multicast-domain holddown-time

Usage Scenario

During the Switch-MDT configuration, the forwarding rate of VPN multicast data may fluctuate above and below the switchover threshold due to network instability. To prevent multicast data traffic from being frequently switched between the Switch-MDT and Share-MDT, the system does not perform the switchover immediately after it finds that the forwarding rate is smaller than the switching threshold. Instead, the system starts the hold-down timer and performs the switchover after the hold-down timer expires.

Prerequisites

A Share-Group has been configured using the multicast-domain share-group binding command.

Precautions

During a switchover, there is a delay about 1 to 30 seconds from the time when the forwarding rate ranges to the time when the system starts the Switch-Delay timer. The delay is not included in the hold-down time. Consequently, the total delay from the time when the forwarding rate changes to the time when the system completes the switchover is 1-30 seconds longer than the hold-down time.

When interval is set to 0, the system triggers a switchover from the Switch-MDT to the Share-MDT immediately after it finds that the forwarding rate is below the threshold.

If a VPN instance has many multicast forwarding entries, the time taken to collect multicast traffic statistics will exceed the default hold-down time. In this case, increase the hold-down time to prevent frequent switchovers between the Switch-MDT and Share-MDT. Table 1 lists the recommended hold-down time values in various conditions.