Can i influence my bgp traffic out having unequal routing prefix received

Unanswered Question
Aug 3rd, 2009

-My internet gateway are connected to two ISP and im redistributing my network to both ISP(multihome)

-Im receiving full routing table from one ISP and partial(summarize) routing table from another ISP.

-Currently all the traffic would go out from the ISP that give full routing table.

-Can I influence my traffic out to choose the partial ISP as the prefered gateway out because the link have bigger bandwidth.

-I've try to influce using bgp attribute like setting local preference, weight, and prepending the AS path and its not working for me.

-Please advice.

I have this problem too.
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chinkevi_2 Mon, 08/03/2009 - 20:45

routing is used to route traffic based on destination address. Those BGP attributes are used to influence routes based on destination address.

if you are trying to do routing based on your source network, you would need to use policy based routing.

Istvan_Rabai Mon, 08/03/2009 - 22:57

Hi Lukman,

If I understand your scenario well, then the problem is caused by the following:

You receive full route table from ISP1 and a summarized route table from ISP2, on the same internet gateway. (Please correct me if I'm wrong.)

The result is that both the components of the full routing table and the summarized routes are installed in the routing table (independently of set weight, local preference, etc), as they are treated as different prefixes by the route table process.

When you send traffic to a particular destination, the router will chose ISP1 (sending the full routes) because the router chooses the route with the longest match in the routing table. (Summarized routes have a shorter prefix length).

One simple solution may be to ask both ISPs to send the same summarized route tables, if you can cooperate with them on that.

Then you can set weight on the received routes and now it will have the desired effect on path selection.



lukman.mdisa Mon, 08/03/2009 - 23:12

Thanks Istvan, you got the correct understanding of the situation that im having.

Im currently working on that method now, but im not having full cooperation from the ISP.

Is there other way from my end to try is(configuration wise)


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