- 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 43: Who Is
Port 43 is assigned by IANA to nicname (Who Is).
43
How nicname works
Other servicesThe client sends a request to port 43 and the nicname service answers.
- Transport
- TCP · UDP
- Exposure risk
- not rated depends on the program listening
- Encryption
- Unknownnot stated by the registry
- IANA status
- Assigned1 registered service
- Range
- Well-known (0-1023)
- Category
- Other services
Is port 43 dangerous?
We have no specific security note for port 43. Its risk depends on the program actually listening on it. General advice for other services services:
IANA registry entries for port 43
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| nicname | 43 | TCP, UDP | Who Is | - | - |
// source: IANA service name and port number registry
Which program uses port 43, and is it reachable?
Linux
sudo ss -ltnup 'sport = :43' # process listening on 43
sudo lsof -nP -i :43macOS
sudo lsof -nP -i :43
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 43 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 43 netstat -ano | findstr :43
From another machine
nmap -p 43 -sV <host> sudo nmap -sU -p 43 <host> nc -zv <host> 43
Block it in the firewall
sudo ufw deny 43/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 43" -Direction Inbound -LocalPort 43 -Protocol TCP -Action Block # Windows
What is port 43 used for?
Port 43 is assigned by IANA to nicname (Who Is).
Is port 43 TCP or UDP?
Port 43 is registered for TCP and UDP.
Is it safe to open port 43?
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 43 is open?
On Linux run "ss -ltnup 'sport = :43'", on macOS "lsof -nP -i :43", and on Windows "netstat -ano | findstr :43" to see the local process. From another machine, "nmap -p 43 <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