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Port 553 (pirp)

IANA assigns port 553 to pirp.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
pirp TCP pirp D J Bernstein -
pirp UDP pirp D J Bernstein -

Check what is listening on port 553

Linux: is anything listening on TCP 553?
sudo ss -tlnp 'sport = :553'
Linux: UDP 553
sudo ss -ulnp 'sport = :553'
Linux / macOS: which process owns the port
sudo lsof -nP -i :553
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':553 '
Windows (Command Prompt)
netstat -ano | findstr :553
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 553 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 553
From Windows
Test-NetConnection HOST -Port 553
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 553

Block port 553 in the firewall

ufw
sudo ufw deny 553/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 553 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 553 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 553' -Direction Inbound -Protocol TCP -LocalPort 553 -Action Block
ufw
sudo ufw deny 553/udp
iptables
sudo iptables -A INPUT -p udp --dport 553 -j DROP
nftables
sudo nft add rule inet filter input udp dport 553 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 553' -Direction Inbound -Protocol UDP -LocalPort 553 -Action Block

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