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Configuring new network for BGP

I'm in the process of configuring a network to implement BGP

Right we have a /24 from ISPa. ISPb is in the process of getting in the building.

1. In order to prepare for BGP with ISPb, should I configure Ext Network with a private ip address range? Right now it's configured with the /24 from ISPa.

2. Can I do load sharing with ISPa & ISPb, as well as failover?

3. I only found one document on cisco about this. ( Is there somewhere else I should be looking for examples/documentation?



Community Member

Re: Configuring new network for BGP

Here's a quick ascii diagram.

Hall of Fame Super Gold

Re: Configuring new network for BGP

Have you got, or are in the process of getting, an AS number ?

Is ISP-b ok with announcing the /24 you got from ISP-A, as coming from your AS?

Unless the answer is yes to both questions above, it is useless to discusses the rest.

Community Member

Re: Configuring new network for BGP

1. working on the AS now

2. my assumption is yes. we have quite a bit of leverage with them.

I found a cisco doc on using hsrp/bgp for redundancy, but I'm still looking for load balancing between the two routers.

Hall of Fame Super Gold

Re: Configuring new network for BGP

You will have outgoing and incoming load balance. Outgoing is easy, you can start with two default routes then adjust as necessary.

Or, you take partial or full tables (depending on you link and routers size), the routers will do that almost automatically.

Incoming is more difficult. I suggest you get to a stable configuration, and familiarize yourself with the BGP operation, before even worrying about it.

Re: Configuring new network for BGP


Try not to assume things. Try to make sure things are the way you assume instead. Both ISPs should agree to what you intend on doing, especially the one that supplied you the subnet in the first place, because he is the one that might have a hole punched into his address space, which means more routes in the Internet routing table in order for you to get some load balancing and avoid the rest of the world prefering the more specific route from the ISP that has not actually given you the subnet. I mean that if the subnet is part of an agreggate, the ISP that gave you the subnet would have to announce to the Internet individual subnets of the aggregate space.

In addition, unless you get your own AS number, there will be 2 different ASs claiming origination of your subnet, which is quite unacceptable.

Kind Regards,


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