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// Other services

Port 2661: OLHOST

Port 2661 is assigned by IANA to olhost (OLHOST).

2661

How olhost works

Other services
client:2661olhostresponse client:2661olhostresponse

The client sends a request to port 2661 and the olhost 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 2661 dangerous?

We have no specific security note for port 2661. 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 2661

ServicePortTransportDescriptionReferenceUpdated
olhost 2661 TCP, UDP OLHOST - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 2661, and is it reachable?

Linux

sudo ss -ltnup 'sport = :2661'      # process listening on 2661
sudo lsof -nP -i :2661

macOS

sudo lsof -nP -i :2661

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 2661 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 2661
netstat -ano | findstr :2661

From another machine

nmap -p 2661 -sV <host>
sudo nmap -sU -p 2661 <host>
nc -zv <host> 2661

Block it in the firewall

sudo ufw deny 2661/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 2661" -Direction Inbound -LocalPort 2661 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 2661 used for?

Port 2661 is assigned by IANA to olhost (OLHOST).

Is port 2661 TCP or UDP?

Port 2661 is registered for TCP and UDP.

Is it safe to open port 2661?

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 2661 is open?

On Linux run "ss -ltnup 'sport = :2661'", on macOS "lsof -nP -i :2661", and on Windows "netstat -ano | findstr :2661" to see the local process. From another machine, "nmap -p 2661 <host>" shows whether it is reachable.

05 Related
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