Day: December 27, 2009

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Forcing NIC to operate at Full Duplex and 100Mb using Ethtool

ethtool is used for querying settings of an ethernet device and changing them. For more information on ethtool, you go to Using ethtool to check and change Ethernet Card Settings and Forcing NIC to operate at Full Duplex using Ethtool

To use ethtool to set NIC to operate at Full Duplex and 100Mb and autonegotiate off, you can use the following commands

# ethtool -s eth0 speed 100 duplex full autoneg off

To force the NIC to use full duplex, 100Mbps, and autonegotiate off and make it permanent, you can put this in /etc/sysconfig/network-scripts/ifcfg-eth0

ETHTOOL_OPTS="speed 100 duplex full autoneg off"

To verify that the settings is correct,do

# ethtool eth0 (or eth1 depending the NIC you are using)
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Configure TCP for faster connections and transfers

On a default Linux Box, the TCP settings may not be optimise for “bigger” available network bandwidth connections and transfer available for 100MB+. Currently, most TCP settings are optimise for 10MB settings. I’m relying on the article from Linux Tweaking from SpeedGuide.net to configure the TCP

The TCP Parameters to be configured are

/proc/sys/net/core/rmem_max – Maximum TCP Receive Window
/proc/sys/net/core/wmem_max – Maximum TCP Send Window
/proc/sys/net/ipv4/tcp_timestamps – timestamps (RFC 1323) add 12 bytes to the TCP header
/proc/sys/net/ipv4/tcp_sack – tcp selective acknowledgements.
/proc/sys/net/ipv4/tcp_window_scaling – support for large TCP Windows (RFC 1323). Needs to be set to 1 if the Max TCP Window is over 65535.

There are 2 methods to apply the changes.

Methods 1: Editing the /proc/sys/net/core/. However, do note that the settings will be lost on reboot.

echo 256960 > /proc/sys/net/core/rmem_default
echo 256960 > /proc/sys/net/core/rmem_max
echo 256960 > /proc/sys/net/core/wmem_default
echo 256960 > /proc/sys/net/core/wmem_max
echo 0 > /proc/sys/net/ipv4/tcp_timestamps
echo 1 > /proc/sys/net/ipv4/tcp_sack
echo 1 > /proc/sys/net/ipv4/tcp_window_scaling

Method 2: For a more permanent settings, you have to configure /etc/sysctl.conf.

net.core.rmem_default = 256960
net.core.rmem_max = 256960
net.core.wmem_default = 256960
net.core.wmem_max = 256960
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_window_scaling = 1

Execute sysctl -p to make these new settings take effect.