Filter Settings for Windows NT Services

Protocol and Ports that Control Access to Services

Internet Customer Unit

April 1999

Microsoft Corporation

Introduction

This document provides filter settings for network operators to review so that they can address security issues in their environment. They can then control the protocols and ports that are accessible on their servers running the Microsoft® Windows NT® Server operating system. Filter settings can be applied optionally on any of the following devices and software:

• Network access servers that support filter settings.
  
  
• Routers.
  
  
• Firewalls
  
  
• Windows NT Server computers with the Routing and RAS (RRAS) services version 1.0 installed.

Note   This document contains information that requires periodic updates so the latest information on this topic can be provided. Use this document as a reference. Please check original source locations for the most recent filter setting updates.

NetBIOS Messages and Name Resolution Behavior

Network operators can apply the following registry key settings to control NetBIOS Messages and Name Resolution behavior on any computer running the Microsoft® Windows NT® Server operating system.

Messages

These settings prevent NetBIOS messages from being sent and listened to on a given server using the messenger service.

Hkey_Local_machine\System\CurrentControlSet
\Alerter
Start         = REG_DWORD   0x3
\Messenger
Start         = REG_DWORD   0x3

Name Resolution

These settings prevent the system from requesting and responding to NetBIOS Name Resolution lookups on user datagram protocol (UDP) ports 137 and 138 respectively.

Hkey_Local_machine\System\CurrentControlSet
\Browser   
Start         = REG_DWORD   0x3
\NetBT\Parameters
      EnableDNS       = REG_DWORD   0x1
      EnableLMHOSTS   = REG_DWORD   0x0
   NodeType      = REG_DWORD    0x2

Services Protocol and Port Usage

Referenced Protocol Numbers

   Tcp      = 6
   Udp      = 17
   Gre [pptp]   = 47

Table of Services/Protocols/Ports

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