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Port 5721 (dtpt)

IANA assigns port 5721 to dtpt: Desktop Passthru Service.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
dtpt TCP Desktop Passthru Service Dan Leising -
dtpt UDP Desktop Passthru Service Dan Leising -

Registry dates for this port: registered 2005-01.

Check what is listening on port 5721

Linux: is anything listening on TCP 5721?
sudo ss -tlnp 'sport = :5721'
Linux: UDP 5721
sudo ss -ulnp 'sport = :5721'
Linux / macOS: which process owns the port
sudo lsof -nP -i :5721
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':5721 '
Windows (Command Prompt)
netstat -ano | findstr :5721
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5721 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 5721
From Windows
Test-NetConnection HOST -Port 5721
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 5721

Block port 5721 in the firewall

ufw
sudo ufw deny 5721/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 5721 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 5721 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 5721' -Direction Inbound -Protocol TCP -LocalPort 5721 -Action Block
ufw
sudo ufw deny 5721/udp
iptables
sudo iptables -A INPUT -p udp --dport 5721 -j DROP
nftables
sudo nft add rule inet filter input udp dport 5721 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 5721' -Direction Inbound -Protocol UDP -LocalPort 5721 -Action Block

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5719dpm-agent5720ms-licensing5722msdfsr5723omhs

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