From: "Marek Küthe" <m-k-mailling-list@mk16.de>
To: wireguard@lists.zx2c4.com
Cc: luizluca@gmail.com
Subject: Re: IPv6 and PPPoE with MSSFIX
Date: Wed, 23 Aug 2023 16:58:40 +0200 [thread overview]
Message-ID: <20230823165840.7bf3b910@parrot> (raw)
In-Reply-To: <CAJq09z6Dz3idziDgB-3-VOVa=YEWk6ZOrLOwLTBctRb5VkLMLA@mail.gmail.com>
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On Tue, 22 Aug 2023 17:39:23 -0300
Luiz Angelo Daros de Luca <luizluca@gmail.com> wrote:
> Hello,
>
> We noticed an issue with clients that use PPPoE and connect to WG
> using IPv6. Both sides start to fragment the encrypted packet leading
> to a severe degradation in performance. We reduced the wireguard MTU
> from the default 1420 to 1400 and the issue was solved. However, I
> wonder if it could be fixed with MSSFIX (in my case, nftables
> equivalent).
PPPoE adds 8 bytes of overhead so that an MTU of 1432 can be used. I
also have to do this at home with my DSL line for example.
The MTU should be set on each side (on both peers) for this to work.
> The server does know that the remote address has a smaller MTU as it
> fragments the packet accordingly when any VPN peer sends some traffic.
Presumably the OS on the server does this and not WireGuard itself. I
could imagine that the server first receives an ICMP Too big message
and only then performs the fragmentation.
> The traffic inside the VPN does adjust the TCP MSS to fit into vpn
> interface MTU (1420 by default, now 1400).
Keep in mind that TCP MSSFIX only applies to TCP and other Layer 4
protocols like UDP might still have problems.
> I could dynamically add firewall rules to clamp MSS per authorized_ips
> but, theoretically, the kernel has all the info to do that
> automatically. I wonder if MSSFIX could detect the best MTU for a
> specific address through the wireguard. It should consider the
> peer-to-peer PMTU, the IP protocol wireguard is using and the normal
> wireguard headers.
As far as I know WireGuard does not do PMTU.
--
Marek Küthe
m.k@mk16.de
er/ihm he/him
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next prev parent reply other threads:[~2023-08-23 16:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-22 20:39 Luiz Angelo Daros de Luca
2023-08-23 14:58 ` Marek Küthe [this message]
2023-08-23 17:14 ` Daniel Gröber
2023-08-23 19:01 ` Luiz Angelo Daros de Luca
2023-08-23 20:47 ` Hugo Slabbert
2023-08-28 22:22 ` Luiz Angelo Daros de Luca
2023-08-23 17:07 ` Daniel Gröber
2023-08-23 19:55 ` Luiz Angelo Daros de Luca
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