What is PLR, Point of Local Repair in MPLS Traffic Engineering ?
PLR is the term is used in the context of Fast Reroute. I briefly mentioned from PLR 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.
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 is directly attached to the failed link.
It is local to the failure.
Thus, Router M is called as point of local repair. The node which repairs the traffic and local point to the failed link or node.
If the traffic flow over red/primary LSP is from Router D to A , in case M-N link fails , who will be called as PLR ?
If you answered the question as Router N , I did my job, congrats..