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// Other services

Port 187: Application Communication Interface

Port 187 is assigned by IANA to aci (Application Communication Interface).

187

How aci works

Other services
client:187aciresponse client:187aciresponse

The client sends a request to port 187 and the aci 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 187 dangerous?

We have no specific security note for port 187. 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 187

ServicePortTransportDescriptionReferenceUpdated
aci 187 TCP, UDP Application Communication Interface - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 187, and is it reachable?

Linux

sudo ss -ltnup 'sport = :187'      # process listening on 187
sudo lsof -nP -i :187

macOS

sudo lsof -nP -i :187

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 187 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 187
netstat -ano | findstr :187

From another machine

nmap -p 187 -sV <host>
sudo nmap -sU -p 187 <host>
nc -zv <host> 187

Block it in the firewall

sudo ufw deny 187/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 187" -Direction Inbound -LocalPort 187 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 187 used for?

Port 187 is assigned by IANA to aci (Application Communication Interface).

Is port 187 TCP or UDP?

Port 187 is registered for TCP and UDP.

Is it safe to open port 187?

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 187 is open?

On Linux run "ss -ltnup 'sport = :187'", on macOS "lsof -nP -i :187", and on Windows "netstat -ano | findstr :187" to see the local process. From another machine, "nmap -p 187 <host>" shows whether it is reachable.

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