From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Stephen Hemminger" <stephen@networkplumber.org>, <dev@dpdk.org>
Subject: Re: [dpdk-dev] [RFC] ethdev: add min/max MTU to device info
Date: Wed, 6 Feb 2019 14:05:34 +0100 [thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35B4265B@smartserver.smartshare.dk> (raw)
In-Reply-To: <20180905164157.844-1-stephen@networkplumber.org>
Good work, Stephen.
It should also be documented how PMDs should interpret this MTU.
Obviously, a VLAN tagged Ethernet frame grows from 1518 to 1522 bytes incl. header and CRC, and should be allowed with an Ethernet MTU of 1500 bytes. There's even a #define ETHER_MAX_VLAN_FRAME_LEN for this, but that's as far as it goes...
But how about frames with even larger headers, e.g. 4 MPLS labels makes a frame 16 bytes longer, i.e. it grows from 1518 to 1534 bytes... is such a frame acceptable with an MTU of 1500 bytes?
According to Wikipedia (https://en.wikipedia.org/wiki/Maximum_transmission_unit), MTU describes the maximum payload size, and is not tied to the maximum frame size. However, the Linux kernel (at least the older versions I have been working with) incorrectly ties the MTU directly to the maximum frame size, so the MTU has to increased to support larger headers (e.g. QinQ or an MPLS stack). Do none, all or some DPDK PMDs suffer from the same error?
Med venlig hilsen / kind regards
- Morten Brørup
next prev parent reply other threads:[~2019-02-06 13:05 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-05 16:41 Stephen Hemminger
2018-09-06 5:51 ` Shahaf Shuler
2018-09-06 6:29 ` Andrew Rybchenko
2018-09-06 10:52 ` Stephen Hemminger
2018-11-22 9:58 ` Stokes, Ian
2018-12-19 2:37 ` Thomas Monjalon
2019-01-16 21:30 ` Stephen Hemminger
2019-02-06 13:05 ` Morten Brørup [this message]
2019-02-06 16:11 ` Stephen Hemminger
2019-02-06 21:58 ` Morten Brørup
2019-02-07 10:25 ` Ananyev, Konstantin
2019-02-07 11:10 ` Morten Brørup
2019-02-07 12:00 ` Ananyev, Konstantin
2019-02-20 16:02 ` Ian Stokes
2019-06-24 13:18 ` Nithin Kumar Dabilpuram
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=98CBD80474FA8B44BF855DF32C47DC35B4265B@smartserver.smartshare.dk \
--to=mb@smartsharesystems.com \
--cc=dev@dpdk.org \
--cc=stephen@networkplumber.org \
/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).