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// Other services

Port 261: IIOP Name Service over TLS/SSL

Port 261 is assigned by IANA to nsiiops (IIOP Name Service over TLS/SSL).

261

How nsiiops works

Other services
client:261#%&@!x9response? client:261#%&@!x9response?

The client sends a request to port 261 and the nsiiops service answers. Everything is encrypted: someone on the path only sees unreadable bytes.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
EncryptedTLS or built-in crypto
IANA status
Assigned1 registered service
Range
Well-known (0-1023)
Category
Other services
01 Security

Is port 261 dangerous?

We have no specific security note for port 261. 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 261

ServicePortTransportDescriptionReferenceUpdated
nsiiops 261 TCP, UDP IIOP Name Service over TLS/SSL - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 261, and is it reachable?

Linux

sudo ss -ltnup 'sport = :261'      # process listening on 261
sudo lsof -nP -i :261

macOS

sudo lsof -nP -i :261

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 261 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 261
netstat -ano | findstr :261

From another machine

nmap -p 261 -sV <host>
sudo nmap -sU -p 261 <host>
nc -zv <host> 261

Block it in the firewall

sudo ufw deny 261/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 261" -Direction Inbound -LocalPort 261 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 261 used for?

Port 261 is assigned by IANA to nsiiops (IIOP Name Service over TLS/SSL).

Is port 261 TCP or UDP?

Port 261 is registered for TCP and UDP.

Is it safe to open port 261?

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 261 is open?

On Linux run "ss -ltnup 'sport = :261'", on macOS "lsof -nP -i :261", and on Windows "netstat -ano | findstr :261" to see the local process. From another machine, "nmap -p 261 <host>" shows whether it is reachable.

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