Port 636 – LDAPS Protocol Specification

Technical analysis, security advisories, vulnerability mitigation, and firewall syntax for TCP/UDP port 636 (LDAPS).

Port Number 636

Transport Protocol TCP

Port Range Type Well-Known (0-1023)

Default Status Restricted / LAN

Service Description & Architectural Context

Lightweight Directory Access Protocol over dedicated SSL/TLS.

IANA / RFC Designation:

Port 636 is assigned to LDAPS under the Internet Assigned Numbers Authority (IANA) service name registry. In enterprise infrastructure and homelab setups, services listening on this port must follow the principle of least privilege.

Security Analysis & Attack Surface Assessment

Preferred over plaintext LDAP. Restrict access via firewall to app servers.

Hardening Recommendations:

Do not expose port 636 to public WAN interfaces unless authenticated TLS or VPN wrapping is strictly enforced.
Enforce rate-limiting using Fail2ban, CrowdSec, or cloud edge DDoS protection.
Audit active listening sockets locally: ss -tulpn | grep :636 or netstat -ano | findstr :636.

Firewall Rule Snippets for Port 636

UFW (Ubuntu / Debian Linux)

sudo ufw allow 636/tcp

iptables (Standard Linux Kernel)

sudo iptables -A INPUT -p tcp --dport 636 -j ACCEPT

Windows PowerShell (Defender Advanced Firewall)

New-NetFirewallRule -DisplayName "Allow Port 636" -Direction Inbound -LocalPort 636 -Protocol TCP -Action Allow

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