[c-nsp] Dumb question

[Jon Lewis]

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                |
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