BGP

[ashok_boin]

Hi,

I am having three providers A, B & C. A is only RX Asymmetric big carrier. So we are establishing BGP with A through B. Our advertisement policy is as following..

to A

192.168.32.0/19

192.168.32.0/21

192.168.40.0/22

192.168.44.0/22

192.168.48.0/20

to B

192.168.32.0/19

192.168.32.0/21

192.168.44.0/22

to C

192.168.32.0/19

192.168.40.0/22

192.168.48.0/20

Our problem is whenever A carrier is down, i am getting complaints from my customers they are not able to connect to some sites. I am even advertising my aggregate 192.168.32.0/19 to all, then where we can suspect BGP misconfiguration problem?

Thanks in advance....

Regards...

--Ashok.

[Gilles Dufour]

you need to do some troubleshooting first before suspecting anything or checking the config.

When your customer complains, check what site they have problem to reach.

Check if you have a route for those sites.

Check where the traffic should be coming from.

Check your BGP session with A - could it be that the BGP session stays up because carried by another provider ?

[ashok_boin]

Hi GDUFOUR,

Whenever the customer complained about a particular site, then i have seen no BGP route but we are having multiple equal default routes to our providers also. And when A is down, i am thinking that the input traffic should divert through remaining carriers because of my aggregate adv to all.

Keeping multiple equal default routes creates any problem? I am aware that "per host load share" for IP packets for equal paths by default for Cisco.

Thanks in advance...

Regards...

--Ashok.

[michaeljmorris]

when you say you are using a BPG aggregate (i.e. aggregate-address 192.168.32.0 255.255.24.0) do the B and C routers have an actual network advertisement for the more specific routes ? When using aggregate routes with BGP the aggregate will not be advertised if the router does not have all of the more specific routes covered by the aggregate in it's BGP table. You can force the advertisement with the "summary-only" keyword on the BGP aggregate-address command.

[ashok_boin]

Hi Michael,

Please refer to my first mail. You meant to say that after B, 192.168.32.0/21 won't be advertised to it's neighbors without configuring "summary-only" option?

-AShok.

[abahl]

Greetings!

Are you advertising aggregate address prefix along with specific prefixes or you are just advertising the aggregate address?

In order to avoid any routing loops, remove address aggregation and reset the bgp sessions, and check the status.

Anuj

[ashok_boin]

Hi Anuj,

Here is my adv policy

to A

192.168.32.0/19

192.168.32.0/21

192.168.40.0/22

192.168.44.0/22

192.168.48.0/20

to B

192.168.32.0/19

192.168.32.0/21

192.168.44.0/22

to C

192.168.32.0/19

192.168.40.0/22

192.168.48.0/20

So my aggregate address is 192.168.32.0/19 and i am advertising this prefix to all. Now please give me a example how routing loop occurs as you suspected in your prev mail

Regards...

--Ashok.