IP addresses and connecting PC's

Two PC’s on a LAN desktop and laptop. Comodo Firewall 5.5.195786.1383 on both

Latop is and desktop today but tomorrow it is reversed.

Is this because the IP is dynamically assigned each time the pc is started?

But how do i set my firewall to allow them to connect and share files and make sure a third one does not.

The third one is old and the AV etc is out of date and it may be part of a DMZ so i want it able to connect to the router but not to the others. Third one also has Comodo firewall not sure what version

Best thing is to give all computers on your LAN a fixed IP address.

Next step is to create a Network Zone with only the two computers and use the Stealth Ports Wizard to create a trusted network (first option in the Wizard).

How do i do that? Thanks

If you check your router documentation, you may well find an option that allows setting a ‘preferred’ IP address for a given PC. Basically, it will always give a PC the same IP address.

This explains how to assign “static” IP addresses to your LAN PCs: http://www.howtogeek.com/howto/19249/how-to-assign-a-static-ip-address-in-xp-vista-or-windows-7/

What it doesn’t explaiin is that you also have to change the DHCP settings on your router. The easiest way to do this for this static address assignment is to leave DHCP auto addressing set on at the router but modify the starting IP address. For this to work, DHCP auto assigned addresses and static addesses must be mutually exclusive; there can be no overlap between the static address range and the auto assigned DHCP range.

An example might help.

My router supports a LAN of 253 devices, one gateway, and one broadcast address. This is the configuration for most home and small business routers. For my router, the gateway address is The broadcast address is The default auto assigned DHCP address range is - starting at address

The router parameter you need to change is the starting DHCP address. Many people use which allow 99 fixed device addresses and 154 auto DHCP generated addresses. Choice is yours.