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I'm looking for this information on google from days with no success and hope to find somebody that knows the answer here.

I have a dedicated server with a real IP configured on eth0 and a secondary IP address configured on eth0:0 as alias and provider has router second IP on the primary IP, so I can ping both IPs from anywhere with success.

I configured a PPTP service on the dedicated server and can connect and surf correctly from any clients, problem is that also if I connect the VPN through the secondary IP address when I check my IP I always see the primary IP address instead the secondary, I tried to route all traffic with:

route add -host IPALIAS dev eth0:0

But no success with it. Somebody know how I can get outbound on internet with the aliased-ip instead real IP?

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1 Answer 1

First PPTP is considered insecure. PPTP is using GRE which is a connectionless protocol. This means that each packet that will exit the eth0 (or any alias like eth0:0) interface will use the primary IP address (the one set on eth0) of the interface as source address.

If you have a stateful firewall between VPN client and VPN concentrator, then the GRE packets from one direction will not match the ones from the other direction, and they will be discarded in one direction.

To debug the problem you should make network captures at the same time at both VPN endpoints. Analise and compare those capture to find out the problem.

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really thank you for your tips and idea how to procede, so do you suggest to use openvpn instead? could be also resolve my problem? –  user2349614 May 4 '13 at 13:56
    
OpenVPN has better security than PPTP. If you have firewall problems you can even use TCP. –  Mircea Vutcovici May 4 '13 at 14:09
    
ok thank you i will try with it, do you think i could also resolve ip problem in this way? –  user2349614 May 4 '13 at 14:12
    
You can solve the IP alias, but this is also depending on your config (VPN, firewall...) –  Mircea Vutcovici May 4 '13 at 14:19
    
sure, i will try tomorrow with a new configuration, thank you so much for your time. –  user2349614 May 4 '13 at 14:27

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