Adjusting Control Parameters for Hello Messages

Context

PIM devices send Hello messages periodically to maintain PIM neighbor relationships. When a PIM device receives a Hello message from a neighbor, the PIM device starts the timer and sets the timer to the holdtime of Hello messages. If the PIM device does not receive a new Hello message from the neighbor within the holdtime, it considers the neighbor invalid or unreachable. Therefore, the interval of Hello messages must be smaller than the holdtime of Hello messages.

If multiple PIM devices transmit Hello messages simultaneously, a conflict occurs on the network. To solve this problem, when a PIM device receives a Hello message, it waits a period before transmitting the Hello message. This period can be a random value and is smaller than the maximum delay for triggering Hello messages.

The interval for sending Hello messages and the holdtime of Hello messages can be set either globally or on an interface. If the two parameters are configured in both the global PIM view and interface view, the configuration in the interface view takes effect.

You can configure the maximum delay for triggering Hello messages only in the interface view.

Default settings

Table 1 lists the default settings of control parameters for Hello messages.

**Table 1** Default settings of control parameters for Hello messages
Parameter	Default Setting
Interval for sending Hello messages	30s
Holdtime of Hello messages	105s
Maximum delay for triggering Hello messages	5s

Procedure

Global configuration
1. Run system-view
  The system view is displayed.
2. Run pim [ vpn-instance vpn-instance-name | all-instance ]
  The PIM view is displayed.
3. Run timer hello interval
  The interval for sending Hello messages is configured.
4. Run hello-option holdtime interval
  The holdtime of Hello messages is configured.
Configuration on an interface
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 pim timer hello interval
  The interval for sending Hello messages is configured.
5. Run pim hello-option holdtime interval
  The holdtime of Hello messages is configured.
6. Run pim triggered-hello-delay interval
  The maximum delay for triggering Hello messages is configured.