Gateway setup

[vlozko]

Hello,

First off, I'm not sure if gateway is the right term. Router, maybe? The setup I have is a Ubuntu box with 2 NIC cards. One connects to the internet on a static IP and the other connects to a switch. Other computers are supposed to be able to go through the Ubuntu box to access the internet.

Here are the contents of my files:

/etc/network/interfaces:
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
address 151.204.227.66
netmask 255.255.255.0
gateway 151.204.227.1

auto eth1
iface eth1 inet static
address 192.168.1.1
network 192.168.1.0
gateway 192.168.1.1
broadcast 192.168.1.255
netmask 255.255.255.0

/etc/resolv.conf
nameserver 71.243.0.12
nameserver 192.168.1.1

I also created a file that gets run at startup to enable the gateway. xxx.xxx.xxx.xxx is replaced by the IP given by my ISP.

/etc/network/if-up.d/gatewaySetup:
#!/bin/sh

PATH=/usr/sbin:/sbin:/bin:/usr/bin

#
# delete all existing rules.
#
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -X

# Always accept loopback traffic
iptables -A INPUT -i lo -j ACCEPT


# Allow established connections, and those not coming from the outside
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW -i ! eth1 -j ACCEPT
iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACC

# Allow outgoing connections from the LAN side.
iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT

iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to xxx.xxx.xxx.xxx

# Don't forward from the outside to the inside.
iptables -A FORWARD -i eth0 -o eth0 -j REJECT

# Enable routing.
echo 1 > /proc/sys/net/ipv4/ip_forward


At this point, the Ubuntu machine works with no problems. However, I ran into a problem with the computers connected to the switch. Since the Ubuntu machine is replacing a broken one, all of the other computers had their DNS server set to 192.168.1.1. However now things only work for the other computers if you use IP addresses to access outside sites rather than their domain names. The workaround that I'm using now is setting up the DNS server to these outside machines to the one my ISP provided. However, I'll need to do that with every machine in the office.

Is there a way make the Ubuntu machine process DNS requests properly? If what I'm asking doesn't make sense, let me know and I'll try to go into greater detail.

[Kieren]

You need to install bind9, it's in the repositories, and configure it to use the ISPs DNS server as it's parent. That way when a client asks your router for to translate an address it will look it up in it's own database and if it can't find it will look up in your ISPs database...