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Port 4051 (cppdp)

IANA assigns port 4051 to cppdp: Cisco Peer to Peer Distribution Protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
cppdp TCP Cisco Peer to Peer Distribution Protocol Susan Sauter -
cppdp UDP Cisco Peer to Peer Distribution Protocol Susan Sauter -

Registry dates for this port: registered 2006-07.

Check what is listening on port 4051

Linux: is anything listening on TCP 4051?
sudo ss -tlnp 'sport = :4051'
Linux: UDP 4051
sudo ss -ulnp 'sport = :4051'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4051
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4051 '
Windows (Command Prompt)
netstat -ano | findstr :4051
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4051 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4051
From Windows
Test-NetConnection HOST -Port 4051
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4051

Block port 4051 in the firewall

ufw
sudo ufw deny 4051/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4051 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4051 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4051' -Direction Inbound -Protocol TCP -LocalPort 4051 -Action Block
ufw
sudo ufw deny 4051/udp
iptables
sudo iptables -A INPUT -p udp --dport 4051 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4051 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4051' -Direction Inbound -Protocol UDP -LocalPort 4051 -Action Block

Related ports

4049wafs4050cisco-wafs4052interact4053ccu-comm-1

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