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Port 9951 (apc-9951)

IANA assigns port 9951 to apc-9951: APC 9951.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
apc-9951 TCP APC 9951 American Power Conve -
apc-9951 UDP APC 9951 American Power Conve -

Check what is listening on port 9951

Linux: is anything listening on TCP 9951?
sudo ss -tlnp 'sport = :9951'
Linux: UDP 9951
sudo ss -ulnp 'sport = :9951'
Linux / macOS: which process owns the port
sudo lsof -nP -i :9951
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':9951 '
Windows (Command Prompt)
netstat -ano | findstr :9951
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 9951 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 9951
From Windows
Test-NetConnection HOST -Port 9951
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 9951

Block port 9951 in the firewall

ufw
sudo ufw deny 9951/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 9951 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 9951 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 9951' -Direction Inbound -Protocol TCP -LocalPort 9951 -Action Block
ufw
sudo ufw deny 9951/udp
iptables
sudo iptables -A INPUT -p udp --dport 9951 -j DROP
nftables
sudo nft add rule inet filter input udp dport 9951 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 9951' -Direction Inbound -Protocol UDP -LocalPort 9951 -Action Block

Related ports

9925xybrid-cloud9950apc-99509952apc-99529953acis

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