[ale] Multihoming, Gateways, DHCP, and you!

[Kevin Krumwiede]

On Sat, 27 Sep 2003 20:29:35 -0400
Howard Fore <mylists at hofo.com> wrote:

> Anyway, the problem is in setting the gateway for eth1, eth2, and eth3.
> How do I configure those NICs to use eth0 as the gateway? Given the
> relative infrequency that Comcast switches the IP on me I suppose I
> could simply give them the address Comcast gives me on eth0, but that
> seems a bit arbitrary. Suggestions or ideas?

You need to configure the routing tables on your firewall/router.  Your upstream routes should be configured automatically by dhcpcd on the router.  You will need to manually add routes between the subnets of your internal interfaces.  Machines connected to those interfaces will use your router as their default gateway; they need know nothing of the networks beyond.  You will also need to configure port forwarding for external connections to your DMZ, source NAT for connections from the LAN to the Internet, and of course firewall rules.

I have a simpler setup with two NICs: eth0 is external and eth1 is the LAN.  Machines on the LAN are configured to use the router's eth1 as their gateway.  aphrodite is my workstation, prometheus is the firewall/router:

root at aphrodite:/root
0:# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     *               255.255.255.0   U     0      0        0 eth0
169.254.0.0     *               255.255.0.0     U     0      0        0 eth0
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
default         prometheus      0.0.0.0         UG    0      0        0 eth0

root at prometheus:/root
0:# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
68.54.20.0      *               255.255.254.0   U     0      0        0 eth0
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
default         ubr02-a-rtr.mai 0.0.0.0         UG    0      0        0 eth0