Wan Failover between Two Branches

[Irshad Mohammed Hussain]

I have 2 Branches connecting to same BGP Network with rest of Branches and HQ, I would like have fail over between these 2 Branches which are also connected P2P over WiMax Link , If obe Branch 1 Wan Fails I would all Traffic to go using Branch 2 Wan Link and Vise Versa. What would be best way to achieve this .  

[Richard Burts]

Your diagram shows both sites running BGP to the ISP. Are these EBGP sessions or IBGP sessions? If they are EBGP then the solution is quite simple. You configure an IBGP connection between the sites using the direct link between sites. Each site will prefer the default route it learns from its EBGP neighbor and if that fails then the site will use the IBGP learned default route through the other site.

HTH

Rick

[Irshad Mohammed Hussain]

Yes, They are EBGP , How can i use IBGP to achieve this , can you please elaborate.   As I am not so good at Routing..

[Richard Burts]

Configuring the routers for IBGP to do what you want is fairly simple. I do not know what AS number you use so for an example I will do it as if your AS number was 123.

Here is what you would configure for Branch 1 (which has IP 172.16.1.1 on the link between branches)

router bgp 123

neighbor 172.16.1.2 remote-as 123

Here is what you would configure for Branch 2 (which has IP 172.16.1.2 on the link between branches)

router bgp 123

neighbor 172.16.1.1 remote-as 123

Now the branches will form an IBGP neighbor relationship and will advertise to each other what they have learned from their ISP, including the learned default route. Each branch will prefer the default route it learned from its connected ISP and will have the default route it learned from the other branch as a backup.

HTH

Rick

[Irshad Mohammed Hussain]

Thanks , as these Branches are connecting to same AS number will it create any loop in network..

[Richard Burts]

Even though these branches connect to the same AS number it will not create any loop in the network. For IBGP the same AS number is assumed and the logic for IBGP takes care of any possible loop.

HTH

Rick

[Irshad Mohammed Hussain]

After i applied below config Branch 1 was stable, but Branch 2 started flapping and lost connectivity, is I am missing anything here..

Branch 1
router bgp 65400
nei 172.16.71.5 remote-as 65400
address-family ipv4
nei 172.16.71.5 act
------------------------------------------------------------

!
Branch 2
router bgp 65400
nei 172.16.71.6 remote-as 65400
address-family ipv4
nei 172.16.71.6 act
-------------------------------------------------------------

[Irshad Mohammed Hussain]

After i applied below config Branch 1 was stable, but Branch 2 started flapping and lost connectivity, is I am missing anything here..

Branch 1
router bgp 65400
nei 172.16.71.5 remote-as 65400
address-family ipv4
nei 172.16.71.5 act
------------------------------------------------------------

!
Branch 2
router bgp 65400
nei 172.16.71.6 remote-as 65400
address-family ipv4
nei 172.16.71.6 act
-------------------------------------------------------------

[Richard Burts]

I have looked through the config files that you posted. They do confirm that each branch establishes an EBGP relationship with an upstream router. So I would expect that configuring an IBGP neighbor relationship between branches would provide failover capability. I am puzzled why doing this would cause Branch 2 to lose connectivity.

What routes is the EBGP neighbor advertising to each branch? I assume that it advertises a default route but what other routes are advertised? It might be helpful if you would post the output of show ip bgp sum and of show ip bgp from each branch.

What we are most interested in is having each router learn the default route from the IBGP neighbor. We don't care about the other routes. So perhaps it would help if you configure a distribute list or a route map to control the advertisement to the IBGP neighbor and limit it to only the default route.

HTH

Rick

[Irshad Mohammed Hussain]

Thanks,

Let me check and update you .

[Giuseppe Larosa]

Hello Irshad,

on Branch1 you are using redistribute connected and you have defined two p2p GRE tunnels.

on Branch2 there are no GRE tunnels but under BGP you have

redistribute connected

redstribute static

Follow Richard's suggestion to send only the default route over the iBGP session

on both devices you can use:

ip prefix-list ONLY-DEFAULT permit 0.0.0.0/0

route-map SEND-DEFAULT permit 10

match ip address prefix ONLY-DEFAULT

on Branch1

router bgp 65400

address-family ipv4 unicast

neighbor 172.16.71.5 route-map SEND-DEFAULT out

on Branch2:

router bgp 65400

address-family ipv4 unicast

neighbor 172.16.71.6 route-map SEND-DEFAULT out

Hope to help

Giuseppe

[Arshad Safrulla]

It will not create any loops as iBGP routes will be installed in RIB only when it cannot learn the same network via eBGP due to high AD for eBGP