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New Member

Multihomed BGP source based routing??


I have a backbone like this


I want to take out to internet some of my ip blocks thru ISP2 which are connected to RT1. The coming from internet cloud is ok just

Anoncing and prepending. But how can i configure an outbound policy to take some customers on RT1 over ISP2 with BGP without using

Route-maps. Actually I just need a less recource using technic if there is any.


  • WAN Routing and Switching
New Member

Re: Multihomed BGP source based routing??


An equal cost default route would get you a 50/50 split between ISP1 and ISP2. If all routers have a complete routing table then one could use LOCAL_PREF to prefer an particular exit point.


New Member

Re: Multihomed BGP source based routing??

Ok. It is true if you want to set your IP blocks to go over RT4 or RT1 to a specific AS or IP block. But as i understand Local Preference is not suitable for source based (not destination) routing. Let me put this way; In RT1 i have two IP blocks, 10.1.x.x and 10.2.x.x. I just want 10.1.x.x go thru ISP1 and 10.2.x.x thru ISP2 for all outdomains. Without using route-map in all routers how can i set this? i can set incoming from ISPs by advertising 10.1.x.x to only ISP1 and 10.2.x.x to ISP2. what about outgoing??



Re: Multihomed BGP source based routing??

Hi Deniz,

For source-based routing, you need to use policy-based routing (not BGP). BGP will not help you with this. However, you do need to use a route-map.

Here's what you can do on RT1:

route-map PBRPolicy permit 10

match ip address 1

set ip next-hop


route-map PBRPolicy permit 20

match ip address 2

set ip next-hop


access-list 1 permit

access-list 2 permit

Then, on the interfaces that go to 10.1.x.x and 10.2.x.x, configure the following command:


interface ethernet 0/0

ip policy route-map PBRPolicy.

Hope that helps,


New Member

Re: Multihomed BGP source based routing??

Hi Paresh

If I do this i need to give the ip address of RT2 in route-map, right? and i need to write this route map in every hop, which is hard to implement for me because one of the router in my path, i.e. RT3 has low resources like cpu,memory, thats' why i just ask are there any other methods that are low resource consuming:)

Thanks in Advance


Re: Multihomed BGP source based routing??

Hi again,

What version of IOS are you running on RT3 ? IOS releases from 12.0+ support CEF switching of PBR traffic so you should not take that much of a hit ...

If you are running anything before IOS 12.0, I'm afraid your options are limited...


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