I had this question today and noticed someone also dropped it on the community forums. The question was if vSphere HA is constantly pinging the default gateway or not. I knew HA would ping the gateway on a regular basis as of vSphere 5.0, and on a more frequently basis if a ping would fail but I wasn’t sure about the timing. I pointed Marc Sevigny from the HA engineering team to the thread on the community forums and he added added some nice juicy details to the it. I figured I would share them with you.
Ordinarily, each host in an HA cluster pings each of the isolation addresses once per hour. If the ping fails, an HA confuguration issue is reported to vCenter, and a more aggressive ping is initiated by each host, pinging once every 5 seconds. The reason for the more aggressive ping is to more quickly resolve the configuration issue once the isolation address(es) once again becomes pingable.
There should be no “flood” of ICMP messages, and it should have little impact on network performance. The ICMP packet is 53 bytes long and sent once every 5 seconds from each of the HA hosts until the address(es) become pingable once again, at which point it returns to pinging once per hour.
If your default gateway is never pingable because of your firewall, you should open up the ports needed by HA. It is also possible to or disable the isolation address monitoring on the default gateway by using an advanced option (das.useDefaultIsolationAddress = false). It is recommended to specify a different isolation address (das.isolationaddress0) when the default gateway is a non-pingable device.