If you have an elderly HP LaserJet 2100 printer like me (works fine, why ditch it), adding it to a new network can be problematic.

The first thing to do is to do a hard-reset. That will clear any assigned IP and allow the printer to pickup an IP from your DHCP server on the network. To initiate a hard-reset, turn the printer off and then on again whilst holding down the cancel and go buttons until all the lights show solid. Then, to see the new settings, you'll need to get the printer to print them out for you. Press and hold down the cancel and go buttons until all the lights flash, and then release. The printer will then print out the settings.

If you need to give your printer fixed IP, maybe outside your DHCP range, you'll need to telnet onto the printer to change the IP address. Unfortunately telnet is no longer installed with the MacOS. The easiest why to get back your telnet is to install it with brew.

brew install telnet

With telnet installed you can connect to the printer and change the IP address.

telnet <IP address from printout>

To see the current settings:

/

To change the IP address to 192.168.1.99:

ip: 192.168.1.99

To save the setting changes and exit:

quit

Now your printer should have the fixed IP address of 192.168.1.99 and can be addressed as such.