<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 16. Networking Primer</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.0"><link rel="start" href="index.html" title="Samba-3 by Example"><link rel="up" href="RefSection.html" title="Part III. Reference Section"><link rel="prev" href="appendix.html" title="Chapter 15. A Collection of Useful Tidbits"><link rel="next" href="gpl.html" title="Appendix A. GNU General Public License"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 16. Networking Primer</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="appendix.html">Prev</a> </td><th width="60%" align="center">Part III. Reference Section</th><td width="20%" align="right"> <a accesskey="n" href="gpl.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="primer"></a>Chapter 16. Networking Primer</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="primer.html#id386080">Requirements and Notes</a></span></dt><dt><span class="sect1"><a href="primer.html#id386216">Introduction</a></span></dt><dd><dl><dt><span class="sect2"><a href="primer.html#id386266">Assignment Tasks</a></span></dt></dl></dd><dt><span class="sect1"><a href="primer.html#id386373">Exercises</a></span></dt><dd><dl><dt><span class="sect2"><a href="primer.html#id386486">Single-Machine Broadcast Activity</a></span></dt><dt><span class="sect2"><a href="primer.html#secondmachine">Second Machine Startup Broadcast Interaction</a></span></dt><dt><span class="sect2"><a href="primer.html#id387580">Simple Windows Client Connection Characteristics</a></span></dt><dt><span class="sect2"><a href="primer.html#id388041">Windows 200x/XP Client Interaction with Samba-3</a></span></dt><dt><span class="sect2"><a href="primer.html#id388566">Conclusions to Exercises</a></span></dt></dl></dd><dt><span class="sect1"><a href="primer.html#chap01conc">Dissection and Discussion</a></span></dt><dd><dl><dt><span class="sect2"><a href="primer.html#id388668">Technical Issues</a></span></dt></dl></dd><dt><span class="sect1"><a href="primer.html#chap01qa">Questions and Answers</a></span></dt></dl></div><p> You are about to use the equivalent of a microscope to look at the information that runs through the veins of a Windows network. We do more to observe the information than to interrogate it. When you are done with this primer, you should have a good understanding of the types of information that flow over the network. Do not worry, this is not a biology lesson. We won't lose you in unnecessary detail. Think to yourself, “<span class="quote">This is easy,</span>” then tackle each exercise without fear. </p><p> Samba can be configured with a minimum of complexity. Simplicity should be mastered before you get too deeply into complexities. Let's get moving: we have work to do. </p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id386080"></a>Requirements and Notes</h2></div></div></div><p> Successful completion of this primer requires two Microsoft Windows 9x/Me Workstations as well as two Microsoft Windows XP Professional Workstations, each equipped with an Ethernet card connected using a hub. Also required is one additional server (either Windows NT4 Server, Windows 2000 Server, or a Samba-3 on UNIX/Linux server) running a network sniffer and analysis application (ethereal is a good choice). All work should be undertaken on a quiet network where there is no other traffic. It is best to use a dedicated hub with only the machines under test connected at the time of the exercises. </p><p><a class="indexterm" name="id386095"></a> Ethereal has become the network protocol analyzer of choice for many network administrators. You may find more information regarding this tool from the <a href="http://www.ethereal.com" target="_top">Ethereal</a> Web site. Ethereal installation files for Windows may be obtained from the Ethereal Web site. Ethereal is provided with SUSE and Red Hat Linux distributions, as well as with many other Linux distributions. It may not be installed on your system by default. If it is not installed, you may also need to install the <code class="literal">libpcap </code> software before you can install or use Ethereal. Please refer to the instructions for your operating system or to the Ethereal Web site for information regarding the installation and operation of Ethereal. </p><p> To obtain <code class="literal">ethereal</code> for your system, please visit the Ethereal <a href="http://www.ethereal.com/download.html#binaries" target="_top">download site</a>. </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> The successful completion of this chapter requires that you capture network traffic using <code class="literal">Ethereal</code>. It is recommended that you use a hub, not an Ethernet switch. It is necessary for the device used to act as a repeater, not as a filter. Ethernet switches may filter out traffic that is not directed at the machine that is used to monitor traffic; this would not allow you to complete the projects. </p></div><p> <a class="indexterm" name="id386154"></a> Do not worry too much if you do not have access to all this equipment; network captures from the exercises are provided on the enclosed CD-ROM. This makes it possible to dive directly into the analytical part of the exercises if you so desire. </p><p><a class="indexterm" name="id386168"></a><a class="indexterm" name="id386179"></a> Please do not be alarmed at the use of a high-powered analysis tool (Ethereal) in this primer. We expose you only to a minimum of detail necessary to complete the exercises. If you choose to use any other network sniffer and protocol analysis tool, be advised that it may not allow you to examine the contents of recently added security protocols used by Windows 200x/XP. </p><p> You could just skim through the exercises and try to absorb the key points made. The exercises provide all the information necessary to convince the die-hard network engineer. You possibly do not require so much convincing and may just want to move on, in which case you should at least read <a href="primer.html#chap01conc" title="Dissection and Discussion">???</a>. </p><p> <a href="primer.html#chap01qa" title="Questions and Answers">???</a> also provides useful information that may help you to avoid significantly time-consuming networking problems. </p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id386216"></a>Introduction</h2></div></div></div><p> The purpose of this chapter is to create familiarity with key aspects of Microsoft Windows network computing. If you want a solid technical grounding, do not gloss over these exercises. The points covered are recurrent issues on the Samba mailing lists. </p><p><a class="indexterm" name="id386228"></a> You can see from these exercises that Windows networking involves quite a lot of network broadcast traffic. You can look into the contents of some packets, but only to see some particular information that the Windows client sends to a server in the course of establishing a network connection. </p><p> To many people, browsing is everything that happens when one uses Microsoft Internet Explorer. It is only when you start looking at network traffic and noting the protocols and types of information that are used that you can begin to appreciate the complexities of Windows networking and, more importantly, what needs to be configured so that it can work. Detailed information regarding browsing is provided in the recommended preparatory reading. </p><p> Recommended preparatory reading: <span class="emphasis"><em>The Official Samba-3 HOWTO and Reference Guide, Second Edition</em></span> (TOSHARG2) Chapter 9, “<span class="quote">Network Browsing,</span>” and Chapter 3, “<span class="quote">Server Types and Security Modes.</span>” </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id386266"></a>Assignment Tasks</h3></div></div></div><p><a class="indexterm" name="id386273"></a> You are about to witness how Microsoft Windows computer networking functions. The exercises step through identification of how a client machine establishes a connection to a remote Windows server. You observe how Windows machines find each other (i.e., how browsing works) and how the two key types of user identification (share mode security and user mode security) are affected. </p><p><a class="indexterm" name="id386287"></a> The networking protocols used by MS Windows networking when working with Samba use TCP/IP as the transport protocol. The protocols that are specific to Windows networking are encapsulated in TCP/IP. The network analyzer we use (Ethereal) is able to show you the contents of the TCP/IP packets (or messages). </p><div class="procedure"><a name="chap01tasks"></a><p class="title"><b>Procedure 16.1. Diagnostic Tasks</b></p><ol type="1"><li><p><a class="indexterm" name="id386318"></a><a class="indexterm" name="id386329"></a><a class="indexterm" name="id386337"></a> Examine network traces to witness SMB broadcasts, host announcements, and name resolution processes. </p></li><li><p> Examine network traces to witness how share mode security functions. </p></li><li><p> Examine network traces to witness the use of user mode security. </p></li><li><p> Review traces of network logons for a Windows 9x/Me client as well as a domain logon for a Windows XP Professional client. </p></li></ol></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id386373"></a>Exercises</h2></div></div></div><p> <a class="indexterm" name="id386381"></a> You are embarking on a course of discovery. The first part of the exercise requires two MS Windows 9x/Me systems. We called one machine <code class="constant">WINEPRESSME</code> and the other <code class="constant">MILGATE98</code>. Each needs an IP address; we used <code class="literal">10.1.1.10</code> and <code class="literal">10.1.1.11</code>. The test machines need to be networked via a <span class="emphasis"><em>hub</em></span>. A UNIX/Linux machine is required to run <code class="literal">Ethereal</code> to enable the network activity to be captured. It is important that the machine from which network activity is captured must not interfere with the operation of the Windows workstations. It is helpful for this machine to be passive (does not send broadcast information) to the network. </p><p> For these exercises, our test environment consisted of a SUSE 9.2 Professional Linux Workstation running VMWare 4.5. The following VMWare images were prepared: </p><div class="itemizedlist"><ul type="disc"><li><p>Windows 98 name: MILGATE98</p></li><li><p>Windows Me name: WINEPRESSME</p></li><li><p>Windows XP Professional name: LightrayXP</p></li><li><p>Samba-3.0.20 running on a SUSE Enterprise Linux 9</p></li></ul></div><p> Choose a workgroup name (MIDEARTH) for each exercise. </p><p> <a class="indexterm" name="id386463"></a> The network captures provided on the CD-ROM included with this book were captured using <code class="constant">Ethereal</code> version <code class="literal">0.10.6</code>. A later version suffices without problems, but an earlier version may not expose all the information needed. Each capture file has been decoded and listed as a trace file. A summary of all packets has also been included. This makes it possible for you to do all the studying you like without the need to perform the time-consuming equipment configuration and test work. This is a good time to point out that the value that can be derived from this book really does warrant your taking sufficient time to practice each exercise with care and attention to detail. </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id386486"></a>Single-Machine Broadcast Activity</h3></div></div></div><p> In this section, we start a single Windows 9x/Me machine, then monitor network activity for 30 minutes. </p><div class="procedure"><a name="id386496"></a><p class="title"><b>Procedure 16.2. Monitoring Windows 9x Steps</b></p><ol type="1"><li><p> Start the machine from which network activity will be monitored (using <code class="literal">ethereal</code>). Launch <code class="literal">ethereal</code>, click <span class="guimenu">Capture</span> → <span class="guimenuitem">Start</span>. </p><p> Click the following: </p><div class="orderedlist"><ol type="1"><li><p>Update list of packets in real time</p></li><li><p>Automatic scrolling in live capture</p></li><li><p>Enable MAC name resolution</p></li><li><p>Enable network name resolution</p></li><li><p>Enable transport name resolution</p></li></ol></div><p> Click <span class="guibutton">OK</span>. </p></li><li><p> Start the Windows 9x/Me machine to be monitored. Let it run for a full 30 minutes. While monitoring, do not press any keyboard keys, do not click any on-screen icons or menus, and do not answer any dialog boxes. </p></li><li><p> At the conclusion of 30 minutes, stop the capture. Save the capture to a file so you can go back to it later. Leave this machine running in preparation for the task in <a href="primer.html#secondmachine" title="Second Machine Startup Broadcast Interaction">???</a>. </p></li><li><p> Analyze the capture. Identify each discrete message type that was captured. Note what transport protocol was used. Identify the timing between messages of identical types. </p></li></ol></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id386612"></a>Findings</h4></div></div></div><p> The summary of the first 10 minutes of the packet capture should look like <a href="primer.html#pktcap01" title="Figure 16.1. Windows Me Broadcasts The First 10 Minutes">???</a>. A screenshot of a later stage of the same capture is shown in <a href="primer.html#pktcap02" title="Figure 16.2. Windows Me Later Broadcast Sample">???</a>. </p><div class="figure"><a name="pktcap01"></a><p class="title"><b>Figure 16.1. Windows Me Broadcasts The First 10 Minutes</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/WINREPRESSME-Capture.png" width="216" alt="Windows Me Broadcasts The First 10 Minutes"></div></div></div><br class="figure-break"><div class="figure"><a name="pktcap02"></a><p class="title"><b>Figure 16.2. Windows Me Later Broadcast Sample</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/WINREPRESSME-Capture2.png" width="226.8" alt="Windows Me Later Broadcast Sample"></div></div></div><br class="figure-break"><p><a class="indexterm" name="id386725"></a><a class="indexterm" name="id386736"></a> Broadcast messages observed are shown in <a href="primer.html#capsstats01" title="Table 16.1. Windows Me Startup Broadcast Capture Statistics">???</a>. Actual observations vary a little, but not by much. Early in the startup process, the Windows Me machine broadcasts its name for two reasons: first to ensure that its name would not result in a name clash, and second to establish its presence with the Local Master Browser (LMB). </p><div class="table"><a name="capsstats01"></a><p class="title"><b>Table 16.1. Windows Me Startup Broadcast Capture Statistics</b></p><div class="table-contents"><table summary="Windows Me Startup Broadcast Capture Statistics" border="1"><colgroup><col align="left"><col align="center"><col align="center"><col align="left"></colgroup><thead><tr><th align="left">Message</th><th align="center">Type</th><th align="center">Num</th><th align="left">Notes</th></tr></thead><tbody><tr><td align="left">WINEPRESSME<00></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.6 sec apart</td></tr><tr><td align="left">WINEPRESSME<03></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.6 sec apart</td></tr><tr><td align="left">WINEPRESSME<20></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.75 sec apart</td></tr><tr><td align="left">MIDEARTH<00></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.75 sec apart</td></tr><tr><td align="left">MIDEARTH<1d></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.75 sec apart</td></tr><tr><td align="left">MIDEARTH<1e></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.75 sec apart</td></tr><tr><td align="left">MIDEARTH<1b></td><td align="center">Qry</td><td align="center">84</td><td align="left">300 sec apart at stable operation</td></tr><tr><td align="left">__MSBROWSE__</td><td align="center">Reg</td><td align="center">8</td><td align="left">Registered after winning election to Browse Master</td></tr><tr><td align="left">JHT<03></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 x 2. This is the name of the user that logged onto Windows</td></tr><tr><td align="left">Host Announcement WINEPRESSME</td><td align="center">Ann</td><td align="center">2</td><td align="left">Observed at 10 sec</td></tr><tr><td align="left">Domain/Workgroup Announcement MIDEARTH</td><td align="center">Ann</td><td align="center">18</td><td align="left">300 sec apart at stable operation</td></tr><tr><td align="left">Local Master Announcement WINEPRESSME</td><td align="center">Ann</td><td align="center">18</td><td align="left">300 sec apart at stable operation</td></tr><tr><td align="left">Get Backup List Request</td><td align="center">Qry</td><td align="center">12</td><td align="left">6 x 2 early in startup, 0.5 sec apart</td></tr><tr><td align="left">Browser Election Request</td><td align="center">Ann</td><td align="center">10</td><td align="left">5 x 2 early in startup</td></tr><tr><td align="left">Request Announcement WINEPRESSME</td><td align="center">Ann</td><td align="center">4</td><td align="left">Early in startup</td></tr></tbody></table></div></div><br class="table-break"><p><a class="indexterm" name="id387071"></a><a class="indexterm" name="id387079"></a> From the packet trace, it should be noted that no messages were propagated over TCP/IP; all messages employed UDP/IP. When steady-state operation has been achieved, there is a cycle of various announcements, re-election of a browse master, and name queries. These create the symphony of announcements by which network browsing is made possible. </p><p><a class="indexterm" name="id387093"></a> For detailed information regarding the precise behavior of the CIFS/SMB protocols, refer to the book “<span class="quote">Implementing CIFS: The Common Internet File System,</span>” by Christopher Hertel, (Prentice Hall PTR, ISBN: 013047116X). </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="secondmachine"></a>Second Machine Startup Broadcast Interaction</h3></div></div></div><p> At this time, the machine you used to capture the single-system startup trace should still be running. The objective of this task is to identify the interaction of two machines in respect to broadcast activity. </p><div class="procedure"><a name="id387125"></a><p class="title"><b>Procedure 16.3. Monitoring of Second Machine Activity</b></p><ol type="1"><li><p> On the machine from which network activity will be monitored (using <code class="literal">ethereal</code>), launch <code class="literal">ethereal</code> and click <span class="guimenu">Capture</span> → <span class="guimenuitem">Start</span>. </p><p> Click: </p><div class="orderedlist"><ol type="1"><li><p>Update list of packets in real time</p></li><li><p>Automatic scrolling in live capture</p></li><li><p>Enable MAC name resolution</p></li><li><p>Enable network name resolution</p></li><li><p>Enable transport name resolution</p></li></ol></div><p> Click <span class="guibutton">OK</span>. </p></li><li><p> Start the second Windows 9x/Me machine. Let it run for 15 to 20 minutes. While monitoring, do not press any keyboard keys, do not click any on-screen icons or menus, and do not answer any dialog boxes. </p></li><li><p> At the conclusion of the capture time, stop the capture. Be sure to save the captured data so you can examine the network data capture again at a later date should that be necessary. </p></li><li><p> Analyze the capture trace, taking note of the transport protocols used, the types of messages observed, and what interaction took place between the two machines. Leave both machines running for the next task. </p></li></ol></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id387234"></a>Findings</h4></div></div></div><p> <a href="primer.html#capsstats02" title="Table 16.2. Second Machine (Windows 98) Capture Statistics">???</a> summarizes capture statistics observed. As in the previous case, all announcements used UDP/IP broadcasts. Also, as was observed with the last example, the second Windows 9x/Me machine broadcasts its name on startup to ensure that there exists no name clash (i.e., the name is already registered by another machine) on the network segment. Those wishing to explore the inner details of the precise mechanism of how this functions should refer to “<span class="quote">Implementing CIFS: The Common Internet File System.</span>” </p><div class="table"><a name="capsstats02"></a><p class="title"><b>Table 16.2. Second Machine (Windows 98) Capture Statistics</b></p><div class="table-contents"><table summary="Second Machine (Windows 98) Capture Statistics" border="1"><colgroup><col align="left"><col align="center"><col align="center"><col align="left"></colgroup><thead><tr><th align="left">Message</th><th align="center">Type</th><th align="center">Num</th><th align="left">Notes</th></tr></thead><tbody><tr><td align="left">MILGATE98<00></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.6 sec apart</td></tr><tr><td align="left">MILGATE98<03></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.6 sec apart</td></tr><tr><td align="left">MILGATE98<20></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.75 sec apart</td></tr><tr><td align="left">MIDEARTH<00></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.75 sec apart</td></tr><tr><td align="left">MIDEARTH<1d></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.75 sec apart</td></tr><tr><td align="left">MIDEARTH<1e></td><td align="center">Reg</td><td align="center">8</td><td align="left">4 lots of 2, 0.75 sec apart</td></tr><tr><td align="left">MIDEARTH<1b></td><td align="center">Qry</td><td align="center">18</td><td align="left">900 sec apart at stable operation</td></tr><tr><td align="left">JHT<03></td><td align="center">Reg</td><td align="center">2</td><td align="left">This is the name of the user that logged onto Windows</td></tr><tr><td align="left">Host Announcement MILGATE98</td><td align="center">Ann</td><td align="center">14</td><td align="left">Every 120 sec</td></tr><tr><td align="left">Domain/Workgroup Announcement MIDEARTH</td><td align="center">Ann</td><td align="center">6</td><td align="left">900 sec apart at stable operation</td></tr><tr><td align="left">Local Master Announcement WINEPRESSME</td><td align="center">Ann</td><td align="center">6</td><td align="left">Insufficient detail to determine frequency</td></tr></tbody></table></div></div><br class="table-break"><p> <a class="indexterm" name="id387506"></a> <a class="indexterm" name="id387513"></a> <a class="indexterm" name="id387520"></a> Observation of the contents of Host Announcements, Domain/Workgroup Announcements, and Local Master Announcements is instructive. These messages convey a significant level of detail regarding the nature of each machine that is on the network. An example dissection of a Host Announcement is given in <a href="primer.html#hostannounce" title="Figure 16.3. Typical Windows 9x/Me Host Announcement">???</a>. </p><div class="figure"><a name="hostannounce"></a><p class="title"><b>Figure 16.3. Typical Windows 9x/Me Host Announcement</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/HostAnnouncment.png" width="221.4" alt="Typical Windows 9x/Me Host Announcement"></div></div></div><br class="figure-break"></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id387580"></a>Simple Windows Client Connection Characteristics</h3></div></div></div><p> The purpose of this exercise is to discover how Microsoft Windows clients create (establish) connections with remote servers. The methodology involves analysis of a key aspect of how Windows clients access remote servers: the session setup protocol. </p><div class="procedure"><a name="id387592"></a><p class="title"><b>Procedure 16.4. Client Connection Exploration Steps</b></p><ol type="1"><li><p> Configure a Windows 9x/Me machine (MILGATE98) with a share called <code class="constant">Stuff</code>. Create a <em class="parameter"><code>Full Access</code></em> control password on this share. </p></li><li><p> Configure another Windows 9x/Me machine (WINEPRESSME) as a client. Make sure that it exports no shared resources. </p></li><li><p> Start both Windows 9x/Me machines and allow them to stabilize for 10 minutes. Log on to both machines using a user name (JHT) of your choice. Wait approximately 2 minutes before proceeding. </p></li><li><p> Start ethereal (or the network sniffer of your choice). </p></li><li><p> From the WINEPRESSME machine, right-click <span class="guimenu">Network Neighborhood</span>, select <span class="guimenuitem">Explore</span>, select <span class="guimenuitem">My Network Places</span> → <span class="guimenuitem">Entire Network</span> → <span class="guimenuitem">MIDEARTH</span> → <span class="guimenuitem">MILGATE98</span> → <span class="guimenuitem">Stuff</span>. Enter the password you set for the <code class="constant">Full Control</code> mode for the <code class="constant">Stuff</code> share. </p></li><li><p> When the share called <code class="constant">Stuff</code> is being displayed, stop the capture. Save the captured data in case it is needed for later analysis. </p></li><li><p> <a class="indexterm" name="id387716"></a> From the top of the packets captured, scan down to locate the first packet that has interpreted as <code class="constant">Session Setup AndX, User: anonymous; Tree Connect AndX, Path: \\MILGATE98\IPC$</code>. </p></li><li><p><a class="indexterm" name="id387733"></a><a class="indexterm" name="id387741"></a> In the dissection (analysis) panel, expand the <code class="constant">SMB, Session Setup AndX Request, and Tree Connect AndX Request</code>. Examine both operations. Identify the name of the user Account and what password was used. The Account name should be empty. This is a <code class="constant">NULL</code> session setup packet. </p></li><li><p> Return to the packet capture sequence. There will be a number of packets that have been decoded of the type <code class="constant">Session Setup AndX</code>. Locate the last such packet that was targeted at the <code class="constant">\\MILGATE98\IPC$</code> service. </p></li><li><p> <a class="indexterm" name="id387782"></a> <a class="indexterm" name="id387788"></a> Dissect this packet as per the previous one. This packet should have a password length of 24 (characters) and should have a password field, the contents of which is a long hexadecimal number. Observe the name in the Account field. This is a User Mode session setup packet. </p></li></ol></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id387800"></a>Findings and Comments</h4></div></div></div><p> <a class="indexterm" name="id387808"></a> The <code class="constant">IPC$</code> share serves a vital purpose<sup>[<a name="id387819" href="#ftn.id387819">15</a>]</sup> in SMB/CIFS-based networking. A Windows client connects to this resource to obtain the list of resources that are available on the server. The server responds with the shares and print queues that are available. In most but not all cases, the connection is made with a <code class="constant">NULL</code> username and a <code class="constant">NULL</code> password. </p><p> <a class="indexterm" name="id387836"></a> The two packets examined are material evidence of how Windows clients may interoperate with Samba. Samba requires every connection setup to be authenticated using valid UNIX account credentials (UID/GID). This means that even a <code class="constant">NULL</code> session setup can be established only by automatically mapping it to a valid UNIX account. </p><p> <a class="indexterm" name="id387853"></a><a class="indexterm" name="id387859"></a> <a class="indexterm" name="id387868"></a> Samba has a special name for the <code class="constant">NULL</code>, or empty, user account: it calls it the <a class="indexterm" name="id387879"></a>guest account. The default value of this parameter is <code class="constant">nobody</code>; however, this can be changed to map the function of the guest account to any other UNIX identity. Some UNIX administrators prefer to map this account to the system default anonymous FTP account. A sample NULL Session Setup AndX packet dissection is shown in <a href="primer.html#nullconnect" title="Figure 16.4. Typical Windows 9x/Me NULL SessionSetUp AndX Request">???</a>. </p><div class="figure"><a name="nullconnect"></a><p class="title"><b>Figure 16.4. Typical Windows 9x/Me NULL SessionSetUp AndX Request</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/NullConnect.png" width="221.4" alt="Typical Windows 9x/Me NULL SessionSetUp AndX Request"></div></div></div><br class="figure-break"><p> <a class="indexterm" name="id387943"></a> <a class="indexterm" name="id387950"></a> <a class="indexterm" name="id387956"></a> When a UNIX/Linux system does not have a <code class="constant">nobody</code> user account (<code class="filename">/etc/passwd</code>), the operation of the <code class="constant">NULL</code> account cannot validate and thus connections that utilize the guest account fail. This breaks all ability to browse the Samba server and is a common problem reported on the Samba mailing list. A sample User Mode session setup AndX is shown in <a href="primer.html#userconnect" title="Figure 16.5. Typical Windows 9x/Me User SessionSetUp AndX Request">???</a>. </p><div class="figure"><a name="userconnect"></a><p class="title"><b>Figure 16.5. Typical Windows 9x/Me User SessionSetUp AndX Request</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/UserConnect.png" width="221.4" alt="Typical Windows 9x/Me User SessionSetUp AndX Request"></div></div></div><br class="figure-break"><p> <a class="indexterm" name="id388029"></a> The User Mode connection packet contains the account name and the domain name. The password is provided in Microsoft encrypted form, and its length is shown as 24 characters. This is the length of Microsoft encrypted passwords. </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id388041"></a>Windows 200x/XP Client Interaction with Samba-3</h3></div></div></div><p> By now you may be asking, “<span class="quote">Why did you choose to work with Windows 9x/Me?</span>” </p><p> First, we want to demonstrate the simple case. This book is not intended to be a detailed treatise on the Windows networking protocols, but rather to provide prescriptive guidance for deployment of Samba. Second, by starting out with the simple protocol, it can be demonstrated that the more complex case mostly follows the same principles. </p><p> The following exercise demonstrates the case that even MS Windows XP Professional with up-to-date service updates also uses the <code class="constant">NULL</code> account, as well as user accounts. Simply follow the procedure to complete this exercise. </p><p> To complete this exercise, you need a Windows XP Professional client that has been configured as a domain member of either a Samba-controlled domain or a Windows NT4 or 200x Active Directory domain. Here we do not provide details for how to configure this, as full coverage is provided earlier in this book. </p><div class="procedure"><a name="id388076"></a><p class="title"><b>Procedure 16.5. Steps to Explore Windows XP Pro Connection Set-up</b></p><ol type="1"><li><p> Start your domain controller. Also, start the ethereal monitoring machine, launch ethereal, and then wait for the next step to complete. </p></li><li><p> Start the Windows XP Client and wait 5 minutes before proceeding. </p></li><li><p> On the machine from which network activity will be monitored (using <code class="literal">ethereal</code>), launch <code class="literal">ethereal</code> and click <span class="guimenu">Capture</span> → <span class="guimenuitem">Start</span>. </p><p> Click: </p><div class="orderedlist"><ol type="1"><li><p>Update list of packets in real time</p></li><li><p>Automatic scrolling in live capture</p></li><li><p>Enable MAC name resolution</p></li><li><p>Enable network name resolution</p></li><li><p>Enable transport name resolution</p></li></ol></div><p> Click <span class="guibutton">OK</span>. </p></li><li><p> On the Windows XP Professional client, press <span class="guimenu">Ctrl-Alt-Delete</span> to bring up the domain logon screen. Log in using valid credentials for a domain user account. </p></li><li><p> Now proceed to connect to the domain controller as follows: <span class="guimenu">Start</span> → <span class="guimenuitem">(right-click) My Network Places</span> → <span class="guimenuitem">Explore</span> → <span class="guimenuitem">{Left Panel} [+] Entire Network</span> → <span class="guimenuitem">{Left Panel} [+] Microsoft Windows Network</span> → <span class="guimenuitem">{Left Panel} [+] Midearth</span> → <span class="guimenuitem">{Left Panel} [+] Frodo</span> → <span class="guimenuitem">{Left Panel} [+] data</span>. Close the explorer window. </p><p> In this step, our domain name is <code class="constant">Midearth</code>, the domain controller is called <code class="constant">Frodo</code>, and we have connected to a share called <code class="constant">data</code>. </p></li><li><p> Stop the capture on the <code class="literal">ethereal</code> monitoring machine. Be sure to save the captured data to a file so that you can refer to it again later. </p></li><li><p> If desired, the Windows XP Professional client and the domain controller are no longer needed for exercises in this chapter. </p></li><li><p> <a class="indexterm" name="id388290"></a> <a class="indexterm" name="id388296"></a> From the top of the packets captured, scan down to locate the first packet that has interpreted as <code class="constant">Session Setup AndX Request, NTLMSSP_AUTH</code>. </p></li><li><p> <a class="indexterm" name="id388315"></a> <a class="indexterm" name="id388322"></a> <a class="indexterm" name="id388328"></a> In the dissection (analysis) panel, expand the <code class="constant">SMB, Session Setup AndX Request</code>. Expand the packet decode information, beginning at the <code class="constant">Security Blob:</code> entry. Expand the <code class="constant">GSS-API -> SPNEGO -> netTokenTarg -> responseToken -> NTLMSSP</code> keys. This should reveal that this is a <code class="constant">NULL</code> session setup packet. The <code class="constant">User name: NULL</code> so indicates. An example decode is shown in <a href="primer.html#XPCap01" title="Figure 16.6. Typical Windows XP NULL Session Setup AndX Request">???</a>. </p></li><li><p> Return to the packet capture sequence. There will be a number of packets that have been decoded of the type <code class="constant">Session Setup AndX Request</code>. Click the last such packet that has been decoded as <code class="constant">Session Setup AndX Request, NTLMSSP_AUTH</code>. </p></li><li><p> <a class="indexterm" name="id388386"></a> In the dissection (analysis) panel, expand the <code class="constant">SMB, Session Setup AndX Request</code>. Expand the packet decode information, beginning at the <code class="constant">Security Blob:</code> entry. Expand the <code class="constant">GSS-API -> SPNEGO -> netTokenTarg -> responseToken -> NTLMSSP</code> keys. This should reveal that this is a <code class="constant">User Mode</code> session setup packet. The <code class="constant">User name: jht</code> so indicates. An example decode is shown in <a href="primer.html#XPCap02" title="Figure 16.7. Typical Windows XP User Session Setup AndX Request">???</a>. In this case the user name was <code class="constant">jht</code>. This packet decode includes the <code class="constant">Lan Manager Response:</code> and the <code class="constant">NTLM Response:</code>. The values of these two parameters are the Microsoft encrypted password hashes: respectively, the LanMan password and then the NT (case-preserving) password hash. </p></li><li><p> <a class="indexterm" name="id388440"></a> <a class="indexterm" name="id388447"></a> The passwords are 24-character hexadecimal numbers. This packet confirms that this is a User Mode session setup packet. </p></li></ol></div><div class="figure"><a name="XPCap01"></a><p class="title"><b>Figure 16.6. Typical Windows XP NULL Session Setup AndX Request</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/WindowsXP-NullConnection.png" width="270" alt="Typical Windows XP NULL Session Setup AndX Request"></div></div></div><br class="figure-break"><div class="figure"><a name="XPCap02"></a><p class="title"><b>Figure 16.7. Typical Windows XP User Session Setup AndX Request</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/WindowsXP-UserConnection.png" width="270" alt="Typical Windows XP User Session Setup AndX Request"></div></div></div><br class="figure-break"><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id388539"></a>Discussion</h4></div></div></div><p><a class="indexterm" name="id388546"></a> This exercise demonstrates that, while the specific protocol for the Session Setup AndX is handled in a more sophisticated manner by recent MS Windows clients, the underlying rules or principles remain the same. Thus it is demonstrated that MS Windows XP Professional clients still use a <code class="constant">NULL-Session</code> connection to query and locate resources on an advanced network technology server (one using Windows NT4/200x or Samba). It also demonstrates that an authenticated connection must be made before resources can be used. </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id388566"></a>Conclusions to Exercises</h3></div></div></div><p> In summary, the following points have been established in this chapter: </p><div class="itemizedlist"><ul type="disc"><li><p> When NetBIOS over TCP/IP protocols are enabled, MS Windows networking employs broadcast-oriented messaging protocols to provide knowledge of network services. </p></li><li><p> Network browsing protocols query information stored on browse masters that manage information provided by NetBIOS Name Registrations and by way of ongoing host announcements and workgroup announcements. </p></li><li><p> All Samba servers must be configured with a mechanism for mapping the <code class="constant">NULL-Session</code> to a valid but nonprivileged UNIX system account. </p></li><li><p> The use of Microsoft encrypted passwords is built right into the fabric of Windows networking operations. Such passwords cannot be provided from the UNIX <code class="filename">/etc/passwd</code> database and thus must be stored elsewhere on the UNIX system in a manner that Samba can use. Samba-2.x permitted such encrypted passwords to be stored in the <code class="constant">smbpasswd</code> file or in an LDAP database. Samba-3 permits use of multiple <em class="parameter"><code>passdb backend</code></em> databases in concurrent deployment. Refer to <span class="emphasis"><em>TOSHARG2</em></span>, Chapter 10, “<span class="quote">Account Information Databases.</span>” </p></li></ul></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="chap01conc"></a>Dissection and Discussion</h2></div></div></div><p> <a class="indexterm" name="id388644"></a> The exercises demonstrate the use of the <code class="constant">guest</code> account, the way that MS Windows clients and servers resolve computer names to a TCP/IP address, and how connections between a client and a server are established. </p><p> Those wishing background information regarding NetBIOS name types should refer to the Microsoft knowledgebase article <a href="http://support.microsoft.com/support/kb/articles/Q102/78/8.asp" target="_top">Q102878.</a> </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id388668"></a>Technical Issues</h3></div></div></div><p> <a class="indexterm" name="id388676"></a> Network browsing involves SMB broadcast announcements, SMB enumeration requests, connections to the <code class="constant">IPC$</code> share, share enumerations, and SMB connection setup processes. The use of anonymous connections to a Samba server involve the use of the <em class="parameter"><code>guest account</code></em> that must map to a valid UNIX UID. </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="chap01qa"></a>Questions and Answers</h2></div></div></div><p> The questions and answers given in this section are designed to highlight important aspects of Microsoft Windows networking. </p><div class="qandaset"><dl><dt> <a href="primer.html#id388717"> What is the significance of the MIDEARTH<1b> type query? </a></dt><dt> <a href="primer.html#id388760"> What is the significance of the MIDEARTH<1d> type name registration? </a></dt><dt> <a href="primer.html#id388826"> What is the role and significance of the <01><02>__MSBROWSE__<02><01> name registration? </a></dt><dt> <a href="primer.html#id388854"> What is the significance of the MIDEARTH<1e> type name registration? </a></dt><dt> <a href="primer.html#id388881"> What is the significance of the guest account in smb.conf? </a></dt><dt> <a href="primer.html#id388948"> Is it possible to reduce network broadcast activity with Samba-3? </a></dt><dt> <a href="primer.html#id389046"> Can I just use plain-text passwords with Samba? </a></dt><dt> <a href="primer.html#id389122"> What parameter in the smb.conf file is used to enable the use of encrypted passwords? </a></dt><dt> <a href="primer.html#id389161"> Is it necessary to specify encrypt passwords = Yes when Samba-3 is configured as a domain member? </a></dt><dt> <a href="primer.html#id389185"> Is it necessary to specify a guest account when Samba-3 is configured as a domain member server? </a></dt></dl><table border="0" summary="Q and A Set"><col align="left" width="1%"><tbody><tr class="question"><td align="left" valign="top"><a name="id388717"></a><a name="id388720"></a></td><td align="left" valign="top"><p> What is the significance of the MIDEARTH<1b> type query? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> <a class="indexterm" name="id388731"></a> <a class="indexterm" name="id388740"></a> This is a broadcast announcement by which the Windows machine is attempting to locate a Domain Master Browser (DMB) in the event that it might exist on the network. Refer to <span class="emphasis"><em>TOSHARG2,</em></span> Chapter 9, Section 9.7, “<span class="quote">Technical Overview of Browsing,</span>” for details regarding the function of the DMB and its role in network browsing. </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id388760"></a><a name="id388762"></a></td><td align="left" valign="top"><p> What is the significance of the MIDEARTH<1d> type name registration? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> <a class="indexterm" name="id388773"></a> <a class="indexterm" name="id388782"></a> This name registration records the machine IP addresses of the LMBs. Network clients can query this name type to obtain a list of browser servers from the master browser. </p><p> The LMB is responsible for monitoring all host announcements on the local network and for collating the information contained within them. Using this information, it can provide answers to other Windows network clients that request information such as: </p><div class="itemizedlist"><ul type="disc"><li><p> The list of machines known to the LMB (i.e., the browse list) </p></li><li><p> The IP addresses of all domain controllers known for the domain </p></li><li><p> The IP addresses of LMBs </p></li><li><p> The IP address of the DMB (if one exists) </p></li><li><p> The IP address of the LMB on the local segment </p></li></ul></div></td></tr><tr class="question"><td align="left" valign="top"><a name="id388826"></a><a name="id388829"></a></td><td align="left" valign="top"><p> What is the role and significance of the <01><02>__MSBROWSE__<02><01> name registration? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> <a class="indexterm" name="id388842"></a> This name is registered by the browse master to broadcast and receive domain announcements. Its scope is limited to the local network segment, or subnet. By querying this name type, master browsers on networks that have multiple domains can find the names of master browsers for each domain. </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id388854"></a><a name="id388856"></a></td><td align="left" valign="top"><p> What is the significance of the MIDEARTH<1e> type name registration? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> <a class="indexterm" name="id388868"></a> This name is registered by all browse masters in a domain or workgroup. The registration name type is known as the Browser Election Service. Master browsers register themselves with this name type so that DMBs can locate them to perform cross-subnet browse list updates. This name type is also used to initiate elections for Master Browsers. </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id388881"></a><a name="id388883"></a></td><td align="left" valign="top"><p> <a class="indexterm" name="id388888"></a> What is the significance of the <em class="parameter"><code>guest account</code></em> in smb.conf? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> This parameter specifies the default UNIX account to which MS Windows networking NULL session connections are mapped. The default name for the UNIX account used for this mapping is called <code class="constant">nobody</code>. If the UNIX/Linux system that is hosting Samba does not have a <code class="constant">nobody</code> account and an alternate mapping has not been specified, network browsing will not work at all. </p><p> It should be noted that the <em class="parameter"><code>guest account</code></em> is essential to Samba operation. Either the operating system must have an account called <code class="constant">nobody</code> or there must be an entry in the <code class="filename">smb.conf</code> file with a valid UNIX account, such as <a class="indexterm" name="id388938"></a>guest account = ftp. </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id388948"></a><a name="id388950"></a></td><td align="left" valign="top"><p> Is it possible to reduce network broadcast activity with Samba-3? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> <a class="indexterm" name="id388962"></a> <a class="indexterm" name="id388968"></a> Yes, there are two ways to do this. The first involves use of WINS (See <span class="emphasis"><em>TOSHARG2</em></span>, Chapter 9, Section 9.5, “<span class="quote">WINS The Windows Inter-networking Name Server</span>”); the alternate method involves disabling the use of NetBIOS over TCP/IP. This second method requires a correctly configured DNS server (see <span class="emphasis"><em>TOSHARG2</em></span>, Chapter 9, Section 9.3, “<span class="quote">Discussion</span>”). </p><p> <a class="indexterm" name="id388998"></a> <a class="indexterm" name="id389005"></a> <a class="indexterm" name="id389014"></a> The use of WINS reduces network broadcast traffic. The reduction is greatest when all network clients are configured to operate in <em class="parameter"><code>Hybrid Mode</code></em>. This can be effected through use of DHCP to set the NetBIOS node type to type 8 for all network clients. Additionally, it is beneficial to configure Samba to use <a class="indexterm" name="id389030"></a>name resolve order = wins host cast. </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> Use of SMB without NetBIOS is possible only on Windows 200x/XP Professional clients and servers, as well as with Samba-3. </p></div></td></tr><tr class="question"><td align="left" valign="top"><a name="id389046"></a><a name="id389048"></a></td><td align="left" valign="top"><p> Can I just use plain-text passwords with Samba? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> Yes, you can configure Samba to use plain-text passwords, though this does create a few problems. </p><p> First, the use of <code class="filename">/etc/passwd</code>-based plain-text passwords requires that registry modifications be made on all MS Windows client machines to enable plain-text passwords support. This significantly diminishes the security of MS Windows client operation. Many network administrators are bitterly opposed to doing this. </p><p> Second, Microsoft has not maintained plain-text password support since the default setting was made disabling this. When network connections are dropped by the client, it is not possible to re-establish the connection automatically. Users need to log off and then log on again. Plain-text password support may interfere with recent enhancements that are part of the Microsoft move toward a more secure computing environment. </p><p> Samba-3 supports Microsoft encrypted passwords. Be advised not to reintroduce plain-text password handling. Just create user accounts by running <code class="literal">smbpasswd -a 'username'</code> </p><p> It is not possible to add a user to the <em class="parameter"><code>passdb backend</code></em> database unless there is a UNIX system account for that user. On systems that run <code class="literal">winbindd</code> to access the Samba PDC/BDC to provide Windows user and group accounts, the <em class="parameter"><code>idmap uid, idmap gid</code></em> ranges set in the <code class="filename">smb.conf</code> file provide the local UID/GIDs needed for local identity management purposes. </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id389122"></a><a name="id389124"></a></td><td align="left" valign="top"><p> What parameter in the <code class="filename">smb.conf</code> file is used to enable the use of encrypted passwords? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> The parameter in the <code class="filename">smb.conf</code> file that controls this behavior is known as <em class="parameter"><code>encrypt passwords</code></em>. The default setting for this in Samba-3 is <code class="constant">Yes (Enabled)</code>. </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id389161"></a><a name="id389163"></a></td><td align="left" valign="top"><p> Is it necessary to specify <a class="indexterm" name="id389168"></a>encrypt passwords = Yes when Samba-3 is configured as a domain member? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> No. This is the default behavior. </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id389185"></a><a name="id389188"></a></td><td align="left" valign="top"><p> Is it necessary to specify a <em class="parameter"><code>guest account</code></em> when Samba-3 is configured as a domain member server? </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> Yes. This is a local function on the server. The default setting is to use the UNIX account <code class="constant">nobody</code>. If this account does not exist on the UNIX server, then it is necessary to provide a <a class="indexterm" name="id389210"></a>guest account = an_account, where <code class="constant">an_account</code> is a valid local UNIX user account. </p></td></tr></tbody></table></div></div><div class="footnotes"><br><hr width="100" align="left"><div class="footnote"><p><sup>[<a name="ftn.id387819" href="#id387819">15</a>] </sup>TOSHARG2, Sect 4.5.1</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="appendix.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="RefSection.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="gpl.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 15. A Collection of Useful Tidbits </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Appendix A. GNU General Public License</td></tr></table></div></body></html>