This article provides a scenario where LSP fails to follow the optimized path, and the solution to correct it.

Starting with Junos OS 16.1, self-ping is enabled (by default) for RSVP based MPLS LSP . The LSP types such as CCC, P2MP, VLAN-based, and non-default instances do not support self-ping. This is documented in the Release Notes: Junos ® OS Release 16.1R7 for the ACX Series, EX Series, MX Series, PTX Series, QFX Series, T Series, and Junos Fusion ; search on self-ping.

The UDP destination port MUST be lsp-self-ping​ UDP Port Number "8503". If this port is not enabled, and if LSP self-ping is enabled (the default), LSP self ping will not succeed. Hence, LSP will get stuck in make-before-break (MBB) and will not respond to better paths. MPLS LSPs will not be able to do Constrained Shortest Path First (CSPF) to even respond to config change.

Perform one of the following work-arounds:

• Enable lo0 firewall filter to accept LSP self-ping packets.
   
  Example: Enable UDP port 8503 under lo0 filter:

  root@root# show firewall family inet filter lo0-filter
  term self-ping {
      from {
          prefix-list {
              core;
          }
          protocol udp;
          port 8503;
      }
      then accept;
  }

  OR
   
• Disable LSP self-ping for these LSPs using the following configuration:
  no-self-ping