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CLI-based Configuration Guide - IP Multicast

AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R007

This document describes the principles and configurations of IP multicast, and provides configuration examples.
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PIM BFD

PIM BFD

A network device must detect a communications fault between adjacent devices quickly so that the upper layer protocol can rectify the fault and prevent a service interruption.

Bidirectional Forwarding Detection (BFD) provides uniform, millisecond-level detection for all media and protocol layers. Two systems set up a BFD session and periodically send BFD control packets along the path between them. If one system does not receive BFD control packets within a specified period, the system considers that a fault has occurred on the path.

Implementation

If the current DR or Assert winner on the shared network segment is faulty in a multicast scenario, other PIM neighbors start a new DR election or Assert election after the neighbor relationship or the Assert timer times out. Consequently, multicast data transmission is interrupted. The interruption period, usually in seconds, is at least as long as the timeout interval of the neighbor relationship or the Assert timer.

Because PIM BFD detects the link status on a shared network segment within milliseconds, it responds quickly to PIM neighbor faults. If an interface enabled with PIM BFD does not receive BFD control packets from the DR or Assert winner within the detection interval, it considers that the DR or Assert winner is faulty. BFD fast notifies the RM of the session status and the RM then notifies the PIM module. The PIM module triggers a new DR election or Assert election without waiting for the neighbor relationship or the Assert timer to expire. PIM BFD reduces the time services are interrupted and makes data transmission more reliable.

Figure 4-15  PIM BFD

Figure 4-15 shows a shared network segment connected to user hosts. Downstream Interface1 on RouterB and downstream Interface2 on RouterC establish a PIM BFD session and send BFD control packets to detect link status.

RouterB functions as the DR and its downstream interface Interface1 is responsible for forwarding multicast data. If Interface1 becomes faulty, BFD fast notifies the RM of the session status and the RM then notifies the PIM module. The PIM module then triggers a new DR election. RouterC quickly begins functioning as the new DR and its downstream interface Interface2 forwards multicast data to the receivers.

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Updated: 2019-06-12

Document ID: EDOC1000097181

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