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[Junos] Failing to allow MPLS LSP self-ping may cause LSP to not follow the optimized path

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Article ID: KB32883 KB Last Updated: 14 Aug 2018Version: 1.0
Summary:

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

Symptoms:

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.

Solution:

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



 
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