Send a zero-I/O UDP port probe with netcat
Build a paste-ready command, then review its compatibility and effects before running it.
nc -vzu -w 3 <host> <port>Complete required fields to copy the generated command.
Compatibility
UDP is connectionlessA successful result does not prove that the application accepted or processed a datagram.
Operational knowledgereview due 2027-01-19
Requirementsncnc must be installed and available on PATH.Network accessThe target must be reachable from the current environment.
Version supportnc Current supported releasesVerified for linux, macos using posix, bash, zsh syntax; consult compatibility notes for platform-specific differences.
Expected signalsConnection to dns.example.com 53 port [udp/domain] succeeded!Representative successful output; values vary with the selected target and system state.
Known errorsnc: command not foundnc is missing or is not available on PATH.
Verifync -vzu -w 3 {{host}} {{port}}The output matches the expected target and exits without an error.Rollback noteNot required: this command is read-only and does not change system state.
Command breakdown
01ncCommandRuns the nc stage of this one-liner.
02-vzuOptionCombines verbose, zero-I/O scanning, and UDP mode for the probe.
03-wOptionStops connecting or waiting for network input after the given timeout.
05<host>ParameterA value supplied in the Fill parameters section.
06<port>ParameterA value supplied in the Fill parameters section.
Example input
nc -vzu -w 3 dns.example.com 53
Example output
Connection to dns.example.com 53 port [udp/domain] succeeded!
Illustrative output — exact values vary by system and data.
Official sources
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