Microsoft Multicast NLB on FortiSwitches managed by FortiGates

Hello

Sometimes TAC support may not help if the issue is related to design or integration.

In your case the issue seems not related to a bug, but is probably due to design, integration or configuration.

Check the below first, I think it may help.

https://docs.fortinet.com/document/fortigate/7.4.2/administration-guide/968606

My SE more or less told me the same thing, I asked for a design guide (Cookbook) rather than stating how we already tried setting it up and it didn't work. 

I appreciate the link you sent, do you have MS NLB working in your environment?

The link to the guide you sent is for multicast forwarding, which we're not doing, we need multicast routing. 

The section for multicast routing and PIM support in the guide indicates a multicast policy needs to be created, however, when trying to create this policy, the destination appears to only allow multicast IP blocks. The catch with MS NLB is, it uses a multicast MAC but a unicast IP, so the few Fortinet guides I have found don't seem to cover this. 

I realize my multicast knowledge is rather limited, so perhaps I not connecting all the dots to make it work, which is why I am reaching out to the community for assistance.