Given three Ethernet devices:

PC A (Win XP)
PC B (Win XP)
Cable Modem (actually ethernet bridge)

All connected to an Ethernet Switch

PC A uses DHCP to get public IP address via Cable Modem

Internet connection is working perfectly

the problem is the ISP will only allocate one IP address per cable
modem

so when PC B sends DHCP request it is refused

all the software NAT solutions expect two interfaces

but my "public" and "private" networks are both on PC A Ethernet
Interface but on different subnets

(using registry hack PC A and B both support DHCP *and* static
192.168.1/24 addresses)

what I need is a software NAT on PC A that will accept IP traffic from
192.168.1 subnet and NAT out to public network

I could just buy a cable router and junk the cable modem

but am now curious if this is possible

On 9 Sep, 21:30, John Rivers <firs...@btinternet.com> wrote:
> Given three Ethernet devices:
>
> PC A (Win XP)
> PC B (Win XP)
> Cable Modem (actually ethernet bridge)
>
> All connected to an Ethernet Switch
>
> PC A uses DHCP to get public IP address via Cable Modem
>
> Internet connection is working perfectly
>
> the problem is the ISP will only allocate one IP address per cable
> modem
>
> so when PC B sends DHCP request it is refused
>
> all the software NAT solutions expect two interfaces
>
> but my "public" and "private" networks are both on PC A Ethernet
> Interface but on different subnets
>
> (using registry hack PC A and B both support DHCP *and* static
> 192.168.1/24 addresses)
>
> what I need is a software NAT on PC A that will accept IP traffic from
> 192.168.1 subnet and NAT out to public network
>
> I could just buy a cable router and junk the cable modem
>
> but am now curious if this is possible

You need to configure your PC B to have PC A as a gateway for ALL
addresses - then configure your PC A to act like a router. But, in
this configuration I do not think that firewall function of this PC A
router will be useful. Because your cable modem (and everybody
outside) will still see your PC B and will be able to access it if you
are not careful in configuring firewall on PC B.