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Port 5420 (cylink-c)

IANA assigns port 5420 to cylink-c: Cylink-C.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
cylink-c TCP Cylink-C John Jobe -
cylink-c UDP Cylink-C John Jobe -

Check what is listening on port 5420

Linux: is anything listening on TCP 5420?
sudo ss -tlnp 'sport = :5420'
Linux: UDP 5420
sudo ss -ulnp 'sport = :5420'
Linux / macOS: which process owns the port
sudo lsof -nP -i :5420
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':5420 '
Windows (Command Prompt)
netstat -ano | findstr :5420
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5420 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 5420
From Windows
Test-NetConnection HOST -Port 5420
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 5420

Block port 5420 in the firewall

ufw
sudo ufw deny 5420/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 5420 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 5420 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 5420' -Direction Inbound -Protocol TCP -LocalPort 5420 -Action Block
ufw
sudo ufw deny 5420/udp
iptables
sudo iptables -A INPUT -p udp --dport 5420 -j DROP
nftables
sudo nft add rule inet filter input udp dport 5420 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 5420' -Direction Inbound -Protocol UDP -LocalPort 5420 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.