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ospf link carrying unequal traffic despite of equal cost!

taimoor.jan
Beginner
Beginner

Dear Friends,

I have three STM1s between a PE & P Router.

All the parameters are the same of these links. Even the OSPF cost is same, but one of the STM1 link is carrying much higher traffic than others.

As a normal behavior all three links should load balance the traffic.

In the below table I have captured the result of "Show ip ospf traffic Pos"

The problematic interface is Pos0/0/2

Pos   0/0/0
InvalidHellosDB-desLS-reqLS-updLS-ackTotal
Rx:03072824040392146472608
Tx:029212220235761610068910

Pos 0/0/1

InvalidHellosDB-desLS-reqLS-updLS-ackTotal
Rx:03073024040332142172507
Tx:02921422051233162382092

Pos 0/0/2

InvalidHellosDB-desLS-reqLS-updLS-ackTotal
Rx:03071324040286146272485
Tx:0292132205330852183064
3 Replies 3

cadet alain
Mentor
Mentor

Hi,

Load-balancing is for the data plane but the outputs you gave us are for the control plane and I  don't see any particular problem here.

Regards.

Alain.

Don't forget to rate helpful posts.

Don't forget to rate helpful posts.

Aileron88
Beginner
Beginner

It's worth remembering that OSPF can either send an implicit or explicit acknowledgement so the stats most likely show no issue at all.

Explicit acknowledgement is when the router sends an LSAck, and implicit acknowledgement is when the router sends the updated LSA header back to the router that sent the origial update in a LSUpdate message. So although you may see disparity between the number of Updates an Acks, if you look at the numbers carefully it will normally be the routers that send less Acks have sent more Updates and vice versa.

Hope this helps,

Adam

Alessio Andreoli
Contributor
Contributor

Hi Jan,

OSPF does not load balancing but it does load sharing. Aside this two golden rules:

Intra area routing over inter area routing over external routing has precedence over the cost:

O>OIA>E1>E2>N1>N2

(type of routes)

and then check if there is any self referencin cost in the config.

Last thing is the domain ID on the PE. essential in your very cool config, especially if you have sham-links around

Take Care

Alessio

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