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I've got a L2TP/IPSec VPN set up on CentOS (Amazon AMI) with racoon, ipsec-tools and xl2tp.

I'm using a version of racoon from this repo, as it allows the use of IPSec ID wildcards (or no specification thereof), following this tutorial.

I'm able to connect to my VPN from both an Android (ICS) and an iPad (iOS 5), however, I'm unable to connect from a Windows machine (have tried several) due to a 691 error.

So, what can I do?

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Are the Windows machines, perhaps trying to prepend their domain to the username, or append their domain suffix to the domain? – HopelessN00b Aug 27 '12 at 3:13
I'm not even using the domain field. ;) – Fredefl Aug 27 '12 at 14:51

I had same problem, after a long time of researching, I found what's wrong. Open xl2tpd.conf and make sure you put external IP address of your server in (not local one, not gateways etc) listen-addr = EXTERNAL_IP

Use these iptables rules:

-A INPUT -p udp -m policy --dir in --pol ipsec -m udp --dport 1701 -j ACCEPT
-A OUTPUT -p udp -m policy --dir out --pol ipsec -m udp --dport 1701 -j ACCEPT

It solved connectivity for iphone and windows, but not for android (as for me) =\

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You cannot connect to a VPN server when your android or ipad is connected in the same network (like WIFI). Can you verify that your device which you want to create the VPN tunnel on is outside your private network or at least in a other network than the VPN server is?

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The VPN server is located in Ireland at Amazon - that means, seperate from the clients. I tried connecting the devices only one at a time and with server software restarts in between. – Fredefl Aug 26 '12 at 18:08
This answer is incorrect. You certainly can connect to a VPN simultaneously from multiple devices on the same network. I do so regularly. – John Gardeniers Aug 26 '12 at 22:05

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