(Optional) Configuring Timers for LDP Session

Context

Table 1 describes the timers for an LDP session.

**Table 1** Timers for an LDP session
LDP Timer	Description	Suggestion
Hello send timer: Link-Hello send timer (for only local LDP sessions) Target-Hello send timer (for only remote LDP sessions)	Used to send Hello messages periodically to notify a peer LSR of the local LSR's presence and establish a Hello adjacency.	On an unstable network, decrease the value of a Hello send timer, speeding up network fault detection.
Hello hold timer: Link-Hello hold timer (for only local LDP sessions) Target-Hello hold timer (for only remote LDP sessions)	Used to exchange Hello messages periodically between two LDP peers to maintain the Hello adjacency. If no Hello message is received after the Hello hold timer expires, the Hello adjacency is torn down.	On a network with unstable links or a large number of packets, increase the value of the Hello hold timer, preventing the LDP session from being torn down and set up frequently.
Keepalive send timer	Used to send Keepalive messages periodically, maintaining the LDP sessions.	On an unstable network, set a smaller value for a Keepalive send timer, speeding up network fault detection.
Keepalive hold timer	Used to send LDP PDUs over an LDP session, maintaining the LDP session. If no LDP PDU is received after the Keepalive hold timer expires, the TCP connection is closed and the LDP session is terminated.	On a network with unstable links, increase the value of the Keepalive hold timer, preventing the LDP session from flapping.
Exponential backoff timer	Started by an LSR that plays an active role after an LDP Initialization message sent by the LSR to another LSR that plays a passive role fails to be processed or parameters carried in the message are rejected. The LSR that plays the active role periodically resends an LDP Initialization message to initiate an LDP session before the Exponential backoff timer expires.	When a device is upgraded, prolong the period for the active role to retry setting up a session. In this case, you can set larger initial and maximum values for the Exponential backoff timer. When a device that bears services tends to alternate between Up and Down, shorten the period for the active role to retry setting up a session. In this case, you can set smaller initial and maximum values for the Exponential backoff timer.

When local and remote LDP sessions coexist, the timeout interval of the Keepalive hold timer of the local and remote LDP sessions must be the same.

Procedure

Configuring timers for a local LDP session
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The view of an interface on which an LDP session is to be established is displayed.
3. (Optional) On an Ethernet interface, run undo portswitch
  The interface is switched to Layer 3 mode.
  
  By default, an Ethernet interface works in Layer 2 mode.
  
  Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
4. Run mpls ldp timer hello-send interval
  A link Hello send timer is configured.
  
  The default value of a link Hello send timer is one third of the value of a link Hello hold timer.
  
  Effective value of a link Hello send timer = Min {Configured value of the link Hello send timer, one third of the value of the link Hello hold timer}
5. Run mpls ldp timer hello-hold interval
  A link Hello hold timer is configured.
  
  The default value of a link Hello hold timer is 15, in seconds.
  
  The smaller value between two configured link Hello hold timers on both ends of the LDP session takes effect.
6. Run mpls ldp timer keepalive-send interval
  A Keepalive send timer is configured.
  
  The default value of a Keepalive send timer is one third of the value of the Keepalive hold timer.
  
  Effective value of a Keepalive send timer = Min { Configured value of the Keepalive send timer, one third of the value of the Keepalive hold timer }
  
  If more than one LDP-enabled links connect two LSRs, the values of Keepalive send timers for all links must be the same. Otherwise, LDP sessions become unstable or fail to be set up.
  
  If there is only one link between two LSRs and both local and remote sessions are configured, the local and remote sessions must have the same Keepalive send timer value. Otherwise, LDP sessions become unstable or fail to be set up.
7. Run mpls ldp timer keepalive-hold interval
  A Keepalive hold timer is configured.
  
  The default value of a Keepalive hold timer is 45, in seconds.
  
  The smaller value between two configured Keepalive hold timers on both ends of the LDP session takes effect.
  
  If more than one LDP-enabled links connect two LSRs, the values of Keepalive hold timers for all links must be the same. Otherwise, LDP sessions become unstable or fail to be set up.
  
  If there is only one link between two LSRs and both local and remote sessions are configured, the local and remote sessions must have the same Keepalive hold timer value. Otherwise, LDP sessions become unstable or fail to be set up.
  
  Changing the Keepalive hold timer value in an instance will interrupt the MPLS service in the instance because the LDP session must be reestablished.
8. Configure an Exponential backoff timer.
  1. Run quit
    
    The system view is displayed.
  2. Run mpls ldp
    
    The MPLS LDP view is displayed.
  3. Run backoff timer init max
    
    An Exponential backoff timer is configured.
    
    By default, the initial value is 15 and the maximum value is 120, in seconds. Setting the initial value of the Exponential backoff timer to be greater than or equal to 15s and the maximum value to be greater than or equal to 120s is recommended.
Configuring timers for a remote LDP session
1. Run system-view
  The system view is displayed.
2. Run mpls ldp remote-peer remote-peer-name
  The remote MPLS LDP peer view is displayed.
3. Run mpls ldp timer hello-send interval
  The target Hello send timer is configured.
  
  The default value of the target Hello send timer is one third of the value of a target Hello hold timer that takes effect.
  
  Effective value of a target Hello send timer = Min { Configured value of the target Hello send timer, One third of the value of the target Hello hold timer }
4. Run mpls ldp timer hello-hold interval
  The target Hello hold timer is configured.
  
  The default value of the target Hello hold timer is 45, in seconds.
  
  The smaller value between two configured target Hello hold timers on both ends of the LDP session takes effect.
5. Run mpls ldp timer keepalive-send interval
  A Keepalive send timer is configured.
  
  The default value of a Keepalive send timer is one third of the value of the Keepalive hold timer.
  
  Effective value of a Keepalive send timer = Min { Configured value of the Keepalive send timer, one third of the value of the Keepalive hold timer }
  
  If more than one LDP-enabled links connect two LSRs, the values of Keepalive send timers for all links must be the same. Otherwise, LDP sessions become unstable or fail to be set up.
  
  If there is only one link between two LSRs and both local and remote sessions are configured, the local and remote sessions must have the same Keepalive send timer value. Otherwise, LDP sessions become unstable or fail to be set up.
6. Run mpls ldp timer keepalive-hold interval
  A Keepalive hold timer is configured.
  
  The default value of a Keepalive hold timer is 45, in seconds.
  
  The smaller value between two configured Keepalive hold timers on both ends of the LDP session takes effect.
  
  If more than one LDP-enabled links connect two LSRs, the values of Keepalive hold timers for all links must be the same. Otherwise, LDP sessions become unstable or fail to be set up.
  
  If there is only one link between two LSRs and both local and remote sessions are configured, the local and remote sessions must have the same Keepalive hold timer value. Otherwise, LDP sessions become unstable or fail to be set up.
  
  Changing the Keepalive hold timer value in an instance may interrupt the MPLS service in the instance because the LDP session must be reestablished.
7. Configure an Exponential backoff timer.
  1. Run quit
    
    The system view is displayed.
  2. Run mpls ldp
    
    The MPLS LDP view is displayed.
  3. Run backoff timer init max
    
    An Exponential backoff timer is configured.
    
    By default, the initial value is 15 and the maximum value is 120, in seconds. Setting the initial value of the Exponential backoff timer to be greater than or equal to 15s and the maximum value to be greater than or equal to 120s is recommended.