When you update a connection that is currently active, eg via
    nmcli connection load "$IFCFG_NAME"
    nmcli connection reload
or
    nmcli connection modify "$CON"
These commands only modify the connection profile. The changes do not take effect immediately on already activated devices. That is intentional.
Note the distinction between
  - connection (profile)
  - actual device (networking interface)




If you want to apply the changed connection, you need do one of:

  # reactivate connection, implicitly doing a down+up
  nmcli connection up "$CON"   

  # reconnect the device, doing a down+up.
  nmcli device connect $DEV

  # legacy initscripts invoke `nmcli connection up`
  ifup $NAME

  # a more graceful way is reapply, which doesn't do a full down+up cycle and 
  # you don't loose connectivey:
  nmcli device reapply $DEV




On the other hand, if you add a connection (or modify a connection that is currently not active), the connection might start autoconnecting right away, depending on it's connection.autoconnect setting. That leads to a confusing situation that:

  nmcli connection add type ethernet con-name T iface '*'
  # at this point, the new connection might already activate on the device
  # with incomplete configuration.
  nmcli connection modify T ipv4.dns 8.8.8.8

The solutions for that are:
  # do all in one step:
  nmcli connection add type ethernet con-name T iface '*' ipv4.dns 8.8.8.8

  # after the last modification, re-activate the connection, see before.
  nmcli connection modify T ipv4.dns 8.8.8.8
  nmcli connection up T

  # don't use autoconnect initially.
  nmcli connection add type ethernet con-name T iface '*' autoconnect no
  nmcli connection modify T ipv4.dns 8.8.8.8 connection.autoconnect yes





> # reload the network
> systemctl restart NetworkManager

> or service network restart

these are two very different things. One restart NetworkManager.service, the other restarts legacy network.service.

Why are you restarting NetworkManager? See above how to apply changes to a connection. Restarting NetworkManager is almost always the wrong thing to do. Certainly it is wrong to restart NM in order to activate a connection. In fact, it does not. On restart, NM will not change the networking configuration
-- contrary to restarting network.target, which calls ifup for each interface.




The mentioned "workaround" is the right way to do it.

Hello, thanks for clearing that up:

service network restart will restart the network.service (legacy network)
systemctl restart NetworkManager will just restart the NM service.

Have no play at all with reflecting changes to ifcfg* files, unless the configuration files are in legacy format. 

Both commands should not be used, instead the 4 commands you have mentioned.
I think I'll create a good kcs to reflect that info.