Establishing LDP Session Steps

BDF.

MPLS LDP (Label Distribution Protocol) Graceful Restart is a mechanism that allows a router to maintain label forwarding state during a switchover or failover without causing any service disruption. When an LDP session is established between two routers, they exchange initialization messages to establish the session. Here are the steps that are included when the RP sends an LDP initialization message to a neighbor to establish an LDP session:

A. Learn from Neighbor (N) flag, set to 1: This flag in the LDP initialization message indicates that the sender is willing to receive label mapping information from the neighbor. If the flag is set to 1, it means that the router is willing to accept label bindings from the neighbor.

B. Recovery Time field: This field in the LDP initialization message indicates the amount of time that the router can retain its label information in case of a switchover or failover. This field is used during the Graceful Restart process to indicate the time for which the router can retain its label information.

C. Type-9 LSA: This is not related to LDP initialization messages. It is a type of OSPF LSA used to advertise MPLS traffic engineering information.

D. Reconnect Timeout field: This field is used during the Graceful Restart process to indicate the time for which the neighbor should wait before trying to re-establish the LDP session after a switchover or failover.

E. Graceful restart capability in OPEN message: This is an optional capability that can be advertised in the BGP OPEN message. If both routers have the capability, they can negotiate the use of Graceful Restart during a BGP session switchover or failover.

F. Learn from Network (L) flag, set to 1: This flag in the LDP initialization message indicates that the sender is willing to advertise label mapping information to the neighbor. If the flag is set to 1, it means that the router is willing to send label bindings to the neighbor.

Therefore, the correct answers are A, B, and F.