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*nix Thread, Ubuntu Routing in Technical; Hi there, I hope someone can point me in the right direction here. All I'm attempting to do is set ...
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    jimothy's Avatar
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    Ubuntu Routing

    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?
    Last edited by jimothy; 9th May 2008 at 12:09 PM.

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    dhicks's Avatar
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    Quote Originally Posted by jimothy View Post
    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

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    kestrel1's Avatar
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    I would have thought that the server version of Ubuntu would have been a better choice.
    Only my opinion, so don't shoot me.

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    whats the output of
    netstat -rn

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    jimothy's Avatar
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    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

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    Quote Originally Posted by jimothy View Post
    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

    ?

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    jimothy's Avatar
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    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.

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

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

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

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    jimothy's Avatar
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    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.

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    Geoff's Avatar
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    And what does bind think is going on?

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    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.

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

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