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Community Member

LDP and OSPF neighbor ship

How do I establish first LDP neighbor ship before established OSPF neighbor ship?

When MPLS and OSPF is running on interface. What are first to establish neighbor ship between LDP and OSPF?

In fact, I test that sequence of LDP and OSPF neighbor ship. but, some interface was established OSPF before LDP neighbor ship. some different interface is LDP neighbor ship was established before OSPF.

I don't know to control this seqeunce.

Any one help me?

5 REPLIES
Cisco Employee

Re: LDP and OSPF neighbor ship

Sun Young,

The LDP neighborship will usually be dependant on the ospf neighborship. This is because LDP establishes a TCP session to the neighbor's router-id (usually the loopback address). So unless you have IP connectivity to the neighbors's loopback address you can't establish the LDP neighborship.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Community Member

Re: LDP and OSPF neighbor ship

thanks for your advice.

I have one more question. if network is below

A - B

\C/

On this network link down occur between router A and router B. but, A is know that loopback interface on router C. because, route advertise from B.

In this case, If recovered link between A and C. Is established LDP neighbor ship first?

Cisco Employee

Re: LDP and OSPF neighbor ship

Two things have to happen for the LDP neighborship to come up. LDP discovery is done on a directly connected link between two routers using LDP hellos (UDP packets to port number 646 using a multicast address 224.0.0.2 (ALL-ROUTERS)). The LDP hello contains the router-id, on which the TCP session will be established.

After the TCP session is established the LDP hellos are still sent at a regular interval. If you don't receive the neighbors LDP hello for the defined holdtime, the TCP session is taken down. So in your scenario, if the link between A and B goes down so will the TCP session between A and B.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Community Member

Re: LDP and OSPF neighbor ship

I'm sorry about that my senario. that's incorrect.

I corrected it.

A - B

\C/

A,B,C router's are running OSPF and LDP on each interface. (assume in same area)

On this network link down occur between router A and router B. but, A is know that loopback interface on router B. because, route advertise from C.

In this case, If recovered link between A and B. Is established LDP neighbor ship first?

Cisco Employee

Re: LDP and OSPF neighbor ship

Sun,

You are absolutely corect that in this case, the LDP neiborship would most probably come up before the OSPF neighborship when you bring the link back up.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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