The P router is connected with PE via 2 link. One is working as primary, and other one working as secondry. When i shut down the primary link, the MPLS traffic works well. But, when i bring the primary link up and shut down the secondry link, MPLS traffic doesn't work. Whereas, there is no problem in the normal IP traffic. But, when i shut and no shut the primary interface, MPLS traffic starts working normal. What could be the problem? Attached is the configuration of PE device for your refrence? By the way, P device is from Huawei. I really need to solve this problem as soon as possible. Please respond.
In fact it should work except of maybe a transient connectivity break because of a race condition. OSPF and LDP will start sending hellos and setting up adjacencies and LDP session, respectively.
Once OSPF is converged it will start using the new/reenabled link. OSPF routing decision does not take LDP availability into account. So when LDP is not ready yet, but OSPF decides to send all traffic over the primary link, there are no labels yet (show mpls forwarding-table, search for "untagged"). Thus connectivity for VPN traffic is broken.
One way of overcoming this is to use targeted LDP:
R(config)# mpls ldp neighbor x.x.x.x targeted ldp
This means the LDP session is kept even if the interface is down, as long as x.x.x.x has IP connectivity.
Now all this said, it should recover without manual intervention. Your config looks fine to me. Have you checked, what the underlying problem is?
show mpls ldp discovery ! are LDP hellos sent and received after link recovery?
show mpls ldp neighbor ! is LDP session reestablished?
show mpls forwarding-table ! are labels entered into LFIB after link recovery?
Targeted LDP might still solve your problem, because you would not loose the LDP session.
Thank you very much to both of you for your quick reply.I am also facing the problem with load balancing, this is the reason that redundany is being used. But, in the case of load-balancing, the MPLS trafic works fine for weeks; and suddenly the problem starts.In order to solve this issue, I thought to use the redundancy option. Equal cost (100) that of the Cisco is configured on the gig interface o Huawei router.
Now coming to mheusinger answer, I didn't try the target ldp command, but I have tried the following command on the Cisco 6509: -
router id loopbak 1
discovery targeted-hello accept
One more thing, I would like to say here is that when I do the continous ping, I have noticed that MPLS traffic works till the OSPF database is full. Once the OSPF database is full, the ping stops.
Do i need to put the loopback IP of the Huawei router or gig interface, while configuring the targeted ldp? LDP session is established in the beining, but stops later on i think. Can we configure the target ldp for point to point link or is it for teh router, which is some hop away?
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