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Bill Gray
Asked: 2009-06-10 14:46:02 +0800 CST

Linux gateway forwarding issue

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how do I enable packet forwarding for an ethernet dsl modem? Must this be done with iptables?

linux adsl

4 Answers

  1. You enable packet forwarding on a Linux (2.6.x kernel) router by executing the following command as root ...

    # echo "1" >/proc/sys/net/ipv4/ip_forward

    You will need to execute this command every time you start/reboot your machine. Add the command to your equivalent of /etc/rc.local so that it is automatically executed for you.

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  2. Log in as root. Type the following exactly as it appears

    echo 1 > /proc/sys/net/ipv4/ip_forward

    Then type this exactly as it appears

    echo "net.ipv4.ip_forward = 1" >> /etc/sysctl.conf

    The first line sets packet forwarding in the kernel; the second line ensures that it survives a reboot.

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  3. I'm assuming this is an DSL router presented as an ethernet device. Are you able to ping the internal interface of the router? If not, there's a configuration problem on the lan side of the device.

    Does the router have diagnostic tools built in? Can you ping out from the router? Can you ping an internal device? If you can, then the problem lies in the forwarding between the two interfaces. It could be a firewall or a possible NAT problem.

    If you can't ping out, then there is a problem with the DSL connection. If you can't ping in, then there's a problem with the LAN interface.

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  4. If I understand your question correctly, iptables won't help you. It sounds like you can ping your ethernet router, but nothing beyond it. To figure this out, you need to tell us what router model you have and whether you have static or dynamic IP addresses.

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