Configuring PIM hello message options
In either a PIM-DM domain or a PIM-SM domain, hello messages exchanged among routers contain the following configurable options:
DR_Priority (for PIM-SM only)—Priority for DR election. The device with the highest priority wins the DR election. You can configure this option for all the routers in a shared-media LAN that directly connects to the multicast source or the receivers.
Holdtime—PIM neighbor lifetime. If a router does not receive a hello message from a neighbor when the neighbor lifetime timer expires, it regards the neighbor failed or unreachable.
LAN_Prune_Delay—Delay of pruning a downstream interface on a shared-media LAN. This option has LAN delay, override interval, and neighbor tracking support (namely, the capability to disable join message suppression).
The LAN delay defines the PIM message propagation delay. The override interval defines a period for a router to override a prune message. If the propagation delay or override interval on different PIM routers on a shared-media LAN are different, the largest ones apply.
On a shared-media LAN, the propagation delay and override interval are used as follows:
If a router receives a prune message on its upstream interface, it means that there are downstream routers on the shared-media LAN. If this router still needs to receive multicast data, it must send a join message to override the prune message within the override interval.
When a router receives a prune message from its downstream interface, it does not immediately prune this interface. Instead, it starts a timer (the propagation delay plus the override interval). If interface receives a join message before the timer expires, the router does not prune the interface. Otherwise, the router prunes the interface.
You can enable neighbor tracking on an upstream router to track the states of the downstream nodes for which the joined state holdtime timer has not expired. If you want to enable neighbor tracking, you must enable it on all PIM routers on a shared-media LAN. Otherwise, the upstream router cannot track join messages from every downstream routers.
Generation ID—A router generates a generation ID for hello messages when an interface is enabled with PIM. The generation ID is a random value, but only changes when the status of the router changes. If a PIM router finds that the generation ID in a hello message from the upstream router has changed, it assumes that the status of the upstream router has changed. In this case, it sends a join message to the upstream router for status update. You can configure an interface to drop hello messages without the generation ID options to promptly know the status of an upstream router.
You can configure hello message options for all interfaces in PIM view or for the current interface in interface view. The configuration made in interface view takes priority over the configuration made in PIM view.
Configuring hello message options globally
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter PIM view. | pim [ vpn-instance vpn-instance-name ] | N/A |
3. Set the DR priority. | hello-option dr-priority priority | The default setting is 1. |
4. Set the neighbor lifetime. | hello-option holdtime time | The default setting is 105 seconds. |
5. Set the PIM message propagation delay. | hello-option lan-delay delay | The default setting is 500 milliseconds. |
6. Set the override interval. | hello-option override-interval interval | The default setting is 2500 milliseconds. |
7. Enable neighbor tracking. | hello-option neighbor-tracking | By default, neighbor tracking is disabled. |
Configuring hello message options on an interface
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter interface view. | interface interface-type interface-number | N/A |
3. Set the DR priority. | pim hello-option dr-priority priority | The default setting is 1. |
4. Set the neighbor lifetime. | pim hello-option holdtime time | The default setting is 105 seconds. |
5. Set the PIM message propagation delay. | pim hello-option lan-delay delay | The default setting is 500 milliseconds. |
6. Set the override interval. | pim hello-option override-interval interval | The default setting is 2500 milliseconds. |
7. Enable neighbor tracking. | pim hello-option neighbor-tracking | By default, neighbor tracking is disabled. |
8. Enable dropping hello messages without the Generation ID option. | pim require-genid | By default, an interface accepts hello messages without the Generation ID option. |