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Port 65 (tacacs-ds)

IANA assigns port 65 to tacacs-ds: TACACS-Database Service.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
tacacs-ds TCP TACACS-Database Service Kathy Huber -
tacacs-ds UDP TACACS-Database Service Kathy Huber -

Check what is listening on port 65

Linux: is anything listening on TCP 65?
sudo ss -tlnp 'sport = :65'
Linux: UDP 65
sudo ss -ulnp 'sport = :65'
Linux / macOS: which process owns the port
sudo lsof -nP -i :65
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':65 '
Windows (Command Prompt)
netstat -ano | findstr :65
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 65 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 65
From Windows
Test-NetConnection HOST -Port 65
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 65

Block port 65 in the firewall

ufw
sudo ufw deny 65/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 65 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 65 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 65' -Direction Inbound -Protocol TCP -LocalPort 65 -Action Block
ufw
sudo ufw deny 65/udp
iptables
sudo iptables -A INPUT -p udp --dport 65 -j DROP
nftables
sudo nft add rule inet filter input udp dport 65 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 65' -Direction Inbound -Protocol UDP -LocalPort 65 -Action Block

Related ports

63whoispp, whois++64covia66sql-net, sql*net67DHCP server (BOOTP)

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