I am having computers hang on Opening Multicast session on certain vlans. On the Vlans that hang, network traffic logging shows that the clients connect to the pxe server, download the boot wim, and then redirect to the site server.  They never talk to the milticast dp (which is a different server). The SMSTS log does not show any errors, it just seems to be waiting. Where would I start to troubleshoot?

Hi,

Have you enabled Enabled scheduled multicast on the DP?

The distribution point can be configured to require a specified number of requests before it begins to multicast, or it can wait a specified number of minutes after the first request before it begins to multicast.

The Session start delay specify how many minutes that Configuration Manager waits before it responds to the first deployment request.

The Minimum session size specify how many requests must be received before Configuration Manager starts to deploy the operating system.

Toggling "Enabled scheduled multicast" did not provide any positive results.  We narrowed the problem to ISAKMP port 500 being blocked between the Multicast DP and the client.  Once this port was opened up, Multicast began to work.

• Marked as answer by Misha Rudiy 15 hours 56 minutes ago