Before vSAN 6.6 we would always recommend to change the multicast address when running multiple vSAN clusters in the same VLAN. Now that with vSAN 6.6 we removed multicast, does this best practice/recommendation still apply? I went looking for a clear statement but couldn’t find any, until Cormac pointed me to the excellent vSAN Networking Guide he wrote together with Paudie. After reading the table a couple of times, this is what I would consider to be the new best practice/recommendation:
If you run a vSAN 6.6 cluster with on-disk format v5.0 then there’s no need to change the multicast address when you have multiple clusters in the same VLAN as there’s no chance older host can be introduced in to the cluster as they will be partitioned instantly.
If you run a vSAN 6.6 cluster with on-disk format pre v5.0 then it is recommend to change the multicast address when you have multiple clusters in the same VLAN as when older hosts are added the cluster switches back to multicast mode. Although this could be considered an “operational consideration”, to avoid problems we would recommend changing the multicast address.
We also stated in the past that you could give each vSAN cluster a different VLAN for the vSAN network, the same applies. You can use a single VLAN for multi clusters, as long as those clusters are vSAN 6.6 and running on-disk format v5.0.
I hope that helps.