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Send an UDP packet with NetCat

  • Sep 07 / 2016
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Send an UDP packet with NetCat

It can be needed to test an UDP connection with a server to ensure that connectivity is working and double check the data received.

Let’s take a simple example with a remote logstash server:
– Server mylogstash.mydomain.local
– Listening on port 5000

On emitter side, we are sending an UDP packet simulating a log line coming from an application:

echo -e '{"version": "1.1","host":"myapp.org","message":"My message","backtrace":"Backtrace of my app\n\nmore stuff"}\0' | nc -u -w 1 mylogstash.mydomain.local 5000

On receiving server side, we are executing a tcpdump to check that packet is correctly coming with good content:

# tcpdump -i any udp port 5000 -A
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
10:43:47.621172 IP mylogstash.mydomain.local.49435 > localhost.5000: UDP, length 108
[email protected]@............./..t..{"version": "1.1","host":"myapp.org","message":"My message","backtrace":"Backtrace of my app

more stuff"}.

Here we are! It’s very simple to control UDP flows or simply check connection between 2 servers.

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