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Check and tune network speed

Fri, 05/06/2011 - 16:56 — sandip

I've had to do this on a couple of servers to check on the network speeds and sysctl tuning.

On the receiving end (192.168.10.1) bring up netcat listening to a port:

while true; do nc -l 8001 >/dev/null ; done

Use the below one liner to send over some data via netcat from 192.168.10.2 which prints out the transfer speed.

( dd if=/dev/zero bs=64K count=1000 | nc 192.168.10.2 8001 ) 2>&1 | awk '/MB/{print $8*8 " " tolower($9)}'

Increase the default maximum TCP buffer size and rerun the above test for proper tuning. Make sure to restart netstat listening socket upon sysctl changes.

The following are recommended:

##
# max TCP buffer size: 16MB (16 * 1024 * 1024).
# Could increase to 32MB for GigE.
#
# Increasing the TCP send buffers will increase the performance
# if you have large files to send.
#
net.core.wmem_max = 16777216

# If you have a lot of large file uploads,
# increasing the receive buffers will help.
#
net.core.rmem_max = 16777216

# increase Linux autotuning TCP buffer limits:
# min, default, and max number of bytes to use
# (only change the 3rd value, and make it 16 MB or more)
#
net.ipv4.tcp_rmem = 4096        87380   16777216
net.ipv4.tcp_wmem = 4096        65535   16777216

# Support for the above large TCP send and receive windows.
# Needs to be set to 1 if the Max TCP Window is over 65535 (64K).
#
net.ipv4.tcp_window_scaling = 1

# Increase backlog to avoid dropped packets and increase throughput.
# Check with `netstat -st | grep packets` and check for
# dropped and packet errors.
#
net.core.netdev_max_backlog = 5000

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