IGP/BGP design question

ML ml at kenweb.org
Thu Jun 18 01:39:46 UTC 2009

We have three main cities wherein eyeballs live.  Currently we have San 
Jose and San Francisco traffic egressing in SF, and Los Angeles 
egressing in LA.  There is one private 2x1gig long haul linking SJC to 
LA and a 1x 10gig linking SJC to SF. i.e SF <-10gig-> SJC <-2gig-> LA

Each area is a separate OSPF domain. Static routes define how to reach 
the RFC1918 space defined for each area. Currently SF and SJC exchange 
their public blocks in iBGP. There isn't an iBGP session between SF and 
SJC to LA.  We would would like to place our public IP blocks into iBGP 
with LA and use the 2gig long haul as a backup path for critical traffic 
destined for the Internet.(Only certain prefixes originated from each 
egress point will be announced out the opposite egress point; 
Appropriately locally-pref down inside our common transit ASN)

Using only one assigned ASN is this a good idea?

Is our IGP setup foobared (I've been mulling around possible changing 
the IGP design)? I can think of a problem or two this IGP design might 
cause us but it's a huge change on our part if we do it.

The egress points are not DFZs, so if either the 10gig or 2gig link go 
down the default route can be taken to reach the public blocks in either 
of the three regions.


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