Configuring Attributes for Hello Packets

Context

IS-IS maintains neighbor relationships by sending and receiving Hello packets. If the local device does not receive Hello packets from its neighbor within a specified period, the device considers the neighbor Down.

In IS-IS, you can set the interval for sending Hello packets and the holding multiplier of neighboring devices to control the holdtime of neighbor relationships between the local device and neighbors.

If the interval for sending Hello packets is too short, more system resources are consumed to send Hello packets, causing a heavy CPU load.
If the holdtime of neighboring devices is too long, the local device needs to spend much time detecting the failure of neighbors, slowing down IS-IS route convergence. If the holdtime of neighboring devices is too short, some Hello packets may be lost or become incorrect because of network transmission delay and errors. This will cause neighbor relationships to frequently alternate between Up and Down and lead to route flapping on the IS-IS network.

You are advised to set the same interval for sending Hello packets and same holding multiplier of neighboring devices on all the devices on the IS-IS network. This method prevents IS-IS route convergence from being slowed down when some devices detect link failures at a lower speed than other devices.

Procedure

Configure an interval for sending Hello packets.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view 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 isis timer hello hello-interval [ level-1 | level-2 ]
  An interval for sending Hello packets is set on an interface.
  
  By default, the interval for sending Hello packets 10 seconds.
  
  Parameters level-1 and level-2 are configured only on a broadcast interface.
  
  On a broadcast link, there are Level-1 and Level-2 Hello packets. For different types of packets, you can set different intervals. If no level is specified, both the Level-1 timer and Level-2 timer are configured. On a P2P link, there is only one type of Hello packets. Therefore, neither level-1 nor level-2 is required.
Set a holding multiplier for neighboring devices.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view 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 isis timer holding-multiplier number [ level-1 | level-2 ]
  A holding multiplier of neighboring devices is set.
  
  The default holding multiplier is 3. The holdtime of neighbor relationships is three times the interval for sending Hello packets.
  
  Parameters level-1 and level-2 are configured only on a broadcast interface.