natd (NAT and IPFW?) on one NIC

InspectorGadget · 09-06-2005, 09:59 PM

I actually have a FreeBSD system, but the issue should be the same as in Linux.

I have a broadband connection with a simple router that serves 4 hard IPs inside (3 FreeBSD and one MacOS servers). I would like to set up an anonymous NAT subnet (on the same Ethernet LAN) served by one of the UNIX servers, so several other workstations can make outgoing connections to the Internet.

I would set the anonymous NAT subnet workstations to gateway to the server, and then have the server redirect the packets through natd and back out the same NIC to the server's gateway, which is the actual router.

I've set up natd on machines with 2 NICs before, and it uses an IPFW rule to redirect LAN packets to natd. My problem is, with one NIC, none of the normal IPFW/natd setup documentation seems to apply; it all depends on IPFW connecting one NIC to another. I've even set up the anonymous subnet by aliasing an anonymous IP address on the server NIC. I can talk to the server from the anonymous workstations, but I need to get them connected to the Internet. IPFW seems to work on the basis of interfaces (NICs), not IP numbers.

Is this possible with a single NIC? Any ideas? Should I ask this question in Networking or Protocols? I'm trying it here, because those other topics seem full of Windows people.

- The Inspector

shuuhen · 09-08-2005, 06:04 PM

If you have eth0 assigned, I think you just need to assign an address to eth0:1, then you should able to set up NAT or IP forwarding the same way you would with two NICs. It's been a while since I've done this in Linux, so I might be remembering wrong...

09-06-2005, 09:59 PM	#1 (permalink)
InspectorGadget Registered User Join Date: May 2005 Location: San Jose, CA Posts: 80 OS: FreeBSD x 2, XP Pro	natd (NAT and IPFW?) on one NIC I actually have a FreeBSD system, but the issue should be the same as in Linux. I have a broadband connection with a simple router that serves 4 hard IPs inside (3 FreeBSD and one MacOS servers). I would like to set up an anonymous NAT subnet (on the same Ethernet LAN) served by one of the UNIX servers, so several other workstations can make outgoing connections to the Internet. I would set the anonymous NAT subnet workstations to gateway to the server, and then have the server redirect the packets through natd and back out the same NIC to the server's gateway, which is the actual router. I've set up natd on machines with 2 NICs before, and it uses an IPFW rule to redirect LAN packets to natd. My problem is, with one NIC, none of the normal IPFW/natd setup documentation seems to apply; it all depends on IPFW connecting one NIC to another. I've even set up the anonymous subnet by aliasing an anonymous IP address on the server NIC. I can talk to the server from the anonymous workstations, but I need to get them connected to the Internet. IPFW seems to work on the basis of interfaces (NICs), not IP numbers. Is this possible with a single NIC? Any ideas? Should I ask this question in Networking or Protocols? I'm trying it here, because those other topics seem full of Windows people. - The Inspector

09-08-2005, 06:04 PM	#2 (permalink)
shuuhen Manager Join Date: Sep 2004 Location: Colorado Posts: 986 OS: Mac OS 9.1, Mac OS X 10.5.8, WinXP Pro, FreeBSD 6.0, Gentoo Linux My System	If you have eth0 assigned, I think you just need to assign an address to eth0:1, then you should able to set up NAT or IP forwarding the same way you would with two NICs. It's been a while since I've done this in Linux, so I might be remembering wrong...