I am now the owner of some recycled industrial hardware. Apparently I need to configure BOOTP in order to give my PLC5's ethernet sidecar an IP address.
Apparently there is a dhcp-option setting for /etc/config/dhcp but both the dnsmasq man page and the OpenWRT DHCP wiki entry are unclear on the proper syntax. There is a static and dynamic BOOTP setting for the dhcp-option if I am reading correctly.
Has anyone got a working dynamic BOOTP setup that can get an example from? Maybe a few tips?
I realize it's been a solid couple of years since this post, but I encountered a similar issue and wanted to post a resolution.
Allen-Bradley PLC-5E controllers way back when supported only BOOTP, and even a modern controller like a ControlLogix can be selected to use either DHCP or BOOTP.
DHCP requests, of course, serve up an address from the DHCP pool that you've configured in OpenWRT.
But (as far as I have found, with OpenWRT), BOOTP requests need a manually-entered IP address matching the MAC ID of the controller.
SSH or keyboard/monitor into your OpenWRT system and add a MAC ID and IP address pair to the end of the /etc/ethers file (I installed the nano text editor specifically because I'm comfortable with it).
Avoid empty lines, and don't indent with a tab (even though the examples show one).
Enable OpenWRT to use that file by checking the "Read /etc/ethers to configure the DHCP-Server" checkbox on the LuCI Network -> DHCP/DNS -> Resolv and Host Files tab, then [Save & Apply].
BOOTP requests are shown in the Syslog via LuCI, so if you have a mystery PLC controller sending out BOOTP requests, you can look for them there.
Remember that most A-B PLC stuff that was built in Twinsburg, OH has a MAC ID beginning with 00:00:BC, but other modern stuff, especially from Rockwell Automation Singapore, may have a different MAC ID prefix.