Posts with the tag network speed

`iperf` – Network Bandwidth Testing

iperf can help you test the bandwidth of your network setup via a TCP connection:

# On one computer:
iperf -s -w 2M -i 1 -p 2222
# On the other computer:
iperf -c -w 2M -i 1 -p 2222

Or test via UDP (be careful,...

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Install OpenVPN

sudo aptitude install openvpn
# open port 1194 (as shown here for the ufw firewall interface):
sudo ufw allow 1194

Become an Certificate Authority

Alternative to this way: Use TinyCA (there are Ubuntu packages available).

sudo mkdir /etc/openvpn/easy-rsa/
sudo cp -R /usr/share/doc/openvpn/examples/easy-rsa/2.0/* /etc/openvpn/easy-rsa/
sudo chown -R $USER /etc/openvpn/easy-rsa/
cat << EOF...

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Slow Network Due to DNS Problems

Let's say you network is kinda slow and you are sure that there is nothing wrong with your hardware (broken cables, bad switches etc.). The first thing you should have a look at are your DNS servers. If the primary one is unreachable and the secondary is, you network works...

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Make SSHd React Faster on Connect

If your ssh connection is established only with a delay of about 2-4 seconds (even when you are connected to a fast network), you can try the tips in this post.

What to try first

Debug you ssh connection: using ssh -p 28 -vvv (note the -vvv switch at the end).

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Network Bandwidth Monitoring Tools

Commonly used tools to monitor or test network bandwith are:

  • bmon
  • bwbar
  • bwm
  • bwm-ng
  • iftop
  • iperf
  • ipfm
  • ttcp
  • speedometer
  • cbm
  • ibmonitor
  • pktstat
  • mactrack
  • MRTG
  • Cacti


I really like bmon for monitoring; it's a light-weight real-time CLI bandwidth monitor. Its status output is given for the individual network interfaces on your computer.

sudo aptitude install bmon

sudo bmon

Press g for console graphics and d for detailed stats.


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React when Network Interface is slow (as in half-duplex mode etc.)

Analyse the situation by taking a look at the configuration and stats:

ifconfig -a
netstat -s

Check if your gateway and DNS servers are reachable. If only one of the dns servers is not reachable edit /etc/resolv.conf manually (will be overwritten by next network change).

To set the network interface eth1 to 100MBits...

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Test Network Speed Using netcat
good (short!):

listen on machine A:

nc -v -v -l -n -p 2222 >/dev/null

on newer versions of netcat (Ubuntu 10.04) you must use

nc.traditional -v -v -l -n -p 2222 >/dev/null

Send from machine B:

time yes|nc -v -v -n 2222 >/dev/null


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