(Optional) Configuring Timers for an LDP Session

An LDP session uses the following timers: link Hello send timer, link Hello hold timer, KeepAlive send timer, KeepAlive hold timer, and Exponential backoff timer.

Context

An LDP session uses the following timers.

**Table 1** Timers for an LDP session
LDP Timers	Description	Suggestion
Link Hello send timer	Used to send Hello messages periodically to notify a peer LSR of the local LSR's presence and establish a Hello adjacency. Similar to a remote LDP session, a local LDP session uses a link Hello send timer.	On an unstable network, decrease the value of a link Hello send timer, speeding up network fault detection.
Link Hello hold timer	Used to exchange Hello messages periodically between two LDP peers to maintain the Hello adjacency. If no Hello message is received after the link Hello hold timer expires, the Hello adjacency is torn down. Similar to a remote LDP session, a local LDP session uses a link Hello hold timer.	On a network with unstable links or a large number of packets, increase the value of the link Hello hold timer, preventing a local LDP session from being torn down and set up frequently.
KeepAlive send timer	Used to send KeepAlive messages periodically, maintaining the local LDP session.	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 local LDP session. If no LDP PDU is received after the KeepAlive hold timer expires, the TCP connection is closed and the local LDP session is terminated.	On a network with unstable links, increase the value of the KeepAlive hold timer, preventing the local 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 LSP 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.

Using default values of these timers are recommended.

Procedure

Perform the following steps to configure a link Hello send timer:
1. Access the system view.
```
system-view
```
2. Access the view of the interface on which an LDP session is to be established.
```
interface interface-type interface-number
```
3. Configure a link Hello send timer.
```
mpls ldp timer hello-send interval
```
  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 }
Perform the following procedure to configure a link Hello hold timer:
1. Access the system view.
```
system-view
```
2. Access the view of the interface on which an LDP session is to be established.
```
interface interface-type interface-number
```
3. Configure a link Hello hold timer.
```
mpls ldp timer hello-hold interval
```
  A smaller value between two configured link Hello hold timers on both ends of the LDP session takes effect.
Configure a KeepAlive send timer.
1. Access the system view.
```
system-view
```
2. Access the view of the interface on which an LDP session is to be established.
```
interface interface-type interface-number
```
3. Configure a KeepAlive send timer.
```
mpls ldp timer keepalive-send interval
```
  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.
  
  Changing the value of a KeepAlive send timer may lead to reestablishment of related LDP sessions.
Configure a KeepAlive hold timer.
1. Access the system view.
```
system-view
```
2. Access the view of the interface on which an LDP session is to be established.
```
interface interface-type interface-number
```
3. Configure a KeepAlive hold timer.
```
mpls ldp timer keepalive-hold interval
```
  A 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 may fail to be set up.
  
  Changing the value of a KeepAlive hold timer may lead to reestablishment of related LDP sessions.
Configure an Exponential backoff timer.
1. Access the system view.
```
system-view
```
2. Access the MPLS-LDP view.
```
mpls ldp
```
3. Configure an Exponential backoff timer.
```
backoff timer init max
```
  Note the following settings:
  - init: specifies the initial value of an Exponential backoff timer. The value is an integer ranging from 5 to 2147483, in seconds. The default value is 15.
  - max: specifies the maximum value of an Exponential backoff timer. The value is an integer ranging from 5 to 2147483, in seconds. The default value is 120.
  Setting the initial value equal to or greater than 15 and the maximum value equal to or greater than 120 is recommended.
  The backoff timer command helps the active role adjust the interval between attempts to establish an LDP session.
  - The initial and maximum values can be increased to allow a longer interval between attempts to establish an LDP session during device upgrade.
  - The initial and maximum values can be decreased to allow a shorter interval between attempts to establish an LDP session if intermittent service interruptions occur.