Commands tagged Network

Using netcat, usuallly installed on debian/ubuntu.

Also to test against a sample server the following two commands may help

echo got milk? | netcat -l -p 25

python -c "import SocketServer; SocketServer.BaseRequestHandler.handle = lambda self: self.request.send('got milk?\n'); SocketServer.TCPServer(('0.0.0.0', 25), SocketServer.BaseRequestHandler).serve_forever()"

this command will send a message to the socket 25 on host 192.168.1.2 in tcp.

works on udp and icmp

understand only IP address, not hostname.

on the other side (192.168.1.2), you can listen to this socket and test if you receive the message.

easy to diagnose a firewall problem or not.

Like many other thing in Linux ,you can see the same thing in different way.

If you need to ssh into a computer on the local network but you're unsure of the ip to use, then ping them and see if you get a response. If you do, print out the address you got it from. Adjust the range to suit your network.

Same thing as above, just uses fetch and ipchicken.com

The example command deletes all aliases for network interface 'em0' assuming that the aliases have netmask of 255.255.255.255 and the master IP has some other netmask (such as 255.255.255.0). See here -> http://my.galagzee.com/2009/07/22/deleting-all-network-interface-aliases/ for more on the rationale of this command.

works on Linux and Solaris. I think it will work on nearly all *nix-es

The curl command retrieve the HTML text containing the IP address. The grep command picks out the IP address from that HTML text.

The socket.gethostname() call returns the host name of the computer. The socket.gethostbyname_ex() call returns a list of three items: The host name, the list of aliases for this host, and a list of IP addresses. Recall that Python?s array starts with index 0, the socket.gethostbyname_ex(?)[2] expression refers to the list of IP addresses. Finally, the print statement prints out the IP addresses, one per line.

Basically an improvement on an earlier ethtool command line.

The report mode of mtr produces a text formated result of the mtr run using the number of ping cycles stated by the command. This text file could then be attached to an email with ease.

I use this also without the ">" portion when writing email from within mutt using VI from the command mode with ":r !mtr --report --report-cycles 10

Replace "en1" with your network interface (on OS X, usually en0, en1, eth0, etc..)

Waiting for your server to finish rebooting? Issue the command above and you will hear a beep when it comes online. The -i 60 flag tells ping to wait for 60 seconds between ping, putting less strain on your system. Vary it to your need. The -a flag tells ping to include an audible bell in the output when a package is received (that is, when your server comes online).

On Linux and Mac systems (I have not tested with other Unix systems), the ping command will keep on pinging until the user interrupts it with Ctrl+C. On Windows system, ping will execute for a number of times then quit. The -c flag on Linux and Mac will make this happen

To connect to the shell run:

Redirect the local port 2000 to the remote port 3000. The same but UDP:

It may be used to "convert" TCP client to UDP server (or viceversa):