Ethernet tethering at regionals

Now that our first regional is behind us (Palmetto), I was wondering about something.

I noticed that Ethernet tethering was hit and miss at the regional with the radio programmed for competition and set in bridge mode. We switched to USB, which I know why it was reliable (the driver assigns a 172 address). So I got to wondering, should we be able to tether over Ethernet? If so, where does the IP address come from? I noticed when it didn’t work, it had an address that started with 169, which is an autoconfigutation address, so no DHCP server. How did it work over ethernet at all if it couldn’t get an IP address?

Where does the IP address come from when the robot is connected to the FMS? Where is the DHCP server in that case?

When you connect to the field, the field AP will act as a DHCP server and dish out addresses.

When you are in the pit the driver station and roboRIO assign themselves a link local address when they cannot find a DHCP. The roboRIO sends out a mDNS notice saying that it is at what ever address it assigned itself and the driver station can receive and understand it to know how to talk to the roboRIO.

There’s more details here:

We had this exact issue at Hatboro-Horsham but I forgot about it until now. Thanks for posting.

Thanks guys. That explains things. I didn’t realize at the event that the fallback 169 addresses will still allow things to communicate in the pits, and that any IP addresses obtained while on the field must be released. And of course, since the ip for the DAP is fixed, it cannot be pinged or accessed.