[c-nsp] route maps and bgp

[Jon Lewis]

On Mon, 3 Oct 2005, Chad Whitten wrote:

> my provider just switched me from a cisco router to a juniper router and my
> bgp session is all funky.  they are telling me i need route maps to filter
> the routes (im advertising my other neighbors routes to them).  im trying to
> advertise two networks out to each neighbor.  my config was basically
>
> router bgp AS#
> network a.b.c.d/24
> network e.f.g.h/20
> neighbor w.x.y.z remote-as ####
> neighbor w.x.y.z version 4
> neighbor 1.2.3.4 remote-as ####
> neighbor 1.2.3.4 version 4
>
> apparently with this simple config, im a transit now - and it is hitting my
> network hard.

First, both your providers are being stupid, as they should have 
prefix-lists or other methods setup for ignoring routes you send them 
other than the few legitimate routes you're supposed to be sending (your 
/24 and /20, and perhaps subnets of the /20).

Second, assuming #### and #### are 2 different transit provider ASNs, eBGP 
by default will advertise your /24 and /20 to each peer, plus any routes 
learned from the other peer.  You need prefix-lists, distribute-lists, 
route-maps, something to limit what you send to your peers.

ip prefix-list 13473-output permit a.b.c.d/24
ip prefix-list 13473-output permit e.f.g.h/20
router bgp 13473
  neighbor w.x.y.z prefix-list 13473-output out
  neighbor 1.2.3.4 prefix-list 13473-output out

ought to do it.  The prefix-list only lets you send the above 2 routes to 
each of the eBGP peers.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                | 
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