Dual Homed BGP Optimization question

rolandshum · ‎03-28-2007

I have 2 border routers, each connect to a different ISP at about the same speed of 20mbs. I only get a default route from both the ISP's. I use HSRP for a failover so all the traffic goes out the main router.

Is there a better way to do this? I'm afraid that if I lose routes but not one of my interfaces at layer 2 I won't fail over properly since HSRP won't detect this. I also don't think outbound traffic will be going out the optimal path but is returning on the optimal path.

royalblues · ‎03-28-2007

Friend,

This would depend on what type of protocol you run between your ISP and how are you exchanging the routes.

If you run BGP, then then any link issues between your provider and CE would cause it bring down causing the peer to flush down the routes you advertise.

You can run IBGP between your edge routers so that even though HSRP doesn't failover the traffic is diverted to the 2nd router (though it adds an additional hop but should be <2ms on the LAN)

The internet would see the route to your subnets as best from the other ISP till the primary link comes up.

There may be issues if you are running static routes with the ISPs. You should be able to achieve it by doing some object tracking but the configurations may be a bit more complex.

HTH, rate if it does

Narayan

rolandshum · ‎03-28-2007

Narayan

I am running BGP to both my ISP's. I have routes that I exchange with them but I'm not getting a full routing table, they are just forwarding a default route to me.

Should I ask them to forward me their routes or their full routing tables? I didn't plan on taxing my router's cpu by processing a full internet routing table which is why I initially set it up with HSRP, that and my lack of experience with BGP.

bjw · ‎03-28-2007

An ISPs Routing table can be huge, I wouldn't recommend that.

Try looking at the following examples it may help:

http://www.cisco.com/warp/public/459/40.html#conf5

royalblues · ‎03-28-2007

As pointed above you should not receive entire routing table.

What i am suggesting is to run another IBGP session between your wan edge routers. Each router should see 2 default routes but the EGBP route would take preference.

Once your BGP to ISP1 fails the router would install the default route from your IBGP peer and take that route.

HSRP will not failover in this case but things work out (just an extra hop is added)

HTH, rate if it does

Narayan

IVAN PEPELNJAK · ‎03-28-2007

You might get some useful ideas here:

http://www.nil.com/ipcorner/SmallSiteMultiHoming/

While I did not cover BGP connectivity, you'll find how to detect next-hop failure and how to solve asymmetrical routing issues with per-interface NAT.