load balancing in 2 serialports of Cisco 2500 series router

[naresh69]

We are using cisco 2501 to connect to our ISP .We are connecting through two serialports ( 2 leasedlines ) .the leased lines are connected tio ISP s cisco2600 series router . we are using IP routing ( no bridging or ipx ) . The problem we are facing is as per the ip routes we are getting the data in both the links but the UPLINK is going through a single link

We gave ip route 0.0.0.0 0.0.0.0 serial 0

Then the whole uplink will go through serial0

even if we add the same troute to serial1 ,then also its going through serial0 only .hence we can not effectively use the uplink .Can any one suggest how we can send the uplink through both the links balancing the load on both the links

Thank you

[worapojr]

Dear naresh69,

I assume that you used BGP to connect with your ISP. You can have 2 ways to do the load balancing, Per Packet basis or Per Destination basis. You could find the detail for how to implement both of them at http://www.cisco.com/warp/public/459/40.html

I would like to suggest you to use Per Destination basis because Per Packet basis will consume a lot of cpu utilization for looking at every single packet and load balances on the number of routes in the routing table for the destination. This way can crash you router.

Brgds,

Worapoj R.

[jscinocca]

The last guy was correct..

If you are using BGP w/ two ISP you cannot load-balance just load-share.

Setup some ACLs and route-map and slit the internet in half over both T1's. This is the best way.

[deep]

Hi,

What if he is not running BGP, assuming he is from India, here most of the leased circuits to customers from ISPs run on static routing , which i feel, he is also using, so I think in that case using the static routes with same metric should work .

Thanks

Deep

[naresh69]

Hi ,

I am not using Bgp .here in india most ISP s run on Static routes and we are also running on them .And secondly the two lines are not from 2 differant ISps.Both the lines are from a single ISp .

Can you suggest any solution.

Thank you

[bbechamp]

The reason why it doesn't work when you have both ip routes in there is because ip route-cache is enabled...

In addtion to your two ip routes add "no ip route-cache" to both serial interface and it will send the information through both Serial interfaces. ("IP route-cache" just remembers which interface the traffic went through and sends all new requests for the same traffic through that interface. "no ip route-cache" does however increase your CPU load.

I encountered a similar problem when setting up a Cisco 4000 with 4 Serial connections.

And as the other guys said... This is just load sharing and not actual load-balancing.

[naresh69]

Thnaks for the reply .But in our router no ip route-cache is alreay there .We are running on static routes (not BGP) and both lines are from same ISp.Can you suggest any solution.Thank you

[ramesh.krishnan]

naresh,

BGP would be the best solution u can use. Let me assume that your upstream provider is not running BGP and workiong on static routes. U must be running RIP...right.If not try it out and in that u have an option of maximum-paths, put the value to 2. Try it out.It should work out.

RK

[jahil]

Forgive me all the Guru, But i know a Simple Solution for this,

ip route 0.0.0.0 0.0.0.0 s0

ip route 0.0.0.0 0.0.0.0 s1

Cisco IOS has a Built in Load Balancing Capability in Static Routes Also.

This should resolve the issue.

Regards

[mbjohnson]

Jahil is right. If you're not running BGP and have 2 T-1s for example connecting to the same ISP, you can use Cisco CEF (Cisco Express Forwarding) to load balance between the 2 links.

You will need the 2 default static routes:

ip route 0.0.0.0 0.0.0.0 s0

ip route 0.0.0.0 0.0.0.0 s1

You will need to enable ip cef.

Also you can choose between per-packet, or per-destination load-balancing. I believe per-destination is the default and works just fine.

Thanks and good luck!