Prevent Outbound NetBIOS Traffic to OpenDNS

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Updated:October 31, 2025
Document ID:225357

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    Introduction

    This document describes how to stop outbound NetBIOS traffic directed to OpenDNS.

    Prerequisites

    Requirements

    There are no specific requirements for this document.

    Components Used

    The information in this document is based on Cisco Umbrella.

    The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

    Problem

    Windows systems can attempt to send NetBIOS traffic to OpenDNS when OpenDNS returns the IP address of a controlled host instead of a standard NXDOMAIN response. Windows interprets this as a valid response and initiates NetBIOS communication with OpenDNS.

    Solution

    To prevent outbound NetBIOS traffic to OpenDNS, complete these steps:

    1. Access the Advanced Settings in your dashboard.

    2. Navigate to Domain Typos > Exceptions for VPN users.

    3. Add the full hostnames of systems on your network to the exceptions list.

    Hostnames added to this list do not get looked up by OpenDNS services.

    Revision History

    Revision Publish Date Comments
    1.0
    31-Oct-2025
    Initial Release
    TAC Authored

    Contributed by Cisco Engineers

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