Configuring the Interval for Detecting IS-IS Neighboring Device Failures

To minimize the impacts of neighboring device failures on IS-IS networks, accelerate the detection IS-IS neighboring device failures.

Context

Connection status between an IS-IS device and its neighboring devices can be monitored by exchanging Hello packets at intervals. An IS-IS neighboring device is considered. Down if the IS-IS device does not receive any Hello packets from the neighboring device within a specified period (holding time). A failure in an IS-IS neighboring device will trigger LSP flooding and SPF calculation, after which IS-IS routes re-converge.

To adjust the fault detection speed, use the following methods to accelerate the detection IS-IS neighboring device failures:

Configure the interval at which Hello packets are sent.
Configure the number of Hello packets that are sent before the local device considers the neighbor Down.

Holding time of neighboring devices = Interval at which Hello packets are sent x Number of Hello packets that are sent before the local device considers the neighbor Down. The maximum value of the holding time is 65535s.
Configure Dynamic BFD for IS-IS.

Configuring IPv4 BFD for IS-IS is recommended because this method ensures faster fault detection than the other two methods.

Procedure

Set an interval at which Hello packets are sent.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. Run isis timer hello hello-interval [ level-1 | level-2 ] [ conservative ]
  The interval at which Hello packets are sent is set.
  If the conservative parameter is specified in the command, the conservative mode is enabled for the holdtime of the IS-IS neighbor relationship.
  - If the parameter is specified and the holdtime of the IS-IS neighbor relationship is less than 20s, the IS-IS neighbor relationship is disconnected when the hold time elapses.
  - If the parameter is not specified and the holdtime of the IS-IS neighbor relationship is less than 20s, the IS-IS neighbor relationship is disconnected when the period of the hold time and a delay elapses.
  A broadcast link can transmit both Level-1 and Level-2 Hello packets. You can set different intervals for these two types of Hello packets. By default, both Level-1 and Level-2 Hello packets are sent.
  
  A P2P link can transmit only one type of Hello packets. Therefore, neither level-1 or level-2 needs to be specified if a P2P link is used.
4. Run commit
  The configuration is committed.
Set the number of Hello packets that are sent before the local device considers the neighbor Down.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. Run isis timer holding-multiplier number [ level-1 | level-2 ]
  The number of Hello packets that are sent before the local device considers the neighbor. Down is configured.
  
  A broadcast link can transmit both Level-1 and Level-2 Hello packets. You can set different intervals for these two types of Hello packets. By default, both Level-1 and Level-2 Hello packets are sent.
  
  A P2P link can transmit only one type of Hello packets. Therefore, neither level-1 or level-2 needs to be specified if a P2P link is used.
4. Run commit
  The configuration is committed.