VMware vSAN 6.6 works only in unicast mode, if you have upgrade all the disks to the last v5 format.

But recently I’ve got a new cluster, build totally from scratch with latest version, that has switched to multicast mode, with the result of all hosts partitioned at network level.

The issue has happen just after I’ve force vCSA to use proxy for the upgrade and after the restart of vCenter (post-update).

This is a well know issue affecting vSAN 6.6. Currently, with actually there is no resolution (at this time).

The behaview is described in KB 2150523 (vSAN Cluster Incorrectly Displays Network Mode as Multicast) and the only options are:

  • Remove the http/https proxy environment variable in vCenter Server.
  • Exclude local hosts from the proxy.
For the second step, potentially you can exclude local hosts from the proxy using a no proxy environmental variable in this way:
  • Open an SSH session to the vCenter Appliance that is managing the vSAN 6.6 cluster.
  • Edit the /etc/sysconfig/proxy file to contain the FQDN of vCenter:
    NO_PROXY=”localhost,, vcenter.domain.local”
  • Restart the vSAN management service
    • In the vSphere Web Client, browse to:
      Administration > Deployment > System Configuration > Services > vSAN Health Service > Actions > Restart).
    • From the VCSA CLI, run this command: /usr/lib/vmware-vmon/vmon-cli -r vsan-health

Unfortunately this was not enough to fix the issue.

The only way to fix the network partition issue and switch back to unicast mode was manually register all the nodes as described in this great post:


Basically you have to populate the list of all the nodes partecipating on the cluster, on all the nodes of the cluster:

[root@esxi-ing2:~] esxcli vsan cluster unicastagent list
 NodeUuid IsWitness Supports Unicast IP Address Port Iface Name
 ------------------------------------ --------- ---------------- -------------- ----- ----------
 59d22edb-cf3c-a02d-870e-f4e9d4a050a0 0 true 12321 vmk2
 59d25308-7f3d-a545-dff8-f4e9d4a0ea00 0 true 12321 vmk2
 59d254ae-9962-310c-59c7-f4e9d4a0cd70 0 true 12321 vmk2
 59d2559b-ba89-17ab-9e6d-f4e9d4a12dc0 0 true 12321 vmk2
 59d25772-d855-512d-11d8-f4e9d4a10f40 0 true 12321 vmk2
 59d25a50-af7c-1140-1b2d-f4e9d4a0df60 0 true 12321 vmk2

In this example, vmk2 is the vmkernel adapter for the vSAN network that is 192.168.10.x.

Still is not enought, you have to disable vCenter authority on vSAN configuration before make the changes, using this command (on all vSAN hosts):

esxcfg-advcfg -s1 /VSAN/IgnoreClusterMemberListUpdates

Then you have to register all the node, restart the vCenter Server (restart the service is not enought).

Then re-enable vCenter authority on vSAN configuration with this command (still on all hosts):

esxcfg-advcfg -s0 /VSAN/IgnoreClusterMemberListUpdates

And fix in vCenter the configuration, by checking on the healt tab.

Andrea MauroAbout Andrea Mauro (2509 Posts)

Virtualization & Cloud Architect. VMUG IT Co-Founder and board member. VMware VMTN Moderator and vExpert (2010, 2011, 2012, 2013, 2014, 2015). PernixPro 2014. Dell TechCenter Rockstar 2014. MVP 2014. Several certifications including: VCDX-DCV, VCP-DCV/DT/Cloud, VCAP-DCA/DCD/CIA/CID/DTA/DTD, MCSA, MCSE, MCITP, CCA, NPP.