Port 636: LDAPS
Port 636 is LDAPS, LDAP directory queries encrypted with TLS. It protects credentials and directory data in transit, unlike plain LDAP on port 389.
| Port number | 636 |
|---|---|
| Service | LDAP over TLS |
| Protocol | TCP |
| Category | Authentication |
| Default encryption | Yes (TLS/SSH) |
How do I check whether port 636 is open?
Port 636 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 636 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 636 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':636 ' | Lists the process bound to port 636 on Linux. On macOS use lsof -nP -iTCP:636 -sTCP:LISTEN, on Windows netstat -ano | findstr :636 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 636 used for?
Port 636 is LDAPS, LDAP directory queries encrypted with TLS. It protects credentials and directory data in transit, unlike plain LDAP on port 389.
Is port 636 TCP or UDP?
Port 636 (LDAPS) uses TCP.
Is port 636 secure?
Yes. Port 636 carries encrypted traffic by default, so data in transit is protected.
Should I open port 636 on my firewall?
Only if you specifically need LDAPS. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.