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// Other services

Port 3876: DirectoryLockdown Agent

Port 3876 is assigned by IANA to dl_agent (DirectoryLockdown Agent), dl-agent (DirectoryLockdown Agent IANA assigned this well-formed service name as a replacement for "dl_agent".).

3876

How dl_agent works

Other services
client:3876dl_agentresponse client:3876dl_agentresponse

The client sends a request to port 3876 and the dl_agent service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned2 registered services
Range
Registered (1024-49151)
Category
Other services
01 Security

Is port 3876 dangerous?

We have no specific security note for port 3876. 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 3876

ServicePortTransportDescriptionReferenceUpdated
dl_agent 3876 TCP, UDP DirectoryLockdown Agent - 2008-12-16
dl-agent 3876 TCP, UDP DirectoryLockdown Agent IANA assigned this well-formed service name as a replacement for "dl_agent". - 2008-12-16

// source: IANA service name and port number registry

03 Check it

Which program uses port 3876, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3876'      # process listening on 3876
sudo lsof -nP -i :3876

macOS

sudo lsof -nP -i :3876

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3876 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3876
netstat -ano | findstr :3876

From another machine

nmap -p 3876 -sV <host>
sudo nmap -sU -p 3876 <host>
nc -zv <host> 3876

Block it in the firewall

sudo ufw deny 3876/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3876" -Direction Inbound -LocalPort 3876 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3876 used for?

Port 3876 is assigned by IANA to dl_agent (DirectoryLockdown Agent), dl-agent (DirectoryLockdown Agent IANA assigned this well-formed service name as a replacement for "dl_agent".).

Is port 3876 TCP or UDP?

Port 3876 is registered for TCP and UDP.

Is it safe to open port 3876?

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 3876 is open?

On Linux run "ss -ltnup 'sport = :3876'", on macOS "lsof -nP -i :3876", and on Windows "netstat -ano | findstr :3876" to see the local process. From another machine, "nmap -p 3876 <host>" shows whether it is reachable.

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