BGP route-map with community tagging not working

[vanjaburic]

This is all done in GNS3 and it got me stumped so any helps is appreciated.

I am trying to advertize only certain routes (24.1.0.0/20) from R1 to ISP via ip community-list but for some reason ISP is not seeing 24.1.0.0/20 the route.

Explanation:

R1(AS20)—R2(AS20)--> ISP(AS10)

R1 and R2 are in the same AS and are directly connected.

24.1.0.0/20 is generated on R1 via aggregate address and tagged by community 300:61100, and then passed down to R2.

R2 sees the 24.1.0.0/20 route as well as its community as you can see from the output:

R2#show ip bgp 24.1.0.0/20

BGP routing table entry for 24.1.0.0/20, version 9

Paths: (1 available, best #1, table Default-IP-Routing-Table)

  Not advertised to any peer

  Local, (aggregated by 20115 96.34.15.2)

    96.34.15.2 (metric 3550) from 96.34.15.2 (96.34.15.2)

      Origin IGP, metric 0, localpref 100, valid, internal, atomic-aggregate, best

      Community: 300:61100

But for some reason it won’t pass it to ISP.

On R2 I have following config:

router bgp 20

neighbor 8.4.4.6 activate

neighbor 8.4.4.6 send-community

neighbor 8.4.4.6 route-map L3-TEST out

!

ip community-list standard REGIONAL-AGGS permit 300:61100

!

route-map L3-TEST permit 10

match community REGIONAL-AGGS

Without the route-map ISP of course sees 24.1.0.0/20 (and everything else) because everything is allowed. But I just want to pass that specific route to the ISP router. What am I doing wrong with this route map?

Note: I do have  send-community command on all routers.

Any help is appreciated.

[Harold Ritter]

Hi,

First, you should make sure that there is no extra blank at the end of the community-list. Could you please post a "show ip bgp route-map L3-TEST" output.

Regards

[vanjaburic]

Thanks for the reply Harold.

Interestingly enough nothing shows up even though route map is there and is applied to the neighbor.

R2# show ip bgp route-map L3-TEST

R2#

I've cleared BGP sessions multiple times. I am clearly doing smething wrong or GNS3 has a bug.

[Harold Ritter]

Hi,

It doesn't look right. Did you check that you do not have a blank at the end community-list? You could try the following instead:

ip community-list expanded REGIONAL-AGGS permit ^300:61100$

Regards

[vanjaburic]

Your syntax worked. But then I've tried to go back to mine (standard one) and it worked too. I've cleared sessions few times just to make sure it will still hold, and it is.

However now when I want to try to add more communities to it (ex. ip community-list standard REGIONAL-AGGS permit 300:61100 300:61101) it will not work. It has to be some bug or something.

Thanks for the help.

[Harold Ritter · Accepted solution]

Hi,

Your community list will only match if both 300:61100 and 300:61101 are present in the update.

You might want to try configuring the matches over multiple line like this instead:

ip community-list standard REGIONAL-AGGS permit 300:61100

ip community-list standard REGIONAL-AGGS permit 300:61101

Regards

[vanjaburic]

Yeah I totally forgot about that. I fixed it now. What I did was I tagged the route with additional community since it has to be there anyway, because I will be using it again and again through out the topology.

It works now

Thanks for your help.