HTTPfy

Port 4991 (vrt)

IANA assigns port 4991 to vrt: VITA Radio Transport.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
vrt TCP VITA Radio Transport Sam Bretheim -
vrt UDP VITA Radio Transport Sam Bretheim -

Registry dates for this port: registered 2009-01-08.

Check what is listening on port 4991

Linux: is anything listening on TCP 4991?
sudo ss -tlnp 'sport = :4991'
Linux: UDP 4991
sudo ss -ulnp 'sport = :4991'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4991
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4991 '
Windows (Command Prompt)
netstat -ano | findstr :4991
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4991 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4991
From Windows
Test-NetConnection HOST -Port 4991
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4991

Block port 4991 in the firewall

ufw
sudo ufw deny 4991/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4991 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4991 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4991' -Direction Inbound -Protocol TCP -LocalPort 4991 -Action Block
ufw
sudo ufw deny 4991/udp
iptables
sudo iptables -A INPUT -p udp --dport 4991 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4991 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4991' -Direction Inbound -Protocol UDP -LocalPort 4991 -Action Block

Related ports

4989parallel4990busycal4999hfcs-manager5002rfe

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