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.
First of all, each ESXi host in a 5.x cluster will ping the isolation address every 5 minutes (300 seconds). Could this flood the isolation device?
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. Note that it is highly recommend to use a device as the default gateway which is as few hops removed from your hosts as possible!