CyberHunter
Local dataset, no network
// Other services

Port 3856: INFORMER

Port 3856 is assigned by IANA to informer (INFORMER).

3856

How informer works

Other services
client:3856informerresponse client:3856informerresponse

The client sends a request to port 3856 and the informer 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 3856 dangerous?

We have no specific security note for port 3856. 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 3856

ServicePortTransportDescriptionReferenceUpdated
informer 3856 TCP, UDP INFORMER - 2003-08

// source: IANA service name and port number registry

03 Check it

Which program uses port 3856, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3856'      # process listening on 3856
sudo lsof -nP -i :3856

macOS

sudo lsof -nP -i :3856

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3856 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3856
netstat -ano | findstr :3856

From another machine

nmap -p 3856 -sV <host>
sudo nmap -sU -p 3856 <host>
nc -zv <host> 3856

Block it in the firewall

sudo ufw deny 3856/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3856" -Direction Inbound -LocalPort 3856 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3856 used for?

Port 3856 is assigned by IANA to informer (INFORMER).

Is port 3856 TCP or UDP?

Port 3856 is registered for TCP and UDP.

Is it safe to open port 3856?

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 3856 is open?

On Linux run "ss -ltnup 'sport = :3856'", on macOS "lsof -nP -i :3856", and on Windows "netstat -ano | findstr :3856" to see the local process. From another machine, "nmap -p 3856 <host>" shows whether it is reachable.

05 Related
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