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Port 3821 (pmcp)

IANA assigns port 3821 to pmcp: ATSC PMCP Standard.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
pmcp TCP ATSC PMCP Standard Graham Jones -
pmcp UDP ATSC PMCP Standard Graham Jones -

Registry dates for this port: registered 2004-11.

Check what is listening on port 3821

Linux: is anything listening on TCP 3821?
sudo ss -tlnp 'sport = :3821'
Linux: UDP 3821
sudo ss -ulnp 'sport = :3821'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3821
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3821 '
Windows (Command Prompt)
netstat -ano | findstr :3821
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3821 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3821
From Windows
Test-NetConnection HOST -Port 3821
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3821

Block port 3821 in the firewall

ufw
sudo ufw deny 3821/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3821 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3821 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3821' -Direction Inbound -Protocol TCP -LocalPort 3821 -Action Block
ufw
sudo ufw deny 3821/udp
iptables
sudo iptables -A INPUT -p udp --dport 3821 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3821 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3821' -Direction Inbound -Protocol UDP -LocalPort 3821 -Action Block

Related ports

3819epl-slp3820scp3822acp-discovery3823acp-conduit

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