HTTPfy

Port 52 (xns-time)

IANA assigns port 52 to xns-time: XNS Time Protocol.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
xns-time TCP XNS Time Protocol Susie Armstrong -
xns-time UDP XNS Time Protocol Susie Armstrong -

Check what is listening on port 52

Linux: is anything listening on TCP 52?
sudo ss -tlnp 'sport = :52'
Linux: UDP 52
sudo ss -ulnp 'sport = :52'
Linux / macOS: which process owns the port
sudo lsof -nP -i :52
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':52 '
Windows (Command Prompt)
netstat -ano | findstr :52
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 52 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 52
From Windows
Test-NetConnection HOST -Port 52
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 52

Block port 52 in the firewall

ufw
sudo ufw deny 52/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 52 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 52 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 52' -Direction Inbound -Protocol TCP -LocalPort 52 -Action Block
ufw
sudo ufw deny 52/udp
iptables
sudo iptables -A INPUT -p udp --dport 52 -j DROP
nftables
sudo nft add rule inet filter input udp dport 52 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 52' -Direction Inbound -Protocol UDP -LocalPort 52 -Action Block

Related ports

49TACACS+50re-mail-ck53DNS54xns-ch

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