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Old 05-21-2004, 11:53 AM   #1
LQ Newbie
Registered: Mar 2004
Posts: 22

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Question linux nat windows xp vpn server

hopefully somebody here can give me a hand with this one. i have been reading howtos for days now and my brain is starting to get numb.

here is the problem
i have cable internet witch is hooked up to a redhat 9 box (kernel 2.4.8-20)
the linux box has 2 nics and is preformin the roll of a nat box / router. on the local network i have a windows xp machine that can allow other computers to connect to it via vpn. i know this vpn connection works as i have had other computers on the local network connect to it with no hickups. what i am pretty sure i have to do to allow internet traffic to connect to the vpn is tell ipchains to forward any vpn requests to the windows box. i have been able to do this with http and ftp no problem, but i cant seem to get it to work for vpn. anyone got any ideas?

i added into my firewall rules the following

$iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 1723 -j DNAT --to
$iptables -t nat -A PREROUTING -i eth1 -p 47 -j DNAT --to

any help would be great
Old 05-21-2004, 12:04 PM   #2
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Registered: Mar 2004
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just had a brain wave. i was missing some lines for my rules so i got that going. now when i connect ir goes to check my password and then i get an error mesage saying that the remote computer did not respond
Old 05-21-2004, 01:31 PM   #3
Registered: May 2004
Location: Montreal,QC,Canada
Distribution: Fedora Core 7
Posts: 210

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Well I read you post and found it very interesting :-)

Did some searches and found

I noticed this

If the VPN server is behind a router, Port Mapping will need to be done on the router. Standard port usage is 1723 for PPTP. You might also need to configure your router for PPTP Passthrough. Port usage for IPSec is 500, 50-51. These ports will have to be forwarded to the VPN server's IP

Are those the missing lines ???

500, 50 and 51 ?
Old 05-21-2004, 03:03 PM   #4
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i have the windows side of things already running and tested. so i know it works, i have port 1723 tcp protocall forwarded to the windows box and port 47 as well. i know that the windows box is expecting pptp im not sure if ipsec is in there too or not. basicly right now it checks my username and password but then never reply to the client computer. so basicly i got half the connecmtion working. im not sure what this pptp passthrough thing is that he speaks of, but he is on the windows side of things where as i know for fact that its my router / nat configuration that needs something... i just dont know what. thank you for your help though LuggerHouse


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