HTTPfy

Port 4841 (quosa)

IANA assigns port 4841 to quosa: QUOSA Virtual Library Service.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
quosa TCP QUOSA Virtual Library Service Uri Blank -
quosa UDP QUOSA Virtual Library Service Uri Blank -

Registry dates for this port: registered 2006-09.

Check what is listening on port 4841

Linux: is anything listening on TCP 4841?
sudo ss -tlnp 'sport = :4841'
Linux: UDP 4841
sudo ss -ulnp 'sport = :4841'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4841
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4841 '
Windows (Command Prompt)
netstat -ano | findstr :4841
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4841 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4841
From Windows
Test-NetConnection HOST -Port 4841
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4841

Block port 4841 in the firewall

ufw
sudo ufw deny 4841/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4841 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4841 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4841' -Direction Inbound -Protocol TCP -LocalPort 4841 -Action Block
ufw
sudo ufw deny 4841/udp
iptables
sudo iptables -A INPUT -p udp --dport 4841 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4841 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4841' -Direction Inbound -Protocol UDP -LocalPort 4841 -Action Block

Related ports

4839varadero-24840opcua-tcp, opcua-udp4842gw-asv4843opcua-tls

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