Today if one try to set speed or duplex and commit the changes you will end up with:

Speed/Duplex missmatch. Must be both auto or manually configured

The available settings for speed are:

vyos@vyos# set interfaces ethernet eth1 speed 
Possible completions:
   auto                 Auto negotiation (default)
   10                   10 Mbit/sec
   100                  100 Mbit/sec
   1000                 1 Gbit/sec
   2500                 2.5 Gbit/sec
   5000                 5 Gbit/sec
   10000                10 Gbit/sec
   25000                25 Gbit/sec
   40000                40 Gbit/sec
   50000                50 Gbit/sec
   100000               100 Gbit/sec

and for duplex:

vyos@vyos# set interfaces ethernet eth1 duplex 
Possible completions:
   auto                 Auto negotiation (default)
   half                 Half duplex
   full                 Full duplex

However configuring it manually at for example "speed 1000" and "duplex full" will still have autoneg enabled (according to output of "ethtool eth1").

This is correct according to IEEE (anything at 1Gbps or higher using TP should have autoneg enabled which also keeps auto mdi/mdix enabled which otherwise gets disabled if autoneg is off).

I would like to propose following changes to speed/duplex settings:

It should be possible to turn off autoneg but also be possible to use autoneg enabled but limit which speeds and duplex combos shall be available to the other side of the connected interface.

Various vendors have solved this differently.

Personally I would prefer to have "autoneg" as a configuration option which defaults to "on" but can be set to "off".

Like so:

set interface ethernet eth1 autoneg off

or (defaults to "on" if not set):

set interface ethernet eth1 autoneg on

And for speed setting be able to select multiple speeds (if autoneg is default or "on"), like so:

set interface ethernet eth1 speed 10 100

Along with "duplex auto" the above would mean that following capabilities would be adveritised with autoneg enabled:

Advertised link modes:  10baseT/Half 10baseT/Full
                        100baseT/Half 100baseT/Full

An even better solution would be to refactor and merge speed/duplex into a single setting where one can select like so:

Possible completions:
   auto                 Auto negotiation (default)
   10-half              10 Mbps/Half Duplex
   10-full              10 Mbps/Full Duplex
   100-half             100 Mbps/Half Duplex
   100-full             100 Mbps/Full Duplex
   1000-half            1 Gbps/Half Duplex
   1000-full            1 Gbps/Full Duplex
   2500-half            2.5 Gbps/Half Duplex
   2500-full            2.5 Gbps/Full Duplex
   5000-half            5 Gbps/Half Duplex
   5000-full            5 Gbps/Full Duplex
   10G-half             10 Gbps/Half Duplex
   10G-full             10 Gbps/Full Duplex
   25G-half             25 Gbps/Half Duplex
   25G-full             25 Gbps/Full Duplex
   40G-half             40 Gbps/Half Duplex
   40G-full             40 Gbps/Full Duplex
   50G-half             50 Gbps/Half Duplex
   50G-full             50 Gbps/Full Duplex
   100G-half            100 Gbps/Half Duplex
   100G-full            100 Gbps/Full Duplex

This way the administrator can choose combinations such as (disable autoneg, only support 100Mbps/Full Duplex - note since autoneg gets disabled auto mdi/mdix is disabled aswell so make sure if you use a straight or crossover TP-cable):

set interface ethernet eth1 autoneg off
set interface ethernet eth1 speed_duplex 100-full

or (enable autoneg, support both 10Mbps/Half Duplex, 100Mbps/Half Duplex and 1Gbps/Full Duplex (dont ask me why, this is just an example)):

set interface ethernet eth1 autoneg on
set interface ethernet eth1 speed_duplex 10-half 100-half 1000-full

The above comes handy for troubleshooting connections towards NBASE-T interfaces where a common workaround is to have autoneg enabled but only advertise the desired speed/duplex:

set interface ethernet eth1 autoneg on
set interface ethernet eth1 speed_duplex 10G-full

Also handy if you want to use 1Gbps/Full Duplex with auto mdi/mdix (select whatever cable you want straight or crossover) but not risking that the interface due to some errors would renegotiate and select a lower speed (since the VyOS interface through configuration only supports 1Gbps/Full Duplex there is nothing to renegotiate into which is lower).