Re: network working one way only?

From: Antony (antony_at_antgel.co.uk)
Date: 06/21/04

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    Date: Mon, 21 Jun 2004 18:07:22 +0100
To: debian-user@lists.debian.org

    On Mon, Jun 21, 2004 at 12:47:54PM -0400, richard lyons wrote:
    > On Monday 21 June 2004 11:42, John Summerfield wrote:
    > > richard lyons wrote:
    > > >I must be in an exceptionally dim mood today. I just noticed that
    > > > my laptop, on which I am writing this, is not accessible from other
    > > > boxes on the network. Ping, nfs, cups are all failing to connect.
    > > > Must be
    > >
    > > Sounds ideal to me. Are you running any firewall setup on the laptop?
    >
    > I did not think I was...
    >
    > [...]
    > > If this command returns a list of machines, your DNS setup is
    > > working: host www.ibm.com
    >
    > $ host www.ibm.com
    > -bash: host: command not found
    > But it must be working, as I can browse the web and ping out to the
    > network. That is a red herring (though I wish I had dig - perhaps I
    > need to install bind to get it.)
    > >
    > > >I can`t at the moment think what to look for next -- quick hint
    > > > anyone?
    > >
    > > Not being able to ping your box can be annoying when you're trying to
    > > diagnose connectivity probs. What does this produce:
    > > iptables -L
    >
    > My output is hugely long. Each of the sections Chain INPUT, FORWARD and
    > OUTPUT have `(policy DROP)`, followed by many other lines. I have
    > never configured a firewall on this computer as the network is behind a
    > firewall. (Accepting that that may not be a good policy). Just the
    > same, I assume this is the problem, as I do get about 150 lines of
    > printout from iptables -L. Can I just turn this off somehow?
    > >
    > > If it is _not_ like this, then that's re reason:
    > > Dolphin:~# iptables -L
    > > Chain INPUT (policy ACCEPT)
    > > target prot opt source destination
    > >
    > > Chain FORWARD (policy ACCEPT)
    > > target prot opt source destination
    > >
    > > Chain OUTPUT (policy ACCEPT)
    > > target prot opt source destination
    > > Dolphin:~#
    > >
    > >
    > > It seems to me you have an unexpectedly secure firewall setup:-)
    >
    > Evidently. :-(
    >
    > Is that half a day of learning, or can I slip out by some cheat?

    You could (as root) try running /etc/init.d/iptables. I believe that
    you then see some possible parameters, one of which is clear. If I'm
    right, run /etc/init.d/iptables clear, and see if that helps.

    Assuming that iptables is being set up on boot by /etc/init.d/iptables,
    it shouldn't be too hard to work out how to save the clear ruleset for
    future boot.

    A 

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