Expert user html not found

[#1]

There used to be http://192.168.1.254/expert_user.html to access advanced features.

This gives 404 not found now, with

Plusnet Hub One | Software version 4.7.5.1.83.8.263 

[#2]

I suspect you are thinking about the Hub 0 or the TG, that option was never available on a Hub 1.

[#3]

any similar URL for the hub1?

in particular, fixing IP assigned to particular MAC addresses so that after reboots all devices keep the same internal IP?

[#4 · Accepted solution]

I don't know about your router but on a Smarthub 6 you go into My Network, select a device and look down the details where there is an 'always use this IP address' option and a Yes/No field, which can be set to Yes..