ospf link carrying unequal traffic despite of equal cost!

[taimoor.jan]

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
	Invalid	Hellos	DB-des	LS-req	LS-upd	LS-ack	Total
Rx:	0	30728	24	0	40392	1464	72608
Tx:	0	29212	22	0	23576	16100	68910
Pos 0/0/1
	Invalid	Hellos	DB-des	LS-req	LS-upd	LS-ack	Total
Rx:	0	30730	24	0	40332	1421	72507
Tx:	0	29214	22	0	51233	1623	82092
Pos 0/0/2
	Invalid	Hellos	DB-des	LS-req	LS-upd	LS-ack	Total
Rx:	0	30713	24	0	40286	1462	72485
Tx:	0	29213	22	0	53308	521	83064

[cadet alain]

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.

[Aileron88]

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]

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