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Port 191 (prospero)

IANA assigns port 191 to prospero: Prospero Directory Service.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
prospero TCP Prospero Directory Service B Clifford Neuman -
prospero UDP Prospero Directory Service B Clifford Neuman -

Check what is listening on port 191

Linux: is anything listening on TCP 191?
sudo ss -tlnp 'sport = :191'
Linux: UDP 191
sudo ss -ulnp 'sport = :191'
Linux / macOS: which process owns the port
sudo lsof -nP -i :191
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':191 '
Windows (Command Prompt)
netstat -ano | findstr :191
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 191 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 191
From Windows
Test-NetConnection HOST -Port 191
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 191

Block port 191 in the firewall

ufw
sudo ufw deny 191/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 191 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 191 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 191' -Direction Inbound -Protocol TCP -LocalPort 191 -Action Block
ufw
sudo ufw deny 191/udp
iptables
sudo iptables -A INPUT -p udp --dport 191 -j DROP
nftables
sudo nft add rule inet filter input udp dport 191 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 191' -Direction Inbound -Protocol UDP -LocalPort 191 -Action Block

Related ports

189qft190gacp192osu-nms193srmp

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