Send udp linux command line

Send and Receive UDP packets via Linux CLI

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.

1. How send TCP packets in Linux?
2. Can we send UDP packet to a TCP port will it accept the packet?
3. How UDP packets are sent?
4. What is UDP Linux?
5. How do I get UDP packets in Linux?
6. Does Netcat use TCP?
7. Does Curl support UDP?
8. Can browsers use UDP?
9. What does a client do when it has User Datagram Protocol UDP to send packet?
10. Does UDP use IP address?
11. Is UDP faster than TCP?
12. Where is UDP used?

How send TCP packets in Linux?

1. Base Command. $ echo «YOUR_MESSAGE» > /dev/TRANSPORT_PROTOCOL/DESTINATION_IP/DESTINATION_PORT
2. UDP. $ echo «This is my UDP message» > /dev/udp/127.0.0.1/30000.
3. TCP. $ echo «This is my TCP message» > /dev/tcp/127.0.0.1/30100.

Can we send UDP packet to a TCP port will it accept the packet?

TCPConn , connected on a port which, in addition to a TCP stream, also has to receive UDP packets and respond with UDP packets. The incoming UDP packet pops out at the server (from a net. TCPConn.

How UDP packets are sent?

A UDP datagram is carried in a single IP packet and is hence limited to a maximum payload of 65,507 bytes for IPv4 and 65,527 bytes for IPv6. . To transmit a UDP datagram, a computer completes the appropriate fields in the UDP header and forwards the data together with the header for transmission by the IP network layer.

What is UDP Linux?

User datagram protocol (UDP), one of the core protocols of the Internet protocol suite, is a connectionless, transport layer protocol that exchanges packets with minimal error recovery services and without guaranteed delivery or acknowledgment. . UDP does not provide the reliability and ordering guarantees that TCP does.

How do I get UDP packets in Linux?

1. To understand nc command in Linux.
2. Use nc command for sending and receiving UDP packets through network.
3. Send some human readable sentences through nc command.
4. Capture the UDP packet sent by nc command.
5. Check network packet in Wireshark.
6. Find out any other command other than netcat for Linux.

Does Netcat use TCP?

By default, netcat operates by initiating a TCP connection to a remote host.

Does Curl support UDP?

No it doesn’t. For HTTP, libcurl only supports TCP or Unix domain socket. . (libcurl supports UDP transfers for a few other protocols.)

Can browsers use UDP?

Websites would be able to launch DDoS attacks by coordinating UDP packet floods from browsers. . UDP packets are not encrypted, so any data sent over these packets could be sniffed and read by an attacker, or even modified in transmit.

What does a client do when it has User Datagram Protocol UDP to send packet?

UDP works by gathering data in a UDP packet and adding its own header information to the packet. This data consists of the source and destination ports to communicate on, the packet length and a checksum. After UDP packets are encapsulated in an IP packet, they’re sent off to their destinations.

Does UDP use IP address?

General. Both TCP and UDP are protocols used for sending bits of data — known as packets — over the Internet. They both build on top of the Internet protocol. In other words, whether you are sending a packet via TCP or UDP, that packet is sent to an IP address.

Is UDP faster than TCP?

A key difference between TCP and UDP is speed, as TCP is comparatively slower than UDP. Overall, UDP is a much faster, simpler, and efficient protocol, however, retransmission of lost data packets is only possible with TCP.

Where is UDP used?

UDP is commonly used for applications that are “lossy” (can handle some packet loss), such as streaming audio and video. It is also used for query-response applications, such as DNS queries.

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Send and Receive UDP packets via Linux CLI

We already know about two main transport layer protocols like TCP and UDP. For more information about TCP and UDP, you can check the reference section. In this article, we will learn how to send and receive UDP packets via the Linux command-line interface (CLI) using nc (mainly) command.

Expectations:

Here are the key points to learn from this article

1. To understand nc command in Linux.
2. Use nc command for sending and receiving UDP packets through network.
3. Send some human readable sentences through nc command.
4. Capture the UDP packet sent by nc command.
5. Check network packet in Wireshark.
6. 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

This is nc from the netcat-openbsd package. An alternative nc is available
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.

Start Server:

To start sever using nc command use below command in System B terminal

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.

Check Connection:

We can check the below command for the confirmation about client connation to server port.

Send UDP packets:

Now we can send udp packet from System A to B and vice versa.

Now go to system A and send any sentences like

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.

Go to System B and send sentence like

Here is the screenshot from System B

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 analyze the first communication:

System A has sent:

We 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

Other command to send UDP packets:

There is another method to send UDP packets

Run below command at System A:

$ echo -n «hello» >/ dev / udp / 192.168.1.102 / 8000
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:

About the author

Bamdeb Ghosh

Bamdeb Ghosh is having hands-on experience in Wireless networking domain.He’s an expert in Wireshark capture analysis on Wireless or Wired Networking along with knowledge of Android, Bluetooth, Linux commands and python. Follow his site: wifisharks.com

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Как отправить TCP или UDP пакет в Linux?

Часто при тестировании каких-либо приложений может возникнуть необходимость проверить, доходят ли определенные пакеты по udp/tcp до адресата, например, при проверке функционирования фаервола или же проверки работоспособности проброса портов. В данной статье будет описан простой способ это сделать с помощью командой строки.

Как отправить TCP пакет на определенный ip:порт в Linux

Для отправки tcp пакета на определенный IP адрес и определенный порт, можно воспользоваться следующей командой:

echo -n "test" >/dev/tcp/1.2.3.4/12345

1.2.3.4 — это IP адрес, на который мы будем посылать наш tcp пакет.
12345 — это порт, на который мы будем посылать наш tcp пакет Альтернативным вариантом может быть использование утилиты nmap:

sudo nmap -sT -p 12345 1.2.3.4

Как отправить UDP пакет на определенный ip:порт в Linux

Для отправки udp пакета на определенный IP адрес и определенный порт, можно воспользоваться следующей командой:

echo -n "test" >/dev/udp/1.2.3.4/12345

1.2.3.4 — это IP адрес, на который мы будем посылать наш udp пакет.
12345 — это порт, на который мы будем посылать наш udp пакет Альтернативным вариантом может быть использование утилиты nmap:

sudo nmap -sU -p 12345 1.2.3.4

Проверить получение tcp и udp пакетов на определенный порт на удаленном компьютере можно с помощью различных утилит, например, с помощью tcpdump.

tcpdump -i eth0 port 12345 -vvv -X

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