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// Other services

Port 4165: ArcLink over Ethernet

Port 4165 is assigned by IANA to altcp (ArcLink over Ethernet).

4165

How altcp works

Other services
client:4165altcpresponse client:4165altcpresponse

The client sends a request to port 4165 and the altcp 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 4165 dangerous?

We have no specific security note for port 4165. 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 4165

ServicePortTransportDescriptionReferenceUpdated
altcp 4165 TCP, UDP ArcLink over Ethernet - 2007-03

// source: IANA service name and port number registry

03 Check it

Which program uses port 4165, and is it reachable?

Linux

sudo ss -ltnup 'sport = :4165'      # process listening on 4165
sudo lsof -nP -i :4165

macOS

sudo lsof -nP -i :4165

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4165 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 4165
netstat -ano | findstr :4165

From another machine

nmap -p 4165 -sV <host>
sudo nmap -sU -p 4165 <host>
nc -zv <host> 4165

Block it in the firewall

sudo ufw deny 4165/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 4165" -Direction Inbound -LocalPort 4165 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 4165 used for?

Port 4165 is assigned by IANA to altcp (ArcLink over Ethernet).

Is port 4165 TCP or UDP?

Port 4165 is registered for TCP and UDP.

Is it safe to open port 4165?

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 4165 is open?

On Linux run "ss -ltnup 'sport = :4165'", on macOS "lsof -nP -i :4165", and on Windows "netstat -ano | findstr :4165" to see the local process. From another machine, "nmap -p 4165 <host>" shows whether it is reachable.

05 Related
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