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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Sat, 14 Apr 2018 16:45:32 +0200
Message-ID: <CAHmME9ra=DZiaUS7pP3xAxC_7H-yqfiTefU3Q8gufpP7e6H2zw@mail.gmail.com>
Subject: Re: Mixed MTU hosts on a network
To: Roman Mamedov <rm@romanrm.net>
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Cc: Luis Ressel <aranea@aixah.de>,
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Hi Roman,

That's strange; I'm unable to reproduce what you've described:

[+] NS1: ip link set wg0 mtu 1412
[+] NS2: ip link set wg0 mtu 1412
[+] NS1: wg set wg0 peer QXloTaPOwUTzqFElVLSD0vBc4sxjyoKtPBSaTkZHokY=
endpoint 127.0.0.1:2
[+] NS2: wg set wg0 peer X0p7+UWc4wjaAmT73xAEuXLY80I6Gv8vTg6KwFHCPGs=
endpoint 127.0.0.1:1
[+] NS0: iptables -A INPUT -m length --length 1473 -j DROP
[+] NS2: ping -c 1 -W 1 -s 1384 192.168.241.1
PING 192.168.241.1 (192.168.241.1) 1384(1412) bytes of data.
1392 bytes from 192.168.241.1: icmp_seq=1 ttl=64 time=0.752 ms

--- 192.168.241.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.752/0.752/0.752/0.000 ms

In this case, WireGuard seems to be doing the right thing. Think you
could come up with some minimal test that exhibits the behavior you're
seeing?

Jason