Configuring Attributes for Hello Packets
Context
IS-IS maintains neighbor relationships between neighbors 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.
- 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 the interval for sending Hello packets.
- (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.
If an Ethernet interface already has Layer 2 configuration, this command fails to be executed on the interface. Before running this command on the interface, delete all the Layer 2 configuration of the interface.
If many Ethernet interfaces need to be switched to Layer 3 mode, run the undo portswitch batch interface-type { interface-number1 [ to interface-number2 ] } &<1-10> command in the system view to switch these interfaces to Layer 3 mode in batches.
- Run isis timer hello hello-interval [ level-1 | level-2 ] [ conservative ]
The 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. Level-1 and Level-2 Hello packets are sent separately and their intervals must be set respectively. There is only one Hello packet on a point-to-point link. Therefore, level-1 and level-2 parameters are not used.
- (On an Ethernet interface), run undo portswitch
- Set the holding multiplier for neighboring devices.
- (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.
If an Ethernet interface already has Layer 2 configuration, this command fails to be executed on the interface. Before running this command on the interface, delete all the Layer 2 configuration of the interface.
If many Ethernet interfaces need to be switched to Layer 3 mode, run the undo portswitch batch interface-type { interface-number1 [ to interface-number2 ] } &<1-10> command in the system view to switch these interfaces to Layer 3 mode in batches.
- Run isis timer holding-multiplier number [ level-1 | level-2 ]
The 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. Level-1 and Level-2 Hello packets are sent separately and their intervals must be set respectively. There is only one Hello packet on a point-to-point link. Therefore, level-1 and level-2 parameters are not used.
- (On an Ethernet interface), run undo portswitch