Check and tune network speed

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

On the receiving end ( 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 which prints out the transfer speed.

( dd if=/dev/zero bs=64K count=1000 | nc 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

Tuning TCP - sysctl.conf

Recent versions of Linux (version 2.6.17 and later) have full autotuning with 4 MB maximum buffer sizes. Except in some rare cases, manual tuning is unlikely to substantially improve the performance of these kernels over most network paths, and is not generally recommended

Since autotuning and large default buffer sizes were released progressively over a succession of different kernel versions, it is best to inspect and only adjust the tuning as needed. When you upgrade kernels, you may want to consider removing any local tuning.

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