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// Other services

Port 90: DNSIX Securit Attribute Token Map

Port 90 is assigned by IANA to dnsix (DNSIX Securit Attribute Token Map).

90

How dnsix works

Other services
client:90dnsixresponse client:90dnsixresponse

The client sends a request to port 90 and the dnsix 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
Well-known (0-1023)
Category
Other services
01 Security

Is port 90 dangerous?

We have no specific security note for port 90. 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 90

ServicePortTransportDescriptionReferenceUpdated
dnsix 90 TCP, UDP DNSIX Securit Attribute Token Map
Reported: PORT 90 also being used unofficially by Pointcast
 - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 90, and is it reachable?

Linux

sudo ss -ltnup 'sport = :90'      # process listening on 90
sudo lsof -nP -i :90

macOS

sudo lsof -nP -i :90

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 90 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 90
netstat -ano | findstr :90

From another machine

nmap -p 90 -sV <host>
sudo nmap -sU -p 90 <host>
nc -zv <host> 90

Block it in the firewall

sudo ufw deny 90/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 90" -Direction Inbound -LocalPort 90 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 90 used for?

Port 90 is assigned by IANA to dnsix (DNSIX Securit Attribute Token Map).

Is port 90 TCP or UDP?

Port 90 is registered for TCP and UDP.

Is it safe to open port 90?

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 90 is open?

On Linux run "ss -ltnup 'sport = :90'", on macOS "lsof -nP -i :90", and on Windows "netstat -ano | findstr :90" to see the local process. From another machine, "nmap -p 90 <host>" shows whether it is reachable.

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