----- Original Message -----
From: "Ouellette, Tim"
> The 2nd router that only has 700 routes in it's routing
> table that it learned from it's IBGP still has the other
> 103k routes in it's adj-rib-in from it's ebgp peer right,
> they are just sitting dormant? So if the other router
> somehow lost it's ebgp peer, it'll send withdraws to the
> ibgp peer and the other guy will take over with 104k
> routes correct?
Exactly...
> Could you define what you meant buy "if an iBGP peer
> learns that another iBGP peer already has a better route
> to a specific prefix, it will issue a withdrawl to that
> peer for the prefix(es)."
Let me see if I can articulate that a little better...
[ eBGP ] [ eBGP ]
[AS 701] [ AS 1 ]
| |
104k| |104K
| |
| |
[ BGP ] [ BGP ]
[AS "X"] [AS "X"]
| |
|
My router that connects to AS 1 has learned roughly 104k prefixes via
eBGP...
My router that connects to AS 701 has also learned roughly 104k
prefixes via eBGP...
Via iBGP, the AS1 connected router tells my other router of the 104k
prefixes that it has learned...
At the same time, my AS701 connected router is transmitting the 104k
prefixes it has learned to the AS1 connected router...
Once each of my routers has finished their mutual exchange of routes,
the AS701 connected router sees that for all but approximately 700
prefixes, the AS1 connected router has an equally good path, and via
the iBGP connection, he issues withdraws for 103.3k of the routes that
he had previously announced to my other router...
At this point, each of the routers has a full table learned via eBGP,
and 'show ip route' yields about 4 gazillion pages of output...
A 'show ip bgp' also yields a ton of output, but the AS701 connected
router shows two entries for each prefix (One learned via the external
peer, and one learned via the internal peer), but the AS1 connected
router has a single entry per prefix.
> If both of those routers are receiving full routes, and
> without any other configuration, how would the routes
> learned from one provider be any better than the other?
With no additional configuration, "customer" routes (those that
originate in a directly connected external AS, or are a single hop
away, if single homed) would be fewer AS hops away... They would be
preferred...
> Thanks and great post!
Thank you... > ;)
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=34550&t=34550
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