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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 24 May 2018 15:59:11 +0200
Message-ID: <CAHmME9pB9RHNQQwNMKDLLrmXZ63OMqQWtipOZeDuiPk_ZzqRZA@mail.gmail.com>
Subject: Re: [wireguard-android] 'roaming' from LTE to WiFi with version
 0.0.20180523
To: =?UTF-8?Q?J=C3=B6rg_Thalheim?= <joerg@higgsboson.tk>
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On Thu, May 24, 2018 at 3:57 PM, J=C3=B6rg Thalheim <joerg@higgsboson.tk> w=
rote:
>
>
> On 2018-05-24 05:16, nnet wrote:
>> So this is how it ends:
>>
>> 05-23 20:33:45.323  9600  9619 D WireGuard/GoBackend/wireguard: peer(AsM=
M=E2=80=A6SeWg) - Sending handshake initiation
>> 05-23 20:33:45.326  9600  9619 E WireGuard/GoBackend/wireguard: peer(AsM=
M=E2=80=A6SeWg) - Failed to send handshake initiation write udp6 [::]:46719=
->[]:41414: sendto: network is unreachable
>> 05-23 20:33:45.326  9600  9619 D WireGuard/GoBackend/wireguard: peer(AsM=
M=E2=80=A6SeWg) - Awaiting keypair
>> 05-23 20:33:50.367  9600  9678 D WireGuard/GoBackend/wireguard: peer(AsM=
M=E2=80=A6SeWg) - Sending handshake initiation
>> 05-23 20:33:50.376  9600  9678 E WireGuard/GoBackend/wireguard: peer(AsM=
M=E2=80=A6SeWg) - Failed to send handshake initiation write udp6 [::]:46719=
->[snip]:41414: sendto: network is unreachable
>> 05-23 20:36:10.188  9600 11291 D WireGuard/GoBackend/wireguard: peer(AsM=
M=E2=80=A6SeWg): Handshake did not complete after 20 attempts, giving up
>> 05-23 20:39:12.258  9600  9677 D WireGuard/GoBackend/wireguard: :peer(As=
MM=E2=80=A6SeWg) Removing all keys, since we haven't received a new one in =
540 seconds
>>
>> Interestingly it's trying to send out to an IPv6 address. The peer endpo=
int IP is IPv4 only (the LTE is IPv4-in-6).
>
> In the wg command it resolves the domain once and picks the preferred pro=
tocol family of the system (which is ipv6 when its available).
> Since this is only done once it will stick to ipv6 for ever until the VPN=
 is reconfigured by wg.
> This is an unsolved known problem.

That's *not* what's going on here. This is an issue with how Go
sockets handle IP addresses and their preference for v4-mapped-v6.