MPLS TE - Multiple Interfaces PE to P

Unanswered Question

I am facing the same problem as below posting.

I had 2 X STM-1 connection from PE2 to P2. The TE explicit path that defined the next-hop address to P2 is the loopback IP of the P2 router (not the physical SMT-1 IP), therfore the loopback IP of P2 is equal cost from the OSPF prespective. So I belived it can be load balance between 2 STM-1 links.

But when I send the traffic down to the tunnel, it seem like traffic when to one of the STM-1 link.

See attached diagram and the PE2 configuration and some show mpls screen shoot.

p/s: the PE2 is running IOS XR.


I have this problem too.
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Harold Ritter Wed, 05/07/2008 - 18:35

Choh Koon Tan,

MPLS TE will pick one link or the other for a given tunnel. If you want to load balance over these two physical links, try setting two TE tunnels to the same tail end, one going explicitly over each physical interface. This will cause the traffic to be load-alanced over the two links.



Yap you are right, but the problem is this PE2 is not have single tunnel to PE3 only. Therefore are about 20 more PEs that this PE2 is build tunnels to. If adding new parallel link require additional tunnels , then the number of tunnel is x2. Which I dont think practical.

I knew another way is P0S-bundles....but at moment I thinks it does not support FRR/TE.


Harold Ritter Thu, 05/08/2008 - 19:45

Choh Koon Tan,

If there is about 20 tunnels to 20 different PEs then you could just configure the explicit path of the first 10 tunnels to go through the first physical interface and the others through the remaining physical interface.

For redundancy, you could have a second path-option on each tunnel to go through the other physical interface in case the first one goes down.


Hi hritter,

I had configured 2 tunnels to the destination via it own stm-1 link. But I do not see the traffic load balancing between 2 tunnels. As

I knew from other posting ..the load sharing is per session load sharing ... and in this network behaviour the host application is making ONE session to destination host and the traffic usage is 90% of the stm-1 bw. Therefore i do not see the traffic flow via second tunnel.

based on the posting below, i tune the cef , " ip cef load-sharing algorithm tunnel "

Now I can see traffic on both tunnels.

But your advice is not turn on per packet load balancing... any reason...can you provide the details and concern.

p/s: if network traffic is http then per session LB work...but if application behaviour is open one session to destination and pumping huge traffic....then LB will not work if the per-packet cef is not turn on.




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