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New Member

BGP Mulithoming

Last year we acquired another company who were an ISP and we have now been asked to connect the two networks. They have their own transit provider and AS number as do we. We are going to create a link between our site and them and use it as a resilient link if our main one goes down. The link we have is a 34Mb upstream connection to INS and the link to the other site is 10Mb. I want to configure BGP to load balance some traffic over to them and set it up so if the INS link goes down it will switch over to the other connection.

If anyone could give me any guidance i would appreciate it,


Ian Warburton

New Member

Re: BGP Mulithoming

First, I am no BGP expert,but

couldn't you run 2 static routes, same admin distance,and add bgp maximim paths 2..?

I dug that out of the halabi book on bgp.

Internet Routing Architectures

Cisco Press, Bassam Halabi

ISBN 1-56205-652-2

New Member

Re: BGP Mulithoming

For BGP multihoming, if you don't have any traffic policy like enter from one As and leave from another AS, then there is no need to configure BGP

but still you can use BGP, you can make both the end routers as EBGP neibours and advertise their network thru network command.

I hope it fulfill your requirement


New Member

Re: BGP Mulithoming


As you said you are multihoming .

to tune your traffic , you have to change your BGP's attribut

local preference for your outgoing traffic .

to prepend your own As for your incoming traffic .

it is very difficult to get 50% on each link

Best Regards,


New Member

Re: BGP Mulithoming

First, I am another non-expert in BGP.

As said by Tran, achieving a perfect load balance using BGP is almost impossible. You can influence how the traffic will leave your AS but you can’t make sure that the returning traffic will take the same path.

You can influence the leaving traffic by just setting the local preferences. As a tentative to influence how the traffic would return, you could append your own AS number into the AS-PATH several times when sending out updates to other ASs then yours. However, don’t count on it since this “padding” can be removed.

A key point that you don’t mention is the link speed between the two companies. Be aware that if you are connecting two end points ASs (ASs that currently have only one connection to the Internet) they can become transit ASs for the Internet. If you do not configure your ASs properly the link between the two companies (ASs) will carry traffic for the Internet.

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