Abstract:
A method, apparatus and computer program product for minimizing or preventing duplicate traffic during point to multipoint tree switching in a network. In its operation, embodiments disclosed herein utilize control plane trigger mechanisms to handle the receipt of duplicate traffic by network entities after the occurrence of a network failure event. Generally, the control plane trigger mechanism prevents a network entity from processing multicast traffic from both old and new upstream data paths resulting from typical network convergence procedures. The methods and apparatus describe herein apply to standard rerouting procedures as well as fast rerouting procedures for multicast traffic in a network.

Description:
BACKGROUND 
     The Internet is a massive network of networks in which computers communicate with each other via use of different communication protocols. The Internet includes packet-routing devices, such as switches, routers and the like, interconnecting many computers. To support routing of information such as packets, each of the packet-routing devices typically maintains routing tables to perform routing decisions in which to forward traffic from a source computer, through the network, to a destination computer. 
     One way of forwarding information through a provider network over the Internet is based on MPLS (Multiprotocol Label Switching) techniques. In an MPLS-network, incoming packets are imposed with a label by a so-called LER (Label Edge Router) receiving the incoming packets. The packets in the MPLS network are forwarded along a predefined Label Switch Path (LSP) defined in the MPLS network based on label on the packets. At internal nodes of the MPLS-network, the packets are forwarded along a predefined LSP through so-called Label Switch Routers. LDP (Label Distribution Protocol) is used to distribute appropriate labels for label-switching purposes. 
     Each Label Switching Router (LSR) in an LSP between respective LERs in an MPLS-type network makes forwarding decisions based solely on a label of a corresponding packet. Depending on the circumstances, a packet may need to travel through many LSRs along a respective path between LERs of the MPLS-network. As a packet travels through a label-switching network, each LSR along an LSP strips off an existing label associated with a given packet and applies a new label to the given packet prior to forwarding to the next LSR in the LSP. The new label informs the next router in the path how to further forward the packet to a downstream node in the MPLS network eventually to a downstream LER that can properly forward the packet to a destination. 
     MPLS service providers have been using unicast technology to enable communication between a single sender and a single receiver in label-switching networks. The term unicast exists in contradistinction to multicast (or point to multipoint “P2MP”), which involves communication between a single sender and multiple receivers. Both of such communication techniques (e.g., unicast and multicast) are supported by Internet Protocol version 4 (IPv4). 
     Service providers have been using so-called unicast Fast Reroute (FRR) techniques for quite some time to provide more robust unicast communications. In general, fast rerouting includes setting up a backup path for transmitting data in the event of a network failure so that a respective user continues to receive data even though the failure occurs. 
     In multicast networks, Reverse Path Forwarding (RPF) techniques are used in building source-specific forwarding paths such that the multicast traffic can flow more efficiently without forwardwarding loops. A network employing RPF issues source-specific joins towards the source node while using the source address to look up a unicast routing table entry. This upstream process continues router by router until the source is reached. The upstream routers then are able to forward the multicast traffic downstream toward the original join. In essence, the traffic is forwarded along the reverse path from the source back to the listener. 
     SUMMARY 
     Conventional mechanisms such as those explained above suffer from a variety of shortcomings. More specifically, label-switching networks that are capable of rerouting P2MP traffic are susceptible to transmitting and receiving duplicate P2MP traffic at various network nodes upon the occurrence of a respective link or node failure in the network. For example, during a fast reroute operation in a multicast network a particular node (e.g., router) may receive duplicate traffic from both the fast reroute backup path and the new upstream multicast path created during network convergence. As such, the reception of duplicate traffic at network entities can significantly encumber network throughput while resulting in noticeable performance degradation by users interacting with the network. 
     Embodiments of the invention significantly overcome such shortcomings and provide mechanisms and techniques for minimizing or preventing duplicate traffic during point to multipoint tree switching in a network. In its operation, embodiments disclosed herein utilize control plane trigger mechanisms to handle the receipt of duplicate traffic by network entities after the occurrence of a network failure event. Essentially, the control plane trigger mechanism prevents a network entity from processing multicast traffic from both old and new upstream data paths resulting from typical network convergence procedures. The methods and apparatus described herein apply to standard rerouting procedures as well as fast rerouting procedures for multicast traffic in a network. 
     In a particular embodiment of a method for minimizing duplicate traffic during P2MP tree switching in a network including a P2MP tree with a source node, the method includes transmitting multicast data traffic from a first router over a primary network path to a second router, wherein the network path supports multicast label switching of multicast data traffic. The method further includes, in response to detecting a failure in the network, initiating a multicast rerouting procedure that comprises, I) transmitting a new switching label via a secondary network path to an upstream router, wherein the secondary network path includes at least one upstream node; and II) upon receiving an acknowledgement notification from the upstream router via the secondary network path, configuring the second router to receive multicast data traffic from the secondary network path in lieu of receiving multicast data traffic from the primary network path. 
     Alternatively, the method includes configuring the network to include at least one backup path between the first router and the second router, wherein the backup path supports multicast label switching of multicast data traffic. The method also includes, in response to detecting the failure in the network, initiating transmission of the multicast data traffic over the at least one backup path between the first router and the second router in lieu of transmitting the multicast data traffic over the primary network path. In addition, the method further includes, upon receiving an acknowledgement notification from the upstream router via the secondary network path, configuring the second router to receive multicast data traffic from the secondary network path in lieu of receiving multicast data traffic from the at least one backup path. 
     Other embodiments include a computer readable medium having computer readable code thereon for providing a method for minimizing duplicate traffic during P2MP tree switching in a network including a P2MP tree with a source node. The computer readable medium also includes instructions operable on a processor to transmit multicast data traffic from a first router over a primary network path to a second router, wherein the network path supports multicast label switching of multicast data traffic. The computer readable medium further includes, in response to detecting a failure in the network, instructions operable on a processor to initiate a multicast rerouting procedure, wherein the multicast rerouting procedure comprises, I) instructions operable on a processor to transmit a new switching label via a secondary network path to an upstream router, wherein the secondary network path includes at least one upstream node; and II) upon receiving an acknowledgement notification from the upstream router via the secondary network path, instructions operable on a processor to configure the second router to receive multicast data traffic from the secondary network path in lieu of receiving multicast data traffic from the primary network path. In addition, the computer readable medium includes instructions operable on a processor to configure the network to include at least one backup path between the first router and the second router, wherein the backup path supports multicast label switching of multicast data traffic. Further, the computer readable medium includes, in response to detecting the failure in the network, instructions operable on a processor to initiate transmission of the multicast data traffic over the at least one backup path between the first router and the second router in lieu of transmitting the multicast data traffic over the primary network path. The computer readable medium also includes, upon receiving an acknowledgement notification from the upstream router via the secondary network path, instructions operable on a processor to configure the second router to receive multicast data traffic from the secondary network path in lieu of receiving multicast data traffic from the at least one backup path. 
     Still other embodiments include a computerized device configured to process all the method operations disclosed herein as embodiments of the invention. In such embodiments, the computerized device includes a memory system, a processor, communications interface in an interconnection mechanism connecting these components. The memory system is encoded with a process that provides a method for method for minimizing duplicate traffic during P2MP tree switching in a network as explained herein that when performed (e.g. when executing) on the processor, operates as explained herein within the computerized device to perform all of the method embodiments and operations explained herein as embodiments of the invention. Thus any computerized device that performs or is programmed to perform processing explained herein is an embodiment of the invention. 
     Other arrangements of embodiments of the invention that are disclosed herein include software programs to perform the method embodiment steps and operations summarized above and disclosed in detail below. More particularly, a computer program product is one embodiment that has a computer-readable medium including computer program logic encoded thereon that when performed in a computerized device provides associated operations providing a method for minimizing duplicate traffic during P2MP tree switching in a network as explained herein. The computer program logic, when executed on at least one processor with a computing system, causes the processor to perform the operations (e.g., the methods) indicated herein as embodiments of the invention. Such arrangements of the invention are typically provided as software, code and/or other data structures arranged or encoded on a computer readable medium such as an optical medium (e.g., CD-ROM), floppy or hard disk or other a medium such as firmware or microcode in one or more ROM or RAM or PROM chips or as an Application Specific Integrated Circuit (ASIC) or as downloadable software images in one or more modules, shared libraries, etc. The software or firmware or other such configurations can be installed onto a computerized device to cause one or more processors in the computerized device to perform the techniques explained herein as embodiments of the invention. Software processes that operate in a collection of computerized devices, such as in a group of data communications devices or other entities can also provide the system of the invention. The system of the invention can be distributed between many software processes on several data communications devices, or all processes could run on a small set of dedicated computers, or on one computer alone. 
     The multicast techniques in this disclosure can be used to extend the multicast FRR backup path procedure as discussed in U.S. patent application Ser. No. 11/336,457, the entire teachings of which are incorporated herein by reference, to include multicast FRR backup path tunnels along with other techniques germane to forwarding multicast data in a label-switching network. 
     Note that techniques herein are well suited for use in applications such as label-switching networks that support routing of multicast data traffic. However, it should be noted that configurations herein are not limited to use in such applications and thus configurations herein and deviations thereof are well suited for other applications as well. 
     It is to be understood that the embodiments of the invention can be embodied strictly as a software program, as software and hardware, or as hardware and/or circuitry alone, such as within a data communications device. The features of the invention, as explained herein, may be employed in data communications devices and/or software systems for such devices such as those manufactured by Cisco Systems, Inc. of San Jose, Calif. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of preferred embodiments of the methods and apparatus for minimizing duplicate traffic during P2MP tree switching in a network, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the methods and apparatus for minimizing duplicate traffic during P2MP tree switching in a network. 
         FIG. 1  depicts a block diagram of a network environment performing fast rerouting procedures involving various routers in a network. 
         FIG. 2  depicts a block diagram of a network environment performing techniques for minimizing duplicate traffic during P2MP tree switching in light of a fast reroute operation. 
         FIG. 3  depicts a block diagram of a network environment performing techniques for minimizing duplicate traffic during P2MP tree switching in light of a fast reroute operation. 
         FIG. 4  depicts a block diagram of a network environment performing techniques for minimizing duplicate traffic during P2MP tree switching in light of a fast reroute operation. 
         FIG. 5  depicts a block diagram of a network environment performing techniques for minimizing duplicate traffic during P2MP tree switching in light of a standard reroute operation. 
         FIG. 6  depicts a block diagram of a network environment performing techniques for minimizing duplicate traffic during P2MP tree switching in light of a standard reroute operation. 
         FIGS. 7 through 10  depict flow diagrams of particular methods for minimizing duplicate traffic during P2MP tree switching in a network. 
         FIG. 11  illustrates an example network device architecture for a computer system that performs minimizing duplicate traffic during P2MP tree switching in a network. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagram of a network  100  (e.g., a communication system such as a label-switching network) in which data communication devices such as routers support point-to-multipoint communications according to an embodiment herein. Note that the term “router” herein refers to any type of data communication device that supports forwarding of data in a network. The term router as used herein then may include a switch, hub or other device that can support point-to-multipoint communications. Routers can be configured to originate data, receive data, forward data, etc. to other nodes or links in network  100 . 
     As shown, network  100  (e.g., a label-switching network) such as that based on MPLS (Multi-Protocol Label Switching) includes router R 1 , router R 2 , router R 3 , and router R 4  for forwarding multicast data traffic (i.e. multicast data communications) over respective communication links such as primary network path  104 , communication link  106 , and communication link  107 . Router R 1  and router R 2  can deliver data traffic (i.e., communication) directly to host destinations or other routers in a respective service provider network towards a respective destination node. Note that network  100  can include many more routers and links than as shown in example embodiments of  FIGS. 1 through 6 . The possible inclusion of additional routers and links is particularly exemplified in  FIGS. 1 through 6  by the use of dotted lines between network entities. 
     In one embodiment, multicast data traffic transmitted through network  100  are sent as serial streams of data packets. The data packets are routed via use of label-switching techniques. For example, network  100  can be configured to support label switching of multicast data traffic from router R 4  (e.g., a root router) to respective downstream destination nodes such as router R 1 , router R 2  and router R 3 . 
     In referencing the example configuration depicted in  FIG. 2 , during a link/node failure  101 , router R 4  forwards multicast data traffic via “next hop”/“next next hop” (NHOP/NNHOP) tunnels to NHOP/NNHOP nodes in accordance with fast reroute techniques disclosed in U.S. patent application Ser. No. 11/336,457, filed Jan. 20, 2006, the entire teachings of which are incorporated herein by reference. In this example, router R 4  forwards multicast data traffic through backup path  105  to router R 2  (e.g., a next hop downstream router) instead of transmitting data packets over primary network path  104  to router R 2  as shown in  FIG. 1 . 
     Router R 2  starts a stale timer and initiates multicast LDP signaling (e.g., RPF) in order to establish a new multicast tree connection with the root node (e.g., R 4 ). As shown in  FIG. 2 , in initiating the reverse path towards the root node R 4 , router R 2  sends a label mapping message  120  with a new label toward a new upstream node (router Rn in this example) via communications link  108 . Since, according to this example, router Rn is in the existing P2MP tree  110 , router Rn will add the new label to its routing table so as to include R 2  as part of the existing P2MP tree  110 . In response, router Rn sends an acknowledgement notification message (ACK)  130  back to router R 2  via communications link  108 . Upon receiving the ACK  130 , router R 2  removes the old label rewrite and sends a label release for the old label. Even though router R 2  receives traffic from both old and new previous hops, router R 2  will sink the traffic from the old previous hop. Thus, in this particular embodiment router R 2  will now only receive P2MP tree  110  traffic from the newly established multicast path  112  (e.g., tunnel) in lieu of receiving multicast traffic (e.g., P2MP tree  110  traffic) from backup path  105 . Stated differently, router R 2  will not use the duplicate multicast traffic since router R 2  terminated the backup (or old) path  105  upon establishing the new P2MP tree path  112 . 
       FIG. 3  shows a similar network configuration  100  in which router R 2  initiates multicast LDP signaling upon detecting a link/node failure  101 . However, in this example configuration router Rn is not in the existing P2MP tree  110 . Therefore, upon receiving the label mapping message  120  from router R 2 , router Rn sends a new label mapping message  121  with a new label to its upstream node (router Rn+1 in this example). Router Rn+1 is in the existing P2MP tree  110 . Similar to the example discussed above, upon receiving the new label mapping message  121  from router Rn, router Rn+1 adds the new label mapping message  121  to its routing table so as to include Rn (and any downstream nodes thereof) as part of the existing P2MP tree  110 . Router Rn+1 then sends an ACK  130  back to router Rn. In turn, router Rn propagates the ACK  130  back to router R 2 . Upon receiving the ACK  130 , router R 2  removes the old label rewrite and sends a release for the old label. Thus, in this particular embodiment router R 2  will now only receive multicast traffic from the newly established path multicast path  113  (e.g., tunnel) in lieu of receiving multicast traffic from backup path  105 . In other words, router R 2  will not use the duplicate multicast traffic since router R 2  terminated the backup path  105  upon establishing the new P2MP tree path  113 . 
     In alternate embodiments, the multicast LDP signaling process described may be extrapolated (as evidenced by the dotted lines in the figures) such that the label mapping messages are sent upstream in the network  100  through as many upstream nodes as necessary to reach a node in the existing P2MP tree  110 . In this manner, each upstream node Rn, Rn+1 . . . Rn+m stemming from router R 2  continues to send label mapping messages upstream until a merging point is reached with a node in the existing P2MP tree  110 . Accordingly, the first node reached in the P2MP tree  110  propagates an ACK  130  back downstream through respective nodes Rn+m . . . Rn+1, Rn until the ACK  130  reaches router R 2  where, upon receipt, router R 2  removes the old rewrite and sends a label release for the old label. 
     It should be noted that in the embodiments described above where a new P2MP path is established through multicast LDP signaling to an upstream node in the P2MP tree  110 , router R 2  cannot be certain of the state of the P2MP tree  110 . In other words, the ACK  130  received by router R 2  from an upstream node does not contain information as to whether the P2MP tree is in a new, old or pre-convergence state (e.g., the state of multicast paths  111  and  113  in  FIGS. 2 and 3 , respectively). As such, these procedures do not completely eliminate the possibility of duplicate traffic. This is because the new P2MP path may associate with pre-convergence multicast tree that will subsequently become obsolete upon network convergence. Nonetheless, such signaling procedures can be accomplished in one or two milliseconds. In addition, the forwarding plane cleanup time is proportional to the number of rewrites processed at the upstream nodes (e.g., Rn, Rn+1, . . . ). This adds the variable delay in quenching the duplicate traffic. Since the duplicate traffic can only be reduced from minutes to milliseconds (ms), the strict time boundary is not possible with this signaling procedure. Generally, if the traffic disruption is less than 300 ms, most real applications can tolerate the disruption. 
     In another embodiment, the duplication of multicast traffic is completely eliminated at a network node that implements fast reroute procedures during P2MP tree switching. In particular, duplicate traffic is eliminated by propagating new label mapping messages upstream to the root node (e.g., R 4 ) of the P2MP tree  110  via a reverse path (e.g, multicast path  112  as shown in  FIG. 2 ). If each upstream node in the reverse path allocates the local label for the new multicast tree, the root node will have two disjoint multicast trees (e.g., the old P2MP tree built before the reroute, and the new P2MP tree built after the reroute). Despite this, all leaf nodes can still receive traffic during the stale period (e.g., before the stale timer has elapsed) from the old P2MP tree built before the reroute. As a result, some broken tree nodes may also receive multicast traffic from NHOP or NNHOP backup LSP&#39;s. However, after network convergence, the root/source node can switch the multicast traffic from the old P2MP tree to the new P2MP tree such that there is no traffic loss or duplication. Furthermore, the upstream nodes with local labels for the new P2MP tree remove the old labels for the old P2MP tree after the stale timer expires by sending label release messages with the old labels. 
       FIG. 4  shows a particular embodiment that is exemplary of P2MP tree switching at the root node whereby the duplication and loss of multicast traffic are eliminated. Router R 2  starts a stale timer and initiates multicast LDP signaling (e.g., RPF) in order to establish a new multicast tree connection with the root node (e.g., R 4 ). Similar to previous embodiments already discussed, router R 2  sends label mapping message  120  with a new label toward the upstream node (router Rn in this example). Upstream nodes Rn, Rn+1 . . . Rn+m propagate respective label mapping messages  121 ,  122  and  123  upstream until the label mapping messages reach the root node (e.g., R 4  in this example). Accordingly, the root node R 4  propagates an ACK  130  back downstream through nodes Rn+m . . . Rn+1, Rn via new P2MP tree path  114  (or reverse path  114 ), until the ACK  130  reaches router R 2 . Upon receipt of an ACK  130 , each router along the new P2MP tree route (the reverse path between R 2  and R 4 ) removes the old rewrite labels and sends label releases for the old labels. As a result, router R 2  will now receive multicast traffic from the new P2MP tree (via new P2MP tree path  114 ) in lieu of receiving multicast traffic from the fast reroute backup path  105 . 
     In alternate embodiments, the reception of duplicate multicast traffic at network nodes may occur during standard reroute procedures. For example,  FIG. 5  shows a network  100  configured to support label-switching of multicast data traffic from router R 4  (e.g., a root router) to respective downstream destination nodes such as R 1 , R 3 , Rz, and Rz- 1  . . . Rz-z. Router Rz-z is a non-adjacent downstream node from router Rz and is not directly subject to a fast reroute operation were an upstream node/link failure to occur. In other words, Rz-z does not have a predetermined upstream backup path for receiving multicast traffic in the event of an upstream network anomaly. However, router Rz-z is still susceptible to receiving duplicate multicast traffic after an upstream link/node failure. Upon detecting an upstream node/link failure, router Rz-z immediately initiates multicast LDP signaling (e.g., RPF) in order to establish a new multicast tree connection with the root node (e.g., R 4 ). However, router Rz-z may still receive multicast traffic from the upstream node, router Rz, since router Rz may still receive multicast traffic via backup path  105  as a result of the fast reroute implementation. Thus, router Rz-z is an indirect beneficiary of the fast reroute procedures applied to its upstream nodes (e.g., Rz as one example). 
     For example, in referring to  FIG. 5 , assume that during a link/node failure  101 , router Rz-z initiates multicast LDP signaling (e.g., RPF) in order to establish a new multicast tree connection with root node R 4 . Similar to methods previously discussed, router Rz-z sends a new label mapping message  120  to upstream router Rn via upstream path communications link  117 . In one embodiment, label mapping messages are propagated upstream until a node in the P2MP tree  110  is reached. Thus, in referring to  FIG. 5 , label mapping messages are propagated upstream through path  118  via Rn, Rn+1 . . . Rn+m until a router in the P2MP tree  110  is reached. Assume for this example that Rn is in the P2MP tree  110 . If so, upon receiving the new label mapping message  120 , Rn sends an ACK  130  back to Rz-z. Upon receiving the ACK  130 , router Rz-z removes the old label rewrite and sends a release for the old label. Thus, in this particular embodiment non-adjacent, downstream router Rz-z will now only receive P2MP tree  110  traffic from the newly established path  118  (e.g., tunnel) via router Rn in lieu of receiving multicast traffic from the previous path  119 . 
     It should be noted that in the embodiments described above where a new P2MP path is established through multicast LDP signaling to an upstream node in the P2MP tree  110 , router Rz-z cannot be certain of the state of the P2MP tree  110 . In other words, the ACK  130  received by router Rz-z from an upstream node does not contain information as to whether the P2MP tree  110  is in a new, old or pre-convergence state. As such, these procedures do not completely eliminate the possibility of duplicate traffic for reasons already described. 
     In another embodiment, the duplication of multicast traffic is completely eliminated at a network node that implements standard reroute procedures during P2MP tree switching. 
       FIG. 6  shows a particular embodiment of P2MP tree switching at the root node whereby the duplication and loss of multicast traffic are eliminated at a node (e.g., Rz-z) implementing standard reroute procedures. Similar to previous embodiments already discussed, upon detecting the link/node failure  101 , router Rz-z sends label mapping message  120  with a new label toward the upstream node (router Rn in this example). Upstream nodes Rn, Rn+1 . . . Rn+m propagate respective label mapping messages  121 ,  122  and  123 , upstream until the label mapping messages reach the root node (e.g., R 4  in this example). Accordingly, the root node R 4  propagates an ACK  130  back downstream through nodes Rn+m . . . Rn+1, Rn via new P2MP tree path  118  (or reverse path  114 ), until the ACK  130  reaches router Rz-z. Upon receipt of an ACK  130 , each router along the new P2MP tree route  118  (the reverse path between Rz-z and R 4 ) removes the old rewrite labels and sends label releases for the old labels. As a result, router Rz-z will receive multicast traffic from new P2MP tree path  118  in lieu of receiving multicast traffic from the previous network path  119 . 
     Flow charts of the presently disclosed methods are depicted in  FIGS. 7 through 10 . The rectangular elements are herein denoted “processing blocks” and represent computer software instructions or groups of instructions. Alternatively, the processing blocks represent steps performed by functionally equivalent circuits such as a digital signal processor circuit or an application specific integrated circuit (ASIC). The flow diagrams do not depict the syntax of any particular programming language. Rather, the flow diagrams illustrate the functional information one of ordinary skill in the art requires to fabricate circuits or to generate computer software to perform the processing required in accordance with the present invention. It should be noted that many routine program elements, such as initialization of loops and variables and the use of temporary variables are not shown. It will be appreciated by those of ordinary skill in the art that unless otherwise indicated herein, the particular sequence of steps described is illustrative only and can be varied without departing from the spirit of the invention. Thus, unless otherwise stated the steps described below are unordered meaning that, when possible, the steps can be performed in any convenient or desirable order. 
       FIGS. 7 through 10  are flow charts that show processing details of a method for minimizing duplicate traffic during P2MP tree switching in a network including a P2MP tree with a source node is shown. The method begins with processing block  200  which discloses transmitting multicast data traffic from a first router over a primary network path to a second router. In this configuration, the network path supports multicast label switching of multicast data traffic. 
     Processing block  201  then states, in response to detecting a failure  101  in the network  100 , initiating a multicast rerouting procedure. This was discussed above in reference to the networking diagrams in  FIGS. 1 through 6 . As per one aspect of the multicast rerouting procedure, processing block  202  recites transmitting a new switching label via a secondary network path to an upstream router (as previously discussed with reference to  FIGS. 2 through 6 ). In this configuration, the secondary network path includes at least one upstream node. An additional aspect of the multicast rerouting procedure is stated in processing block  203  which discloses, upon receiving an acknowledgement notification from the upstream router via the secondary network path, configuring the second router to receive multicast data traffic from the secondary network path in lieu of receiving multicast data traffic from the primary network path (as previously discussed with reference to  FIGS. 2 through 6 ). 
     The method continues with processing block  204  in  FIG. 8 , which discloses configuring the network to include at least one backup path between the first router and the second router (as previously discussed with reference to fast rerouting procedures specifically shown in  FIG. 1 ). In such a configuration, the backup path supports multicast label switching of multicast data traffic. In addition, processing block  205  states, in response to detecting the failure in the network, initiating transmission of the multicast data traffic over the at least one backup path between the first router and the second router in lieu of transmitting the multicast data traffic over the primary network path. Stated differently, a backup path is established between the first router and the second router in accordance with multicast fast rerouting procedures as shown in  FIG. 1 . Processing block  206  recites, upon receiving an acknowledgement notification from the upstream router via the secondary network path, configuring the second router to receive multicast data traffic from the secondary network path in lieu of receiving multicast data traffic from the at least one backup path (as previously discussed with reference to  FIGS. 2 through 4  in light of fast rerouting procedures). 
     Processing block  207  additionally states removing, from the second router, a backup path switching label that the second router normally uses for receiving multicast data traffic via the at least one backup path. Further, processing block  208  discloses receiving, at the second router, multicast data traffic in accordance with the new switching label used for the secondary network path (as previously discussed with reference to  FIGS. 2 through 4  in light of fast rerouting procedures). 
     In  FIG. 9 , the method continues with processing block  210  which discloses initiating a multicast rerouting procedure by implementing a reverse path forwarding procedure (as previously discussed with reference to  FIGS. 2 through 6 ). Processing block  211  further states determining whether the upstream router is receiving multicast data traffic, and when the upstream router is receiving multicast data traffic, adding the new switching label to a routing table at the upstream node. In addition, processing block  211  discloses transmitting the acknowledgement notification to the second router via the secondary network path (as previously discussed with reference to  FIGS. 2 through 6 ). 
     Processing block  212  recites removing, from the second router, a primary switching label that the second router normally uses for receiving multicast data traffic via the primary network path. Processing block  213  states receiving, at the second router, multicast data traffic in accordance with the new switching label used for the secondary network path (as previously discussed with reference to  FIGS. 2 through 6 ). 
     As per  FIG. 10 , processing block  220  recites determining whether the upstream router is receiving multicast data traffic, and when the upstream router is not receiving multicast data traffic, repeating the step of transmitting a respective switching label to a next upstream router via the secondary network path until the upstream router is receiving multicast data traffic. Processing block  221  also states propagating the acknowledgement notification from the upstream router receiving multicast data traffic to the second router via the secondary network path (as previously discussed with reference to  FIGS. 3 and 5 ). 
     The method still further continues with processing block  222  which discloses determining whether the upstream router is the source node of the P2MP tree, and when the upstream router is not the source node of the P2MP tree, repeating the steps of transmitting a respective switching label to a next upstream router via the secondary network path until the upstream router is the source node of the P2MP tree. Further, processing block  223  states propagating the acknowledgement notification from the source node of the P2MP tree to the second router via the secondary network path (as previously discussed with reference to  FIGS. 4 and 6 ). 
       FIG. 11  illustrates example architectures of a network device that is configured as a host computer system  340 . The network device  340  may be any type of computerized system such as a personal computer, workstation, portable computing device, mainframe, server or the like. In this example, the system includes an interconnection mechanism  311  that couples a memory system  312 , a processor  313 , a communications interface  314 , and an I/O interface  315 . The communications interface  314  and I/O interface  315  allow the computer system  340  to communicate with external devices or systems. 
     The memory system  312  may be any type of computer readable medium that is encoded with an application  355 -A that represents software code such as data and/or logic instructions (e.g., stored in the memory or on another computer readable medium such as a disk) that embody the processing functionality of embodiments of the invention for the agent  355  as explained above. The processor  313  can access the memory system  312  via the interconnection mechanism  311  in order to launch, run, execute, interpret or otherwise perform the logic instructions of the applications  355 -A for the host in order to produce a corresponding agent process  355 -B. In other words, the agent process  355 -B represents one or more portions of the agent application  355 -A performing within or upon the processor  313  in the computer system. 
     It is to be understood that embodiments of the invention include the applications (i.e., the un-executed or non-performing logic instructions and/or data) encoded within a computer readable medium such as a floppy disk, hard disk or in an optical medium, or in a memory type system such as in firmware, read only memory (ROM), or, as in this example, as executable code within the memory system  312  (e.g., within random access memory or RAM). It is also to be understood that other embodiments of the invention can provide the applications operating within the processor  313  as the processes. While not shown in this example, those skilled in the art will understand that the computer system may include other processes and/or software and hardware components, such as an operating system, which have been left out of this illustration for ease of description of the invention. 
     Having described preferred embodiments of the invention it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts may be used. Additionally, the software included as part of the invention may be embodied in a computer program product that includes a computer useable medium. For example, such a computer usable medium can include a readable memory device, such as a hard drive device, a CD-ROM, a DVD-ROM, or a computer diskette, having computer readable program code segments stored thereon. Accordingly, it is submitted that that the invention should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the appended claims.