Quick OSPF Q. about load bal

[jigsaw2026]

Hello,

If 2 routes are advertised from different OSPF processes, would they still load balance the same as if they were part of the same process (assuming they are of equal weight)?

I can't see why they wouldn't but just need to double-check there's no weird preference rules.

Thanks!

J

[amit-singh]

They should.I have not tried it practically but should work.

-amit singh

[ruwhite · Accepted solution]

We don't ever load share between two routing processes. One or the other process will win, and install its route in the local RIB, and the traffic will take that path.

In OSPF, the older route usually wins.

:-)

Russ

[amit-singh]

Thanks Russ, I wasnot sure about it.

It think its the same case with EIGRP as well.

-amit singh

[ruwhite]

We won't load share between two EIGRP processes, either, but the method used to choose which process wins is different between OSPF and EIGRP.

OSPF:

Lowest admin distance wins (Covers manually configured admin distances)

Oldest route wins

EIGRP:

Lowest admin distance wins (Covers manually configured admin distances)

Internals win over externals

Lowest metric wins

Lowest process ID wins

In other words, in EIGRP, if you have two identical routes learned in two processes, the process with the lower ID wins. The reason OSPF doesn't do this is that OSPF process ID's aren't significant, in the way EIGRP process IDs are.

Oh--had to edit to add this in.... There is a featurette request (defect) filed to allow OSPF processes to compare metrics and route types between processes. I don't know when it's going to be coded--but we did just get backing from a large customer for this functionality, so it might be pushed a little higher on the list.

HTH

:-)

Russ

[jigsaw2026]

That's great, many thanks guys for your help.