Bundle router serial links of different bandwidths

[m.saufi]

Hello Netpros,

I have 2 routers linked together with 3 leased lines of 512k, 1mb and 2mb. Both routers are running OSPF with the links using OSPF authentication. Until now I cannot seem to find a way to use OSPF to load-balance the links evenly and have redundacy as well.

Question is how do I bundle all 3 links and still continue to functions even if any one or two of the 3 links them fails?

Many thanks.

[amit-singh]

Hi,

There are 2 ways to do it.

1. Ospf doesnot do un-equal cost path load-balancing.You can make the cost equal on each and every interface of the links and ospf will install all the 3 routes and will perform equal cost path load-balancing. Got to each and every interface and use command " ip ospf cost x " where X is the cost value defined on the interfaces.

2. Bind all the interfaces together, using Multilink PPP and advertise the multilink route in OSPF.I have not practically tried it but its worth to give it a try.

Note: In both the cases, your least bandwidth link might be oversubscribed.

HTH,

-amit singh

[m.saufi]

Amit,

Appreciate your fast repsonse.

Already tried OSPF cost, but the end results is not what I wanted.

For PPP multilink, I'm still trying to get the right configuration. If you can direct me to the right source or url, then it will probably helps a lot.

Thanks again.

[tekha]

To the best of my knowledge you can't get OSPF to do unequal loadbalancing.

So you are stuck with either EIGRP (http://www.cisco.com/warp/public/103/19.html) or static routes and secondary IP's (http://www.tek-tips.com/faqs.cfm?fid=387) in combination with Object oriented tracking (http://www.cisco.com/en/US/products/sw/iosswrel/ps5413/products_feature_guide09186a00801d862d.html#wp1071672), in order to cover your needs.

Personally I would go for the EIGRP solution.

[m.saufi]

Tekha,

Thanks for the prompt response.

Yes indeed OSPF can't do unequal loadbalancing.I've tried playing with cost but always ended up the lowest bandwidth being heavily utilised.

EIGRP is a no go since that's where I've migrated from.

Now looking at PPP Multilink to distribute the load.

[tekha]

I'm not sure how you would make unequal load balancing using PPP multilink. Infact this guideline says not to use links of unequal bandwidth (http://www.cisco.com/en/US/products/hw/switches/ps1938/products_configuration_guide_chapter09186a0080423761.html#wp1177514).

If you don't want to use EIGRP then I guess you are stuck with unequal loadbalancing using static routes and secondary IP's.

Please let us know what you come up with.

[st_kannan]

Hi,

As per cisco site

http://www.cisco.com/univercd/cc/td/doc/product/wanbu/8850px45/rel51/mpsm/mlpppcfg.htm

"All PPP links in a MLPPP bundle must have the same bandwidth to fully use the link. However, you can add links of unequal bandwidth if you wish. This might result in under utilization of the bundle bandwidth."

Your router is supporting CEF?

Just go through the below document it may helpful to you.

http://www.cisco.com/warp/public/105/loadbal_cef.html

Regards,

Kannan.S.T.

[m.saufi]

Thanks Kannan.

Yes,PPP links will probably not help much.

Both of my routers supports CEF and infact it's already enabled. But your url to CEF load balancing helps me understand better about CEF.Will try either the load-sharing per-packet or per destination and hope to see better utilisation of the 3 links.

Thanks again.

Regards,

MSaufi

[st_kannan]

Hi,

If your network has voice traffic use per-destination otherwise only date traffic means use per-packet load sharing.

If you are configuring policy based routing point all voice traffic towards high BW interface.

Regards,

kannan.S.T.