From: Joshua Peterson (joshua@xxxxxxxxxx)
Date: Thu Sep 16 1999 - 22:03:52 GMT-3
Synchronization is unnecessary if you are running BGP on all routers in your
AS or your AS is not acting as a transit area.
If your AS is acting as a transit area and you are not running BGP on all
routers in your AS it is possible that transit traffic may be passed to a
router not running BGP. This router may be unable to make a sensible
routing decision because it has no knowledge of the destination network.
For example
All routers are running BGP except RtrC
RtrA(AS100)----RtrB(AS200)----RtrC(AS200)----RtrD(AS200)----RtrE(AS300)
RtrB is advertising a path to networks in AS300 to RtrA
RtrA sends traffic for networks in AS300 to RtrB
RtrB then passes it to RtrC, but RtrC has no entry in it's routing table for
the destination network
If synchronization were enabled, RtrB would not advertise the networks in
AS300 until it's IGP had a route to those networks.
I hope this helps. My explanation works much better with a white board and a
few beers.
----- Original Message -----
From: Peter Van Oene <vantech@sympatico.ca>
To: <ccielab@groupstudy.com>
Sent: Thursday, September 16, 1999 10:11 PM
Subject: BGP confusion
> Ok, I have an IBGP router with a bunch of routes in its BGP table. Unless
> I disable synch, it does not post them in the main routing table. I
assume
> this is because it does not have an IGP route for the listed networks.
>
> This confuses me somewhat though. If you have a ton of networks learned
> via BGP and you are a transit AS that requires the use of intermediary
> IGBP routers, why do you have to duplicate all of the routes via IGP just
> to do routing? If thats the case why run BGP internally at all? Why no
> just redist into OSPF? Obviously I'm missing something key.
>
> Can anyone tell me where my thinking is awry here?
>
>
> Peter Van Oene
> Senior Systems Engineer
> UNIS LUMIN Inc.
> www.unislumin.com
>
>
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