Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

Load balancing dual connections to a single ISP

I'm sure I've seen this on the Forum before, but could not find it.

I'm trying to implement a load-balanced connection to Sprint ISP. I plan to use GLPB on the Ethernet side but does anyone have a caned script to tweak BGP to load balance across tow equal paths to the same ISP? Or does anyone have any other suggestions other than "out of the box" BGP as it really doesn't load balance.



Hall of Fame Super Gold

Re: Load balancing dual connections to a single ISP


If we knew a bit more about your environment we could give better advice. Is Sprint your only provider, or is there another provider that you did not mention? Are your two outbound paths on the same router or on different routers?

Based on what you have described so far, I do not see much need to run BGP. It seems to me that a simple solution of a pair of default routes pointing out both of the exit paths would give you load balancing and be much simpler.



Community Member

Re: Load balancing dual connections to a single ISP

I'm looking at two separate routers (3825's) with a DS3 in each and both connecting to sprint.

Some of the challenges I see are that the firewall nats all outbound traffic to a single source address which makes GLBP and other protocols not work properly as the balancing metrics are based on the source address.

And with BGP using the AS hop count, I will need some help balancing the WAN traffic as all the destinations will have the same metric. I was thinking we'd need to route specifically to destinations but that would make my routing table extremely large.

I added a Visio attachment

Thanks, Jack

Community Member

Re: Load balancing dual connections to a single ISP


You have two options. One is set default routes to both ISPs redistributed into your BGP, this will load"share" among both ISPs in a random fashion, and you have no control over how much load-sharing takes place. The other and best option is to recieve all routes to the internet on both your routers, your routers will recieve about 150000 routes each but I believe your 3845s are more than capable of handling that, I have seen some work well with 512 Mb upgraded DRAM. Using this method will make your eBGP to choose the best path to an internet host if your ISP sprint has multiple BGP peers to connect to on their backbone, so enquire with your ISP of their infrastructure before commiting to any configs.

HTH - please rate all helpful posts


CreatePlease to create content