- 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 91: MIT Dover Spooler
Port 91 is assigned by IANA to mit-dov (MIT Dover Spooler).
91
How mit-dov works
Other servicesThe client sends a request to port 91 and the mit-dov 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 91 dangerous?
We have no specific security note for port 91. Its risk depends on the program actually listening on it. General advice for other services services:
IANA registry entries for port 91
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| mit-dov | 91 | TCP, UDP | MIT Dover Spooler | - | - |
// source: IANA service name and port number registry
Which program uses port 91, and is it reachable?
Linux
sudo ss -ltnup 'sport = :91' # process listening on 91
sudo lsof -nP -i :91macOS
sudo lsof -nP -i :91
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 91 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 91 netstat -ano | findstr :91
From another machine
nmap -p 91 -sV <host> sudo nmap -sU -p 91 <host> nc -zv <host> 91
Block it in the firewall
sudo ufw deny 91/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 91" -Direction Inbound -LocalPort 91 -Protocol TCP -Action Block # Windows
What is port 91 used for?
Port 91 is assigned by IANA to mit-dov (MIT Dover Spooler).
Is port 91 TCP or UDP?
Port 91 is registered for TCP and UDP.
Is it safe to open port 91?
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 91 is open?
On Linux run "ss -ltnup 'sport = :91'", on macOS "lsof -nP -i :91", and on Windows "netstat -ano | findstr :91" to see the local process. From another machine, "nmap -p 91 <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