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Port 91 (mit-dov)

IANA assigns port 91 to mit-dov: MIT Dover Spooler.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
mit-dov TCP MIT Dover Spooler Eliot Moss -
mit-dov UDP MIT Dover Spooler Eliot Moss -

Check what is listening on port 91

Linux: is anything listening on TCP 91?
sudo ss -tlnp 'sport = :91'
Linux: UDP 91
sudo ss -ulnp 'sport = :91'
Linux / macOS: which process owns the port
sudo lsof -nP -i :91
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':91 '
Windows (Command Prompt)
netstat -ano | findstr :91
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 91 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 91
From Windows
Test-NetConnection HOST -Port 91
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 91

Block port 91 in the firewall

ufw
sudo ufw deny 91/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 91 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 91 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 91' -Direction Inbound -Protocol TCP -LocalPort 91 -Action Block
ufw
sudo ufw deny 91/udp
iptables
sudo iptables -A INPUT -p udp --dport 91 -j DROP
nftables
sudo nft add rule inet filter input udp dport 91 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 91' -Direction Inbound -Protocol UDP -LocalPort 91 -Action Block

Related ports

89su-mit-tg90dnsix92npp93dcp

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.