IPMasq doesn't work

I've set up IPMasq using the example rc.firewall from the IPMasq
HOWTO, and am running DNSMasq to provide DNS to the internal machines.
Internal machines are set to Gateway/192.168.0.1 and DNS 192.168.0.1,
but when I attempt to access the internet they get as far as "Site
found, waiting for reply...." and then timeout. Internal machines can
ping machines on the internet by name and by address, but can't seem
to receive data from the internet. The server machine can connect to
the internet just fine.

My IPTABLES setup lines:

IPTABLES=/usr/sbin/iptables
EXTIF=ippp0
INTIF=eth0

echo "1" > /proc/sys/net/ipv4/ip_forward
echo "1" > /proc/sys/net/ipv4/ip_dynaddr
$IPTABLES -P INPUT ACCEPT
$IPTABLES -F INPUT
$IPTABLES -P OUTPUT ACCEPT
$IPTABLES -F OUTPUT
$IPTABLES -P FORWARD DROP
$IPTABLES -F FORWARD
$IPTABLES -t nat -F
$IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state --state
ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT
$IPTABLES -A FORWARD -j LOG
$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE

(E-Mail Removed) (Chris Smowton) wrote
news:(E-Mail Removed) om:
> $IPTABLES -P FORWARD DROP

Try first with a more "cool" forwarding

$IPTABLES -P FORWARD ACCEPT

Antoine EMERIT <(E-Mail Removed)> wrote in message news:<XnF94C87E1C9B1antoineemeritonlinef@212.27.42 .68>...
> (E-Mail Removed) (Chris Smowton) wrote
> news:(E-Mail Removed) om:
> > $IPTABLES -P FORWARD DROP
>
> Try first with a more "cool" forwarding
>
> $IPTABLES -P FORWARD ACCEPT

Unfortunately that doesn't work either... I think I may have found
what is causing the problem though - the network monitor iptraf is
showing a large number of packets with bad checksums on the external
interface. Whilst packets are getting forwarded, I imagine the remote
router is then dropping them, and so I get no reply. I am using an
ASUSCOM ISDN TA with the HiSax driver. Any idea why I would get a high
bad packet rate? This doesn't happen in Windows 2000, which the
machine in question dual-boots.