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New Member

Slow BGP convergence

Hi,

I set up Catalyst6500 Quad-SUP VSS system.
I have a problem with slow BGP convergence(80sec) on VSS switchover.
Each chassis has a bgp peer and "bgp graceful-restart" is disabled.
I investigated BGP behavior with "debug ip bgp events" and "debug ip bgp update".
I found that BGP process waited a peer to reply until timeout and after the timeout BGP table was calculated.
I guess this timer makes the convergence slow.
How can I adjust this timer value?

----------------- debug message ------------------
*Aug  8 14:56:09.989 JST: BGP(0): 1.1.1.1 was the first peer to be established for IPv4 Unicast
*Aug  8 14:56:09.989 JST: BGP: nopeerup-delay post-boot, set to default, 60s
*Aug  8 14:56:09.989 JST: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Up
*Aug  8 14:56:09.989 JST: BGP(IPv4 Unicast): waiting on established peer 1.1.1.1 EOR
*Aug  8 14:56:09.993 JST: BGP(0): 1.1.1.1 rcvd UPDATE w/ attr: nexthop 1.1.1.1, origin i, metric 100, merged path 11111, AS_PATH 11111
*Aug  8 14:56:09.993 JST: BGP(0): 1.1.1.1 rcvd 0.0.0.0/0
*Aug  8 14:56:10.509 JST: BGP(IPv4 Unicast): waiting on non-established peer 2.2.2.2 for 70s (initial peer up)
*Aug  8 14:56:10.785 JST: BGP(IPv4 Unicast): waiting on non-established peer 2.2.2.2 for 70s (initial peer up)
*Aug  8 14:56:11.533 JST: BGP(IPv4 Unicast): waiting on non-established peer 2.2.2.2 for 70s (initial peer up)
*Aug  8 14:56:12.557 JST: BGP(IPv4 Unicast): waiting on non-established peer 2.2.2.2 for 70s (initial peer up)
*Aug  8 14:56:13.581 JST: BGP(IPv4 Unicast): waiting on non-established peer 2.2.2.2 for 70s (initial peer up)
- snip -
*Aug  8 14:57:19.117 JST: BGP(IPv4 Unicast): waiting on non-established peer 2.2.2.2 for 70s (initial peer up)
*Aug  8 14:57:20.141 JST: BGP(IPv4 Unicast): computed bestpaths, table version went from 10 to 34
----------------- debug message end ------------------

Everyone's tags (2)
6 REPLIES

Slow BGP convergence

Hi Jun,

please find these references:

http://ieoc.com/forums/p/6115/21381.aspx

and

http://stack.nil.com/ipcorner/DesigningBGPNetworks/

but keep in mind that BGP has been designed to be slow and it is NOT a good protocol to replace the job of an IGP.

Hope it helps

Alessio

New Member

Slow BGP convergence

Hi Alessio,

thank you for your reply.

I didn't write that all BGP peers are directly connected EBGP neighbors.

And I've checked that "fast-external-fallover" is enabled by default.

In this case, a BGP initialization occurs on the routing engine(supervisor) switchover.

Why does the BGP process wait the peer connected to rebooting chassis in the BGP initialization process?

Is there any workaround?

Slow BGP convergence

You can adjust your timers globally or per neighbor:

router bgp 1

timers bgp 7 21

OR

router bgp 1

neighbor x.x.x.x timers 7 21

I wouldn't recommend anything lower than 7 for a keepalive if this is an ebgp peer. For ibgp, I set mine to 5 and 15. The lower of the of the 2 timers is used between the peer, but the peer needs to be cleared before the new timer goes into effect.

HTH,

John

HTH, John *** Please rate all useful posts ***
New Member

Slow BGP convergence

Hi John,

thank you for your reply.

I set BGP timers to "10 30", but this didn't solve the problem.

New Member

Slow BGP convergence

Hi,

I solved this problem by setting "bgp update-delay xx".

New Member

Slow BGP convergence

What bgp update-delay value did you set to improve convergence time?

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