On Mon, Feb 02, 2015 at 07:27:10AM +0000, David Woodhouse wrote: > On Sun, 2015-02-01 at 21:07 -0800, David Miller wrote: > > > We might as well have not have implemented the IPSEC stack at all, > > because as a result of the userland VPN stuff our IPSEC stack is > > largely unused except by a very narrow group of users. > > Well, I'd love to make better use of it if I can. I do suspect it makes > most sense for userspace to continue to manage the probing of UDP > connectivity, and the fallback to TCP mode — and I suspect it also makes > sense to continue to use tun for passing packets up to the VPN client > when it's using the TCP transport. > > So the question would be how we handle redirecting the packet flow to > the optional UDP transport, when the VPN client determines that it's > available. For the sake of the user setting up firewall and routing > rules, I do think it's important that it continues to appear to > userspace as the *same* device for the entire lifetime of the session, > regardless of which transport the packets happen to be using at a given > moment in time. It doesn't *have* to be tun, though. > > You don't seem to like my suggestion of somehow pushing down an XFRM > state to the tun device to direct the packets out there instead of up to > userspace. Do you have an alternative suggestion... or a specific > concern that would help me come up with something you like better?
Maybe you want to use a virtual tunnel interface (vti) what we have already. Everything that is routed through such an interface is guaranteed to be either encrypted if a matching xfrm state is present or dropped. Same on the rceive side, everything that is received by this interface is guaranteed to be IPsec processed. So you can do a routing based decision about the IPsec processing. While I'm sure it could handle the ESP in UDP encapsulation, I'm not that sure about your TCP fallback because this requires a valid xfrm state to allow packets to pass. Using the same interface for both is probably not possible.