[WireGuard] Header / MTU sizes for Wireguard

Roman Mamedov rm at romanrm.net
Wed Aug 23 16:15:44 UTC 2023

On Thu, 17 Aug 2023 20:14:52 +0000
blurt_overkill882 at simplelogin.com wrote:

> I see here[1] that if you're using IPv4 exclusively, you can get away with
> an MTU of 1440. If my client only has IPv4 internet, however the server
> issues an IPv6 address for use by the client, can the client still use 1440
> without fragmentation, or must the client use 1420, because even though
> their connection is IPv4, they are issued an IPv6 address within the tunnel?
> [1] https://lists.zx2c4.com/pipermail/wireguard/2017-December/002201.html

Yes they can. This is only affected by whether or not WG itself runs over
v4/v6, not whether you use v4 or v6 inside WG.

Be aware though that some residential Internet connections use MTU-reducing
tunnels for ISP authentication. The most popular one would be PPPoE with 8
bytes that you need to substract, but there also can be L2TP or PPTP with
larger overheads.

With respect,

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