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Cisco Bug: CSCvt39175 - PWHE programms incorrect label to forward l2vpn traffic which causes complete traffic drop

Last Modified

Sep 12, 2020

Products (11)

  • Cisco ASR 9000 Series Aggregation Services Routers
  • Cisco ASR 9910 Router
  • Cisco IOS XR Software
  • Cisco ASR 9922 Router
  • Cisco ASR 9010 Router
  • Cisco ASR 9904 Router
  • Cisco ASR 9006 Router
  • Cisco ASR 9901 Router
  • Cisco ASR 9001 Router
  • Cisco ASR 9906 Router
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Known Affected Releases

6.4.2.BASE 6.4.2.MPLS

Description (partial)

Symptom:
On IOS-XR device PWHE use incorrect label to forward l2vpn traffic which causes complete traffic drop.

Conditions:
On problematic IOS-XR device route for remote pseudowire peer loopback is learned via IGP(ISIS) and backup route(post convergence) is learned as BGP LU.

Trigger: On problematic IOS-XR device primary route goes down and it now learns pseudowire peer loopback as a BGP LU. Till now everything works fine.
Now when primary ISIS route comes up problematic IOS-XR still use BGP LU label in pseudowire forwarding.

CLI outputs to verify if you hit the issue:

1. Get the internal label for VC
IOS-XR#show l2vpn xconnect group Eth-TEST-TAC det | i Internal
Fri Mar  6 04:54:34.399 EST
    Internal label: 24582

 2. Check forwarding output. If there is any lspa_label observed then you are hitting same issue.
 
Non-working state:

IOS-XR#sh mpls forwarding labels 24582 hardware egress location 0/0/cpU0 | i "lspa_label|flags"
Fri Mar  6 05:06:53.654 EST
flags: 0x1, rldi_table_idx: 0x1975, num_entries: 0x1, urpf_ptr: 0x0
                  lspa_label:    24008     exp: 0     eos: 1. >>>>>>>>>>>>>> lspa_label is there and CE to CE ping drops started.
  flags: 0x1, proto: 2, npaths: 0, nbuckets: 1
RP/0/RSP0/CPU0:ASR9006-D#
 
Working state:

IOS-XR#sh mpls forwarding labels 24582 hardware egress location 0/0/cpU0 | i "lspa_label|flags".  >>>>> There is no lspa_label before trigger, no ping drops.
Fri Mar  6 04:57:09.319 EST
flags: 0x1, rldi_table_idx: 0x1975, num_entries: 0x1, urpf_ptr: 0x0
  flags: 0x1, proto: 2, npaths: 0, nbuckets: 1
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