HTTPfy

Port 516 (videotex)

IANA assigns port 516 to videotex.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
videotex TCP videotex Daniel Mavrakis -
videotex UDP videotex Daniel Mavrakis -

Check what is listening on port 516

Linux: is anything listening on TCP 516?
sudo ss -tlnp 'sport = :516'
Linux: UDP 516
sudo ss -ulnp 'sport = :516'
Linux / macOS: which process owns the port
sudo lsof -nP -i :516
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':516 '
Windows (Command Prompt)
netstat -ano | findstr :516
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 516 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 516
From Windows
Test-NetConnection HOST -Port 516
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 516

Block port 516 in the firewall

ufw
sudo ufw deny 516/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 516 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 516 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 516' -Direction Inbound -Protocol TCP -LocalPort 516 -Action Block
ufw
sudo ufw deny 516/udp
iptables
sudo iptables -A INPUT -p udp --dport 516 -j DROP
nftables
sudo nft add rule inet filter input udp dport 516 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 516' -Direction Inbound -Protocol UDP -LocalPort 516 -Action Block

Related ports

514Syslog (UDP) / rsh (TCP)515LPD / LPR517talk519utime

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