From: Jay Hennigan (jay@west.net)
Date: Mon May 12 2003 - 18:01:32 GMT-3
On Mon, 12 May 2003, OhioHondo wrote:
> When you redistribute external prefixes into BGP, I believe that you should
> NEVER redistribute them back into BGP. It can only cause problems.
Agreed in practice. But the lab may ask you to do so.
> That means that on your IGP to BGP redistributions, you should have a route
> map that filters out the externally learned BGP prefixes. (you can use other
> means also.)
Yes. So the trick that he is looking for is that he has an OSPF IGP that
may accept external routes from other sources or protocols that he wants
to redistribute into BGP, but it is also taking routes redistributed from
one BGP AS, and must ensure that those routes are not redistributed into
a second AS on a different router, while allowing other external routes
to be redistributed into both BGP peers.
I gave him a hint.
> If you take care not to "re-redistribute", you only need the ip as-path
> access-list ^$ to ensure that your AS is not a transit AS.
Or you can use community strings.
-- Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net NetLojix Communications, Inc. - http://www.netlojix.com/ WestNet: Connecting you to the planet. 805 884-6323
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