check for common kernel network settings in RHEL 5 and 6

check-tweak.sh

#!/bin/bash

echo Tweaking the linux kernel...

echo disable pmtu discovery
echo /proc/sys/net/ipv4/ip_no_pmtu_disc: 
cat  /proc/sys/net/ipv4/ip_no_pmtu_disc
echo recommended value is 1

echo enable workaround when broken window scaling is detected.
echo /proc/sys/net/ipv4/tcp_workaround_signed_windows:
cat  /proc/sys/net/ipv4/tcp_workaround_signed_windows
echo recommended value is 1

echo globally disable ip4 tcp window scaling
echo /proc/sys/net/ipv4/tcp_window_scaling:
cat /proc/sys/net/ipv4/tcp_window_scaling
echo recommended value is 0

echo globally disable ip4 tcp sack
echo /proc/sys/net/ipv4/tcp_sack:
cat  /proc/sys/net/ipv4/tcp_sack
echo recommended value is 0

echo globally disable ip4 tcp timestamps
echo /proc/sys/net/ipv4/tcp_timestamps:
cat  /proc/sys/net/ipv4/tcp_timestamps
echo recommended value is 0

echo Decrease the time default value for tcp_fin_timeout connection in seconds
echo /proc/sys/net/ipv4/tcp_fin_timeout:
cat  /proc/sys/net/ipv4/tcp_fin_timeout
echo recommended value is 15 seconds

echo Decrease the time default value for tcp_keepalive_time connection in seconds.
echo /proc/sys/net/ipv4/tcp_keepalive_time:
cat  /proc/sys/net/ipv4/tcp_keepalive_time
echo recommended value is 400 seconds

echo Lower syn retry rates.
echo /proc/sys/net/ipv4/tcp_synack_retries:
cat  /proc/sys/net/ipv4/tcp_synack_retries
echo recommended value is 2

echo /proc/sys/net/ipv4/tcp_syn_retries:
cat  /proc/sys/net/ipv4/tcp_syn_retries
echo recommended value is 3 

echo Turn off logging of bogus icmp error messages.
echo /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses:
cat  /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses
echo recommended value is 1

echo Set mss on eth0 to mtu which is small enought not to fail.
/sbin/ifconfig eth0 | grep mtu
echo recommended value is 1492

echo Done

To actually adjust those settings (in a temporary way)

echo Tweaking the linux kernel...
#disable pmtu discovery
echo 1 > /proc/sys/net/ipv4/ip_no_pmtu_disc
#enable workaround when broken window scaling is detected.
echo 1 > /proc/sys/net/ipv4/tcp_workaround_signed_windows
#globally disable ip4 tcp window scaling
echo 0 > /proc/sys/net/ipv4/tcp_window_scaling
#globally disable ip4 tcp sack
echo 0 > /proc/sys/net/ipv4/tcp_sack
#globally disable ip4 tcp timestamps
echo 0 > /proc/sys/net/ipv4/tcp_timestamps
# Decrease the time default value for tcp_fin_timeout connection in seconds
echo 15 > /proc/sys/net/ipv4/tcp_fin_timeout
# Decrease the time default value for tcp_keepalive_time connection in seconds.
echo 400 > /proc/sys/net/ipv4/tcp_keepalive_time
## Lower syn retry rates
#echo 2 > /proc/sys/net/ipv4/tcp_synack_retries
#echo 3 > /proc/sys/net/ipv4/tcp_syn_retries
## Turn off logging of bogus icmp error messages.
#echo 1 > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses
#set mss on eth0
/sbin/ifconfig eth0 mtu 1492
echo 'Done's