Network Issues
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Testing network performance
netcat
Netcat
From client machine to server ...
On server:
netcat -l -p 1234 > /dev/null
On client:
dd if=/dev/zero bs=1M count=1000 |netcat server 1234
From server to client machine ... On client:
netcat -l -p 1234 > /dev/null
On server:
dd if=/dev/zero bs=1M count=1000 |netcat client 1234
You can exchange /dev/zero with e.g. /dev/md0 (for a raid device) or /dev/sda for testing your harddisk performance.
Combine
If you like to get the real disk perfance use e.g.
dd if=/dev/sda of=/dev/null bs=1M Ctrl + C
or with hdparm (the buffered disk read is for interest!):
hdparm -tT /dev/disk
For realistic results you should also consider local disk read/writes for the operating system, other running tasks and that all components share the same (!) PCI bus. For that reason you have to sum up disk usage and network usage.
iperf
Messures the network perfomance.
On the server do (start iperf in server mode)
iperf -s
On the client machine do
iperf -c server_ip -i 1 -t 10
Typical values
- 15-25 Mbits/sec for a 54Mbit Wireless LAN
- 300-350 Mbits/sec for a Gigabit LAN
The values depend heavily to
- quality of the network card
- quality of the cable (already CAT 6 !?) or wireless connection
- bus speed
- processor speed
ethtool
Ethtool gives you important informations over your network card, its settings and actual modes:
ethtool eth0
sysctl
Settings for tpc ip settings:
for i in rmem wmem mem; do sysctl net.ipv4.tcp_${i}; done
gives e.g. on an older machine (366MHz AMD K6, 33MHz bus)
net.ipv4.tcp_rmem = 4096 87380 577600 net.ipv4.tcp_wmem = 4096 16384 577600 net.ipv4.tcp_mem = 13536 18050 27072
and on a "newer" system (AMD Athlon XP 2000+, 133MHz bus)
net.ipv4.tcp_rmem = 4096 87380 4194304 net.ipv4.tcp_wmem = 4096 16384 4194304 net.ipv4.tcp_mem = 170592 227456 341184
I can be set with e.g.:
sysctl -w net.ipv4.tcp_wmem="4096 16384 1048576"
But consider: better know what you are doing! On modern linux systems this should not be necessary.
MTU
So called "Jumbo Frames" can reduce the CPU usage on the server. The network throughput is _NOT_ improved very much. Kernel greater than 2.6.17 support frame bigger than 1500 bythes. Note, that both network card (driver) and used switches must support this kind of settings. So be careful and test e.g. with
ifconfig eth0 mtu 9000; sleep 30 ; ifconfig eth0 mtu 16436
16436 is the default setting on actual systems.
Network configuration files /etc/sysconfig/network-script/ifcfg-eth0 (CentOS / RHEL / Fedora Linux)
MTU=9000
Debian / Ubuntu Linux use /etc/network/interfaces configuration file.
mtu 9000
Test with
/etc/init.d/networking restart ip route get IP-address