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<?xml version="1.0" encoding="iso-8859-1"?>
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<!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
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<title>Networking Primer</title>
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You are about to use the equivalent of a microscope to look at the information
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that runs through the veins of a Windows network. We do more to observe the information than
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to interrogate it. When you are done with this primer, you should have a good understanding
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of the types of information that flow over the network. Do not worry, this is not
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a biology lesson. We won't lose you in unnecessary detail. Think to yourself, <quote>This
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is easy,</quote> then tackle each exercise without fear.
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Samba can be configured with a minimum of complexity. Simplicity should be mastered
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before you get too deeply into complexities. Let's get moving: we have work to do.
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<title>Requirements and Notes</title>
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Successful completion of this primer requires two Microsoft Windows 9x/Me Workstations
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as well as two Microsoft Windows XP Professional Workstations, each equipped with an Ethernet
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card connected using a hub. Also required is one additional server (either Windows
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NT4 Server, Windows 2000 Server, or a Samba-3 on UNIX/Linux server) running a network
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sniffer and analysis application (Wireshark is a good choice). All work should be undertaken
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on a quiet network where there is no other traffic. It is best to use a dedicated hub
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with only the machines under test connected at the time of the exercises.
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<primary>Wireshark</primary>
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Wireshark (formerly Ethereal) has become the network protocol analyzer of choice for many network administrators.
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You may find more information regarding this tool from the
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<ulink url="http://www.wireshark.org">Wireshark</ulink> Web site. Wireshark installation
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files for Windows may be obtained from the Wireshark Web site. Wireshark is provided with
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SUSE and Red Hat Linux distributions, as well as with many other Linux distributions. It may
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not be installed on your system by default. If it is not installed, you may also need
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to install the <command>libpcap</command> software before you can install or use Wireshark.
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Please refer to the instructions for your operating system or to the Wireshark Web site
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for information regarding the installation and operation of Wireshark.
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To obtain <command>Wireshark</command> for your system, please visit the Wireshark
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<ulink url="http://www.wireshark.org/download.html">download site</ulink>.
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The successful completion of this chapter requires that you capture network traffic
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using <command>Wireshark</command>. It is recommended that you use a hub, not an
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Ethernet switch. It is necessary for the device used to act as a repeater, not as a
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filter. Ethernet switches may filter out traffic that is not directed at the machine
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that is used to monitor traffic; this would not allow you to complete the projects.
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<indexterm><primary>network</primary><secondary>captures</secondary></indexterm>
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Do not worry too much if you do not have access to all this equipment; network captures
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from the exercises are provided on the enclosed CD-ROM. This makes it possible to dive directly
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into the analytical part of the exercises if you so desire.
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<primary>network</primary>
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<secondary>sniffer</secondary>
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</indexterm><indexterm>
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<primary>protocol analysis</primary>
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Please do not be alarmed at the use of a high-powered analysis tool (Wireshark) in this
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primer. We expose you only to a minimum of detail necessary to complete
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the exercises. If you choose to use any other network sniffer and protocol
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analysis tool, be advised that it may not allow you to examine the contents of
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recently added security protocols used by Windows 200x/XP.
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You could just skim through the exercises and try to absorb the key points made.
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The exercises provide all the information necessary to convince the die-hard network
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engineer. You possibly do not require so much convincing and may just want to move on,
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in which case you should at least read <link linkend="chap01conc"/>.
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<link linkend="chap01qa"/> also provides useful information
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that may help you to avoid significantly time-consuming networking problems.
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<title>Introduction</title>
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The purpose of this chapter is to create familiarity with key aspects of Microsoft Windows
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network computing. If you want a solid technical grounding, do not gloss over these exercises.
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The points covered are recurrent issues on the Samba mailing lists.
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<primary>network</primary>
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<secondary>broadcast</secondary>
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You can see from these exercises that Windows networking involves quite a lot of network
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broadcast traffic. You can look into the contents of some packets, but only to see
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some particular information that the Windows client sends to a server in the course of
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establishing a network connection.
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To many people, browsing is everything that happens when one uses Microsoft Internet Explorer.
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It is only when you start looking at network traffic and noting the protocols
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and types of information that are used that you can begin to appreciate the complexities of
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Windows networking and, more importantly, what needs to be configured so that it can work.
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Detailed information regarding browsing is provided in the recommended
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Recommended preparatory reading: <emphasis>The Official Samba-3 HOWTO and Reference Guide, Second
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Edition</emphasis> (TOSHARG2) Chapter 9, <quote>Network Browsing,</quote> and Chapter 3,
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<quote>Server Types and Security Modes.</quote>
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<title>Assignment Tasks</title>
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<primary>browsing</primary>
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You are about to witness how Microsoft Windows computer networking functions. The
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exercises step through identification of how a client machine establishes a
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connection to a remote Windows server. You observe how Windows machines find
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each other (i.e., how browsing works) and how the two key types of user identification
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(share mode security and user mode security) are affected.
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<primary>network</primary>
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<secondary>analyzer</secondary>
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The networking protocols used by MS Windows networking when working with Samba
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use TCP/IP as the transport protocol. The protocols that are specific to Windows
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networking are encapsulated in TCP/IP. The network analyzer we use (Wireshark)
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is able to show you the contents of the TCP/IP packets (or messages).
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<procedure id="chap01tasks">
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<title>Diagnostic Tasks</title>
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<step><para><indexterm>
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<primary>network</primary>
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<secondary>trace</secondary>
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</indexterm><indexterm>
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<primary>host announcement</primary>
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</indexterm><indexterm>
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<primary>name resolution</primary>
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Examine network traces to witness SMB broadcasts, host announcements,
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and name resolution processes.
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Examine network traces to witness how share mode security functions.
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Examine network traces to witness the use of user mode security.
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Review traces of network logons for a Windows 9x/Me client as well as
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a domain logon for a Windows XP Professional client.
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<title>Exercises</title>
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<indexterm><primary>wireshark</primary></indexterm>
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You are embarking on a course of discovery. The first part of the exercise requires
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two MS Windows 9x/Me systems. We called one machine <constant>WINEPRESSME</constant> and the
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other <constant>MILGATE98</constant>. Each needs an IP address; we used <literal>10.1.1.10</literal>
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and <literal>10.1.1.11</literal>. The test machines need to be networked via a <emphasis>hub</emphasis>. A UNIX/Linux
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machine is required to run <command>Wireshark</command> to enable the network activity to be captured.
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It is important that the machine from which network activity is captured must not interfere with
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the operation of the Windows workstations. It is helpful for this machine to be passive (does not
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send broadcast information) to the network.
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For these exercises, our test environment consisted of a SUSE 9.2 Professional Linux Workstation running
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VMWare 4.5. The following VMWare images were prepared:
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<listitem><para>Windows 98 &smbmdash; name: MILGATE98</para></listitem>
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<listitem><para>Windows Me &smbmdash; name: WINEPRESSME</para></listitem>
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<listitem><para>Windows XP Professional &smbmdash; name: LightrayXP</para></listitem>
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<listitem><para>Samba-3.0.20 running on a SUSE Enterprise Linux 9</para></listitem>
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Choose a workgroup name (MIDEARTH) for each exercise.
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<indexterm><primary>ethereal</primary></indexterm>
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The network captures provided on the CD-ROM included with this book were captured using <constant>Ethereal</constant>
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version <literal>0.10.6</literal>. A later version suffices without problems (i.e. you should be using Wireshark), but an earlier version may not
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expose all the information needed. Each capture file has been decoded and listed as a trace file. A summary of all
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packets has also been included. This makes it possible for you to do all the studying you like without the need to
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perform the time-consuming equipment configuration and test work. This is a good time to point out that the value
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that can be derived from this book really does warrant your taking sufficient time to practice each exercise with
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care and attention to detail.
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<title>Single-Machine Broadcast Activity</title>
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In this section, we start a single Windows 9x/Me machine, then monitor network activity for 30 minutes.
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<title>Monitoring Windows 9x Steps</title>
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Start the machine from which network activity will be monitored (using <command>Wireshark</command>).
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Launch <command>Wireshark</command>, click
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<guimenu>Capture</guimenu>
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<guimenuitem>Start</guimenuitem>
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<listitem><para>Update list of packets in real time</para></listitem>
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<listitem><para>Automatic scrolling in live capture</para></listitem>
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<listitem><para>Enable MAC name resolution</para></listitem>
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<listitem><para>Enable network name resolution</para></listitem>
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<listitem><para>Enable transport name resolution</para></listitem>
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Click <guibutton>OK</guibutton>.
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Start the Windows 9x/Me machine to be monitored. Let it run for a full 30 minutes. While monitoring,
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do not press any keyboard keys, do not click any on-screen icons or menus, and do not answer any dialog boxes.
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At the conclusion of 30 minutes, stop the capture. Save the capture to a file so you can go back to it later.
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Leave this machine running in preparation for the task in <link linkend="secondmachine"/>.
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Analyze the capture. Identify each discrete message type that was captured. Note what transport protocol
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was used. Identify the timing between messages of identical types.
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<title>Findings</title>
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The summary of the first 10 minutes of the packet capture should look like <link linkend="pktcap01"/>.
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A screenshot of a later stage of the same capture is shown in <link linkend="pktcap02"/>.
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<figure id="pktcap01">
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<title>Windows Me &smbmdash; Broadcasts &smbmdash; The First 10 Minutes</title>
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<imagefile scale="40">WINREPRESSME-Capture</imagefile>
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<figure id="pktcap02">
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<title>Windows Me &smbmdash; Later Broadcast Sample</title>
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<imagefile scale="42">WINREPRESSME-Capture2</imagefile>
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<primary>Local Master Browser</primary>
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</indexterm><indexterm>
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<primary>LMB</primary>
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Broadcast messages observed are shown in <link linkend="capsstats01"/>.
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Actual observations vary a little, but not by much.
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Early in the startup process, the Windows Me machine broadcasts its name for two reasons:
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first to ensure that its name would not result in a name clash, and second to establish its
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presence with the Local Master Browser (LMB).
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<table id="capsstats01">
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<title>Windows Me &smbmdash; Startup Broadcast Capture Statistics</title>
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<colspec align="left" colwidth="3*"/>
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<colspec align="center"/>
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<colspec align="center"/>
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<colspec align="left" colwidth="3*"/>
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<entry>Message</entry>
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<entry>WINEPRESSME<00></entry>
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<entry>4 lots of 2, 0.6 sec apart</entry>
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<entry>WINEPRESSME<03></entry>
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<entry>4 lots of 2, 0.6 sec apart</entry>
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<entry>WINEPRESSME<20></entry>
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<entry>4 lots of 2, 0.75 sec apart</entry>
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<entry>MIDEARTH<00></entry>
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<entry>4 lots of 2, 0.75 sec apart</entry>
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<entry>MIDEARTH<1d></entry>
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<entry>4 lots of 2, 0.75 sec apart</entry>
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<entry>MIDEARTH<1e></entry>
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<entry>4 lots of 2, 0.75 sec apart</entry>
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<entry>MIDEARTH<1b></entry>
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<entry>300 sec apart at stable operation</entry>
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<entry>__MSBROWSE__</entry>
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<entry>Registered after winning election to Browse Master</entry>
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<entry>JHT<03></entry>
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<entry>4 x 2. This is the name of the user that logged onto Windows</entry>
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<entry>Host Announcement WINEPRESSME</entry>
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<entry>Observed at 10 sec</entry>
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<entry>Domain/Workgroup Announcement MIDEARTH</entry>
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<entry>300 sec apart at stable operation</entry>
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<entry>Local Master Announcement WINEPRESSME</entry>
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<entry>300 sec apart at stable operation</entry>
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<entry>Get Backup List Request</entry>
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<entry>6 x 2 early in startup, 0.5 sec apart</entry>
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<entry>Browser Election Request</entry>
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<entry>5 x 2 early in startup</entry>
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<entry>Request Announcement WINEPRESSME</entry>
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<entry>Early in startup</entry>
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<primary>election</primary>
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</indexterm><indexterm>
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<primary>browse master</primary>
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From the packet trace, it should be noted that no messages were propagated over TCP/IP;
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all messages employed UDP/IP. When steady-state operation has been achieved, there is a cycle
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of various announcements, re-election of a browse master, and name queries. These create
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the symphony of announcements by which network browsing is made possible.
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<primary>CIFS</primary>
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For detailed information regarding the precise behavior of the CIFS/SMB protocols,
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refer to the book <quote>Implementing CIFS: The Common Internet File System,</quote>
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by Christopher Hertel, (Prentice Hall PTR, ISBN: 013047116X).
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<sect2 id="secondmachine">
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<title>Second Machine Startup Broadcast Interaction</title>
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At this time, the machine you used to capture the single-system startup trace should still be running.
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The objective of this task is to identify the interaction of two machines in respect to broadcast activity.
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<title>Monitoring of Second Machine Activity</title>
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On the machine from which network activity will be monitored (using <command>Wireshark</command>),
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launch <command>Wireshark</command> and click
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<guimenu>Capture</guimenu>
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<guimenuitem>Start</guimenuitem>
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<listitem><para>Update list of packets in real time</para></listitem>
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<listitem><para>Automatic scrolling in live capture</para></listitem>
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<listitem><para>Enable MAC name resolution</para></listitem>
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<listitem><para>Enable network name resolution</para></listitem>
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<listitem><para>Enable transport name resolution</para></listitem>
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Click <guibutton>OK</guibutton>.
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Start the second Windows 9x/Me machine. Let it run for 15 to 20 minutes. While monitoring, do not press
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any keyboard keys, do not click any on-screen icons or menus, and do not answer any dialog boxes.
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At the conclusion of the capture time, stop the capture. Be sure to save the captured data so you
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can examine the network data capture again at a later date should that be necessary.
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Analyze the capture trace, taking note of the transport protocols used, the types of messages observed,
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and what interaction took place between the two machines. Leave both machines running for the next task.
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<title>Findings</title>
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<link linkend="capsstats02"/> summarizes capture statistics observed. As in the previous case,
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all announcements used UDP/IP broadcasts. Also, as was observed with the last example, the second
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Windows 9x/Me machine broadcasts its name on startup to ensure that there exists no name clash
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(i.e., the name is already registered by another machine) on the network segment. Those wishing
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to explore the inner details of the precise mechanism of how this functions should refer to
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<quote>Implementing CIFS: The Common Internet File System.</quote>
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<table id="capsstats02">
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<title>Second Machine (Windows 98) &smbmdash; Capture Statistics</title>
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<colspec align="left" colwidth="3*"/>
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<colspec align="center"/>
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<colspec align="center"/>
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<colspec align="left" colwidth="3*"/>
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<entry>Message</entry>
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<entry>MILGATE98<00></entry>
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<entry>4 lots of 2, 0.6 sec apart</entry>
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<entry>MILGATE98<03></entry>
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<entry>4 lots of 2, 0.6 sec apart</entry>
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<entry>MILGATE98<20></entry>
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<entry>4 lots of 2, 0.75 sec apart</entry>
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<entry>MIDEARTH<00></entry>
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<entry>4 lots of 2, 0.75 sec apart</entry>
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<entry>MIDEARTH<1d></entry>
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<entry>4 lots of 2, 0.75 sec apart</entry>
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<entry>MIDEARTH<1e></entry>
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<entry>4 lots of 2, 0.75 sec apart</entry>
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<entry>MIDEARTH<1b></entry>
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<entry>900 sec apart at stable operation</entry>
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<entry>JHT<03></entry>
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<entry>This is the name of the user that logged onto Windows</entry>
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<entry>Host Announcement MILGATE98</entry>
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<entry>Every 120 sec</entry>
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<entry>Domain/Workgroup Announcement MIDEARTH</entry>
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<entry>900 sec apart at stable operation</entry>
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<entry>Local Master Announcement WINEPRESSME</entry>
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<entry>Insufficient detail to determine frequency</entry>
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<indexterm><primary>host announcement</primary></indexterm>
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<indexterm><primary>Local Master Announcement</primary></indexterm>
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<indexterm><primary>Workgroup Announcement</primary></indexterm>
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Observation of the contents of Host Announcements, Domain/Workgroup Announcements,
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and Local Master Announcements is instructive. These messages convey a significant
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level of detail regarding the nature of each machine that is on the network. An example
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dissection of a Host Announcement is given in <link linkend="hostannounce"/>.
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<figure id="hostannounce">
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<title>Typical Windows 9x/Me Host Announcement</title>
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<imagefile scale="41">HostAnnouncment</imagefile>
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<title>Simple Windows Client Connection Characteristics</title>
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The purpose of this exercise is to discover how Microsoft Windows clients create (establish)
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connections with remote servers. The methodology involves analysis of a key aspect of how
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Windows clients access remote servers: the session setup protocol.
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<title>Client Connection Exploration Steps</title>
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Configure a Windows 9x/Me machine (MILGATE98) with a share called <constant>Stuff</constant>.
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Create a <parameter>Full Access</parameter> control password on this share.
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Configure another Windows 9x/Me machine (WINEPRESSME) as a client. Make sure that it exports
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Start both Windows 9x/Me machines and allow them to stabilize for 10 minutes. Log on to both
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machines using a user name (JHT) of your choice. Wait approximately 2 minutes before proceeding.
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Start Wireshark (or the network sniffer of your choice).
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From the WINEPRESSME machine, right-click <guimenu>Network Neighborhood</guimenu>, select
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<guimenuitem>Explore</guimenuitem>, select
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<guimenuitem>My Network Places</guimenuitem>
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<guimenuitem>Entire Network</guimenuitem>
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<guimenuitem>MIDEARTH</guimenuitem>
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<guimenuitem>MILGATE98</guimenuitem>
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<guimenuitem>Stuff</guimenuitem>
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Enter the password you set for the <constant>Full Control</constant> mode for the
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<constant>Stuff</constant> share.
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When the share called <constant>Stuff</constant> is being displayed, stop the capture.
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Save the captured data in case it is needed for later analysis.
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<indexterm><primary>session setup</primary></indexterm>
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From the top of the packets captured, scan down to locate the first packet that has
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interpreted as <constant>Session Setup AndX, User: anonymous; Tree Connect AndX,
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Path: \\MILGATE98\IPC$</constant>.
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<step><para><indexterm>
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<primary>Session Setup</primary>
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</indexterm><indexterm>
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<primary>Tree Connect</primary>
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In the dissection (analysis) panel, expand the <constant>SMB, Session Setup AndX Request,
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and Tree Connect AndX Request</constant>. Examine both operations. Identify the name of
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the user Account and what password was used. The Account name should be empty.
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This is a <constant>NULL</constant> session setup packet.
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Return to the packet capture sequence. There will be a number of packets that have been
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decoded of the type <constant>Session Setup AndX</constant>. Locate the last such packet
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that was targeted at the <constant>\\MILGATE98\IPC$</constant> service.
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<indexterm><primary>password length</primary></indexterm>
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<indexterm><primary>User Mode</primary></indexterm>
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Dissect this packet as per the previous one. This packet should have a password length
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of 24 (characters) and should have a password field, the contents of which is a
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long hexadecimal number. Observe the name in the Account field. This is a User Mode
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session setup packet.
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<title>Findings and Comments</title>
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<indexterm><primary>IPC$</primary></indexterm>
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The <constant>IPC$</constant> share serves a vital purpose<footnote><para>TOSHARG2, Sect 4.5.1</para></footnote>
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in SMB/CIFS-based networking. A Windows client connects to this resource to obtain the list of
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resources that are available on the server. The server responds with the shares and print queues that
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are available. In most but not all cases, the connection is made with a <constant>NULL</constant>
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username and a <constant>NULL</constant> password.
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<indexterm><primary>account credentials</primary></indexterm>
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The two packets examined are material evidence of how Windows clients may
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interoperate with Samba. Samba requires every connection setup to be authenticated using
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valid UNIX account credentials (UID/GID). This means that even a <constant>NULL</constant>
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session setup can be established only by automatically mapping it to a valid UNIX
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<indexterm><primary>NULL session</primary></indexterm><indexterm>
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<primary>guest account</primary>
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<indexterm><primary>nobody</primary></indexterm>
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Samba has a special name for the <constant>NULL</constant>, or empty, user account:
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it calls it the <smbconfoption name="guest account"/>. The
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default value of this parameter is <constant>nobody</constant>; however, this can be
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changed to map the function of the guest account to any other UNIX identity. Some
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UNIX administrators prefer to map this account to the system default anonymous
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FTP account. A sample NULL Session Setup AndX packet dissection is shown in
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<link linkend="nullconnect"/>.
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<figure id="nullconnect">
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<title>Typical Windows 9x/Me NULL SessionSetUp AndX Request</title>
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<imagefile scale="41">NullConnect</imagefile>
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<indexterm><primary>nobody</primary></indexterm>
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<indexterm><primary>/etc/passwd</primary></indexterm>
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<indexterm><primary>guest account</primary></indexterm>
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When a UNIX/Linux system does not have a <constant>nobody</constant> user account
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(<filename>/etc/passwd</filename>), the operation of the <constant>NULL</constant>
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account cannot validate and thus connections that utilize the guest account
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fail. This breaks all ability to browse the Samba server and is a common
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problem reported on the Samba mailing list. A sample User Mode session setup AndX
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is shown in <link linkend="userconnect"/>.
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<figure id="userconnect">
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<title>Typical Windows 9x/Me User SessionSetUp AndX Request</title>
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<imagefile scale="41">UserConnect</imagefile>
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<indexterm><primary>encrypted</primary></indexterm>
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The User Mode connection packet contains the account name and the domain name.
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The password is provided in Microsoft encrypted form, and its length is shown
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as 24 characters. This is the length of Microsoft encrypted passwords.
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<title>Windows 200x/XP Client Interaction with Samba-3</title>
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By now you may be asking, <quote>Why did you choose to work with Windows 9x/Me?</quote>
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First, we want to demonstrate the simple case. This book is not intended to be a detailed treatise
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on the Windows networking protocols, but rather to provide prescriptive guidance for deployment of Samba.
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Second, by starting out with the simple protocol, it can be demonstrated that the more complex case mostly
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follows the same principles.
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The following exercise demonstrates the case that even MS Windows XP Professional with up-to-date service
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updates also uses the <constant>NULL</constant> account, as well as user accounts. Simply follow the procedure
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to complete this exercise.
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To complete this exercise, you need a Windows XP Professional client that has been configured as
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a domain member of either a Samba-controlled domain or a Windows NT4 or 200x Active Directory domain.
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Here we do not provide details for how to configure this, as full coverage is provided earlier in this book.
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<title>Steps to Explore Windows XP Pro Connection Set-up</title>
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Start your domain controller. Also, start the Wireshark monitoring machine, launch Wireshark,
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and then wait for the next step to complete.
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Start the Windows XP Client and wait 5 minutes before proceeding.
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On the machine from which network activity will be monitored (using <command>Wireshark</command>),
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launch <command>Wireshark</command> and click
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<guimenu>Capture</guimenu>
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<guimenuitem>Start</guimenuitem>
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<listitem><para>Update list of packets in real time</para></listitem>
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<listitem><para>Automatic scrolling in live capture</para></listitem>
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<listitem><para>Enable MAC name resolution</para></listitem>
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<listitem><para>Enable network name resolution</para></listitem>
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<listitem><para>Enable transport name resolution</para></listitem>
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Click <guibutton>OK</guibutton>.
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On the Windows XP Professional client, press <guimenu>Ctrl-Alt-Delete</guimenu> to bring
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up the domain logon screen. Log in using valid credentials for a domain user account.
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Now proceed to connect to the domain controller as follows:
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<guimenu>Start</guimenu>
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<guimenuitem>(right-click) My Network Places</guimenuitem>
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<guimenuitem>Explore</guimenuitem>
823
<guimenuitem>{Left Panel} [+] Entire Network</guimenuitem>
824
<guimenuitem>{Left Panel} [+] Microsoft Windows Network</guimenuitem>
825
<guimenuitem>{Left Panel} [+] Midearth</guimenuitem>
826
<guimenuitem>{Left Panel} [+] Frodo</guimenuitem>
827
<guimenuitem>{Left Panel} [+] data</guimenuitem>
828
</menuchoice>. Close the explorer window.
832
In this step, our domain name is <constant>Midearth</constant>, the domain controller is called
833
<constant>Frodo</constant>, and we have connected to a share called <constant>data</constant>.
837
Stop the capture on the <command>Wireshark</command> monitoring machine. Be sure to save the captured data
838
to a file so that you can refer to it again later.
842
If desired, the Windows XP Professional client and the domain controller are no longer needed for exercises
847
<indexterm><primary>NTLMSSP_AUTH</primary></indexterm>
848
<indexterm><primary>session setup</primary></indexterm>
849
From the top of the packets captured, scan down to locate the first packet that has
850
interpreted as <constant>Session Setup AndX Request, NTLMSSP_AUTH</constant>.
854
<indexterm><primary>GSS-API</primary></indexterm>
855
<indexterm><primary>SPNEGO</primary></indexterm>
856
<indexterm><primary>NTLMSSP</primary></indexterm>
857
In the dissection (analysis) panel, expand the <constant>SMB, Session Setup AndX Request</constant>.
858
Expand the packet decode information, beginning at the <constant>Security Blob:</constant>
859
entry. Expand the <constant>GSS-API -> SPNEGO -> netTokenTarg -> responseToken -> NTLMSSP</constant>
860
keys. This should reveal that this is a <constant>NULL</constant> session setup packet.
861
The <constant>User name: NULL</constant> so indicates. An example decode is shown in
862
<link linkend="XPCap01"/>.
866
Return to the packet capture sequence. There will be a number of packets that have been
867
decoded of the type <constant>Session Setup AndX Request</constant>. Click the last such packet that
868
has been decoded as <constant>Session Setup AndX Request, NTLMSSP_AUTH</constant>.
872
<indexterm><primary>encrypted password</primary></indexterm>
873
In the dissection (analysis) panel, expand the <constant>SMB, Session Setup AndX Request</constant>.
874
Expand the packet decode information, beginning at the <constant>Security Blob:</constant>
875
entry. Expand the <constant>GSS-API -> SPNEGO -> netTokenTarg -> responseToken -> NTLMSSP</constant>
876
keys. This should reveal that this is a <constant>User Mode</constant> session setup packet.
877
The <constant>User name: jht</constant> so indicates. An example decode is shown in
878
<link linkend="XPCap02"/>. In this case the user name was <constant>jht</constant>. This packet
879
decode includes the <constant>Lan Manager Response:</constant> and the <constant>NTLM Response:</constant>.
880
The values of these two parameters are the Microsoft encrypted password hashes: respectively, the LanMan
881
password and then the NT (case-preserving) password hash.
885
<indexterm><primary>password length</primary></indexterm>
886
<indexterm><primary>User Mode</primary></indexterm>
887
The passwords are 24-character hexadecimal numbers. This packet confirms that this is a User Mode
888
session setup packet.
893
<figure id="XPCap01">
894
<title>Typical Windows XP NULL Session Setup AndX Request</title>
895
<imagefile scale="50">WindowsXP-NullConnection</imagefile>
898
<figure id="XPCap02">
899
<title>Typical Windows XP User Session Setup AndX Request</title>
900
<imagefile scale="50">WindowsXP-UserConnection</imagefile>
904
<title>Discussion</title>
907
<primary>NULL-Session</primary>
909
This exercise demonstrates that, while the specific protocol for the Session Setup AndX is handled
910
in a more sophisticated manner by recent MS Windows clients, the underlying rules or principles
911
remain the same. Thus it is demonstrated that MS Windows XP Professional clients still use a
912
<constant>NULL-Session</constant> connection to query and locate resources on an advanced network
913
technology server (one using Windows NT4/200x or Samba). It also demonstrates that an authenticated
914
connection must be made before resources can be used.
922
<title>Conclusions to Exercises</title>
925
In summary, the following points have been established in this chapter:
930
When NetBIOS over TCP/IP protocols are enabled, MS Windows networking employs broadcast-oriented messaging protocols to provide knowledge of network services.
934
Network browsing protocols query information stored on browse masters that manage
935
information provided by NetBIOS Name Registrations and by way of ongoing host
936
announcements and workgroup announcements.
940
All Samba servers must be configured with a mechanism for mapping the <constant>NULL-Session</constant>
941
to a valid but nonprivileged UNIX system account.
945
The use of Microsoft encrypted passwords is built right into the fabric of Windows
946
networking operations. Such passwords cannot be provided from the UNIX <filename>/etc/passwd</filename>
947
database and thus must be stored elsewhere on the UNIX system in a manner that Samba can
948
use. Samba-2.x permitted such encrypted passwords to be stored in the <constant>smbpasswd</constant>
949
file or in an LDAP database. Samba-3 permits use of multiple <parameter>passdb backend</parameter>
950
databases in concurrent deployment. Refer to <emphasis>TOSHARG2</emphasis>, Chapter 10, <quote>Account Information Databases.</quote>
958
<sect1 id="chap01conc">
959
<title>Dissection and Discussion</title>
962
<indexterm><primary>guest account</primary></indexterm>
963
The exercises demonstrate the use of the <constant>guest</constant> account, the way that
964
MS Windows clients and servers resolve computer names to a TCP/IP address, and how connections
965
between a client and a server are established.
969
Those wishing background information regarding NetBIOS name types should refer to
970
the Microsoft knowledgebase article
971
<ulink url="http://support.microsoft.com/support/kb/articles/Q102/78/8.asp">Q102878.</ulink>
975
<title>Technical Issues</title>
978
<indexterm><primary>guest account</primary></indexterm>
979
Network browsing involves SMB broadcast announcements, SMB enumeration requests,
980
connections to the <constant>IPC$</constant> share, share enumerations, and SMB connection
981
setup processes. The use of anonymous connections to a Samba server involve the use of
982
the <parameter>guest account</parameter> that must map to a valid UNIX UID.
989
<sect1 id="chap01qa">
990
<title>Questions and Answers</title>
993
The questions and answers given in this section are designed to highlight important aspects of Microsoft
997
<qandaset defaultlabel="chap01qa" type="number">
1002
What is the significance of the MIDEARTH<1b> type query?
1009
<indexterm><primary>Domain Master Browser</primary><see>DMB</see></indexterm>
1010
<indexterm><primary>DMB</primary></indexterm>
1011
This is a broadcast announcement by which the Windows machine is attempting to
1012
locate a Domain Master Browser (DMB) in the event that it might exist on the network.
1013
Refer to <emphasis>TOSHARG2,</emphasis> Chapter 9, Section 9.7, <quote>Technical Overview of Browsing,</quote>
1014
for details regarding the function of the DMB and its role in network browsing.
1024
What is the significance of the MIDEARTH<1d> type name registration?
1031
<indexterm><primary>Local Master Browser</primary><see>LMB</see></indexterm>
1032
<indexterm><primary>LMB</primary></indexterm>
1033
This name registration records the machine IP addresses of the LMBs.
1034
Network clients can query this name type to obtain a list of browser servers from the
1039
The LMB is responsible for monitoring all host announcements on the local network and for
1040
collating the information contained within them. Using this information, it can provide answers to other Windows
1041
network clients that request information such as:
1046
The list of machines known to the LMB (i.e., the browse list)
1050
The IP addresses of all domain controllers known for the domain
1054
The IP addresses of LMBs
1058
The IP address of the DMB (if one exists)
1062
The IP address of the LMB on the local segment
1073
What is the role and significance of the <01><02>__MSBROWSE__<02><01>
1081
<indexterm><primary>Browse Master</primary></indexterm>
1082
This name is registered by the browse master to broadcast and receive domain announcements.
1083
Its scope is limited to the local network segment, or subnet. By querying this name type,
1084
master browsers on networks that have multiple domains can find the names of master browsers
1095
What is the significance of the MIDEARTH<1e> type name registration?
1102
<indexterm><primary>Browser Election Service</primary></indexterm>
1103
This name is registered by all browse masters in a domain or workgroup. The registration
1104
name type is known as the Browser Election Service. Master browsers register themselves
1105
with this name type so that DMBs can locate them to perform cross-subnet
1106
browse list updates. This name type is also used to initiate elections for Master Browsers.
1116
<indexterm><primary>guest account</primary></indexterm>
1117
What is the significance of the <parameter>guest account</parameter> in smb.conf?
1124
This parameter specifies the default UNIX account to which MS Windows networking
1125
NULL session connections are mapped. The default name for the UNIX account used for
1126
this mapping is called <constant>nobody</constant>. If the UNIX/Linux system that
1127
is hosting Samba does not have a <constant>nobody</constant> account and an alternate
1128
mapping has not been specified, network browsing will not work at all.
1132
It should be noted that the <parameter>guest account</parameter> is essential to
1133
Samba operation. Either the operating system must have an account called <constant>nobody</constant>
1134
or there must be an entry in the &smb.conf; file with a valid UNIX account, such as
1135
<smbconfoption name="guest account">ftp</smbconfoption>.
1145
Is it possible to reduce network broadcast activity with Samba-3?
1152
<indexterm><primary>WINS</primary></indexterm>
1153
<indexterm><primary>NetBIOS</primary></indexterm>
1154
Yes, there are two ways to do this. The first involves use of WINS (See <emphasis>TOSHARG2</emphasis>, Chapter 9,
1155
Section 9.5, <quote>WINS &smbmdash; The Windows Inter-networking Name Server</quote>); the
1156
alternate method involves disabling the use of NetBIOS over TCP/IP. This second method requires
1157
a correctly configured DNS server (see <emphasis>TOSHARG2</emphasis>, Chapter 9, Section 9.3, <quote>Discussion</quote>).
1161
<indexterm><primary>broadcast</primary></indexterm>
1162
<indexterm><primary>NetBIOS</primary><secondary>Node Type</secondary></indexterm>
1163
<indexterm><primary>Hybrid</primary></indexterm>
1164
The use of WINS reduces network broadcast traffic. The reduction is greatest when all network
1165
clients are configured to operate in <parameter>Hybrid Mode</parameter>. This can be effected through
1166
use of DHCP to set the NetBIOS node type to type 8 for all network clients. Additionally, it is
1167
beneficial to configure Samba to use <smbconfoption name="name resolve order">wins host cast</smbconfoption>.
1171
Use of SMB without NetBIOS is possible only on Windows 200x/XP Professional clients and servers, as
1172
well as with Samba-3.
1182
Can I just use plain-text passwords with Samba?
1189
Yes, you can configure Samba to use plain-text passwords, though this does create a few problems.
1193
First, the use of <filename>/etc/passwd</filename>-based plain-text passwords requires that registry
1194
modifications be made on all MS Windows client machines to enable plain-text passwords support. This
1195
significantly diminishes the security of MS Windows client operation. Many network administrators
1196
are bitterly opposed to doing this.
1200
Second, Microsoft has not maintained plain-text password support since the default setting was made
1201
disabling this. When network connections are dropped by the client, it is not possible to re-establish
1202
the connection automatically. Users need to log off and then log on again. Plain-text password support
1203
may interfere with recent enhancements that are part of the Microsoft move toward a more secure computing
1208
Samba-3 supports Microsoft encrypted passwords. Be advised not to reintroduce plain-text password handling.
1209
Just create user accounts by running <command>smbpasswd -a 'username'</command>
1213
It is not possible to add a user to the <parameter>passdb backend</parameter> database unless there is
1214
a UNIX system account for that user. On systems that run <command>winbindd</command> to access the Samba
1215
PDC/BDC to provide Windows user and group accounts, the <parameter>idmap uid, idmap gid</parameter> ranges
1216
set in the &smb.conf; file provide the local UID/GIDs needed for local identity management purposes.
1226
What parameter in the &smb.conf; file is used to enable the use of encrypted passwords?
1233
The parameter in the &smb.conf; file that controls this behavior is known as <parameter>encrypt
1234
passwords</parameter>. The default setting for this in Samba-3 is <constant>Yes (Enabled)</constant>.
1244
Is it necessary to specify <smbconfoption name="encrypt passwords">Yes</smbconfoption>
1245
when Samba-3 is configured as a domain member?
1252
No. This is the default behavior.
1262
Is it necessary to specify a <parameter>guest account</parameter> when Samba-3 is configured
1263
as a domain member server?
1270
Yes. This is a local function on the server. The default setting is to use the UNIX account
1271
<constant>nobody</constant>. If this account does not exist on the UNIX server, then it is
1272
necessary to provide a <smbconfoption name="guest account">an_account</smbconfoption>,
1273
where <constant>an_account</constant> is a valid local UNIX user account.
added
removed
docs-xml/Samba3-ByExample/SBE-Appendix2.xml
