From: Slava Bacherikov <mail@slava.cc>
To: xiyou.wangcong@gmail.com, willemb@google.com
Cc: open list <linux-kernel@vger.kernel.org>,
netdev@vger.kernel.org, kuba@kernel.org
Subject: BUG: Incorrect MTU on GRE device if remote is unspecified
Date: Mon, 25 Jan 2021 22:10:10 +0200 [thread overview]
Message-ID: <e2dde066-44b2-6bb3-a359-6c99b0a812ea@slava.cc> (raw)
Hi, I'd like to report a regression. Currently, if you create GRE
interface on the latest stable or LTS kernel (5.4 branch) with
unspecified remote destination it's MTU will be adjusted for header size
twice. For example:
$ ip link add name test type gre local 127.0.0.32
$ ip link show test | grep mtu
27: test@NONE: <NOARP> mtu 1452 qdisc noop state DOWN mode DEFAULT group
default qlen 1000
or with FOU
$ ip link add name test2 type gre local 127.0.0.32 encap fou
encap-sport auto encap-dport 6666
$ ip link show test2 | grep mtu
28: test2@NONE: <NOARP> mtu 1436 qdisc noop state DOWN mode DEFAULT
group default qlen 1000
The same happens with GUE too (MTU is 1428 instead of 1464).
As you can see that MTU in first case is 1452 (1500 - 24 - 24) and with
FOU it's 1436 (1500 - 32 - 32), GUE 1428 (1500 - 36 - 36). If remote
address is specified MTU is correct.
This regression caused by fdafed459998e2be0e877e6189b24cb7a0183224 commit.
next reply other threads:[~2021-01-25 20:22 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 20:10 Slava Bacherikov [this message]
2021-01-28 0:56 ` BUG: Incorrect MTU on GRE device if remote is unspecified Jakub Kicinski
2021-01-28 1:38 ` Cong Wang
2021-01-28 2:12 ` Vadim Fedorenko
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=e2dde066-44b2-6bb3-a359-6c99b0a812ea@slava.cc \
--to=mail@slava.cc \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=willemb@google.com \
--cc=xiyou.wangcong@gmail.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.