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// Other services

Port 4011: Alternate Service Boot

Port 4011 is assigned by IANA to altserviceboot (Alternate Service Boot).

4011

How altserviceboot works

Other services
client:4011altservicebootresponse client:4011altservicebootresponse

The client sends a request to port 4011 and the altserviceboot 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 4011 dangerous?

We have no specific security note for port 4011. 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 4011

ServicePortTransportDescriptionReferenceUpdated
altserviceboot 4011 TCP, UDP Alternate Service Boot - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 4011, and is it reachable?

Linux

sudo ss -ltnup 'sport = :4011'      # process listening on 4011
sudo lsof -nP -i :4011

macOS

sudo lsof -nP -i :4011

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4011 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 4011
netstat -ano | findstr :4011

From another machine

nmap -p 4011 -sV <host>
sudo nmap -sU -p 4011 <host>
nc -zv <host> 4011

Block it in the firewall

sudo ufw deny 4011/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 4011" -Direction Inbound -LocalPort 4011 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 4011 used for?

Port 4011 is assigned by IANA to altserviceboot (Alternate Service Boot).

Is port 4011 TCP or UDP?

Port 4011 is registered for TCP and UDP.

Is it safe to open port 4011?

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 4011 is open?

On Linux run "ss -ltnup 'sport = :4011'", on macOS "lsof -nP -i :4011", and on Windows "netstat -ano | findstr :4011" to see the local process. From another machine, "nmap -p 4011 <host>" shows whether it is reachable.

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