[systemd-devel] networkd: Is auto-negotiation turned off when specifying parameters in a link file?

Lennart Poettering lennart at poettering.net
Fri Apr 3 07:47:14 PDT 2015

On Thu, 02.04.15 13:11, Paul Menzel (paulepanter at users.sourceforge.net) wrote:

> Dear systemd folks,
> some network cards with certain cables and devices take up to five
> seconds so that the link is up [1].
>         $ sudo journalctl -u systemd-networkd
>         -- Logs begin at Fr 2015-03-20 17:39:31 CET, end at So 2015-03-22 08:39:39 CET. --
>         Mär 20 17:39:31 myhostname systemd-networkd[245]: lo              : gained carrier
>         Mär 20 17:39:31 myhostname systemd-networkd[245]: eth0            : link configured
>         Mär 20 17:39:34 myhostname systemd-networkd[245]: eth0            : gained carrier
> This is annoying if the system is up, but you cannot log into a server
> because the NIC is so slow configuring the link.
> The Linux kernel module developers from the e1000-devel mailing list
> suggested the following [2]:
> > Both sides either need to be forced or both sides need to be auto-neg.
> > Otherwise the auto-negotiation process will usually detect link (the
> > physical signal) but fail to find duplex (since one side is not
> > talking) and default to the lowest common denominator, e.g. half
> > duplex.  So, you could try forcing speed, it may look right on your
> > end but if you have no visibility to the other end it could be running
> > at half duplex.
> >
> > You may be able to speed up the auto negotiation process by
> > exclusively advertising 1000 Mbps Full Duplex.
> >
> > # ethtool -s ethX advertise 0x20
> In the IRC channel #systemd at irc.freenode.net somebody told me to look
> into systemd’s network link configuration (`man systemd.link`).
> Reading the manual page, it’s not clear to me, if auto-negotiation is
> going to be disabled, if the following is set.
>         BitsPerSecond=1G
>         Duplex=Full
> Is that equivalent to `ethtool -s ethX advertise 0x20`? If not, how
> could I set that up?

BitsPerSecond= and Duplex= are equivalent to "ethtool speed" and
"ethtool duplex". 

We currently have no setting in .link files that was equivalent to
"ethtool advertise". Maybe we could add that, Tom?

Paul, are you sure that this will really cut 5s from the configuration
time? Did you try this?


Lennart Poettering, Red Hat

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