please can someone help me.

I have moved from a win2k RRAS server as my NAT router to a Fedora Core 1
(yarrow) system and for some reason most of my outgoing PPTP VPN connections
(from an XP Pro machine behind the router) are failing to connect. 1 works,
the other 4 or so don't. If I shove my dsl back into the win2k router and
use that for NAT, they work fine.

Is there something I need to specify to iptables get gre/pptp connections
masqueraded properly?

here's my very basic NAT script at the moment:

/sbin/iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward


I should also mention that my external interface is a Conexant AccessRunner
PCI ADSL Card, using linuxatm and ppp atm plugin if this makes a difference.

TIA

carl