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It so happens that I have a NIC that is only able to establish a connection with the current network when auto negotiation is set to false. In windows, this can be achieved rather easily by changing the NIC properties via Device Manager. Currently I am only able to do so in Ubuntu (10.04 if that matters) via the following after login:

sudo ethtool -s eth0 autoneg off speed 100 duplex full

sudo service network-manager restart

PS: I have read reports from ubuntu forums that it may be necessary to remove network-manager and only use /etc/network/interfaces for configuration, but I intend to do so only as a last resort. I would also appreciate it if someone can add auto-negotiation ethtool to the list of tags.

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up vote 1 down vote accepted

There seems to be no way to do it within Network Manager. Editing /etc/network/interfaces on the other hand is clumsy and causes delays in later editions of Ubuntu like 12.04 (see this and this). In the end the solution offered here turns out to be best (for now), by adding the ethtool command to rc.local:

sudo gedit /etc/rc.local

ethtool -s eth0 autoneg off speed 100 duplex full    # put this above 'exit 0'
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I've had better results putting ethtool scripts in /etc/network/if-up.d . According to Network Manager documentation, scripts in /etc/NetworkManager/dispatcher.d will be run after NM 'fiddles with interfaces'. On my 12.04 system, the only script is 01ifupdown, which will then run scripts in /etc/network/if-up.d (also /etc/network/if-post-down.d).

This sequence of events seems to happen well after the login screen appears on my system. I've found many occurrences of the following line in the system log which may explain what is causing the delay:

NetworkManager[871]: (eth0): carrier now OFF (device state 100, deferring action for 4 seconds).

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