Wednesday, April 8, 2015

vMotion Fails - Failed to connect to remote host. Network unreachable.

When migrating a VM using vMotion, the migration may stall at 14% and eventually fail with the following error:

Migration [xxxx:xxxx] failed to connect to remote host <x.x.x.x> from host <y.y.y.y>: Network unreachable.

Usually this is a pretty straightforward fix: correct whatever network issue is preventing communication between the vmkernel ports.  However, I recently encountered an issue where the network was configured properly, traffic was flowing, and vMotion still failed.

Everything with the multi-NIC vMotion config checked out:
  • Two separate VMkernel ports on the relevant vSwitch with IPs on the same subnet.
  • One vmnic active and one standby for each VMkernel port.
  • Active/standby adapters on the second VMkernel port were the inverse of the first.
  • vMotion enabled on the vMotion VMkernel ports.
  • 9000 MTU on each vSwitch and VMkernel port
  • 9000 MTU on the relevant switch and switchports.
  • Relevant switchports tagged for the appropriate VLAN.

(The configuration is pretty straightforward, as outlined in the VMware KB: