[kwlug-disc] Puzzling network issue ...

[Khalid Baheyeldin]

On Thu, Nov 20, 2025 at 9:57 PM Francisco <fxdoming at gmail.com> wrote:

> try lowering your mtu to 1,200 from 1,500 to see if it helps
>

Indeed it was an MTU issue.
It was odd that short responses would get through, but longer ones didn't.
And it seems that the response was queued somewhere, showing up in netstat,
but not being sent.

There was no change that I did that caused the problem.
And there was no MTU defined in Wireguard's configuration at all.

But once I added it, the server was accessible via VPN once more.

[Interface]
Address = 10.10.0.4/24
MTU = 1380 # This is the fix
DNS = 10.10.0.1
PostUp = wg set %i private-key /etc/wireguard/%i.key

[Peer]
PublicKey = foo
AllowedIPs = 10.10.0.0/24
Endpoint = x.x.x.x:51820
PersistentKeepalive = 15
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