If auto neg is set on one end, and not on the other end, then the
standards says set things to 100mb/half (for gbit cards) since you
were unable to get information from the other end I believe this was
judged the most likely to work reasonably by the people who write the
standard.  On 100mbit adapters the fail-safe was 10mb/half.

If the device on the other end is not doing auto-neg then I would
expect 100/half.

Either set the other end to auto-neg or figure out what the other end
does and set the computer end to match how it is explicitly set (if
not auto-neg).

If both ends are set to auto-neg and you are getting 100/half then
something is being detected to be wrong with the wiring and both ends
are using what they believe will run on the given wiring.  This could
be broken wires, badly terminated wires, or not quite plugged in
right, or a number of other things.

On Tue, Feb 13, 2018 at 1:16 AM, Terry Barnaby <ter...@beam.ltd.uk> wrote:
> On 12/02/18 21:51, Ed Greshko wrote:
>> On 02/13/18 05:43, Stephen Morris wrote:
>>> I am using a home plug device to get ethernet access across the home
>>> electrical
>>> wires. The home plug device is provide 500 Mb/s, so having seen this
>>> thread I've
>>> checked my ethernet configuration and like Terry is saying my settings
>>> have auto
>>> negotiate unchecked and the link speed is set at 100 Mb/s and Half
>>> Duplex. I have
>>> not explicitly set that configuration but what I don't know, because I
>>> haven't
>>> really taken any notice of it as I only use this connection as a backup
>>> to
>>> wireless, is whether or not those settings have always been there. I have
>>> done any
>>> changes to the configuration since I set it up in F26.
>> One can always use
>> ethtool <devname>     to determine what is available and what the current
>> settings are...
>> This is the view from the Fedora side....
>> This is what the Fedora side it telling the outside world what the HW
>> supports
>>          Advertised link modes:  10baseT/Half 10baseT/Full
>>                                  100baseT/Half 100baseT/Full
>>                                  1000baseT/Half 1000baseT/Full
>> This is what the device that the Fedora system is connected to is  saying
>> what it
>> supports.
>>          Link partner advertised link modes:  10baseT/Half 10baseT/Full
>>                                               100baseT/Half 100baseT/Full
>>                                               1000baseT/Full
>> FWIW, I have never seen an advertised link speed of 500 Mb/s.
> Yes, I used ethtool to find out what was happening after the performance of
> NFS went down to 10 MBytes/s.
> I think what has happened is:
> 1. I updated these systems (5 off) from F25. This was a clean/new install
> but some configuration files were copied from the previous systems.
> 2. The /etc/sysconfig/network-scripts/ifcfg-Wired_connection_1 file (or
> appropriate named one) was copied from the previous system.
> 3. These files did not have the new ETHTOOL_OPTS="autoneg on" entry.
> 4. All was working fine (Gigabit full duplex) for a month or so until
> someone/something updated the ifcfg file. If you use the KDE-Plasma
> NetworkManager settings tool and it sees no ETHTOOL_OPTS entry, it sets the
> GUI settings to manual 100Mbits/s half duplex rather than auto. So if you
> don't notice this and save the settings the Ethernet will be set to this. I
> will try and enter a bug report for this somewhere.
> In my case I don't believe I changed the Ethernet settings using the
> KDE-Plasma NetworkManager settings tool, certainly not on all of the
> systems. I think something else may have written the ETHTOOL_OPTS="100mbps"
> entry somehow with an RPM update within the last week.
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