LDP , hello and keep alive message, purpose.

[sarahr202]

Hi everybody.

I hope you guys are doing great. It has been a while since last visited the forum.  I have been focusing on my new job.

I have few questions about LDP:

R1-f0/0-------199.199.199.0/24----F0/0-R2

R1: loopback1 : 1.1.1.1 ( Used as ldp id)

R1: f0/0: 199.199.199.1

R2: loopback2 : 2.2.2.2 ( Used as ldp id)

R2: f0/0: 199.199.199.2

In a steady normal state, we see following messages being exchanged between R1 and R2.

27","19.721000","199.199.199.1","224.0.0.2","LDP","76","Hello Message "

"29","20.151000","199.199.199.2","224.0.0.2","LDP","76","Hello Message "

"6","6.264000","2.2.2.2","1.1.1.1","LDP","72","Keep Alive Message "

"25","18.731000","1.1.1.1","2.2.2.2","LDP","72","Keep Alive Message

1) Hello messages help build ldp neighbor relationship.

2) Keep alive helps ensure that dead neighbor can be detected

Now but why do we have hello messages being exchanged eventhough neighbor relationship has been establised. You might say we want to keep track if our neighbor is alive and kicking so that is why we want to keep exchanging these hellos  . But we are already acheiving this purpose using keep alive.

I appreciate your insight .

Thanks and have a great weekend

[dominic.caron · Accepted solution]

Hi,

Let say you are on a shared network that work like an hub. The udp hello are part of the discovery process. The device can build multiple peering on the same interface.

The tcp keepalive are part of the peering process and not discovery.




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