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.
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