Ubuntu Routing

[jimothy]

Hi there,

 

I hope someone can point me in the right direction here. All I'm attempting to do is set up Ubuntu Desktop 8.04 as a Transparent Proxy. I've done all the work on the proxy and that's working fine. I want to be able to communicate with the DNS Servers on eth0 from clients on the eth1 interface.

 

But I can't figure out how Ubuntu routes traffic

 

Here's my test network:

 

Client PC 192.168.40.40/23 (DG: 192.168.30.3 DNS: 192.168.10.10)

l

L Ubuntu eth1 192.168.40.3/23

Ubuntu eth0 192.168.10.50/23 (DG: 192.168.10.1 DNS: 192.168.10.10)

l

L DNS Server 192.168.10.10

 

I've tried setting: net.ipv4.ip_forward=1 in /etc/sysctl.conf as I thought this should pass traffic forward.

 

I've looked at IP Tables but this looks just like a Firewall and not a router?

 

Any help would be great?

Edited May 9, 2008 by jimothy

[dhicks]

I want to be able to communicate with the DNS Servers on eth0 from clients on the eth1 interface.

 

Do you need to run a DNS server on your filtering machine that deals with requests on eth1 and uses the DNS server available on eth0 as its parent server?

 

--

David Hicks

[kestrel1]

I would have thought that the server version of Ubuntu would have been a better choice.

Only my opinion, so don't shoot me.

[CyberNerd]

whats the output of

netstat -rn

[jimothy]

Thanks for the replies

 

@ dhicks. I thought about that, installing BIND, but I thought it may confuse matters more? If possible I could do that but how do I ensure that DNS is published on the eth1 interface and not on the eth0?

 

@CyberNerd: The routing table looks like this:

 

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

192.168.10.0 0.0.0.0 255.255.254.0 U 0 0 0 eth0

192.168.40.0 0.0.0.0 255.255.254.0 U 0 0 0 eth1

169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1

0.0.0.0 192.168.10.1 0.0.0.0 UG 0 0 0 eth0

[keithu]

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

192.168.10.0 0.0.0.0 255.255.254.0 U 0 0 0 eth0

192.168.40.0 0.0.0.0 255.255.254.0 U 0 0 0 eth1

169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1

0.0.0.0 192.168.10.1 0.0.0.0 UG 0 0 0 eth0

 

Shouldn't that second line be:

192.168.30.0 0.0.0.0 255.255.254.0 U 0 0 0 eth1

 

?

[jimothy]

Yeah, should be. I changed the subnet which the eth1 was on as I've already got a VLAN on the eth0 side which is already on 192.168.30.0/23.

 

I wanted to ensure that there was no weird routing going on.

[Geoff]

Run a caching DNS server on your Ubuntu box. Point the clients behind the ubuntu box at that.

[jimothy]

Cheers Geoff, any good HowTo's on DNS Caching?

[Geoff]

A default install of bind9 from the repo leaves it configured as a caching DNS server, just configure the forwarders.

[jimothy]

Installed BIND9 and left as default. Configured DNS forwarders: 192.168.10.10.

 

Clients on the eth1 interface pick up DHCP with 192.168.40.3 as their DG and DNS server.

 

Still no DNS resolution for clients.

[Geoff]

And what does bind think is going on?

[jimothy]

Not sure how to pull out BIND config, but if this is any help:

 

/etc/resolve.conf has: servername 192.168.10.10 specified.

 

I can dig 127.0.0.1 from the Ubuntu box and it shows it's using 192.168.10.10:53 to resolve the address.

[Geoff]

I'd imagine the log files are in /var/log/bind/ the configuration will be hiding in /etc/bind/