Ospf unequal cost load balancing with same cost

[Arivazhagan S]

Hi All,

Refer the Exhibit
-routing protocol ospf
-Both link ospf cost 10
-ospf equal cost load sharing
-load sharing per packet

-Maximum we can use 5MB on each link , so total BW =10MB
-Total BW 15 MB but we can able to use 10MB only
-How to utilize remaing 5MB ? Is there any protocal or mechanisam to enable ?

[Jon Marshall]

EIGRP can do unequal cost load balancing using variance.

Jon

[Arivazhagan S]

Hi Jon,

That's fine. But my question is i want load share between two links (one 10MB & another 5 MB) which is having equal cost in OSPF. I want to utilize total 15 MB. Is there any protocal or mechanisam to enable ?

[Jon Marshall]

You asked if there was any protocol and EIGRP is a routing protocol which is why I suggested it.

If you mean is there any way within OSPF then not as far as I am aware because OSPF only supports equal cost load balancing so you have to make the links equal even if they are not.

Jon

[Arivazhagan S]

Thanks Jon for your inputs. Is there any other way to achieve this in OSPF. 

[Jon Marshall]

A suggestion I have seen on these forums was to use tunnels ie. create two tunnels across the 10Mbps link then set the tunnels and the other link all to the same cost.

I can't say for sure it would work as expected though as I have never tried it.

Jon

[Joseph W. Doherty]

The two tunnels across the 2x bandwidth should do the trick with OSPF, as it would then "see" equal cost paths.  Of course, tunnels bring their own issues.

The key, though, for routing that supports ECMP, is to provide twice the number of next hops on the 2x bandwidth path.

Besides tunnels, if your link supported subinterfaces, that too should allow OSPF to see two paths across the one physical link.

If your platform supports PfR, the PIRO variants, I believe, can use the unequal bandwidth with OSPF.  One big advantage of PfR, unlike "normal" routing, it can dynamically load balance your two paths, not just proportionally balance number of flows.

BTW, I would highly recommend you not do per packet load balancing.