BGP multi-path or BGP multi-hop

Unanswered Question
Oct 15th, 2007

I have a requirement to load balance 2 internet links to the same provider. what is the better option? multipath or multi-hop BGP (using loopback to peer). beside using single peer and multipeer what would be the advantage and dis-advantage of using these load sharing methods.

thanks,

san

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gaurav_thapar79 Mon, 10/15/2007 - 23:42

Hi,

If your ISP and you are using ESR routers with per-packet load-sharing, then go-ahead with per-packet load-sharing. You can use loopback ip address to peer eBGP with your upstream provider.

incase of multihoming, you can configure different Loopback IP s and run EBGP seesions in similar fashion.

This would give you an ease to troubleshoot.

san-pandey Tue, 10/16/2007 - 01:35

Hi Gaurav,

Thanks for your post. we are going to use the default 'per-destination' load sharing.

What I wanted to know more is the advantages and disadvantages of both methods and which is the best option in terms of design and operations.

Thanks,

San

Bharat Negi Tue, 10/16/2007 - 02:06

Hi San

Just to add to your conversations:

1. eBGP multihop can be helpful and recommended if your both links are from single ISP router and terminating on Single router at your end.

2. Multipath will help you if you have connection from two different routers of same ISP terminating on single router at your end.

Also, if you don't want Internet routes at your end router, I suggest you to run Static routes to load balance.

For more info refer: http://www.cisco.com/warp/public/459/40.html

Rgds/bsn

gaurav_thapar79 Tue, 10/16/2007 - 04:11

Dear San/BSN,

In addition to this, per-destination would not help in terms of downllink traffic over multiple links between your router and ISP router.Infact, your customer may start complainig of download problems like FTP etc and would result in congestion on single link.

Pls revert with your comments and rate the post.

Phillip Hichens Tue, 10/16/2007 - 05:12

Hi

If you can use a single neighbour statement to your ISPs loopback with the ebgp-multihop it is the way to go.

Advantages include a single tcp session (BGP uses tcp on port 179 for routing updates), and routing updates being sent only once to and from your ISP (saving you CPU cycles).

Remember your IGP needs to be able to reach your neighbours loopback.

Regards

Phillip

san-pandey Tue, 10/16/2007 - 06:20

Hi Gaurav, Bharat and Phillip,

Thanks for all your comment. After reading your comments I think it makes more sense to use ebgp-multihop. It would have been nice to terminate to two different ISP routers, but because of RR etc in the ISP network we have to terminate to the same router. The advantage highlighted by Phillip on single neighbout statement on the ISP makes sense to both the customer and the ISP.

Gaurav, I will take note of your concern on single link saturation. This is a high speed connectivity so I do not see this problem. In the past I have used 'per-packet' load sharing, so if there are any problems I will not rule out using this method.

BTW, static is not an option here as the customer has multiple upstream providers and is using community tag from these service providers.

thanks,

san

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