MPLS-Enabled Applications: Emerging Developments and New Technologies

3.7. NODE PROTECTION

Link failures are the most common type of failure in a network. A link failure may happen because of a problem with the link itself or it may be caused by a failure of the node at the other end of the link. In the latter case, the link protection mechanisms described in the previous section will not work if they rely on the adjacent node to act as the MP. Node protection covers this case by setting up the backup tunnel around the protected node to the next next-hop in the path, in the case of facility protection, or towards the egress point of the main LSP in the case of 1:1 protection. Note that in the case of 1:1 protection, the procedure to set up state and the resultant label operations are virtually the same for the node protection case as the link protection case discussed in the previous section. For this reason, the emphasis in this section is on the procedures and label operations for the facility protection case.

Figure 3.15. Setting up a protection tunnel around node B

Figure 3.15 shows LSPxy from X to Y, along the path X-A-B-Z-Y. LSPxy is protected against node B's failure by a backup tunnel taking the path A-C-D-Z that merges back into LSPxy at node Z downstream from node B. When node B fails, traffic from LSPxy (the protected path) is placed on this backup at A and delivered to Z, where it continues on its normal path to destination Y. The figure ...