Wireguard address binding - how to fix?

[Janne Johansson]

Den tis 21 maj 2024 kl 09:50 skrev Nico Schottelius
<nico.schottelius at ungleich.ch>:
> Hello Jason,
> do you mind applying the patch from Daniel? Or is there anything wrong with it?
>
> Daniel: amazing work, I was not aware that you have already put in the
> hard work, thank you so very much!
>
> The world (*) is suffering because of the lack of IP address binding in wireguard.
>
> (*) With world I refer to every engineer that needs to run wireguard in
> non-trivial situations with multiple IP addresses on one host, which is
> extremely common for anything that routes.

Well, the main reason for wg to NOT do anything special is because
routing generally is done by looking at the destination ip and then
using the routing rules which the kernel uses to tell the packet which
interface is considered "best" in order to reach that ip, which is why
icmp and udp acts like this. I am certain that many engineers
hope/think it would be more logical (or fit their designs better) if
it responded on the same interface as the packet came in or whatever
but the reason for wg to act like it does is because this is how
connection-less packets have been acting since ages. The point that
many engineers design wg endpoints "the wrong way" is probably a fault
of education when it comes to how TCP/IP stacks did and do manage IP
output.

I have zero power to decide anything regarding how wg chooses to
implement a workaround for IP being designed the way it is designed,
but I can at least see why it hasn't immediately been accepted even if
it would make some engineers suffer(*) less, at least in the short
term.

There are a lot of workarounds for the times when you did design the
udp service as if it would act like tcp does in multihomed situations,
which includes firewall tricks, or VRF/namespace/routing-domains to
make sure the inner and outer address-pairs for the wg tunnel see
different views of the network to handle this without changing how wg
sends packets.

-- 
May the most significant bit of your life be positive.