"How do I fix this and how do I discover where this mysterious 10.18.0.1 address is coming from?
Your pc is using DHCP to configure networking, including DNS. This ip address is the LAN side of your network gateway and is used for local DNS lookups on your LAN. Which you might only have the 1 pc connected to your ISP's network device and don't have a need for local DNS lookups There's nothing nefarious going on here. This is standard DHCP network configuration. If you don't want this, you'll have to figure out to disable DNS configuration via DHCP in the netconfig script.
