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// Directory & authentication

Port 4043: Neighbour Identity Resolution

Port 4043 is assigned by IANA to nirp (Neighbour Identity Resolution).

4043

How nirp works

Directory & authentication
userdirectorynirpresponse userdirectorynirpresponse

The client proves who it is on port 4043 and gets an answer (or a ticket) it can use with other services.

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
Directory & authentication
01 Security

Is port 4043 dangerous?

We have no specific security note for port 4043. Its risk depends on the program actually listening on it. General advice for directory & authentication services:

  • Keep directory and authentication services on internal networks.
  • Require signing or TLS and disable anonymous queries.
  • Monitor authentication failures for spraying and brute force.
02 Registry

IANA registry entries for port 4043

ServicePortTransportDescriptionReferenceUpdated
nirp 4043 TCP, UDP Neighbour Identity Resolution - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 4043, and is it reachable?

Linux

sudo ss -ltnup 'sport = :4043'      # process listening on 4043
sudo lsof -nP -i :4043

macOS

sudo lsof -nP -i :4043

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4043 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 4043
netstat -ano | findstr :4043

From another machine

nmap -p 4043 -sV <host>
sudo nmap -sU -p 4043 <host>
nc -zv <host> 4043

Block it in the firewall

sudo ufw deny 4043/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 4043" -Direction Inbound -LocalPort 4043 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 4043 used for?

Port 4043 is assigned by IANA to nirp (Neighbour Identity Resolution).

Is port 4043 TCP or UDP?

Port 4043 is registered for TCP and UDP.

Is it safe to open port 4043?

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. Keep directory and authentication services on internal networks.

How do I check if port 4043 is open?

On Linux run "ss -ltnup 'sport = :4043'", on macOS "lsof -nP -i :4043", and on Windows "netstat -ano | findstr :4043" to see the local process. From another machine, "nmap -p 4043 <host>" shows whether it is reachable.

05 Related
:389 LDAP tcp · udp · high risk :636 LDAPS tcp · udp · moderate risk :88 Kerberos tcp · udp · high risk :3268 Global Catalog (LDAP) tcp · udp · high risk :1812 RADIUS udp · tcp · moderate risk :31 MSG Authentication tcp · udp :49 Login Host Protocol (TACACS) tcp · udp :56 XNS Authentication tcp · udp

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