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Port 522 (ulp)

IANA assigns port 522 to ulp: ULP.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
ulp TCP ULP Max Morris -
ulp UDP ULP Max Morris -

Check what is listening on port 522

Linux: is anything listening on TCP 522?
sudo ss -tlnp 'sport = :522'
Linux: UDP 522
sudo ss -ulnp 'sport = :522'
Linux / macOS: which process owns the port
sudo lsof -nP -i :522
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':522 '
Windows (Command Prompt)
netstat -ano | findstr :522
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 522 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 522
From Windows
Test-NetConnection HOST -Port 522
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 522

Block port 522 in the firewall

ufw
sudo ufw deny 522/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 522 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 522 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 522' -Direction Inbound -Protocol TCP -LocalPort 522 -Action Block
ufw
sudo ufw deny 522/udp
iptables
sudo iptables -A INPUT -p udp --dport 522 -j DROP
nftables
sudo nft add rule inet filter input udp dport 522 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 522' -Direction Inbound -Protocol UDP -LocalPort 522 -Action Block

Related ports

520efs, router521ripng523ibm-db2524ncp

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