BGP routing question

[julxu]

hi expert

I have BGP setting, that is export route xxx.yyy.0.0.  that means if ibgp xxx.yyy.0.0 route existed, than export it.

Now, I have a new link, which is direct connected xxx.yyy.zzz.0. Can I configure the BGP so that, it ignore the direct conection of xxx.yyy.zzz.0 only look the ibgp route and export it. If so, how can I do it?

Any comments will be appreciated

Thanks in advance

julxu

[Vaibhava Varma]

HI julxu

Can you be more descriptive for your query of the network setup and the overall objective.

Regards

Varma

[julxu]

Thanks for the reply, my problem is:

if the internal router is router A (10.2.2.1), and it sends bgp route 10.1.0.0/16 to router B (border router, 10.3.3.1). So on the border router B there was only route:

B     10.1.0.0/16 [200/0] via 10.2.2.1 4w4d

now, I have a static route 10.1.5.0/24 configured into router B from router C (10.6.6.1), now on router B there has routes:

     10.1.0.0/16 is variable subnetted,

B     10.1.0.0/16 [200/0] via 10.2.2.1  4w4d

S     10.1.5.0/24 [1/0] via 10.6.6.1 

now I have problem:

     if the link between internal router A and border router B is down, than I want the border router B do not advice route 10.1.0.0/16 to internet.

     but, now there is a static route 10.1.5.0/24 or ( dynomic route maybe) existed, that means when A->B down,

the route 10.1.0.0/16 will still existed in border router B. and route B will advice it out.

I want find a solution, which has a policy or sla or something else, so that if A->B down, the route 10.1.0.0/16 will not adviced from border router to internet, even the static route existed and alive.

the router configuration for router B to internet looks like;

neighbor aaa.bbb.ccc.ddd remote-as eee

neighbor aaa.bbb.ccc.ddd route-map internet-out out

...

route-map intenet-out permit 5

match ip address v101

set metric 5

ip access-list standard v101

permit 10.1.0.0

deny any

Could I get some advice on if /how I can solve this problem with less changes?

Any comments will be appreciated

Thanks in advance

julxu

[Kishore Chennupati · Accepted solution]

hi,

You could use conditional advertisements in BGP. Please see below link that gives you more info on this

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a0080094309.shtml

Regards,

Kishore

Please rate if helps

[Marwan ALshawi · Accepted solution]

as Kishore mentioned the conditional BGP advertisment can do it

but how router B advertise the /16 to router A ?

as in normal cases if B advertise /16 to A and even if you have more spicific static route the /16 should disapear from A in the case the peering between A and B is down ?

[Vaibhava Varma · Accepted solution]

Hi Julxu

As marwanshawi has precisely mentioned when the peering between A & B is down there will be no iBGP route 10.1.0.0/16 in the BGP Table of Router B and hence it will not be announced. The present of any specific prefix in the Routing Table does not means that same would be exorted by default in BGP update. We need to do it manually via network command or redistribute command.

Always remember that in BGP only those routes are announced which are either present in the BGP Table already or which have a matching route for the network statement we put under BGP.

In your question the iBGP route goes off when A_to_B peering is down and then you do not have a network statement under BGP for 10.1.0.0/16 neither any valid route for 10.1.0.0/16 in Routing Table. So here you need not do anything.

What you are trying to achieve will happen automatically by default behaviour of BGP.

Hope this helps to answer your query.

Regards

Varma

[Kishore Chennupati]

True. I should have explained that bit as well. Just thought julxu  wanted to knwo about conditinal adv.in BGP

[Kishore Chennupati]

Thanks julxu   for the ratings. Appreciate that and also thanks for markign the thread as answered.