Understanding Protocol / State Machine

Understanding Protocol / State Machine

[Iain Douglas]

Hi,

I have been investigating what happens when a peer crashes/goes away for
some reason and the configuration is reset.

My test setup is quite simple, I have 2 peers and one is acting as a
gateway for the other for the remote address 8.8.8.8.
I can ping 8.8.8.8 and traffic goes over the WireGuard link as expected.
When I want to test I delete the key on the peer and add it again. 
Wireguard is te lates version from CentOS repo 0.0.20181218-1.

I see three different things happening depending on when the last
handshake took place.

1. Handshake < 119 seconds ago the link takes ~ 15 seconds to recover
2. Handshake between 120 and 179 seconds ago - 1st packet is lost then
link recovers
3. Handshake >=180 second ago - link just works as normal.

It is (2) that I don't understand. When I look at the packets sent I see

ping out
handshake out
handshake response

No reply to the ping

However for (3) above I see

handshake out
handshake response
ping
ping reply

So for (3) I guess that the ping is queued until after the handshake
occurs.
Having watched Jason's talk at the Linux Plumbers conference I was
expecting what happens at (3) to be at (2).
Can someone enlighten me as to why the first packet at (2) is sent
before the handshake?

Cheers


Iain 




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Re: Understanding Protocol / State Machine

[Jason A. Donenfeld]

On Wed, Jan 2, 2019 at 7:03 PM Iain Douglas <wireguard@1n6.org.uk> wrote:
> 1. Handshake < 119 seconds ago the link takes ~ 15 seconds to recover
> 2. Handshake between 120 and 179 seconds ago - 1st packet is lost then
> link recovers
> 3. Handshake >=180 second ago - link just works as normal.

For 1, it's hitting the timeout of detecting the dead peer before
reestablishing the handshake, since it still believes it has a valid
session.
For 2, it's the same as 1, except that when sending packets when your
current session is older than two minutes, it will start trying to
create a new one. The way to think of this that sessions live
optimally for only 2 minutes and maximally for 3.
For 3, the current session is unusable and already cleared from
memory, since it expired after 3 minutes, and so a new session is
established before the packet is sent.
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