I went down that path on the experience/recommendation of Roderick who has seen similar behavior.
I would be more comfortable if that was called an observation rather than a recommendation. But I guess I did recommend testing with the firewall off.
I will work with Will to do some separate diagnosis on my router, but for those here, I have another observation.
When I use my Android phone running Gizmo to try to connect to a MC Server running on my Workstation it fails.
If I then run either PingTools or Bingo SSDP (the JRiver tool) on the phone, then try Gizmo again it succeeds.
If I keep using Gizmo it continues to work. If I close it for a while, and then try to use it again within a few minutes, it connects successfully.
If I close Gizmo for more than a few minutes, maybe ten, then again it will fail.
My conclusion from this so far is that a temporary record is being created in the router ARP Table by running PingTools or Bingo SSDP. That record is maintained while it is in use, but then purged after a few minutes if it is not used.
The interesting thing with the above? Gizmo will connect to the MC Server on my HTPC first time, every time. Well, as long as I haven't been messing with the network and a lot of software. Let's say failures are
extremely rare. I can remember one.
Networking is such fun.
BTW, using a switch might be a solution, although it means running another device, power, etc. I guess a router in bridged mode, so operating as a switch would also work.
Using another router has issues such as keeping the DHCP Server on one device, so all wired and wireless devices are on the same network segment. Also I don't want Double NAT with using two routers. Plus I want to use my landline and Mobile Broadband failover provided by the ISP router.
But I'll discuss all that in a separate thread.