[c-nsp] Dumb question
Jon Lewis
jlewis at lewis.org
Wed Aug 3 09:30:24 EDT 2011
On Wed, 3 Aug 2011, Ziv Leyes wrote:
> Hi all,
> I have the following scenario (excuse my lousy ascii art...)
>
>
>
> ISP1
> /
> /
> /
> RTR1 -----iBGP----- RTR2
> \
> \
> \
> ISP2
>
> For the simplicity of the case, I have two prefixes, 1.1.1.1/24 and
> 2.2.2.2/24, I want to advertise prefix 1.1.1.1/24 to ISP1 as best, and
> 2.2.2.2/24 to ISP1 with prepends, and the opposite too, prefix
> 2.2.2.2/24 to ISP2 as best and prefix 1.1.1.1/24 to ISP1 with prepends.
>
> What I'm trying to do is to set up all in a way that the only place I
> set up my decision is on RTR1 only, and that will be reflected via the
> iBGP to RTR2 about how I want the prefixes to be advertised to my eBGP
> neighbors ISP1 and ISP2 I tried setting communities, but all I got is
> RTR2 to see and match the communities, but based on this, I couldn't get
> the prefixes advertised to the ISPs at all.
>
> What kind of manipulation I need to do in order for the RTR2 after
> matching the communities coming from RTR1, to advertise it to the ISPs
> according to the priorities I've mentioned before?
This should be reasonably simple to do by setting communities on the
prefixes on RTR1 (assuming RTR1 is exporting these prefixed into BGP...use
a route-map there to set the communities). On RTR2, you'll need
output route-maps for ISP1 and ISP2 that permit / permit and prepend based
on community strings.
i.e. on RTR1, you'd set multiple community strings on 1.1.1.1/24 and
2.2.2.2/24, first a string that indicates this is a route you want to
advertise to the internet in general, then a second string that indicates
you want some number of prepends when going out ISPx. In the output
route-maps on RTR2, you'd check for these prepend community strings first,
and the general "announce to internet" string last.
----------------------------------------------------------------------
Jon Lewis, MCP :) | I route
Senior Network Engineer | therefore you are
Atlantic Net |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
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