On Sep 2, 2009, at 1:51 PM, Randy McAnally wrote:
We have two sites advertising unique subnets via the same AS. Since
the
subnets originate from the same AS they apparently get dropped from
the tables
at each site.
Each site has at least 3 upstreams taking full tables from each with
a 6509.
Site a has a single border router with dual supervisors.
Site b actually has dual border routers. Each router handles
different
upstreams and trades routes via iBGP.
So I think I need to set up a multihop session between the sites.
Right now, traffic between sites is taking the floating default
route and
causes issues between sites when one of our BGP peers is down for
whatever reason.
What are the things to look out for when setting up this multihop?
Are there
gotcha's to deal with given one site has dual active routers?
Multihop BGP is not a good idea in this example. You'll want to use
something like neighbor x.x.x.x allowas-in on your eBGP sessions.
However, you'll also want to setup a BGP filter to deny your own
sourced prefixes to prevent loops/flapping. Meaning, when you allow
prefixes from site A into site B, setup a BGP filter on site B denying
B's prefixes and vice versa.
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