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I have a third-party VPN server configured with only 4 credentials given to me: server ip, preshared key, user name and user password. Under Windows 7, i can easily connect to this VPN via standard "new VPN connection" wizard. But under Linux (Ubuntu etc) if i use vpnc client it is asking for "IPSec ID" (group ID) that i need to enter. If i enter empty value, i got "no response from target". If i enter any value, i got "hash comparison failed - check group passsword" error.

How it happens that Windows can establish connection without this "IPSec ID"? Maybe it's some default value available that can be used?

P.S. Also, on OSX "group name" is also marked as "optional" and VPN connection perfectly works without it.

share|improve this question
Are you sure your VPN provider uses L2TP/IPsec (as your title suggests) and not just plain IPsec? (What did you choose on Mac OS X? Cisco IPsec?) Because if it does, vpnc is not the right client. And even if your provider does not use L2TP vpnc will not be able to connect if the provider does not support Aggressive Mode, which is the only mode of operation supported by vpnc. If the latter is the case you should try a different IPsec client like strongSwan, Openswan, Libreswan, or raccoon. – ecdsa Aug 3 '13 at 8:01
In Windows, i select "Cisco L2TP/Ipsec". I'm sure it's something 2-layer since it uses preshared key for secured transport and login/password for some kind of authentication. Where can i read more about this "Aggresive Mode" and another modes of operation? – Eye of Hell Aug 3 '13 at 8:23
@ecdsa Also, i have checked specification and i'm not sure that it's possible to use preshared key in main mode. – Eye of Hell Aug 3 '13 at 8:41

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