From: Roman Mamedov <rm@romanrm.net>
To: wireguard@lists.zx2c4.com
Subject: Re: Mixed MTU hosts on a network
Date: Fri, 16 Mar 2018 21:20:13 +0500 [thread overview]
Message-ID: <20180316212013.52a325ec@natsu> (raw)
In-Reply-To: <20180316155343.09a0f1bc@natsu>
On Fri, 16 Mar 2018 15:53:43 +0500
Roman Mamedov <rm@romanrm.net> wrote:
> But guess what, turns out that didn't work either. Tried both OUTPUT and
> POSTROUTING chains on the "mangle" table, and set-mss all the way down to
> 1220, no matter what, the iperf3 output looked the same as before.
Actually the iptables bit is easy to explain. Even if initial MSS is forced
to a low value on the sender, it's get negotiated back up to the maximum value
according to MTU on the receiver (changed both IPs since then):
21:13:38.641531 IP6 fd39:30::f5a8:e923:f8cd:24b5.40052 > fd39:30::e84f:942d:7f93:ddc1.5001: Flags [S], seq 2397878391, win 27200, options [mss 1220,sackOK,TS val 566161815 ecr 0,nop,wscale 9], length 0
21:13:38.641574 IP6 fd39:30::e84f:942d:7f93:ddc1.5001 > fd39:30::f5a8:e923:f8cd:24b5.40052: Flags [S.], seq 1221117548, ack 2397878392, win 26800, options [mss 1352,sackOK,TS val 2726162536 ecr 566161815,nop,wscale 9], length 0
21:13:38.716047 IP6 fd39:30::f5a8:e923:f8cd:24b5.40052 > fd39:30::e84f:942d:7f93:ddc1.5001: Flags [.], ack 1, win 54, options [nop,nop,TS val 566161889 ecr 2726162536], length 0
21:13:38.716444 IP6 fd39:30::f5a8:e923:f8cd:24b5.40052 > fd39:30::e84f:942d:7f93:ddc1.5001: Flags [P.], seq 1341:1605, ack 1, win 54, options [nop,nop,TS val 566161889 ecr 2726162536], length 264
21:13:38.716458 IP6 fd39:30::e84f:942d:7f93:ddc1.5001 > fd39:30::f5a8:e923:f8cd:24b5.40052: Flags [.], ack 1, win 55, options [nop,nop,TS val 2726162611 ecr 566161889,nop,nop,sack 1 {1341:1605}], length 0
So the other side really needs to have a proper MTU set. And the highest working
wg0 MTU on PPPoE turned out to be 1408, not 1412 as I assumed. As for why 1412
also works but only if set on the sender side, I've no explanation for that yet.
--
With respect,
Roman
next prev parent reply other threads:[~2018-03-16 16:09 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-16 9:25 Roman Mamedov
2018-03-16 9:35 ` Matthias Ordner
2018-03-16 10:53 ` Roman Mamedov
2018-03-16 16:20 ` Roman Mamedov [this message]
2018-03-16 10:01 ` Kalin KOZHUHAROV
2018-03-26 19:12 ` Luis Ressel
2018-04-14 1:38 ` Jason A. Donenfeld
2018-04-14 2:40 ` Jason A. Donenfeld
2018-04-14 13:16 ` Jason A. Donenfeld
2018-04-14 13:40 ` Roman Mamedov
2018-04-14 14:15 ` Jason A. Donenfeld
2018-04-14 14:38 ` Roman Mamedov
2018-04-14 14:45 ` Jason A. Donenfeld
2018-04-14 15:20 ` Roman Mamedov
2018-04-14 23:08 ` Jason A. Donenfeld
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180316212013.52a325ec@natsu \
--to=rm@romanrm.net \
--cc=wireguard@lists.zx2c4.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).