Riverstone Networks WICT1-12 - Manual (Page 330)

17-22 Riverstone Networks RS Switch Router User Guide Release 8.0
LDP Configuration MPLS Configuration
17.4.2 Monitoring LDP Sessions
In addition to discovering LDP peers, sending hello packets also allows LDP nodes to detect link or peer node failures.
When LDP is started, the RS sends out LDP hello packets every 5 seconds by default. The hello message includes a
hold time value that tells the router’s peers how long to wait for a hello message. Since the hold time is set by each
LDP router, its neighbors can assume that a router or link is down if they do not receive a hello packet from the router
within the specified hold time. The default hello hold time used by LDP on the RS is 15 seconds. You can use the
ldp
set interface
command to specify a different hello hold time for LDP peers on a specific interface or on all router
interfaces. For example, the following command sets the LDP hello hold time to 20 seconds on the interface ‘int1’:
LDP neighbors do not have to set the same hold time value. For example, router R1 can set a hold time of 15 seconds,
while its neighbor R2 can set a hold time of 20 seconds.
Once an LDP session is established, LDP keepalive packets are used to monitor the status of the session. On the RS,
keepalive packets are sent at 10 second intervals and if the LDP peer does not respond in 30 seconds, the session is
considered down. The default session timeout on the RS is 30 seconds. You can use the
ldp set interface
command to specify a different LDP session timeout for LDP peers on a specific interface or on all router interfaces.
For example, the following command sets the LDP session timeout to 40 seconds on the interface ‘int1’:
Table 17-5 shows the default times used by the RS to monitor LDP sessions on both directly-connected LDP peers
and remote LDP peers. (For more information about remote LDP peers, see Section 17.4.3, "Remote Peers." )
ldp set interface int1 link-hello-hold-time 20
ldp set interface int1 keepalive-timeout 40
Table 17-5 Default LDP session monitoring parameters
Session monitoring parameters Direct-connect LDP peer Remote LDP peer
Hello Messages:
Send interval (not configurable - 1/3 of hold time) 5 seconds 5 seconds
Hold time 15 seconds 15 seconds
Session Keepalive Messages:
Send interval (not configurable - 1/3 of timeout) 10 seconds 10 seconds
Timeout 30 seconds 30 seconds