BGP Auto fail back

[gkurunthasalam]

We are having two routers running ebgp to service providers and ibgp in between these two routers through LAN.

No back to back cable for ibgp, running through LAN.

We have configured HSRP for LAN redundancy. When we make LAN down or interface down, it is taking 3 minutes to siwtch to 2nd router from primary router. 3 minutes is quite high time for a failover.

If i want to reduce this fall back time to 1minute or less, please explain and configuration to achieve the fall back within less than a minute.

Thanks

Gokul

[Philip D'Ath]

Three minutes, or 180s, is the BGP hold timer before declaring a neighbour dead.

Lets pretend we have R1 and R2.

When you unplug the LAN cable on R1, HSRP fails over to R2.  R1 will declare the iBGP relationship dead.  However R2 (now the HSRP master) does not know BGP has gone down on R1, and will wait the 180s before giving up on it and declaring it dead.

You have many options to resolve it.

1. If you have spare router interfaces, consider using Etherchannel so a single link failure does not take it down.

2. Rather than iBGP between the router interfaces that connect to a switch, connect the routers point to point, and run iBGP over that.  Then if the link goes down for one router the other router can detect it immediately (because its interface will go down).  You need extra interfaces to do this.

3. Change the timers to the iBGP peer with something like (20s keepalive, 60s hold down timer):

R1(config-router)# neighbor a.b.c.d timers 20 60

Note you need to restart the BGP session for this to take effect.  This will make it recover within 60s rather than 180s.

[paul driver]

Hello

another solution without tweaking  the bgp timers would be to try BFD (Bidirectional Forwarding Detection) 

Int x/x ( physical interface of peer)
bfd interval 500 min_rx 500 multiplier 3 <----- how often to send and receive the bfds and how many before it deems unreachable 

router bgp xxx
neighbor x.x.x.x remote-as xxxx
neighbor x.x.x.x fall-over bfd

I would also recommend go with the suggestion that Philip mentioned regards a direct physical connection between the two Ibgp peers if it is physically possible.

res

paul

[Philip D'Ath]

I know you can use BFD on point to point links.  Does it also work when connecting routers with a switch with a subnet used by many devices (aka, not point to point)?