If equal cost routes exist, OSPF uses CEF load balancing?

[nivetha01]

Hi All,

Can anyone explain about:

. If equal cost routes exist, OSPF uses CEF load balancing?

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Yes (assuming CEF is enabled).

[Richard Burts]

I would take a somewhat different approach to the question then Joseph does. Load balancing is about how we forward traffic and CEF can be part of how we process to forward traffic. OSPF is a routing protocol and its responsibility is to generate routing entries that can be put into the IP routing table. OSPF does not forward traffic so CEF is not involved with OSPF.

HTH

Rick

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Rick is correct, but if his response, with mine, causes any confusion. . .

To OP's original question:

If equal cost routes exist, OSPF uses CEF load balancing?

The answer is technically no, for the reason Rick describes.

But if we rephrase, such as:

Does CEF load balance across multiple equal cost routes generated by OSPF?

The answer would be yes.

I suspect the latter question is what the OP really had in mind, but again, Rick is correct to distinguish that OSPF doesn't use CEF.

[Richard Burts]

I think that Joseph's suggestion that the original question was not well phrased is on the mark. And if the OP is really asking about how the router forwards traffic (not about OSPF) then it is correct to say that (in recent versions) IOS by default will use CEF to achieve load balancing when multiple equal cost routes exist in the routing table.

HTH

Rick