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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