TFTP Monitoring

I've got a couple of tftp servers I'm wanting to load balance for pxe. I've got the appropriate ports/iRules in place to make it work, but need to setup a health monitor that does more than the standard icmp checks.

 

 

I don't have access to the disk to upload a check file, as I've seen in some examples. I'm wondering if there's a way to do a send/response using the UDP (69) health check profile. I just don't have a good knowledge of how to send/recieve commands to the server to get that working. (never done it before)

 

 

If I were scripting something myself, I'd just use nmap to knock on the door and get a response. Is this documented anywhere? I would expect it to be striaght-forward and easy.