VMkernel ports are used for system traffic for vMotion, IP storage, Fault Tolerance, vSAN, and others. Ensuring inter-connectivity between your hosts on each of these interfaces is an integral requirement for HA Clusters.
Communication issues can occur for a number of reasons, but in my experience it is usually due to a misconfiguration of the IP details, the switch configuration or the assigned physcial adapter. Testing that your hosts can communicate with eachother is obviously essential before you should put a host into production. To do this we can use the vmkping command. This allows us to specify a VMkernel interface to ping from and usefully lets us set the packet size so that we can ensure correct end-to-end configuration of Jumbo frames
vmkping [args] [host]
args:
-4 use IPv4 (default)
-6 use IPv6
-c set packet count
-d set DF bit (IPv4) or disable fragmentation (IPv6)
-D vmkernel TCP stack debug mode
-i set interval (secs)
-I outgoing interface - for IPv6 scope or IPv4
bypasses routing lookup
-N set IP*_NEXTHOP - bypasses routing lookup
for IPv4, -I option is required
-s set the number of ICMP data bytes to be sent.
The default is 56, which translates to a 64 byte
ICMP frame when added to the 8 byte ICMP header.
(Note: these sizes does not include the IP header).
-t set IPv4 Time To Live or IPv6 Hop Limit
-v verbose
-W set timeout to wait if no responses are
received (secs)
-X XML output format for esxcli framework.
-S The network stack instance name. If unspecified
the default netstack instance is used.
NOTE: In vmkernel TCP debug mode, vmkping traverses
VSI and pings various configured addresses.
vmkping -I vmk# 10.10.10.# -s 8994
Jumbo Frames on some switches are configured at either 8994 or 9000. This usually depends on wether the switch is including the headers in this setting or not. If a test with 8994 works but 9000 does not, this is still confirmation that Jumbo Frames configuration is working.