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Port 1891 (childkey-notif)

IANA assigns port 1891 to childkey-notif: ChildKey Notification.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
childkey-notif TCP ChildKey Notification - -
childkey-notif UDP ChildKey Notification - -

Check what is listening on port 1891

Linux: is anything listening on TCP 1891?
sudo ss -tlnp 'sport = :1891'
Linux: UDP 1891
sudo ss -ulnp 'sport = :1891'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1891
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1891 '
Windows (Command Prompt)
netstat -ano | findstr :1891
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1891 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1891
From Windows
Test-NetConnection HOST -Port 1891
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1891

Block port 1891 in the firewall

ufw
sudo ufw deny 1891/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1891 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1891 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1891' -Direction Inbound -Protocol TCP -LocalPort 1891 -Action Block
ufw
sudo ufw deny 1891/udp
iptables
sudo iptables -A INPUT -p udp --dport 1891 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1891 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1891' -Direction Inbound -Protocol UDP -LocalPort 1891 -Action Block

Related ports

1889unify-adapter1890wilkenlistener1892childkey-ctrl1893elad

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.