Q: How to disable auto-negotiation option of my network interface card and set up half/full duplex mode manually from Linux command line (CLI)? By the way, how to see current settings?
A: There are several Linux utilities coming with almost any distribution including Debian, Ubuntu, Fedora, RedHat, Mandriva, Centos whatever. See details below.
This is rather powerful utility can display and change settings of ethernet network interface card. You can easily disable/enable autonegotiation option for your NIC, also it’s possible to manually set up duplex mode, configure wake-on-lan options, set speed settings. Just look through full manual page for ethtool. Here are several ethtool usage examples:
ethtool eth0 – shows current NIC settings
Settings for eth0: Supported ports: [ TP MII ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full Advertised auto-negotiation: No Speed: 10Mb/s Duplex: Half Port: MII PHYAD: 32 Transceiver: internal Auto-negotiation: off Supports Wake-on: pumbg Wake-on: d Current message level: 0x00000007 (7) Link detected: yes
ethtool -s eth0 duplex half autoneg off – disables auto-negotiation, enables Half Duplex.
ethtool -s eth1 duplex full speed 1000 autoneg off – disables auto-negotiation, enables Falf Duplex and sets up Speed to 1000 Mb/s.
According to manual it allows to manipulate and see media-independent interface status. Let’s see examples:
bash-3.1# mii-tool eth0 – shows 100 Mbps speed, Full Duplex, Auto-negotiation is on.
eth0: negotiated 100baseTx-FD, link ok
bash-3.1# mii-tool eth0 -F 10baseT-HD – enables 10 Mb/s Half Duplex connection.
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