Re: ipfwadm help?

From: Riley Williams (rhw@@MemAlpha.cx)
Date: Tue Aug 14 2001 - 03:31:28 EEST

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    Hi Paul.

    > I could use some advice on a problem I am having here on my gateway.

    I'll see what I can do...

    > I am unable to get packets out from from my ampr.org address.
    Incoming
    > packets are working OK.

    > For the incoming rule:
    > /sbin/ipfwadm -F -p accept
    > /sbin/ipfwadm -F -a a -P all -S 0.0.0.0/0 -D 44.16.2.32/27

    > For the outgoing rule:
    > /sbin/ipfwadm -F -a m -P all -S 44.16.2.32/27 -D 0.0.0.0/0

    > With the 'm' in place packets can go out but are masqueraded as my
    dynamic
    > IP address. If I remove the 'm' no packets go out. What rule do I
    need to
    > get packets out with my ampr.org IP address?

    I have to admit to using ipchains here with the 2.2 kernels, and I
    think ipfwadm goes with the 2.0 kernels (you don't say which).
    However, here's the rules I would use, with explanation:

    First, start with a clean slate.

     Q> ipchains -F
     Q> ipchains -X

    Next, set the default policies for input, forward and output.

     Q> ipchains -P input DENY
     Q> ipchains -P forward DENY
     Q> ipchains -P output ACCEPT

    Next, ensure that only valid IP sources arrive on each interface.

     Q> ipchains -A input -i lo -j ACCEPT
     Q> ipchains -A input -i eth+ -j ACCEPT -s 192.168.0.0/16
     Q> ipchains -A input -i sl+ -j ACCEPT -s 44.0.0.0/8

    Next, ensure that internal ports are correctly forwarded. This deals
    with all traffic internal to your local network.

     Q> ipchains -A forward -s 192.168.0.0/16 -d 192.168.0.0/16 -j ACCEPT
     Q> ipchains -A forward -s 192.168.0.0/16 -d 44.0.0.0/8 -j ACCEPT
     Q> ipchains -A forward -s 44.0.0.0/8 -d 192.168.0.0/16 -j ACCEPT

    Next, ensure that traffic to the Internet is correctly masqueraded.
    Traffic internal to your local network never gets down to this rule,
    so can be ignored.

     Q> ipchains -A forward -s 192.168.0.0/16 -j MASQ

    That's all that should be needed.

    > Any and all comments are most welcome!

    Hope the above helps.

    Best wishes from Riley.

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