HTTPfy

Port 56 (xns-auth)

IANA assigns port 56 to xns-auth: XNS Authentication.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
xns-auth TCP XNS Authentication Susie Armstrong -
xns-auth UDP XNS Authentication Susie Armstrong -

Check what is listening on port 56

Linux: is anything listening on TCP 56?
sudo ss -tlnp 'sport = :56'
Linux: UDP 56
sudo ss -ulnp 'sport = :56'
Linux / macOS: which process owns the port
sudo lsof -nP -i :56
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':56 '
Windows (Command Prompt)
netstat -ano | findstr :56
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 56 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 56
From Windows
Test-NetConnection HOST -Port 56
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 56

Block port 56 in the firewall

ufw
sudo ufw deny 56/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 56 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 56 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 56' -Direction Inbound -Protocol TCP -LocalPort 56 -Action Block
ufw
sudo ufw deny 56/udp
iptables
sudo iptables -A INPUT -p udp --dport 56 -j DROP
nftables
sudo nft add rule inet filter input udp dport 56 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 56' -Direction Inbound -Protocol UDP -LocalPort 56 -Action Block

Related ports

54xns-ch55isi-gl57any private terminal access58xns-mail

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