When your iSCSI initiator sessions won't connect

I use a lot of iSCSI initiator sessions to connect my iSCSI SAN to my Windows Servers. From time to time and for whatever reason (but particularly after rebooting the VM guest) I find one or more of these connections doesn't reconnect. When I tried to force the connection I'd get some message about its inability to get the job done, or that the login wasn't working, or the drive was hidden.

In the old days, I would just reboot the guest, and usually by the time it came back up the drives would map correctly.

But it turns out that isn't necessary. I've since learned you can simply go to the command prompt and flush the arp cache with

arp -d *

then try the reconnect.

I've never had that not work.

Now if only someone could tell me why...