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Port 2721 (smart-diagnose)

IANA assigns port 2721 to smart-diagnose: Smart Diagnose.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
smart-diagnose TCP Smart Diagnose Geoffry Meek -
smart-diagnose UDP Smart Diagnose Geoffry Meek -

Check what is listening on port 2721

Linux: is anything listening on TCP 2721?
sudo ss -tlnp 'sport = :2721'
Linux: UDP 2721
sudo ss -ulnp 'sport = :2721'
Linux / macOS: which process owns the port
sudo lsof -nP -i :2721
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':2721 '
Windows (Command Prompt)
netstat -ano | findstr :2721
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 2721 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 2721
From Windows
Test-NetConnection HOST -Port 2721
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 2721

Block port 2721 in the firewall

ufw
sudo ufw deny 2721/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 2721 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 2721 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 2721' -Direction Inbound -Protocol TCP -LocalPort 2721 -Action Block
ufw
sudo ufw deny 2721/udp
iptables
sudo iptables -A INPUT -p udp --dport 2721 -j DROP
nftables
sudo nft add rule inet filter input udp dport 2721 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 2721' -Direction Inbound -Protocol UDP -LocalPort 2721 -Action Block

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