Как узнать в Debian Linux, в full-duplex работает сетевая или в half-duplex?

Ставим утилиту:

apt-get install -y ethtool

ethtool eth0 | grep Duplex
Duplex: Full

http://www.cyberciti.biz/faq/howto-setup-linux-lan-card-find-out-full-duplex-half-speed-or-mode/

Сбрасываются ли настройки ethtool после рестарта сети?

Нет!

ethtool -k eth0
Offload parameters for eth0:
Cannot get device udp large send offload settings: Operation not supported
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: off
udp fragmentation offload: off
generic segmentation offload: off
generic-receive-offload: off


root@CentOS-54-64-minimal ~ # /etc/init.d/network restart
Shutting down interface eth0: [ OK ]
Shutting down interface venet0: Shutting down interface venet0:
[ OK ]
Shutting down loopback interface: [ OK ]
Disabling IPv4 packet forwarding: net.ipv4.ip_forward = 0
[ OK ]
Bringing up loopback interface: [ OK ]
Bringing up interface eth0:
Determining IP information for eth0... done.
RTNETLINK answers: File exists
[ OK ]
Bringing up interface venet0: Bringing up interface venet0:
Configuring interface venet0:
net.ipv4.conf.venet0.send_redirects = 0
[ OK ]


root@CentOS-54-64-minimal ~ # ethtool -k eth0
Offload parameters for eth0:
Cannot get device udp large send offload settings: Operation not supported
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: off
udp fragmentation offload: off
generic segmentation offload: off
generic-receive-offload: off

А вот при перезагрузке они все же сбрасываются :)