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hacizeynal
Beginner

BGP announces routes very late

Hi ,we have 2 IBRs which faces to 2 ISP ,we have BGP neighors with both of them ,of course first traffic is going out from first IBR ,but if any failure our second IBR should be up immediately ,but strange thing second router goes internet after 5 or 6 minutes ,even though it has route to outside ,we are prepending as-path 5 times ,I decreased it to one ,so now it takes 130 seconds to go to internet ,what should be reason ?

3 REPLIES 3
Mark Malone
VIP Mentor

the reason could vary depending on topology, configuration setup , ISP etc there's no enough info there to really take a guess, but have you tried to speed up failover with ip sla with bgp as an option

Good example of it

http://www.networking-forum.com/blog/?p=2401

paul driver
VIP Mentor

Hello

In addition BFD, You can always drop you bgp timers to a lower value other than the default 60 sec interval 180 sec hold time although setting it to low can have a negative effect on your network and convergence.


router bgp xx
timers bgp 10 30

res
Paul 



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
pedersen
Beginner

Is there any BGP session between the two IBRs? Also are you receiving full BGP table from both providers?

If so, you need to remember that if the primary BGP peer is lost, then between the routers a withdraw of all learned routes, this takes a bit of time depending on the platform and the BGP scanner.

if you're not having BGP between the two IBRs but rather using first hop redundancy, like HSRP, then the virtual IP doesn't change unless some policy is configured, this causes the first and active IBR when loosing all BGP routes to recalculate the routing table and send it perhaps via an IGP over the other IBR.

A logical topology would help a lots explain the issue, above is guessing based on the short description :-)

Note: never go configure/change timers or adding on, before knowing why and have a valid reason for it.

/Anders.