From: Roman Mamedov <rm@romanrm.net>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: WireGuard mailing list <wireguard@lists.zx2c4.com>,
zrm <zrm@trustiosity.com>, StarBrilliant <coder@poorlab.com>,
Baptiste Jonglez <baptiste@bitsofnetworks.org>,
Joe Holden <jwh@zorins.us>,
Nico Schottelius <nico.schottelius@ungleich.ch>,
Vasili Pupkin <diggest@gmail.com>,
peter@fiberdirekt.se
Subject: Re: potentially disallowing IP fragmentation on wg packets, and handling routing loops better
Date: Mon, 7 Jun 2021 23:50:34 +0500 [thread overview]
Message-ID: <20210607235034.024e6c6b@natsu> (raw)
In-Reply-To: <20210607164617.6bf015d1@natsu>
On Mon, 7 Jun 2021 16:46:17 +0500
Roman Mamedov <rm@romanrm.net> wrote:
> On Mon, 7 Jun 2021 13:27:10 +0200
> "Jason A. Donenfeld" <Jason@zx2c4.com> wrote:
>
> > Can you walk me through your use case a bit more, so I can wrap my mind
> > around the requirements?
> >
> > ingress --plain--> wireguard --wireguard[plain]--> vxlan --vxlan[wireguard[plain]]--> egress
>
> Not sure I understand your scheme correctly. In any case, the path of a
> packet would be...
>
> On peer 1:
>
> * plain Ethernet -> wrapped into VXLAN -> encrypted into WireGuard
>
> On peer 2:
>
> * decrypted from WireGuard -> unwrapped from VXLAN -> plain Ethernet
>
> > So my question is, why can't you set wireguard's MTU to 80 bytes less
> > than vxlan's MTU? What's preventing that or making it infeasible?
>
> To transparently bridge two Ethernet LANs, a VXLAN interface needs to join an
> L2 bridge. All interfaces that are members of a bridge must have the same MTU.
>
> As such, br0 members on both sides:
> eth0 (MTU 1500)
> vx0 (MTU 1500)
>
> VXLAN transports full L2 frames encapsulating them into UDP. To fit the
> full 1500-byte packet and accounting for VXLAN and related IP overheads,
> the resulting packet size is 1574 bytes.
>
> So this same host that just generated the 1574-byte encapsulated VXLAN packet
> with something it received via its eth0 port, now needs to send it further to
> its WG peer(s). For this to succeed, the in-tunnel WG MTU needs to be 1574 or
> more, not 1412 or 1420, as VXLAN itself can't be fragmented[1]; or even if it
> could, that would mean a much worse overhead ratio than currently.
>
> [1] https://datatracker.ietf.org/doc/html/rfc7348#section-4.3
In case you are not convinced by this case, would you consider at least
allowing fragmentation when WG's in-tunnel MTU is set to >=1500? Because this
is the user effectively saying "yes I know this is not gonna fit in one
packet, I want to rely on WG packets being fragmented", but without the need
for extra knobs.
--
With respect,
Roman
next prev parent reply other threads:[~2021-06-07 18:50 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-06 9:13 Jason A. Donenfeld
2021-06-06 9:32 ` Nico Schottelius
2021-06-06 10:39 ` Vasili Pupkin
2021-06-06 11:14 ` Peter Linder
2021-06-07 11:58 ` Derek Fawcus
2021-06-06 19:03 ` Roman Mamedov
2021-06-06 22:33 ` Joe Holden
2021-06-07 9:34 ` Jason A. Donenfeld
2021-06-07 11:13 ` Roman Mamedov
2021-06-07 11:27 ` Jason A. Donenfeld
2021-06-07 11:46 ` Roman Mamedov
2021-06-07 11:55 ` Peter Linder
2021-06-07 18:50 ` Roman Mamedov [this message]
2021-06-07 11:18 ` Nico Schottelius
2021-06-09 23:26 ` Vasili Pupkin
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