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Cisco Bug: CSCvt71360 - Sub-second flaps on multiple links between routers results in misprogramming of Adj-SIDs with OSPF

Last Modified

Sep 02, 2020

Products (11)

  • Cisco ASR 9000 Series Aggregation Services Routers
  • Cisco ASR 9910 Router
  • Cisco ASR 9922 Router
  • Cisco IOS XR Software
  • Cisco ASR 9010 Router
  • Cisco ASR 9904 Router
  • Cisco ASR 9006 Router
  • Cisco ASR 9001 Router
  • Cisco ASR 9901 Router
  • Cisco ASR 9912 Router
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Known Affected Releases

6.6.2.ROUT

Description (partial)

Symptom:
OSPF adjacency SID entry is mis-programmed with the primary path pointing to some other interface than the one over which adjacency is formed even with that primary link/adjacency is up.

show mpls lsd forwarding labels 24695 detail 
Thu Apr  2 13:37:33.616 GST
In_Label, (ID), Path_Info: <Type>
24695, (SR Adj Segment IPv4, index=0, type=1, intf=Hu0/14/0/0, nh=195.229.0.107), 2 Paths, 
        Owner=OSPF(A):ospf-100
   1/2: IPv4_STACK, 'default':4U, Hu0/5/0/6, nh=195.229.3.121, lbls={ 3 }  
            flags=0x0, ext_flags=0x0 path_flags=0x40 [Protected]
            nh-id=0x0, path-id=1, backup-path-id=2, load-metric=0, parent-intf=None
   2/2: IPv4_STACK, 'default':4U, Hu0/4/0/0, nh=195.229.31.195, lbls={ 3 }  
            flags=0x0, ext_flags=0x0 path_flags=0x100 [Backup]
            nh-id=0x0, path-id=2, backup-path-id=0, load-metric=0, parent-intf=None
      BCDL priority:1, LSD queue:0, version:900842,
      flags: 0x8, fwd_flags: 0x0 (), 
      Installed Apr  1 12:31:56.761 (1d01h ago)

This can cause mis-routing or packet drops.

Conditions:
OSPF is enabled with Segment Routing. Multiple link failures happen towards the same neighbor with some of these flaps being sub-second duration and specific timing conditions are hit where a neighbor is not yet fully up while we are updating the adjacency SID entry for adjacency SID protection.
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