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// Other services

Port 1891: ChildKey Notification

Port 1891 is assigned by IANA to childkey-notif (ChildKey Notification).

1891

How childkey-notif works

Other services
client:1891childkey-notifresponse client:1891childkey-notifresponse

The client sends a request to port 1891 and the childkey-notif 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 1891 dangerous?

We have no specific security note for port 1891. 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 1891

ServicePortTransportDescriptionReferenceUpdated
childkey-notif 1891 TCP, UDP ChildKey Notification - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1891, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1891'      # process listening on 1891
sudo lsof -nP -i :1891

macOS

sudo lsof -nP -i :1891

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1891 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1891
netstat -ano | findstr :1891

From another machine

nmap -p 1891 -sV <host>
sudo nmap -sU -p 1891 <host>
nc -zv <host> 1891

Block it in the firewall

sudo ufw deny 1891/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1891" -Direction Inbound -LocalPort 1891 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1891 used for?

Port 1891 is assigned by IANA to childkey-notif (ChildKey Notification).

Is port 1891 TCP or UDP?

Port 1891 is registered for TCP and UDP.

Is it safe to open port 1891?

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 1891 is open?

On Linux run "ss -ltnup 'sport = :1891'", on macOS "lsof -nP -i :1891", and on Windows "netstat -ano | findstr :1891" to see the local process. From another machine, "nmap -p 1891 <host>" shows whether it is reachable.

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