[c-nsp] Three ISPs - Three Edge Routers - iBGP Mesh

[Pete Templin]

On 11/22/11 8:41 AM, Mark Mason wrote:
> Two of our DC's are about to get their 3rd internet drop. Each ISP
> connection has its own edge router. HSRP is running facing on the LAN
> side. Please see
> https://supportforums.cisco.com/message/3496562#3496562 for topology
> and further discussions. I expect that packets leaving the DC will
> hit the HSRP active, perform the route lookup and exit via the best
> path BGP has selected (and/or the best path my PfR setup has
> installed). Does anyone see any gotcha's with just letting BGP do its
> thing; no local-pref changing, no path prepending?

Yes, a vast majority of your traffic will exit via the provider on the 
HSRP active, which may present balancing problems in the outbound 
direction.  Step 9 in the PSA is 'prefer external path over internal 
path', so if neither of the two other links have been given a higher 
weight, carry a higher LP, present a shorter AS path, somehow have a 
better origin code, it'll go out the directly-connected link.

Your inbound will balance "easily", except that inbound isn't easy to 
balance.

pt