What is MP, Merge Point in MPLS Traffic Engineering ? Understanding Merge Point in MPLS Traffic Engineering will help you to understand the MPLS TE – Fast Reroute
MP (Merge Point) is the term is used in the context of Fast Reroute. I briefly mentioned from Merge Point in the MPLS Traffic Engineering Fast Reroute Link Protection post earlier and in this post, will explain it in more detail.
Let’s look at the below topology.
MPLS TE FRR Link Protection – Source: CCDE In-Depth by Orhan Ergun
As it is depicted in the topology as well, red is primary LSP , which means working path, so it carries the traffic.
Green is the backup LSP and it is just standby and incase of failure it will be used.
With MPLS Traffic Engineering Fast Reroute, link and node failure can be protected. This picture shows us the link failure, because M- N link failure is protected (Traffic will be redirected immediately in case M-N link fails)
Link between Router M and N. If that link fails, network traffic can not be carried between A and D through red LSP, which is the primary path.
It will be broken between Router M and N.
But if the requirement is to continue carrying traffic over an alternate path within 50 msec, fast reroute is used. If the traffic flow from router A to D, in case Router M to N link failures, who can send the traffic towards green LSP ?
Router M right ?
Because, Router M will learn first about the link failure when Router M – N link fails.
Router M as it is directly attached to the failed link , redirect the traffic to the green LSP. Both primary LSP and Green LSP is terminated on the node N.
In case M-N link fails, if traffic reaches again to the node N, node N can continue forward the traffic to the destination which is Router D.
Node N is called a Merge Point (MP), because backup LSP is merged to the primary LSP at that router/node.