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[Junos] CSPF failure after changing ISIS system ID (iso ID) in a running network

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Article ID: KB36812 KB Last Updated: 04 May 2021Version: 1.0
Summary:

This article explains the issue seen with protocol ISIS where changing the system ID on a transit node (on the fly) causes LSP down and traffic outages.

Symptoms:

Note: Changing the System ID on the fly is not recommended and may cause unexpected behavior in the network.

Example output:

​root@vmx101# show | compare 
[edit interfaces lo0 unit 0 family iso]
+       address 49.0011.0110.0000.0101.00;
-       address 49.0011.0110.0000.2101.00;


root@vmx106> show mpls lsp name to-vmx101 extensive 
Ingress LSP: 2 sessions

11.0.0.101
  From: 11.0.0.106, State: Up, ActiveRoute: 0, LSPname: to-vmx101
  ActivePath:  (primary)
  LSPtype: Static Configured, Penultimate hop popping
  LoadBalance: Random
  Follow destination IGP metric
  Encoding type: Packet, Switching type: Packet, GPID: IPv4
  LSP Self-ping Status : Enabled
 *Primary                    State: Up
    Priorities: 7 0
    SmartOptimizeTimer: 180
    Flap Count: 0
    MBB Count: 1
    Reoptimization in 135 second(s).
    Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 600)
 11.105.106.1 S 11.101.105.1 S 
    Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt 20=Node-ID):
          11.105.106.1(Label=4610) 11.101.105.1(Label=3)
   21 Apr 14 09:46:08.681 CSPF failed: no route toward 11.0.0.101[3 times, first Apr 14 09:45:31.820]
   20 Apr 14 09:45:31.820 CSPF: link down/deleted: 11.101.105.2(11.0.0.105:359)(vmx105.00/11.0.0.105)->11.101.105.1(11.0.0.101:354)(vmx101.00/11.0.0.101)
 
root@vmx106> show ted database 11.0.0.101    
TED database: 62 ISIS nodes 35 INET nodes
ID                            Type Age(s) LnkIn LnkOut Protocol
0110.0000.2101.00(11.0.0.101) Rtr       6     0      1 IS-IS(2)     <-- stale entry in TED
    To: vmx105.00(11.0.0.105), Local: 11.101.105.1, Remote: 11.101.105.2
      Local interface index: 354, Remote interface index: 359

root@vmx106> show ted database vmx101        
TED database: 61 ISIS nodes 34 INET nodes
ID                            Type Age(s) LnkIn LnkOut Protocol
vmx101.00                     ---      22     1      0              <-- Current entry has No IPs associated with new TED entry
 
Solution:

Take the follow steps to avoid this issue:

  1. Overload the device
  2. Deactivate ISIS
  3. Change System ID 
  4. Activate ISIS 
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