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Cisco Bug: CSCvi83758 - BGP doesn't reclaim per-vrf label if all prefixes are withdrawn between lsd down and up event.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

Jun 18, 2018

Products (1)

  • Cisco Network Convergence System 6000 Series Routers

Known Affected Releases

6.5.1.BASE

Description (partial)

Symptom:
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.

Conditions:
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3) All prefixes in the vrf VRF1 gets withdrawn.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.
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