Question GRE and ESP protocols

gtsolid

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Jan 14, 2016
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Hi,
i configured a L2TP VPN in my WS2012 and i started to port forward the necessary ports.
From this page i notice that i have to open some ports. I have doubts about the protocol i cannot open in my router: he manages only UDP and TCP, but what about GRE, ESP, etc...?
How can i check they are open and what's their goal?
 
The router need special support to pass these through the NAT. Since there are no "ports" so NAT does not work. Many routers use other tricks to make this work but it is still somewhat restricted and some routers do not have any support. You really have to dig to find this information. There is no setting to turn it on or off in most routers. The router just has the feature or it does not. Many times it is called something like vpn pass through.

This is one of the reasons things like openvpn are so popular even though they are much slower than GRE or ESP for vpn.
 
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