Simple network debugging – ESXi and VCSA

I ran into an old issue yesterday with ESXi 5.5 and vCenter disconnecting after 60 seconds. The issues is described in KB1029919 and is due to heartbeat UDP packets from ESXi not reaching vCenter on port 902 within 60 seconds or at all.

Now how to test this! Luckily the KB has a simple Python script that allows you to send UDP packets. Just edit the script and insert the IP of your vCenter server and run it. It will default send 10 packets of 100 bytes.

Now the KB mentions using Wireshark as an option on the vCenter side but when using VCSA that is not really an option. Luckily VCSA 6.5 comes with tcpdump installed! 5.5 and 6.0 don’t but worry not, VMware to the rescue. You can install tcpdump on 5.5 and 6.0 by following KB2084896. This gives you access to a client on ESXi to send UDP packets and a monitoring option on VCSA to see if the packets arrive.

All that needs to be done then is run the following:

#on the VCSA
tcpdump -i eth0 udp port 902 -vv | grep <srcIP>

#on ESXi

And then look at the results. You can lose the “| grep <srcIP>” if you want to see all packets but depending on your setup there may be many ESXi hosts sending heartbeat.