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oam/knowledge base/nmap's netcat.md
2025-11-21 23:02:37 +01:00

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# Nmap's netcat
1. [TL;DR](#tldr)
1. [Further readings](#further-readings)
1. [Sources](#sources)
## TL;DR
Options of interest:
| Option | Summary |
| ------------------- | --------------------------------------------------------------------------------- |
| `-l`, `--listen` | bind to the port given in input and listen for incoming connections (server mode) |
| `-k`, `--keep-open` | accept multiple connections in listen mode |
| `-n`, `--nodns` | do not resolve hostnames via DNS |
| `-p` | specify the source port to use |
| `-t` | use telnet negotiation |
| `-u` | use UDP |
| `-v` | set verbosity level; can be used several times |
| `-w=SECS` | timeout for connects and final net reads, in seconds |
| `-z` | zero-I/O mode, exit once connected |
```sh
# Install
brew install 'nmap'
dnf install 'nmap-ncat'
yum install 'nmap-ncat'
# Check ports on hosts.
nc -Nnvz 192.168.0.81 22-25
nc -Nvz host.name 443
nc -Nvz -u dns.server 123
# List hosts with a specific port open.
# But you might just want to use `nmap`.
parallel -j 0 "nc -Nnvz -w 2 192.168.0.{} 22 2>&1" ::: {2..254} \
| grep -v "timed out"
# Wait for a host to be up.
until nc -Nvz -w 3 pi.lan 22; do sleep 3; done
# Server mode.
nc -l 5666
nc -lk 8080
```
## Further readings
### Sources
- [How To use Netcat to establish and test TCP and UDP connections]
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[how to use netcat to establish and test tcp and udp connections]: https://www.digitalocean.com/community/tutorials/how-to-use-netcat-to-establish-and-test-tcp-and-udp-connections