Description

Self-ping is a feature which helps to verify the LSP data plane programming along the path of the LSP. Self-ping is triggered once the LSP path comes UP and self-ping success indicates the data plane programming along the path of the LSP is fine.

In Junos/Junos EVO initially self-ping was implemented in the following way:

  • self-ping starts on any point-to-point LSP when the LSP goes UP;
  • the results of self-ping is used only for new paths in make before brake (MBB) feature. So the traffic will be moved to the new path during MBB only after successful self-ping via new path.
  • besides MBB case, the results of LSP self-ping are not used: so the new LSP goes UP even if LSP self-ping is not successful (for example, due to firewall filter discards).

In the PR1597233 the described behavior was changed so LSP self-ping should be successful before an LSP becomes UP. So even the new LSP will remain in DOWN state untill self-ping is successbul.

The Junos/Junos EVO releases with the changes from the PR1597233 can be seen in the PR.
 

Symptoms

In the releases with the fix from the PR1597233, if lsp-ping is not successful, the LSP remains in DOWN state: 
router-re0> show mpls lsp name lsp1 extensive
Ingress LSP: 5 sessions
 
192.18.1.1
  From: 192.18.1.2, State: Dn, ActiveRoute: 0, LSPname: lsp1, LSPid: 5
  ActivePath: (none)
  Node/Link protection desired
  LSPtype: Static Configured, Penultimate hop popping
  LoadBalance: Random
  Follow destination IGP metric
  Encoding type: Packet, Switching type: Packet, GPID: IPv4
  Time remaining before reverting: 25
  LSP Self-ping Status : Enabled
  Primary   primary-path     State: Up
    Priorities: 7 0
    OptimizeTimer: 1800
    SmartOptimizeTimer: 180
          Exclude: international do-not-use
    Flap Count: 5
    MBB Count: 0
    Reoptimization in 1679 second(s).
    Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 10)
192.18.114.19 S
    Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt 20=Node-ID):
          192.18.1.1(flag=0x20) 62.127.114.19(Label=0)
   98 Nov 16 11:31:50.896 Up
   97 Nov 16 11:31:50.896 Self-ping started
   96 Nov 16 11:31:50.896 Self-ping enqueued
   95 Nov 16 11:31:50.896 Record Route:  192.18.1.1(flag=0x20) 192.18.114.19(Label=0)
   94 Nov 16 11:31:50.894 LSP-ID: 9 created
   93 Nov 16 11:31:50.894 Originate Call
   92 Nov 16 11:31:50.894 CSPF: computation result accepted  192.18.114.19
   91 Nov 16 11:31:50.894 Clear Call
   90 Nov 16 11:31:50.893 Deselected as active
   89 Nov 16 11:31:50.893 Link-protection Down

In the above output that Self-ping enqueued, started but there is no indication that self-ping was successful so the LSP remains in DOWN state. For the case where self-ping is successful, the example operation history is: 
   99 Nov 16 11:34:28.680 Self-ping ended successfully
   98 Nov 16 11:31:50.896 Up
   97 Nov 16 11:31:50.896 Self-ping started
   96 Nov 16 11:31:50.896 Self-ping enqueued





 

Solution

Due to the new behavior it is crutial to make sure that LSP self-ping traffic is allowed by firewall filters in the network (destination UDP port 8503).

Modification History

2023-12-08 : Article Created