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BGP advertisements with multiple ISP's

tomstallings
Level 1
Level 1

I have a client of mine that is using us to advertise his /24 to us.  Everything works accordingly, however the client will change his main ISP to other ISP's at random for security reasons and failover reasons.  In the past this has not been a problem, however we have some other clients trying to access their website and when they are not advertising out to us, the route stops at our router where the client connects.

I have temporarily solved the issue by shutting down the BGP for that client, however, is there a way that I can still keep the BGP route up and put in a static route with a larger admin distance so that if the advertised route is not there, it sends it out to my edge router?  Or is there another way that we can do that as well?

5 Replies 5

clin
Level 1
Level 1

hi Tom

so your client A advertise their /24 to a new ISP beyond your control ? i don't you very clearly , if that why the other customers need access client A via your route ?

Yes in a way, so our customer has us connected to router B that advertises the route to us, as of right now router A is advertising out to another ISP out of our control.

The problem lies when another client on our network goes the the route, because of BGP, it will take the path to our router and stop because the BGP is up, just not the advertised route.  I hope I am explaing this right, basically the BGP works but because the client switches ISP's, my clients can no longer take the correct route unless I shut down the BGP peer

clin
Level 1
Level 1

do you have your BGP router and client BGP router as iBGP ?

if that, you can advertise /24 on both side but add path preference to let eBGP peer learn from your client side.

Ah ha, do you have an example of this?  I am semi noob to BGP

Have a look at this link for configuration and examples:

first scenario is when the customer has one router and the second scenario is when the customer has 2 routes.

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf4

HTH

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