3com S7906E 설치 설명서

1-16

Figure 1-9

Network diagram for label advertisement control

Downstream

device A

Downstream

device B

Label

Upstream

device C

Label control policy on device B:
Advertise labels that match prefix
list x.x.x.x/m to upstream neighbor
device C.

In the same LDP management domain, for two LSR neighbors, the inbound filtering policy on the
upstream LSR can be implemented by configuring an outbound filtering policy on the downstream LSR.
To reduce the processing load of downstream LSRs, you are recommended to configure only outbound
filtering policies.

LDP GR

For details about Graceful Restart (GR), refer to GR Overview in the High Availability Volume.

During MPLS LDP session establishment, the LDP peers need to perform Fault Tolerance (FT) and GR
capability negotiation. Only when both devices support GR, can the established session be FT/GR
capable. To support GR, a GR device must backup the FECs and label information.

When an LDP session is GR capable:

1) Whenever the GR restarter restarts, a GR helper will detect that the related LDP session is down

and will keep its neighborship with the GR restarter and retain information about the session until
the reconnect timer times out.

2) If the GR helper receives a session request from the GR restarter before the reconnect timer times

out, it retains the LSP and label information of the session and restores the session with the GR
restarter. Otherwise, it deletes all LSP and label information associated with the session.

3) After the session recovers, the GR restarter and helper activate the neighbor liveness timers and

recovery timers, restore all LSP information related to the session, and send to each other label
mapping and label request messages.

4) Upon receipt of the mapping messages from each other, the GR restarter and helper delete the

LSP stale flag. After the neighbor liveness timer and recovery timer time out, the GR restarter and
helper will delete all LSP information of the session.