You can now enable buffering of the first packet in a multicast session when the multicast route or forwarding information base (FIB) entry does not, yet, exist for the corresponding multicast group. By default, the firewall does not buffer the first multicast packet in a new session; instead, it uses the first packet to set up the multicast route. This is expected behavior for multicast traffic. You need to enable multicast route setup buffering only if your content servers are directly connected to the firewall and your custom application cannot withstand the first packet in the session being dropped.
Enable Multicast Route Setup Buffering
Enable buffering of the first packet in the multicast session. Select Device > Setup > Session and edit the Session Settings. Select Multicast Route Setup Buffering to enable the feature. If you want to modify the buffer size, continue to the next step. Otherwise, click OK to save the setting.
( Optional ) Tune the multicast route setup buffer. The firewall can buffer a maximum of 5,000 packets. In the Session Settings dialog, set the Buffer Size per flow to a value from 1-2,000. To save the settings, click OK.
( Optional ) Tune the amount of time a multicast route stays in the routing table. Select Network > Virtual Router and select the virtual router that handles the multicast traffic. Select Multicast > Advanced. Set the Multicast Route Age Out Time (sec) to a value from 210 (default) to 7,200. To save the settings, click OK.
Save the configuration. Click Commit.

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