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// Directory & authentication

Port 2821: VERITAS Authentication Service

Port 2821 is assigned by IANA to vrts-at-port (VERITAS Authentication Service).

2821

How vrts-at-port works

Directory & authentication
userdirectoryvrts-at-portresponse userdirectoryvrts-at-portresponse

The client proves who it is on port 2821 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 2821 dangerous?

We have no specific security note for port 2821. 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 2821

ServicePortTransportDescriptionReferenceUpdated
vrts-at-port 2821 TCP, UDP VERITAS Authentication Service - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 2821, and is it reachable?

Linux

sudo ss -ltnup 'sport = :2821'      # process listening on 2821
sudo lsof -nP -i :2821

macOS

sudo lsof -nP -i :2821

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 2821 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 2821
netstat -ano | findstr :2821

From another machine

nmap -p 2821 -sV <host>
sudo nmap -sU -p 2821 <host>
nc -zv <host> 2821

Block it in the firewall

sudo ufw deny 2821/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 2821" -Direction Inbound -LocalPort 2821 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 2821 used for?

Port 2821 is assigned by IANA to vrts-at-port (VERITAS Authentication Service).

Is port 2821 TCP or UDP?

Port 2821 is registered for TCP and UDP.

Is it safe to open port 2821?

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 2821 is open?

On Linux run "ss -ltnup 'sport = :2821'", on macOS "lsof -nP -i :2821", and on Windows "netstat -ano | findstr :2821" to see the local process. From another machine, "nmap -p 2821 <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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