CyberHunter
Local dataset, no network
// Other services

Port 3821: ATSC PMCP Standard

Port 3821 is assigned by IANA to pmcp (ATSC PMCP Standard).

3821

How pmcp works

Other services
client:3821pmcpresponse client:3821pmcpresponse

The client sends a request to port 3821 and the pmcp service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Other services
01 Security

Is port 3821 dangerous?

We have no specific security note for port 3821. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 3821

ServicePortTransportDescriptionReferenceUpdated
pmcp 3821 TCP, UDP ATSC PMCP Standard - 2004-11

// source: IANA service name and port number registry

03 Check it

Which program uses port 3821, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3821'      # process listening on 3821
sudo lsof -nP -i :3821

macOS

sudo lsof -nP -i :3821

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3821 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3821
netstat -ano | findstr :3821

From another machine

nmap -p 3821 -sV <host>
sudo nmap -sU -p 3821 <host>
nc -zv <host> 3821

Block it in the firewall

sudo ufw deny 3821/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3821" -Direction Inbound -LocalPort 3821 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3821 used for?

Port 3821 is assigned by IANA to pmcp (ATSC PMCP Standard).

Is port 3821 TCP or UDP?

Port 3821 is registered for TCP and UDP.

Is it safe to open port 3821?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Close the port if nothing on the host needs it.

How do I check if port 3821 is open?

On Linux run "ss -ltnup 'sport = :3821'", on macOS "lsof -nP -i :3821", and on Windows "netstat -ano | findstr :3821" to see the local process. From another machine, "nmap -p 3821 <host>" shows whether it is reachable.

05 Related
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp

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