holddown-time (IPv6 address family MVPN-SPMSI view)

Usage Scenario

In some cases, the multicast data forwarding rate may fluctuate around the specified switching threshold. To prevent multicast data from being frequently switched between the I-PMSI and S-PMSI tunnels, a VPN instance does not immediately switch multicast data back to the I-PMSI tunnel when detecting that the multicast data forwarding rate is below the specified switching threshold. Instead, the VPN instance starts a hold timer. Before the timer expires, the VPN instance continues to detect the multicast data forwarding rate. If the rate remains consistently below the specified switching threshold throughout the timer lifecycle, the VPN instance switches multicast data back to the I-PMSI tunnel. Otherwise, the VPN instance still uses the S-PMSI tunnel to send multicast data. The holddown-time command allows you to configure the hold timer value.

Configuration Impact

If the holddown-time command is run more than once, the latest configuration overrides the previous one.

Precautions

In actual switching from an S-PMSI tunnel to the I-PMSI tunnel, due to necessary traffic rate calculation and protocol processing, there is a lag of 1 to 30 seconds between the time the multicast data forwarding rate changes and the time a VPN instance starts the hold timer. As a result, the actual hold time is 1 to 30 seconds longer than the specified hold time.

The interval for sampling the multicast data forwarding rate may be prolonged when a large number of multicast entries exist. As a result, MVPN traffic may be switched back from the S-PMSI tunnel to the I-PMSI tunnel earlier than expected, causing the loss of a small number of data packets. To prevent this problem, you are advised to increase the holddown-time based on the device performance and the number of existing multicast entries.