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Strongwan + Windows VPN IKEv2 + IPv6
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| Problem Statement | |
| ----------------- | |
| The Windows native VPN client does not configure the default IPv6 route through the tunnel, even if the negociated remote traffic selector is ::/0. | |
| Causes | |
| ------ | |
| Windows sends router solicitations and awaits router advertisement from the other side. To this end, it uses link-local unicast and multicast addresses, just like a machine would on a broadcast-capable link (e.g. Ethernet). | |
| If you only configured a Virtual IP (rightsourceip) in Strongswan, the traffic selectors negociated would not allow traffic coming from Windows having a source address of fe80::/10 through the tunnel, and sniffing the protected traffic would not reveal Windows attemps at router discovery. | |
| Solution | |
| -------- | |
| - Enable the libipsec plugin in Strongswan (this creates a ipsec0 interface in your system) to allow radvd to work | |
| - Configure a static link-local address on ipsec0 | |
| # ip a a fe80::1/64 dev ipsec0 | |
| - Use the radvd daemon to advertise the /64 prefix containing your rightsourceip + the MTU (e.g. 1400) on the ipsec0 interface | |
| - Add fe80::/64 to remote traffic selectors in your connection in ipsec.conf (in addition to rightsourceip) | |
| rightsubnet=fe80::/64 | |
| Caveats | |
| ------- | |
| - The configured link-local address on ipsec0 is not persistent through Strongswan restarts. Maybe use an up_down script ? | |
| - radvd should be (re-)started only when the ipsec0 interface exists (when Strongswan has started) and the link-local address is configured | |
| - I haven't tested communication between two Windows client connected to the same Strongswan server when both have a Virtual IP in the same /64. Windows seems to use Neighbor Discory over IPsec (for DAD only?) and the RA sent by a Windows VPN server says the /64 prefix is on-link... | |
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@jice, can you please provide configs that work for you? I didn't manage to configure it to make it work. Windows sends router solicitations, radvd answers with router advertisements, but it still doesn't work.