How to test udp port

Test if the udp port is open

Article overview: How to test the remote UDP port, we generally use the TCP port for the application service, but in some cases, we also need to open the UDP port. This article briefly describes how to test whether the UDP port is normal?

Everyone knows the TCP port. For example, port 80 can use telnet ip 80 to verify whether the port is listening properly. Can the UDP port be tested the same? The details are as follows:

Let's test it. Port 123 is the UDP port opened by the server 42.11.12.13.

Udp 0 0 42.11.12.13:123 0.0.0.0:* 1472/ntpd

1. We first use telnet connection, as follows

[root@kr-sg-test ~]# telnet 42.11.12.13 123

Trying 42.11.12.13...

Telnet: connect to address 42.11.12.13: ConnecTIon refused

Telnet: Unable to connect to remote host: ConnecTIon refused

Obviously, the telnet connection was rejected and could not be tested successfully.

2. We use nc to test, as follows

[root@kr-sg-test ~]# nc -vuz 42.11.12.13 123

ConnecTIon to 42.11.12.13 123 port [udp/ntp] succeeded!

The result proves that the UDP 123 port is listening normally.

Nc command usage:

Usage: nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port]

[-s source_ip_address] [-T ToS] [-w TImeout] [-X proxy_version]

[-x proxy_address[:port]] [hostname] [port[s]]

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