Troubleshooting LDAPS Connectivity: Using Built-in Windows Tools to Audit Firewall Compliance As organizations move toward more secure infrastructure, migrating from standard LDAP (Port 389) to LDAPS (Port 636) is a critical step. However, this transition often reveals “silent” failures where a network firewall might allow the initial connection but block the subsequent SSL/TLS handshake.

At Van den Boom Online, we understand that a smooth user experience starts with a robust backend. In this guide, we’ll show you how to perform packet capturing using only built-in Windows tools to verify if your traffic is reaching its destination or being dropped by security appliances.

Why Packet Capture for LDAPS? When a connection fails, the error message is often a generic “Server Unavailable.” By capturing the packets, you can see the exact stage of failure:

TCP Three-Way Handshake: Is the server even responding to the initial SYN request?

TLS Client Hello: Is the client sending its encryption requirements?

TLS Server Hello: Is the server responding with its certificate, or is the connection being reset (RST) by a firewall?

Step 1: Capturing Traffic with Pktmon Since Windows 10 (Version 2004) and Windows Server 2019, Microsoft has included a powerful tool called Packet Monitor (Pktmon). You don’t need to install third-party software like Wireshark on a sensitive server to get the data you need.

  1. Open an Elevated Command Prompt Right-click your Command Prompt or PowerShell and select Run as Administrator.

  2. Set a Filter for LDAPS To avoid “noise” from other background traffic, filter specifically for Port 636:

1pktmon filter add -p 636
  1. Start the Capture Run the following command to begin logging. The –etw flag ensures it captures events in a format Windows can process:
1pktmon start --etw

Now, attempt your LDAPS login or connection. Once the failure occurs, move to the next step.

  1. Stop the Capture
1pktmon stop

Step 2: Converting the Data for Analysis The resulting file (PktMon.etl) is a binary format. To make it readable for an AI tool or for manual inspection, you can convert it to a text format or a Wireshark-compatible file.

To convert to a text file for quick analysis:

1pktmon format PktMon.etl > ldaps_analysis.txt

Now let an AI tool analyse the text file.

Step 3: What to Look For Once you open your log, look for the following sequence to determine if the firewall is the culprit:

SYN -> SYN-ACK -> ACK: If you see this, the TCP layer is open. Your firewall allows basic connectivity.

Client Hello: The client sends this to start the TLS process.

Missing Server Hello: If you see a “Client Hello” followed by a TCP RST (Reset) or no response at all, your firewall is likely performing “Deep Packet Inspection” (DPI) and blocking the encrypted traffic because it doesn’t recognize the certificate or the TLS version.

Conclusion Connectivity issues shouldn’t be a guessing game. By using pktmon, you can prove exactly where the chain breaks. If you see a successful TCP handshake but a failed TLS “Hello” exchange, you have the evidence needed to request a firewall policy change from your network team.

Are you looking to secure your online platforms or optimize your server communication? Van den Boom Online provides the technical expertise to ensure your digital infrastructure is both fast and secure. Contact us today to learn more.