RE: DHCP with reservations...
Hi NickD,
It sounds like your router is using DHCP to assign IP addresses to your machine on the local network. For some reason, your machine disconnects from the router, perhaps because it goes to sleep? When your machine asks to reconnect to the router, the router gives it a new IP address, thus your changing IP address.
If this is indeed what is happening, then you can eliminate this problem by configuring your router to use DHCP with Reservations whereby the router reserves certain IP addresses for certain machines. These machines will always get assigned the same IP address by the router whenever they connect. Machines that don't have reserved IP addresses will be assigned other non-reserved IPs by DHCP.
Regards,
Switon