- Close the port if nothing on the host needs it.
- Identify the process that listens on it (commands below) before opening it in a firewall.
- Expose a service only to the networks that use it.
Port 42: Host Name Server
Port 42 is assigned by IANA to name (Host Name Server), nameserver (Host Name Server).
42
How name works
Other servicesThe client sends a request to port 42 and the name service answers.
- Transport
- TCP · UDP
- Exposure risk
- not rated depends on the program listening
- Encryption
- Unknownnot stated by the registry
- IANA status
- Assigned2 registered services
- Range
- Well-known (0-1023)
- Category
- Other services
Is port 42 dangerous?
We have no specific security note for port 42. Its risk depends on the program actually listening on it. General advice for other services services:
IANA registry entries for port 42
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| name | 42 | TCP, UDP | Host Name Server | - | - |
| nameserver | 42 | TCP, UDP | Host Name Server | - | - |
// source: IANA service name and port number registry
Which program uses port 42, and is it reachable?
Linux
sudo ss -ltnup 'sport = :42' # process listening on 42
sudo lsof -nP -i :42macOS
sudo lsof -nP -i :42
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 42 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 42 netstat -ano | findstr :42
From another machine
nmap -p 42 -sV <host> sudo nmap -sU -p 42 <host> nc -zv <host> 42
Block it in the firewall
sudo ufw deny 42/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 42" -Direction Inbound -LocalPort 42 -Protocol TCP -Action Block # Windows
What is port 42 used for?
Port 42 is assigned by IANA to name (Host Name Server), nameserver (Host Name Server).
Is port 42 TCP or UDP?
Port 42 is registered for TCP and UDP.
Is it safe to open port 42?
It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Close the port if nothing on the host needs it.
How do I check if port 42 is open?
On Linux run "ss -ltnup 'sport = :42'", on macOS "lsof -nP -i :42", and on Windows "netstat -ano | findstr :42" to see the local process. From another machine, "nmap -p 42 <host>" shows whether it is reachable.
Other other services ports
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp