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

[Paul Menzel]

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?


Thanks,

Paul


[1] http://sourceforge.net/p/e1000/mailman/message/33623906/
[2] http://sourceforge.net/p/e1000/mailman/message/33635403/
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