Expectations:
Here are the key points to learn from this article
- To understand nc command in Linux.
- Use nc command for sending and receiving UDP packets through network.
- Send some human readable sentences through nc command.
- Capture the UDP packet sent by nc command.
- Check network packet in Wireshark.
- Find out any other command other than netcat for Linux.
Netcat Command:
Netcat(nc) command is installed by default in Linux OS. Open one terminal [Shortcut Alt+Ctrl+t] and use below command to check if nc is present or not.
Here is the expected output
in the netcat-traditional package.
usage: nc [-46bCDdhjklnrStUuvZz] [-I length] [-i interval] [-O length]
[-P proxy_username] [-p source_port] [-q seconds] [-s source]
[-T toskeyword] [-V rtable] [-w timeout] [-X proxy_protocol]
[-x proxy_address[:port]] [destination] [port]
This means nc command is already exist in Linux.
General Set Up Diagram:
Send UDP packet:
Let’s take an example like we will send UDP packet from System A to System B. So, in server-client concept, we have to run server at System B side and client at System A side.
Also we have valid IP addresses.
System B IP: 192.168.1.102
Start Server:
To start sever using nc command use below command in System B terminal
Here is the screenshot
This command does not have any output to show as of now. This is just listening mode on port 9999.
Start Client:
To connect to server using nc command use below command in System A terminal
Now system A has to connect to System B. So we have provided server IP address and port number.
Here is the screenshot
Check Connection:
We can check the below command for the confirmation about client connation to server port.
Here is the screenshot
Send UDP packets:
Now we can send udp packet from System A to B and vice versa.
Step 1:
Now go to system A and send any sentences like
Screenshot:
Step 2:
We should able to see this in System B side. Here is the screenshot
We can also send UDP packets from System B to System A.
Step 1:
Go to System B and send sentence like
Here is the screenshot from System B
Step 2:
Here is the screenshot from System A
Check packets in Wireshark:
Now while we have been sending UDP packets from System A to System B and vice verse, we can start Wireshark in either System A or System B. Here we have the capture file, let’s do some analysis and confirm if this server and client communication used UDP protocol.
Note that,
- We will only analyse the first communication.
System A has sent “Hi i am from LinuxHint[System A 192.168.1.6]”
To
- Will use filter “udp.port == 9999” to get only related packets in Wireshark.
Refer below screenshot for analysis from Wireshark capture.
To know how to use Wireshark refer below link
https://linuxhint.com/wireshark_basics_how_to_use/
Other command to send UDP packets:
There is another method to send UDP packets
Run server at System B:
Run below command at System A:
192.168.1.102: System B’s IP
8000: The server port
Message sent: “hello”
But we are able to send only one time “hello”. If we kill server and rerun then it’s working.
Conclusion:
From the above exercise we have learned the mechanism to send some messages using UDP protocol. And the best method is to use nc command in Linux.
References:
To understand TCP: https://linuxhint.com/tcp_packet_capture_analysis/
To understand UDP: https://linuxhint.com/udp_wireshark_analysis/
from Linux Hint https://ift.tt/2Pn7KN5
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