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Port 93 (dcp)

IANA assigns port 93 to dcp: Device Control Protocol.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
dcp TCP Device Control Protocol Daniel Tappan -
dcp UDP Device Control Protocol Daniel Tappan -

Check what is listening on port 93

Linux: is anything listening on TCP 93?
sudo ss -tlnp 'sport = :93'
Linux: UDP 93
sudo ss -ulnp 'sport = :93'
Linux / macOS: which process owns the port
sudo lsof -nP -i :93
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':93 '
Windows (Command Prompt)
netstat -ano | findstr :93
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 93 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 93
From Windows
Test-NetConnection HOST -Port 93
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 93

Block port 93 in the firewall

ufw
sudo ufw deny 93/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 93 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 93 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 93' -Direction Inbound -Protocol TCP -LocalPort 93 -Action Block
ufw
sudo ufw deny 93/udp
iptables
sudo iptables -A INPUT -p udp --dport 93 -j DROP
nftables
sudo nft add rule inet filter input udp dport 93 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 93' -Direction Inbound -Protocol UDP -LocalPort 93 -Action Block

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