VPN Passthrough and How It Works
September 28, 2011 Leave a comment
VPN Passthrough is a feature of routers which allows computers on a private network to establish outbound VPNs unhindered. VPN passthrough has nothing to do with inbound VPNs, only outbound ones. The term comes from allowing the VPN traffic to “passthrough” the router. NO ports need opening to enable VPN passthrough, it will automatically work.
There are different types of VPNs but the most dominant ones are PPTP VPNs and IPsec VPNs. When a router states it supports VPN passthrough it actually means it supports both these types of VPNs. To be exact VPN passthrough is just the combination of PPTP passthrough and IPsec passthrough. This is important as you will see next because PPTP passthrough is handled differently to IPsec Passthrough.
Why Is VPN Passthrough Is Needed
Almost all routers implement a feature called NAT to allow several computers to share the same internet connection; this is how your home router works. Both PPTP and IPsec VPNs don’t work with NAT natively. Since most routers implement NAT this is a problem.
PPTP passthrough deals with this by replacing GRE (the part of PPTP that doesn’t work with NAT) with enhanced GRE which does work with NAT.