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Functions

send echo to socket network

Terminal - send echo to socket network
echo "foo" > /dev/tcp/192.168.1.2/25
2009-09-12 16:48:05
User: mobidyc
Functions: echo
23
send echo to socket network

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.

Alternatives

There are 6 alternatives - vote for the best!

Terminal - Alternatives
echo foo | netcat 192.168.1.2 25
2009-09-13 01:33:02
User: pykler
Functions: echo
2

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()"

echo foo | ncat [ip address] [port]
2012-10-26 10:53:47
User: dragonauta
Functions: echo
-1

you can use a pair of commands to test firewalls.

1st launch this command at destination machine

ncat -l [-u] [port] | cat

then use this command at source machine to test remote port

echo foo | ncat [-u] [ip address] [port]

First command will listen at specified port.

It will listen TCP. If you use -u option will listen UDP.

Second command will send "foo" through ncat and will reach defined IP and port.

Know a better way?

If you can do better, submit your command here.

What others think

This syntax is a shell feature, not of the OS, and I know it is part of bash, if not in more in shells. But annoyingly in the default debian packaging for bash, /dev/tcp files are disabled, since you can get the same functionality and more with netcat (or socat). The manpage says these net redirections can produce "completely unexpected results."

Comment by bwoodacre 263 weeks and 3 days ago

It would be nice if commercial Unixes shipped with netcat, or the black gang in operations could compile freely.

FWIW, Solaris 10 ships with this feature enabled, and I believe it defaults to ON for at least some BSDs.

The fuller syntax is /dev/[tcp|udp]/[host]/[port]

Comment by lbonanomi 263 weeks and 3 days ago

Just a correction to your description. This does not work for ICMP packets (ping, etc.) Although it would be kinda cool if it did.

Comment by deltaray 225 weeks ago

Your point of view

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