PE router10E to encapsulate network packets with PBB headers, such as source and destination B-MAC addresses.

In some examples, forwarding engine86arranges forwarding structures as next hop data that can be chained together as a series of “hops” along an internal packet forwarding path for the network device. In many instances, the forwarding structures perform lookup operations within internal memory of ASICs included in forwarding engine86, where the lookup may be performed against a tree (or trie) search, a table (or index) search. Other example operations that may be specified with the next hops include filter determination and application, or a rate limiter determination and application. Lookup operations locate, within a lookup data structure (e.g., a lookup tree), an item that matches packet contents or another property of the packet or packet flow, such as the inbound interface of the packet. The result of packet processing in accordance with the operations defined by the next hop forwarding structure within ASICs determines the manner in which a packet is forwarded or otherwise processed by forwarding engine86from its input interface on one of IFCs88to its output interface on one of IFCs88.

As shown inFIG. 2, forwarding information106includes B-MAC table107. B-MAC table107includes data representing mappings or associations between B-MAC addresses and Ethernet Segments. For instance, B-MAC table107includes a B-MAC address as key and a list of identifiers of PE routers included in an Ethernet Segment that corresponds to the B-MAC address. Forwarding information106also includes C-MAC table109. C-MAC table109includes data representing mappings or associations between C-MAC addresses and B-MAC addresses. In some examples, C-MAC table109includes a C-MAC address as a key and a B-MAC address as the corresponding value, or vice versa. Forwarding information106may also include aliasing data113. Aliasing data113may include data representing mappings or associations between B-MAC addresses and identifiers of Ethernet Segments.

Forwarding information may also include lookup structures111. Lookup structures111may, given a key, such as an address, provide one or more values. In some examples, the one or more values may be one or more next hops. A next hop may be implemented as microcode, which when executed, perform one or more operations. One or more next hops may be “chained,” such that a set of chained next hops perform a set of operations for respective different next hops when executed. Examples of such operations may include applying one or more services to a packet, dropping a packet, and/or forwarding a packet using an interface and/or interface identified by the one or more next hops.

As described above, in system2ofFIG. 1, PE routers10A and10B initially operate in all-active redundancy mode for B-MAC1 and Ethernet Segment14A. PE router10E is initially not configured for B-MAC1 and Ethernet Segment14A. PE router10A initially sends a network packet to PE router10C with a C-MAC that PE router10C has not previously learned, PE router10C will learn the C-MAC by storing the C-MAC in the C-MAC table of PE router10C.

After PE router10C has learned the C-MAC, PE router10E may come online and be configured for B-MAC1 and Ethernet Segment14A. At initial configuration and startup, PE router10E discovers all remote PE routers for a PBB I-SID in which PE router10E is included. For instance, RPD99may communicate with PBB101, BGP93, and EVPN87to generate a MAC Advertisement Route message (as described in draft-ietf-l2vpn-pbb-evpn-10) that includes B-MAC1, which may be configured by an administrator or operator of PE router10E. PE router10E may send the MAC Advertisement Router message to other PE routers in the PBB I-SID that includes PE router10E. In this way, other PE routers in service provider network12determine that B-MAC1 is reachable via PE router10E. The PE routers that received the MAC Advertisement Router message may similarly send PE router10E respective MAC Advertisement Router messages that indicate the reachability of the same B-MAC1 and/or other B-MACs via the respective PE routers.

PE router10C may later receive a network packet destined for customer network6after PE router10C has configured its B-MAC table to include an association between B-MAC1 and an identifier of PE router10E. PE router10C may determine that the network packet includes the previously learned C-MAC by performing a lookup in the C-MAC table that includes an association between the C-MAC and B-MAC1. Based on the association between the C-MAC and B-MAC1, PE router10C may perform a lookup in its B-MAC table which includes B-MAC1 associated with identifiers of PE routers10A,10B, and10E. PE router10C may use the identifier of PE router10E to forward the network packet to PE router10E. For instance, PE router10C may encapsulate the packet with B-MAC2 as the source B-MAC, B-MAC1 as the destination B-MAC, and attach an MPLS label previously advertised by PE router10E that identifies PE router10E the PBB-EVPN. PE router10C may then forward the encapsulated packet as known unicast traffic to PE router10E using a logical interface of PE router10C that corresponds to PE router10E.

PE router10E may initially receive the encapsulated packet at interface88A. Forwarding engine86determines the destination C-MAC included in the encapsulated packet and determines whether C-MAC table109includes the destination C-MAC. In the examples ofFIGS. 1 and 2, PE router10E has not yet learned the destination C-MAC of the packet, when PE router10C forwards the packet to PE router10E. As such, when forwarding engine86performs a lookup on C-MAC table109, forwarding engine86determines that the C-MAC is not in table109. If the C-MAC were included in C-MAC table109, then PE router10E would forward the network packet using the egress interface for the C-MAC in C-MAC table109.

Because the C-MAC is not included in C-MAC table109, forwarding engine106, in accordance with techniques of the disclosure identifies the destination B-MAC1 in the encapsulated network packet. Forwarding engine106determines whether destination B-MAC1 is included in B-MAC table107. If forwarding engine106determines that B-MAC1 is not included in B-MAC table107, then forwarding engine106treats the packet as BUM traffic and drops the packet because PE router10E is not the DF in Ethernet Segment14A. If, however, forwarding engine106determines that B-MAC1 is included in B-MAC table107, then PE router10E determines the egress interface for Ethernet Segment14A based on an association in aliasing data113between B-MAC1 and an identifier of Ethernet Segment14A. That is, upon determining that Ethernet Segment14A is associated with B-MAC1, PE router10A determines the egress interface for Ethernet Segment14A. Forwarding engine86forwards the network packet using the egress interface to CE router8C.

The architecture of PE router10E illustrated inFIG. 2is shown for example purposes only. The invention is not limited to this architecture. In other examples, PE router10E may be configured in a variety of ways. In one example, some of the functionality of control unit82may be distributed within IFCs88. In another example, control unit82may comprise a plurality of packet forwarding engines operated as slave routers.

Control unit82may be implemented solely in software, or hardware, or may be implemented as a combination of software, hardware, or firmware. For example, control unit82may include one or more processors which execute software instructions. In that case, the various software modules of control unit82may comprise executable instructions stored on a computer-readable medium, such as computer memory or hard disk.

FIGS. 3A-3Bare example block diagrams of a PBB-EVPN header and B-MAC table, in accordance with techniques of the disclosure.FIG. 3Aillustrates an example PBB-EVPN header and L2 payload. As shown inFIG. 3A, header150includes an outer transport label152and inner MPLS service label154. MPLS service label154may be an MPLS label that uniquely identifies PE router10E within an EVPN Instance (EVI). For instance, PE router10E may advertise MPLS service label154to other PE routers in the same EVI. Outer transport label152may be an MPLS label advertised by a provider router in provider network12that is one hop away from PE router10C. PBB-EVPN header150includes destination B-MAC address156and source B-MAC address158. In the examples ofFIGS. 1-2 and 4-5, PE router10C, may when sending a network packet to PE router10E, include B-MAC1 as destination B-MAC address156and B-MAC2 as source B-MAC address158. When PE router10E later determines that destination C-MAC164is not included in the C-MAC table of PE router10E, PE router10E may determine whether destination B-MAC address156is included in the B-MAC table of PE router10E.

PBB-EVPN header150also includes Ethertype160and ISID162. Ethertype160may be a unique value that indicates the type of packet, i.e., a PBB-EVPN packet. ISID162may be an identifier of a PBB B-Service instance that includes B-MAC1. PBB-EVPN header150also includes destination C-MAC address164and source C-MAC address166. In the examples ofFIGS. 1-2 and 4-5, when PE router10C sends a network packet to PE router10E, destination C-MAC address164may be a C-MAC address of customer equipment4E and source C-MAC166may be a C-MAC address of customer equipment4A. When PE router10E receives a network packet from PE router10C, prior to learning source C-MAC address166, PE router10E may determine destination B-MAC address156is included in the B-MAC table of PE router10E. Based on determining that destination B-MAC address156is included in the B-MAC table, PE router10E determines an egress interface included the Ethernet Segment14A that is associated with destination B-MAC1 and forwards the network packet using the egress interface to customer network6C.

FIG. 3Billustrates a B-MAC table170of PE router10C. B-MAC table170includes columns for Ethernet Segment Identifier (ESI), B-MAC address, and VPN. For instance, entry172includes an ESI value174. In some examples, ESI value174is a unique identifier of Ethernet Segment14A. In such cases, PE router10E includes a separate data structure that includes ESI value174associated with a list that includes identifiers of PE routers included in Ethernet Segment14A. In other examples, ESI value174is a pointer or reference to a list of identifiers of PE routers included in Ethernet Segment14A. As shown inFIG. 3B, ESI value174is a pointer to a list of identifiers of PE routers10A,10B, and10C. The identifiers of PE routers10A,10B, and10E may be IP addresses, MAC addresses, MPLS labels advertised by the respective PE routers, or any other suitable identifier for identifying a PE router. Entry172also includes B-MAC1, which is associated with Ethernet Segment14A. Because B-MAC1 is included in the same entry172as ESI value174, B-MAC1 is associated with PE routers included in Ethernet Segment14A, and more generally, associated with Ethernet Segment14A. Entry172also includes a Route Target178. In accordance with techniques of the disclosure, if PE router10E receives a network packet from PE router10C that is destined for customer network6C and PE router10E determines that the destination C-MAC is not included in the C-MAC table of PE router10E, then PE router10E performs a lookup on B-MAC table170and determines that entry172includes B-MAC1. PE router10E performs a lookup on aliasing data as described inFIG. 2to determine whether B-MAC1 is associated with an Ethernet Segment that includes PE router10E. PE router10E may determine that B-MAC1 is included in the aliasing data, further determine that B-MAC1 is associated with Ethernet Segment14A. PE router10E may determine the egress interface associated with Ethernet Segment14A and forward the packet using the egress interface, rather than treating the packet as BUM traffic and dropping the packet.

FIG. 4is a flowchart illustrating example operations of system2, in accordance with techniques of the disclosure. Example operations in accordance with techniques of the disclosure are illustrated for example purposes with respect to PE router10E. As described inFIGS. 1-3 and 5, PE router10E may join Ethernet Segment14A and B-MAC1 and later receive a network packet from PE router10C that is destined for customer network6C but prior to PE router10E learning the destination C-MAC of the network packet. As shown inFIG. 4, in response to receiving the network packet, PE router10E identifies an EVI for the network packet based on the MPLS service label included in the network packet (160). For instance, PE router10E may determine MPLS service label154corresponds to a particular EVI. PE router10E may determine the destination B-MAC, e.g., B-MAC1, included in the network packet (161). For instance, the destination B-MAC may be destination B-MAC156as shown inFIG. 3A. PE router10E may identify the customer bridge domain based on the ISID included in the network packet header (162). Determining the customer bridge domain enables PE router10E to determine the C-MAC table for the ISID.

PE router10E performs MAC learning of the source C-MAC address (163). For instance, PE router10E stores an entry in its C-MAC table for the ISID of the packet, which indicates an association between the source-CMAC and source B-MAC2. PE router10E then performs a MAC lookup in the C-MAC table for the destination C-MAC address (164). PE router10E determines whether the destination C-MAC is included in the C-MAC table (165). If the destination C-MAC is in the C-MAC table, then PE router10E determines the B-MAC corresponding to the destination C-MAC and identifies the egress interface associated with the B-MAC. PE router10E forwards the network packet using the egress interface (166).

In the example ofFIG. 4, the destination C-MAC of the network packet is not included in the C-MAC table for the ISID. In accordance with techniques of the disclosure, PE router10E determines whether the destination B-MAC is included in the B-MAC table for the ISID (167). PE router10E determines that the destination B-MAC1 from the network packet is included in the B-MAC table. Accordingly, PE router10E determines an egress interface associated with Ethernet Segment14A, based on using aliasing data to determine that Ethernet Segment14A corresponds to B-MAC1 (168). PE router10E forwards the packet using the egress interface (166). If the B-MAC table of PE router10E does not include the destination B-MAC1, then PE router10E performs BUM forwarding (169). For instance, if PE router10E is not the DF for Ethernet Segment14A, then PE router10E drops the packet. If PE router10E is the DF for Ethernet Segment14A, then PE router10E floods the packet within Ethernet Segment14A to PE routers10A and10B.

FIG. 5is a flowchart illustrating example operations of system2, in accordance with techniques of the disclosure. Example operations in accordance with techniques of the disclosure are illustrated for example purposes with respect to PE routers10A,10B and10E. As shown inFIG. 5, PE router10A may initially receive a first packet from CE router8C that is destine for customer network6A. PE router10A may perform a lookup on the source C-MAC and determine that the source C-MAC of the packet is not included in the C-MAC table of PE router10A. PE router10A may perform MAC learning by storing the source C-MAC in the C-MAC table in association with B-MAC1, which is associated with Ethernet Segment14A. PE router10A forwards the network packet to PE router10C (200). As described in this disclosure, PE router10A may encapsulate the first network packet with a PBB header that includes at least a source B-MAC1 and a destination B-MAC2.

PE router10C receives the first network packet with the PBB header. PE router10C performs MAC learning based on source C-MAC and source B-MAC1 by storing data in the C-MAC table of PE router10C that indicates an association between the source C-MAC and source B-MAC1 (201). In this way, PE router10C, when receiving traffic from customer network6A that is destined for customer network6C, may forward the network traffic as known unicast traffic to B-MAC1. PE router10C, upon determining that the destination C-MAC of the first network packet corresponds to customer network6A, sends the first network packet to customer network6A.

At a later time, PE router10E joins Ethernet Segment14A, which corresponds to B-MAC1. PE router10E sends MAC Route Advertisements to at least PE routers10B and10C that indicate PE router10E is included in B-MAC1 (206). PE routers10C and10A receive respective MAC Route Advertisements, update their respective forwarding information to associate PE router10E with PE routers10A and10C (208,204). As an example, PE router10C creates an entry in its B-MAC table that indicates an association between B-MAC1 and an identifier of PE router10E (e.g., IP address, MAC address, MPLS label advertised by PE router10E, etc.). PE router10A creates a similar entry in its B-MAC table like PE router10C.

After PE router10C has updated its B-MAC table to include B-MAC1, PE router10C may receive a second network packet from CE router8A that is destined for customer network6C (210). PE router10C may identify the destination C-MAC of the network packet and perform a lookup in the C-MAC table of PE router10C (212). Since PE router10C previously learned the destination C-MAC, which is stored in the C-MAC table, PE router10C may determine that B-MAC1 is associated with the destination C-MAC. PE router10C may perform a lookup on B-MAC1 to select one of PE routers10A,10B, or10E to forward the second network packet. Because each of PE routers10A,10B, and10E are each associated with B-MAC1 in PE router10C's B-MAC table, PE router10C may perform one or more load-balancing operations (e.g., round-robin, header-based hashing, or any other suitable load-balancing technique) to select PE router10E. PE router10C determines an interface associated with PE router10E and forwards the second network packet to service provider network12(214). As described in this disclosure, PE router10C may attach a source B-MAC1 and destination B-MAC2 to the second network packet. PE router10C may attach an MPLS label previously advertised by PE router10E for forwarding network packets to PE router10E through service provider network12(e.g., an inner service label). PE router10E may also attach an MPLS label that corresponds to a direct next hop (e.g., provider router) in service provider network12to which PE router10C forwards the second network packet (e.g., an outer transport label).

PE router10E receives the second network packet. Upon receiving the second network packet PE router10E performs a lookup based on the destination C-MAC included in the network packet. PE router10E determines that the destination C-MAC is not included in the C-MAC table of PE router10E because PE router10E has not previously learned the destination C-MAC (216). For instance, PE router10E has not previously received a network packet that included the destination C-MAC as a source C-MAC and has not stored such as source C-MAC in the C-MAC table of PE router10E in association with B-MAC1. Rather than discarding the second network packet as BUM traffic because PE router10E is not the DF for Ethernet Segment14A, PE router10E performs an additional lookup in the B-MAC table of PE router10E. To perform the lookup, PE router10E determines whether the destination B-MAC1 is included in the B-MAC table of PE router10E. If the destination B-MAC1 is not included in the B-MAC table, then PE router10E treats the packet as BUM traffic and drops the packet. However, in the example ofFIG. 5, PE router10E determines that B-MAC1 is included in the B-MAC table of PE router10E. PE router10E determines the egress interface for Ethernet Segment14A based on an association between B-MAC1 and an identifier of Ethernet Segment14A. Upon determining the egress interface, PE router10E forwards the second network packet to customer network16C using the egress interface (220).