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Cisco Bug: CSCvi83758 - BGP doesn't reclaim per-vrf label if all prefixes are withdrawn between lsd down and up event.

Last Modified

Jan 17, 2019

Products (9)

  • Cisco Network Convergence System 6000 Series 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 9912 Router

Known Affected Releases


Description (partial)

Label collision for the per-vrf label can be seen if lsd connection with bgp flaps.
It will cause traffic drop for prefixes in that vrf.

Issue will happen if following events happen in chronological order:
1) In steady state bgp has allocated label L1 for vrf VRF1 with per-vrf label mode on.
2) LSD connection goes down.
3) All prefixes in the vrf VRF1 gets withdrawn.
4) LSD connection comes up.
5) BGP doesn't now reclaim label L1 from lsd. (At this point lsd  thinks label L1 is free for use.)
6) Prefix gets learned in VRF1. BGP thinks label L1 is active and starts using it.
7) LSD assigns label L1 to someone else. Lets's say some other vrf in bgp. 
This causes label collision.

Related Community Discussions

ASR 9k MPLS LDP Non-Stop Routing (NSR) issue
We are running a textbook MPLS VPN using EIGRP as the IGP on ASR 9006s running a mix of IOS XR 6.2.3 and 5.3.4.   Before Non-Stop Routing (NSR) was enabled for LDP we experienced a 60+ second outage on VPN traffic when performing a 'redundancy switchover' on a transit router.   After enabling NSR for LDP this outage was reduced to ~10 seconds.   mpls ldp nsr router-id interface TenGigE0/1/0/16 ! interface TenGigE0/1/0/17 ! interface Serial0/0/0/0/1/1/3:0 Both routing and LDP neighborships ...
Latest activity: Jul 26, 2018
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