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This article provides step-by-step instructions on how to manually configure vSAN Unicast networking from esxcli.

Note: vSAN Unicast mode is a feature that was introduced in vSAN 6.6 (vSphere 6.5.0d)
Unicast replaced legacy multicast networking in order to simplify the network requirements of maintaining a vSAN cluster's Quorum.

1. Occasionally when upgrading vSAN Clusters to vSphere 6.5.0d or later, one or more hosts may fail to inherit the Cluster Member Updates from vCenter.

2. In some cases, the list of vSAN nodes maintained by vCenter and the number of actual nodes may differ due to nodes being added or removed while vCenter was unavailable.

You can use the following steps to manually rebuild the Unicast agent list on each host:

1. Identifying necessary vSAN Cluster information.
2. Building the vSAN Unicast agent list.
3. Last Steps.
 

1. Identify the VMkernel port used for vSAN, its IP address, and the node UUID on each host in the cluster.
 

  Note: The IP address of vmk2 on this host is: 172.16.15.11

 

cmmds-tool whoami

2.2.1 Check the current unicast agent list with the following command
 

esxcli vsan cluster unicastagent list


 Note: In the output above, the unicast agent list was cleared out.

Example on host 1

esxcfg-advcfg -s 0 /VSAN/IgnoreClusterMemberListupdates

If you find that you have completed your upgrade to vSAN 6.6 including the on-disk upgrade process and your hosts are still utilizing multicast for cluster communications, confirm that you do not have an orphaned/dead host information stuck in cmmds as this can prevent the conversion from occurring naturally.

Network partitioning is a risk if the Unicast agent list is not properly rebuilt. In most situations, the vSAN cluster has already formed multiple partitions. The goal of rebuilding the table is to form one vSAN cluster.

Note: When building a Unicast agent list on an ESXi host, add entries for all the other hosts, but never add the IP of the host whose table is being configured.

When a vSAN Data Node or Witness Node has its own IP address in its Unicast agent list, many networking problems can arise and could lead to a PSOD.