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// Databases & caches

Port 66: Oracle SQL*NET IANA assigned this well-formed service name as a replacement for "sql*net".

Port 66 is assigned by IANA to sql-net (Oracle SQL*NET IANA assigned this well-formed service name as a replacement for "sql*net".), sql*net (Oracle SQL*NET).

66

How sql-net works

Databases & caches
app:66sql-net app:66sql-net

The application sends a SQL query to the sql-net server on port 66, which returns rows from its tables.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned2 registered services
Range
Well-known (0-1023)
Category
Databases & caches
01 Security

Is port 66 dangerous?

We have no specific security note for port 66. Its risk depends on the program actually listening on it. General advice for databases & caches services:

  • Bind the service to localhost or a private network, never to a public address.
  • Enable authentication, use per-application accounts and require TLS.
  • Watch for exposed Docker ports: publish them on 127.0.0.1 only.
02 Registry

IANA registry entries for port 66

ServicePortTransportDescriptionReferenceUpdated
sql-net 66 TCP, UDP Oracle SQL*NET IANA assigned this well-formed service name as a replacement for "sql*net". - -
sql*net 66 TCP, UDP Oracle SQL*NET - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 66, and is it reachable?

Linux

sudo ss -ltnup 'sport = :66'      # process listening on 66
sudo lsof -nP -i :66

macOS

sudo lsof -nP -i :66

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 66 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 66
netstat -ano | findstr :66

From another machine

nmap -p 66 -sV <host>
sudo nmap -sU -p 66 <host>
nc -zv <host> 66

Block it in the firewall

sudo ufw deny 66/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 66" -Direction Inbound -LocalPort 66 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 66 used for?

Port 66 is assigned by IANA to sql-net (Oracle SQL*NET IANA assigned this well-formed service name as a replacement for "sql*net".), sql*net (Oracle SQL*NET).

Is port 66 TCP or UDP?

Port 66 is registered for TCP and UDP.

Is it safe to open port 66?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Bind the service to localhost or a private network, never to a public address.

How do I check if port 66 is open?

On Linux run "ss -ltnup 'sport = :66'", on macOS "lsof -nP -i :66", and on Windows "netstat -ano | findstr :66" to see the local process. From another machine, "nmap -p 66 <host>" shows whether it is reachable.

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