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Community Member

Load balance Backup ISP and OSPF

I am in the process of implementing a backup Line for our current WAN. we currently have frame and we are going to use an ISP that uses ATM. they provided us with a router that will just be an "Ethernet hand off" so i have a 2611 with 2 Ethernet ports and 1 T1 WIC. originally we just was going to assign cost to each link and have the slower link e1/0 come up on failure but now I would like to use this additional bandwidth. i was wondering if it is possible to have a 2611 IOS 12.0 load balance two different speed links from two different ISP's or at least be able to redirect certain traffic to the slower speed link and still have it fail over if the primary line died.

3 REPLIES
Bronze

Re: Load balance Backup ISP and OSPF

The only routing protocol which will enable you to load balance over unequal cost paths in EIGRP, using the variance command but it is very unlikely that your ISP would support this.

You can force load balancing by assigning equal bandwidth/costs but that is not necessarily recommended. The router will automatically load balance over, up to 4, equal cost paths but on a per session rather than on a per packet basis. This means that all traffic for some sessions will use the slower link.

You can force load sharing on a per packet basis by disabling fast switching, 'no ip route-cache' on the interface but this is not recommended for 2 reasons. Not only will it severly impact the performance of the router but some packets will arrive the destination out of sequence and require resequencing, effectively reducing the througput to the speed of the slower link.

Community Member

Re: Load balance Backup ISP and OSPF

>You can force load balancing by assigning equal bandwidth/costs but that is >not necessarily recommended. The router will automatically load balance >over, up to 4, equal cost paths but on a per session rather than on a per >packet basis. This means that all traffic for some sessions will use the >slower link.

is it possible to use an acl to force certain type of traffic to another interface?

Silver

Re: Load balance Backup ISP and OSPF

Yes. What you are looking for is called policy routing and is discussed frequently in association with ISP/BGP load balancing. You may also be able to do the job using BGP routing if you are taking local or full routes from your providers, but that does not work under all conditions and increases the loading on your routers.

Ask again if you need more info. There is a surplus of data on policy routing on cisco's web site, and many posts with examples on news://comp.dcom.sys.cisco, try a google groups search.

Good luck and good hunting!

Vincent C Jones

www.networkingunlimited.com

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