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From: gypsy <gypsy@iswest.com>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] Firewalling certain IP ranges
Date: Sun, 22 Aug 2004 02:22:39 +0000	[thread overview]
Message-ID: <4128036F.F6FC0583@iswest.com> (raw)
In-Reply-To: <41274A9D.8020002@iinet.net.au>

Patrick Coleman wrote:
> How can I provide some services, but no internet access to untrusted hosts, yet still allow trusted
> clients on wireless to access the internet (clearly I cant simply firewall off the access point)?
> 
> Thanks in advance,
> Patrick

Why not?  That's exactly what I do at work.

The work setup is a linux box with 2 NICs; eth0 internal NW and eth1
external.  DNAT.  The firewall script reads /etc/firewall/ACL which
contains the IPs of the machines allowed internet access.  More
specifically, ACL contains:
192.168.1.4;tcp;1024:65535;-m mport
--dports;20:23,25,80,110,113,119,123,143,443,873
192.168.1.4;udp;123;--dport;123
192.168.1.4;tcp;1024:65535;--dport;1024:65535
192.168.1.4;udp;1024:65535;--dport;1024:65535

Note that I chose semicolon as a delimiter because it was the first
thing I thought of that would work.  I have as many of those 4-line
entries as there are allowed computers.  Most have a much more limited
first line --dport list than I show here because they don't need all
those services.

Then the applicable part of the iptables script:
# Access control:
if [ -f /etc/firewall/ACL ]; then
  while read FWD ; do
    IP=`echo "$FWD" | cut -d ';' -f 1`
    PROTO=`echo "$FWD" | cut -d ';' -f 2`
    SPORT=`echo "$FWD" | cut -d ';' -f 3`
    PLURAL=`echo "$FWD" | cut -d ';' -f 4` # either "--dport" or "-m
mport --dports"
    DPORT=`echo "$FWD" | cut -d ';' -f 5 | cut -d '#' -f 1`
    iptables -A FORWARD -i $IFI -o $IFE -s $IP -p $PROTO --sport $SPORT
$PLURAL $DPORT -j ACCEPT
  done </etc/firewall/ACL
fi
iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

The DPORT line allows "inline" comments at the end of any line.  $IFE
and $IFI should be self explanatory.  Everything on the FORWARD chain
that is not specifically allowed is denied (DROPped).

HTH
gypsy
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      reply	other threads:[~2004-08-22  2:22 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-08-21 13:14 [LARTC] Firewalling certain IP ranges Patrick Coleman
2004-08-22  2:22 ` gypsy [this message]

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