| blob | 45d9711940b802871e0d8e591a70150c6e22c5b0 |
1 <?xml version="1.0" encoding="iso-8859-1"?>
2 <!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
3 <appendix id="primer">
4 <title>Networking Primer</title>
6 <para>
7 You are about to use the equivalent of a microscope to look at the information
8 that runs through the veins of a Windows network. We do more to observe the information than
9 to interrogate it. When you are done with this chapter, you should have a good understanding
10 of the types of information that flow over the network. Do not worry, this is not
11 a biology lesson. We won't lose you in unnecessary detail. Think to yourself, <quote>This
12 is easy,</quote> then tackle each exercise without fear.
13 </para>
15 <para>
16 Samba can be configured with a minimum of complexity. Simplicity should be mastered
17 before you get too deeply into complexities. Let's get moving, we have work to do.
18 </para>
20 <sect1>
21 <title>Requirements and Notes</title>
22 <para>
23 Successful completion of this chapter requires two Microsoft Windows 9x/Me Workstations,
24 as well as two Microsoft Windows XP Professional Workstations, each equipped with an Ethernet
25 card connected using a hub. Also required is one additional server (either Windows
26 NT4 Server, Windows 2000 Server, or a Samba-3 on UNIX/Linux server) running a network
27 sniffer and analysis application (ethereal is a good choice). All work should be undertaken
28 on a quiet network where there is no other traffic. It is best to use a dedicated hub
29 with only the machines under test connected at the time of the exercises.
30 </para>
32 <para><indexterm>
33 <primary>Ethereal</primary>
34 </indexterm>
35 Ethereal has become the network protocol analyzer of choice for many network administrators.
36 You may find more information regarding this tool from the
37 <ulink url="http://www.ethereal.com">Ethereal</ulink> Web site. Ethereal installation
38 files for Windows may be obtained from the Ethereal Web site. Ethereal is provided with
39 SUSE and Red Hat Linux distributions, as well as many other Linux distributions. It may
40 not be installed on your system by default. If it is not installed, you may also need
41 to install the <command>libpcap </command> software before you can install or use Ethereal.
42 Please refer to the instructions for your operating system or to the Ethereal Web site
43 for information regarding the installation and operation of Ethereal.
44 </para>
46 <para>
47 To obtain <command>ethereal</command> for your system, please visit the Ethereal
48 <ulink url="http://www.ethereal.com/download.html#binaries">download site.</ulink>
49 </para>
51 <note><para>
52 The successful completion of this chapter requires that you capture network traffic
53 using <command>ethereal</command>. It is recommended that you use a hub, not an
54 etherswitch. It is necessary for the device used to act as a repeater, not as a
55 filter. Ethernet switches may filter out traffic that is not directed at the machine
56 that is used to monitor traffic; this would not allow you to complete the projects.
57 </para></note>
59 <para>
60 <indexterm><primary>network</primary><secondary>captures</secondary></indexterm>
61 Do not worry too much if you do not have access to all this equipment; network captures
62 from the exercises are provided on the enclosed CD-ROM. This makes it possible to dive directly
63 into the analytical part of the exercises if you so desire.
64 </para>
66 <para><indexterm>
67 <primary>network</primary>
68 <secondary>sniffer</secondary>
69 </indexterm><indexterm>
70 <primary>protocol analysis</primary>
71 </indexterm>
72 Please do not be alarmed at the use of a high-powered analysis tool (ethereal) in this
73 first chapter. We expose you only to a minimum of detail necessary to complete
74 the exercises in this chapter. If you choose to use any other network sniffer and protocol
75 analysis tool, be advised that it may not allow you to examine the contents of
76 recently added security protocols used by Windows 200x/XP.
77 </para>
79 <para>
80 You could just skim through the exercises and try to absorb the key points made.
81 The exercises provide all the information necessary to convince the die-hard network
82 engineer. You possibly do not require so much convincing and may just want to move on,
83 in which case you should at least read <link linkend="chap01conc"/>.
84 </para>
86 <para>
87 <link linkend="chap01qa"/> also provides useful information
88 that may help you to avoid significantly time-consuming networking problems.
89 </para>
90 </sect1>
92 <sect1>
93 <title>Introduction</title>
95 <para>
96 The purpose of this chapter is to create familiarity with key aspects of Microsoft Windows
97 network computing. If you want a solid technical grounding, do not gloss over these exercises.
98 The points covered are recurrent issues on the Samba mailing lists.
99 </para>
101 <para><indexterm>
102 <primary>network</primary>
103 <secondary>broadcast</secondary>
104 </indexterm>
105 You can see from these exercises that Windows networking involves quite a lot of network
106 broadcast traffic. You can look into the contents of some packets, but only to see
107 some particular information that the Windows client sends to a server in the course of
108 establishing a network connection.
109 </para>
111 <para>
112 To many people, browsing is everything that happens when one uses Microsoft Internet Explorer.
113 It is only when you start looking at network traffic and noting the protocols
114 and types of information that are used that you can begin to appreciate the complexities of
115 Windows networking and, more importantly, what needs to be configured so that it can work.
116 Detailed information regarding browsing is provided in the recommended
117 preparatory reading.
118 </para>
120 <para>
121 Recommended preparatory reading: <emphasis>The Official Samba-3 HOWTO and Reference Guide</emphasis> (TOSHARG)
122 Chapter 9, <quote>Network Browsing,</quote> and Chapter 3, <quote>Server Types and
123 Security Modes.</quote>
124 </para>
126 <sect2>
127 <title>Assignment Tasks</title>
129 <para><indexterm>
130 <primary>browsing</primary>
131 </indexterm>
132 You are about to witness how Microsoft Windows computer networking functions. The
133 exercises step through identification of how a client machine establishes a
134 connection to a remote Windows server. You observe how Windows machines find
135 each other (i.e., how browsing works), and how the two key types of user identification
136 (share mode security and user mode security) are affected.
137 </para>
139 <para><indexterm>
140 <primary>network</primary>
141 <secondary>analyzer</secondary>
142 </indexterm>
143 The networking protocols used by MS Windows networking when working with Samba
144 use TCP/IP as the transport protocol. The protocols that are specific to Windows
145 networking are encapsulated in TCP/IP. The network analyzer we use (ethereal)
146 is able to show you the contents of the TCP/IP packets (or messages).
147 </para>
149 <procedure id="chap01tasks">
150 <title>Chapter 1 &smbmdash; Tasks</title>
152 <step><para><indexterm>
153 <primary>network</primary>
154 <secondary>trace</secondary>
155 </indexterm><indexterm>
156 <primary>host announcement</primary>
157 </indexterm><indexterm>
158 <primary>name resolution</primary>
159 </indexterm>
160 Examine network traces to witness SMB broadcasts, host announcements,
161 and name resolution processes.
162 </para></step>
164 <step><para>
165 Examine network traces to witness how share mode security functions.
166 </para></step>
168 <step><para>
169 Examine network traces to witness the use of user mode security.
170 </para></step>
172 <step><para>
173 Review traces of network logons for a Windows 9x/Me client as well as
174 a Domain logon for a Windows XP Professional client.
175 </para></step>
176 </procedure>
178 </sect2>
179 </sect1>
181 <sect1>
182 <title>Exercises</title>
184 <para>
185 <indexterm><primary>ethereal</primary></indexterm>
186 You are embarking on a course of discovery. The first part of the exercise requires
187 two MS Windows 9x/Me systems. We called one machine <constant>WINEPRESSME</constant> and the
188 other <constant>MILGATE98</constant>. Each needs an IP address; we used <literal>10.1.1.10</literal>
189 and <literal>10.1.1.11</literal>. The test machines need to be networked via a <emphasis>hub</emphasis>. A UNIX/Linux
190 machine is required to run <command>ethereal</command> to enable the network activity to be captured.
191 It is important that the machine from which network activity is captured must not interfere with
192 the operation of the Windows workstations. It is helpful for this machine to be passive (does not
193 send broadcast information) to the network.
194 </para>
196 <para>
197 For these exercises, our test environment consisted of a SUSE 9.2 Professional Linux Workstation running
198 VMWare 4.5. The following VMWare images were prepared:
199 </para>
201 <itemizedlist>
202 <listitem><para>Windows 98 &smbmdash; name: MILGATE98.</para></listitem>
203 <listitem><para>Windows Me &smbmdash; name: WINEPRESSME.</para></listitem>
204 <listitem><para>Windows XP Professional &smbmdash; name: LightrayXP.</para></listitem>
205 <listitem><para>Samba-3.0.12 running on a SUSE Enterprise Linux 9.</para></listitem>
206 </itemizedlist>
208 <para>
209 Choose a workgroup name (MIDEARTH) for each exercise.
210 </para>
212 <para>
213 <indexterm><primary>ethereal</primary></indexterm>
214 The network captures provided on the CD-ROM at the back of this book were captured using <constant>ethereal</constant>
215 version <literal>0.10.6</literal>. A later version suffices without problems, but an earlier version may not
216 expose all the information needed. Each capture file has been decoded and listed as a trace file. A summary of all
217 packets has also been included. This makes it possible for you to do all the studying you like without the need to
218 perform the time-consuming equipment configuration and test work. This is a good time to point out the value
219 that can be derived from this book really does warrant your taking sufficient time to practice each exercise with
220 care and attention to detail.
221 </para>
223 <sect2>
224 <title>Single Machine Broadcast Activity</title>
226 <para>
227 In this section, we start a single Windows 9x/Me machine, then monitor network activity for 30 minutes.
228 </para>
230 <procedure>
231 <step><para>
232 Start the machine from which network activity will be monitored (using <command>ethereal</command>).
233 Launch <command>ethereal</command>, click
234 <menuchoice>
235 <guimenu>Capture</guimenu>
236 <guimenuitem>Start</guimenuitem>
237 </menuchoice>.
238 </para>
240 <para>
241 Click the following:
242 <orderedlist>
243 <listitem><para>Update list of packets in real time</para></listitem>
244 <listitem><para>Automatic scrolling in live capture</para></listitem>
245 <listitem><para>Enable MAC name resolution</para></listitem>
246 <listitem><para>Enable network name resolution</para></listitem>
247 <listitem><para>Enable transport name resolution</para></listitem>
248 </orderedlist>
249 Click <guibutton>OK</guibutton>.
250 </para></step>
252 <step><para>
253 Start the Windows 9x/Me machine to be monitored. Let it run for a full 30 minutes. While monitoring,
254 do not press any keyboard keys, do not click any on-screen icons or menus; and do not answer any dialog boxes.
255 </para></step>
257 <step><para>
258 At the conclusion of 30 minutes, stop the capture. Save the capture to a file so you can go back to it later.
259 Leave this machine running in preparation for the task in <link linkend="secondmachine"/>.
260 </para></step>
262 <step><para>
263 Analyze the capture. Identify each discrete message type that was captured. Note what transport protocol
264 was used. Identify the timing between messages of identical types.
265 </para></step>
267 </procedure>
269 <sect3>
270 <title>Findings</title>
272 <para>
273 The summary of the first 10 minutes of the packet capture should look like <link linkend="pktcap01"/>.
274 A screenshot of a later stage of the same capture is shown in <link linkend="pktcap02"/>.
275 </para>
277 <image id="pktcap01">
278 <imagedescription>Windows Me &smbmdash; Broadcasts &smbmdash; The First 10 Minutes</imagedescription>
279 <imagefile scale="40">WINREPRESSME-Capture</imagefile>
280 </image>
282 <image id="pktcap02">
283 <imagedescription>Windows Me &smbmdash; Later Broadcast Sample</imagedescription>
284 <imagefile scale="42">WINREPRESSME-Capture2</imagefile>
285 </image>
287 <para><indexterm>
288 <primary>Local Master Browser</primary>
289 <see>LMB</see>
290 </indexterm><indexterm>
291 <primary>LMB</primary>
292 </indexterm>
293 Broadcast messages observed are shown in <link linkend="capsstats01"/>.
294 Actual observations vary a little, but not by much.
295 Early in the startup process, the Windows Me machine broadcasts its name for two reasons;
296 first to ensure that its name would not result in a name clash, and second to establish its
297 presence with the Local Master Browser (LMB).
298 </para>
300 <table id="capsstats01">
301 <title>Windows Me &smbmdash; Startup Broadcast Capture Statistics</title>
302 <tgroup cols="4">
303 <colspec align="left" colwidth="3*"/>
304 <colspec align="center"/>
305 <colspec align="center"/>
306 <colspec align="left" colwidth="3*"/>
307 <thead>
308 <row>
309 <entry>Message</entry>
310 <entry>Type</entry>
311 <entry>Num</entry>
312 <entry>Notes</entry>
313 </row>
314 </thead>
315 <tbody>
316 <row>
317 <entry>WINEPRESSME<00></entry>
318 <entry>Reg</entry>
319 <entry>8</entry>
320 <entry>4 lots of 2, 0.6 sec apart.</entry>
321 </row>
322 <row>
323 <entry>WINEPRESSME<03></entry>
324 <entry>Reg</entry>
325 <entry>8</entry>
326 <entry>4 lots of 2, 0.6 sec apart.</entry>
327 </row>
328 <row>
329 <entry>WINEPRESSME<20></entry>
330 <entry>Reg</entry>
331 <entry>8</entry>
332 <entry>4 lots of 2, 0.75 sec apart.</entry>
333 </row>
334 <row>
335 <entry>MIDEARTH<00></entry>
336 <entry>Reg</entry>
337 <entry>8</entry>
338 <entry>4 lots of 2, 0.75 sec apart.</entry>
339 </row>
340 <row>
341 <entry>MIDEARTH<1d></entry>
342 <entry>Reg</entry>
343 <entry>8</entry>
344 <entry>4 lots of 2, 0.75 sec apart.</entry>
345 </row>
346 <row>
347 <entry>MIDEARTH<1e></entry>
348 <entry>Reg</entry>
349 <entry>8</entry>
350 <entry>4 lots of 2, 0.75 sec apart.</entry>
351 </row>
352 <row>
353 <entry>MIDEARTH<1b></entry>
354 <entry>Qry</entry>
355 <entry>84</entry>
356 <entry>300 sec apart at stable operation.</entry>
357 </row>
358 <row>
359 <entry>__MSBROWSE__</entry>
360 <entry>Reg</entry>
361 <entry>8</entry>
362 <entry>Registered after winning election to Browse Master.</entry>
363 </row>
364 <row>
365 <entry>JHT<03></entry>
366 <entry>Reg</entry>
367 <entry>8</entry>
368 <entry>4 x 2. This is the name of the user that logged onto Windows.</entry>
369 </row>
370 <row>
371 <entry>Host Announcement WINEPRESSME</entry>
372 <entry>Ann</entry>
373 <entry>2</entry>
374 <entry>Observed at 10 sec.</entry>
375 </row>
376 <row>
377 <entry>Domain/Workgroup Announcement MIDEARTH</entry>
378 <entry>Ann</entry>
379 <entry>18</entry>
380 <entry>300 sec apart at stable operation.</entry>
381 </row>
382 <row>
383 <entry>Local Master Announcement WINEPRESSME</entry>
384 <entry>Ann</entry>
385 <entry>18</entry>
386 <entry>300 sec apart at stable operation.</entry>
387 </row>
388 <row>
389 <entry>Get Backup List Request</entry>
390 <entry>Qry</entry>
391 <entry>12</entry>
392 <entry>6 x 2 early in startup, 0.5 sec apart.</entry>
393 </row>
394 <row>
395 <entry>Browser Election Request</entry>
396 <entry>Ann</entry>
397 <entry>10</entry>
398 <entry>5 x 2 early in startup.</entry>
399 </row>
400 <row>
401 <entry>Request Announcement WINEPRESSME</entry>
402 <entry>Ann</entry>
403 <entry>4</entry>
404 <entry>Early in startup.</entry>
405 </row>
406 </tbody>
407 </tgroup>
408 </table>
410 <para><indexterm>
411 <primary>election</primary>
412 </indexterm><indexterm>
413 <primary>browse master</primary>
414 </indexterm>
415 From the packet trace, it should be noted that no messages were propagated over TCP/IP;
416 all employed UDP/IP. When steady state operation has been achieved, there is a cycle
417 of various announcements, re-election of a browse master, and name queries. These create
418 the symphony of announcements by which network browsing is made possible.
419 </para>
421 <para><indexterm>
422 <primary>CIFS</primary>
423 </indexterm>
424 For detailed information regarding the precise behavior of the CIFS/SMB protocols, the
425 reader is referred to the book <quote>Implementing CIFS: The Common Internet File System,</quote>
426 by Christopher Hertel, Publisher: Prentice Hall PTR, ISBN: 013047116X.
427 </para>
429 </sect3>
431 </sect2>
433 <sect2 id="secondmachine">
434 <title>Second Machine Startup Broadcast Interaction</title>
436 <para>
437 At this time, the machine you used to capture the single system startup trace should still be running.
438 The objective of this task is to identify the interaction of two machines in respect to broadcast activity.
439 </para>
441 <procedure>
442 <step><para>
443 On the machine from which network activity will be monitored (using <command>ethereal</command>),
444 launch <command>ethereal</command> and click
445 <menuchoice>
446 <guimenu>Capture</guimenu>
447 <guimenuitem>Start</guimenuitem>
448 </menuchoice>.
449 </para>
451 <para>
452 Click:
453 <orderedlist>
454 <listitem><para>Update list of packets in real time</para></listitem>
455 <listitem><para>Automatic scrolling in live capture</para></listitem>
456 <listitem><para>Enable MAC name resolution</para></listitem>
457 <listitem><para>Enable network name resolution</para></listitem>
458 <listitem><para>Enable transport name resolution</para></listitem>
459 </orderedlist>
460 Click <guibutton>OK</guibutton>.
461 </para></step>
463 <step><para>
464 Start the second Windows 9x/Me machine. Let it run for 15-20 minutes. While monitoring, do not press
465 any keyboard keys, do not click any on-screen icons or menus, and do not answer any dialog boxes.
466 </para></step>
468 <step><para>
469 At the conclusion of the capture time, stop the capture. Be sure to save the captured data so you
470 can examine the network data capture again at a later date should that be necessary.
471 </para></step>
473 <step><para>
474 Analyze the capture trace, taking note of the transport protocols used, the types of messages observed,
475 and what interaction took place between the two machines. Leave both machines running for the next task.
476 </para></step>
477 </procedure>
479 <sect3>
480 <title>Findings</title>
482 <para>
483 <link linkend="capsstats02"/> summarizes capture statistics observed. As in the previous case,
484 all announcements used UDP/IP broadcasts. Also, as was observed with the last example, the second
485 Windows 9x/Me machine broadcasts its name on startup to ensure that there exists no name clash
486 (i.e., the name is already registered by another machine) on the network segment. Those wishing
487 to explore the inner details of the precise mechanism of how this functions should refer to
488 the book <quote>Implementing CIFS: The Common Internet File System,</quote> referred to previously.
489 </para>
491 <table id="capsstats02">
492 <title>Second Machine (Windows 98) &smbmdash; Capture Statistics</title>
493 <tgroup cols="4">
494 <colspec align="left" colwidth="3*"/>
495 <colspec align="center"/>
496 <colspec align="center"/>
497 <colspec align="left" colwidth="3*"/>
498 <thead>
499 <row>
500 <entry>Message</entry>
501 <entry>Type</entry>
502 <entry>Num</entry>
503 <entry>Notes</entry>
504 </row>
505 </thead>
506 <tbody>
507 <row>
508 <entry>MILGATE98<00></entry>
509 <entry>Reg</entry>
510 <entry>8</entry>
511 <entry>4 lots of 2, 0.6 sec apart.</entry>
512 </row>
513 <row>
514 <entry>MILGATE98<03></entry>
515 <entry>Reg</entry>
516 <entry>8</entry>
517 <entry>4 lots of 2, 0.6 sec apart.</entry>
518 </row>
519 <row>
520 <entry>MILGATE98<20></entry>
521 <entry>Reg</entry>
522 <entry>8</entry>
523 <entry>4 lots of 2, 0.75 sec apart.</entry>
524 </row>
525 <row>
526 <entry>MIDEARTH<00></entry>
527 <entry>Reg</entry>
528 <entry>8</entry>
529 <entry>4 lots of 2, 0.75 sec apart.</entry>
530 </row>
531 <row>
532 <entry>MIDEARTH<1d></entry>
533 <entry>Reg</entry>
534 <entry>8</entry>
535 <entry>4 lots of 2, 0.75 sec apart.</entry>
536 </row>
537 <row>
538 <entry>MIDEARTH<1e></entry>
539 <entry>Reg</entry>
540 <entry>8</entry>
541 <entry>4 lots of 2, 0.75 sec apart.</entry>
542 </row>
543 <row>
544 <entry>MIDEARTH<1b></entry>
545 <entry>Qry</entry>
546 <entry>18</entry>
547 <entry>900 sec apart at stable operation.</entry>
548 </row>
549 <row>
550 <entry>JHT<03></entry>
551 <entry>Reg</entry>
552 <entry>2</entry>
553 <entry>This is the name of the user that logged onto Windows.</entry>
554 </row>
555 <row>
556 <entry>Host Announcement MILGATE98</entry>
557 <entry>Ann</entry>
558 <entry>14</entry>
559 <entry>Every 120 sec.</entry>
560 </row>
561 <row>
562 <entry>Domain/Workgroup Announcement MIDEARTH</entry>
563 <entry>Ann</entry>
564 <entry>6</entry>
565 <entry>900 sec apart at stable operation.</entry>
566 </row>
567 <row>
568 <entry>Local Master Announcement WINEPRESSME</entry>
569 <entry>Ann</entry>
570 <entry>6</entry>
571 <entry>Insufficient detail to determine frequency.</entry>
572 </row>
573 </tbody>
574 </tgroup>
575 </table>
577 <para>
578 <indexterm><primary>host announcement</primary></indexterm>
579 <indexterm><primary>Local Master Announcement</primary></indexterm>
580 <indexterm><primary>Workgroup Announcement</primary></indexterm>
581 Observation of the contents of Host Announcements, Domain/Workgroup Announcements,
582 and Local Master Announcements is instructive. These messages convey a significant
583 level of detail regarding the nature of each machine that is on the network. An example
584 dissection of a Host Announcement is given in <link linkend="hostannounce"/>.
585 </para>
588 <image id="hostannounce">
589 <imagedescription>Typical Windows 9x/Me Host Announcement</imagedescription>
590 <imagefile scale="41">HostAnnouncment</imagefile>
591 </image>
592 </sect3>
594 </sect2>
596 <sect2>
597 <title>Simple Windows Client Connection Characteristics</title>
599 <para>
600 The purpose of this exercise is to discover how Microsoft Windows clients create (establish)
601 connections with remote servers. The methodology involves analysis of a key aspect of how
602 Windows clients access remote servers: the session setup protocol.
603 </para>
605 <procedure>
606 <step><para>
607 Configure a Windows 9x/Me machine (MILGATE98) with a share called <constant>Stuff</constant>.
608 Create a <parameter>Full Access</parameter> control password on this share.
609 </para></step>
611 <step><para>
612 Configure another Windows 9x/Me machine (WINEPRESSME) as a client. Make sure that it exports
613 no shared resources.
614 </para></step>
616 <step><para>
617 Start both Windows 9x/Me machines and allow them to stabilize for 10 minutes. Log on to both
618 machines using a user name (JHT) of your choice. Wait approximately two minutes before proceeding.
619 </para></step>
621 <step><para>
622 Start ethereal (or the network sniffer of your choice).
623 </para></step>
625 <step><para>
626 From the WINEPRESSME machine, right-click <guimenu>Network Neighborhood</guimenu>, select
627 <guimenuitem>Explore</guimenuitem>, select
628 <menuchoice>
629 <guimenuitem>My Network Places</guimenuitem>
630 <guimenuitem>Entire Network</guimenuitem>
631 <guimenuitem>MIDEARTH</guimenuitem>
632 <guimenuitem>MILGATE98</guimenuitem>
633 <guimenuitem>Stuff</guimenuitem>
634 </menuchoice>.
635 Enter the password you set for the <constant>Full Control</constant> mode for the
636 <constant>Stuff</constant> share.
637 </para></step>
639 <step><para>
640 When the share called <constant>Stuff</constant> is being displayed, stop the capture.
641 Save the captured data in case it is needed for later analysis.
642 </para></step>
644 <step><para>
645 <indexterm><primary>session setup</primary></indexterm>
646 From the top of the packets captured, scan down to locate the first packet that has
647 interpreted as <constant>Session Setup AndX, User: anonymous; Tree Connect AndX,
648 Path: \\MILGATE98\IPC$</constant>.
649 </para></step>
651 <step><para><indexterm>
652 <primary>Session Setup</primary>
653 </indexterm><indexterm>
654 <primary>Tree Connect</primary>
655 </indexterm>
656 In the dissection (analysis) panel, expand the <constant>SMB, Session Setup AndX Request,
657 and Tree Connect AndX Request</constant>. Examine both operations. Identify the name of
658 the user Account and what password was used. The Account name should be empty.
659 This is a <constant>NULL</constant> session setup packet.
660 </para></step>
662 <step><para>
663 Return to the packet capture sequence. There will be a number of packets that have been
664 decoded of the type <constant>Session Setup AndX</constant>. Locate the last such packet
665 that was targeted at the <constant>\\MILGATE98\IPC$</constant> service.
666 </para></step>
668 <step><para>
669 <indexterm><primary>password length</primary></indexterm>
670 <indexterm><primary>User Mode</primary></indexterm>
671 Dissect this packet as per the one above. This packet should have a password length
672 of 24 (characters) and should have a password field, the contents of which is a
673 long hexadecimal number. Observe the name in the Account field. This is a User Mode
674 session setup packet.
675 </para></step>
676 </procedure>
678 <sect3>
679 <title>Findings and Comments</title>
681 <para>
682 <indexterm><primary>IPC$</primary></indexterm>
683 The <constant>IPC$</constant> share serves a vital purpose<footnote><para>TOSHARG, Sect 4.5.1</para></footnote>
684 in SMB/CIFS based networking. A Windows client connects to this resource to obtain the list of
685 resources that are available on the server. The server responds with the shares and print queues that
686 are available. In most but not all cases, the connection is made with a <constant>NULL</constant>
687 username and a <constant>NULL</constant> password.
688 </para>
690 <para>
691 <indexterm><primary>account credentials</primary></indexterm>
692 The two packets examined are material evidence with respect to how Windows clients may
693 interoperate with Samba. Samba requires every connection setup to be authenticated using
694 valid UNIX account credentials (UID/GID). This means that even a <constant>NULL</constant>
695 session setup can be established only by automatically mapping it to a valid UNIX
696 account.
697 </para>
699 <para>
700 <indexterm><primary>NULL session</primary></indexterm><indexterm>
701 <primary>guest account</primary>
702 </indexterm>
703 <indexterm><primary>nobody</primary></indexterm>
704 Samba has a special name for the <constant>NULL</constant>, or empty, user account.
705 It calls that the <smbconfoption name="guest account"/>. The
706 default value of this parameter is <constant>nobody</constant>; however, this can be
707 changed to map the function of the guest account to any other UNIX identity. Some
708 UNIX administrators prefer to map this account to the system default anonymous
709 FTP account. A sample NULL Session Setup AndX packet dissection is shown in
710 <link linkend="nullconnect"/>.
711 </para>
713 <image id="nullconnect">
714 <imagedescription>Typical Windows 9x/Me NULL SessionSetUp AndX Request</imagedescription>
716 <imagefile scale="41">NullConnect</imagefile>
717 </image>
719 <para>
720 <indexterm><primary>nobody</primary></indexterm>
721 <indexterm><primary>/etc/passwd</primary></indexterm>
722 <indexterm><primary>guest account</primary></indexterm>
723 When a UNIX/Linux system does not have a <constant>nobody</constant> user account
724 (<filename>/etc/passwd</filename>), the operation of the <constant>NULL</constant>
725 account cannot validate and thus connections that utilize the guest account
726 fail. This breaks all ability to browse the Samba server and is a common
727 problem reported on the Samba mailing list. A sample User Mode Session Setup AndX
728 is shown in <link linkend="userconnect"/>.
729 </para>
731 <image id="userconnect">
732 <imagedescription>Typical Windows 9x/Me User SessionSetUp AndX Request</imagedescription>
733 <imagefile scale="41">UserConnect</imagefile>
734 </image>
736 <para>
737 <indexterm><primary>encrypted</primary></indexterm>
738 The User Mode connection packet contains the account name and the domain name.
739 The password is provided in Microsoft encrypted form, and its length is shown
740 as 24 characters. This is the length of Microsoft encrypted passwords.
741 </para>
743 </sect3>
745 </sect2>
747 <sect2>
748 <title>Windows 200x/XP Client Interaction with Samba-3</title>
750 <para>
751 By now you may be asking, <quote>Why did you choose to work with Windows 9x/Me?</quote>
752 </para>
754 <para>
755 First, we want to demonstrate the simple case. This book is not intended to be a detailed treatise
756 on the Windows networking protocols, but rather to provide prescriptive guidance for deployment of Samba.
757 Second, by starting out with the simple protocol, it can be demonstrated that the more complex case mostly
758 follows the same principles.
759 </para>
761 <para>
762 The following exercise demonstrates the case that even MS Windows XP Professional with up-to-date service
763 updates also uses the <constant>NULL</constant> account, as well as user accounts. Simply follow the procedure
764 to complete this exercise.
765 </para>
767 <para>
768 To complete this exercise, you need a Windows XP Professional client that has been configured as
769 a Domain Member of either a Samba controlled domain or a Windows NT4 or 200x Active Directory domain.
770 Here we do not provide details for how to configure this, as full coverage is provided later in this book.
771 </para>
773 <procedure>
775 <step><para>
776 Start your Domain Controller. Also, start the ethereal monitoring machine, launch ethereal,
777 and then wait for the next step to complete.
778 </para></step>
780 <step><para>
781 Start the Windows XP Client and wait five minutes before proceeding.
782 </para></step>
784 <step><para>
785 On the machine from which network activity will be monitored (using <command>ethereal</command>),
786 launch <command>ethereal</command> and click
787 <menuchoice>
788 <guimenu>Capture</guimenu>
789 <guimenuitem>Start</guimenuitem>
790 </menuchoice>.
791 </para>
793 <para>
794 Click:
795 <orderedlist>
796 <listitem><para>Update list of packets in real time</para></listitem>
797 <listitem><para>Automatic scrolling in live capture</para></listitem>
798 <listitem><para>Enable MAC name resolution</para></listitem>
799 <listitem><para>Enable network name resolution</para></listitem>
800 <listitem><para>Enable transport name resolution</para></listitem>
801 </orderedlist>
802 Click <guibutton>OK</guibutton>.
803 </para></step>
805 <step><para>
806 On the Windows XP Professional client: Press <guimenu>Ctrl-Alt-Delete</guimenu> to bring
807 up the domain logon screen. Log in using valid credentials for a domain user account.
808 </para></step>
810 <step><para>
811 Now proceed to connect to the Domain Controller as follows:
812 <menuchoice>
813 <guimenu>Start</guimenu>
814 <guimenuitem>(right-click) My Network Places</guimenuitem>
815 <guimenuitem>Explore</guimenuitem>
816 <guimenuitem>{Left Panel} [+] Entire Network</guimenuitem>
817 <guimenuitem>{Left Panel} [+] Microsoft Windows Network</guimenuitem>
818 <guimenuitem>{Left Panel} [+] Midearth</guimenuitem>
819 <guimenuitem>{Left Panel} [+] Frodo</guimenuitem>
820 <guimenuitem>{Left Panel} [+] data</guimenuitem>
821 </menuchoice>. Close the explorer window.
822 </para>
824 <para>
825 In this step, our domain name is <constant>Midearth</constant>, the domain controller is called
826 <constant>Frodo</constant>, and we have connected to a share called <constant>data</constant>.
827 </para></step>
829 <step><para>
830 Stop the capture on the <command>ethereal</command> monitoring machine. Be sure to save the captured data
831 to a file so that you can refer to it again later.
832 </para></step>
834 <step><para>
835 If desired, the Windows XP Professional client and the Domain Controller are no longer needed for exercises
836 in this chapter.
837 </para></step>
839 <step><para>
840 <indexterm><primary>NTLMSSP_AUTH</primary></indexterm>
841 <indexterm><primary>session setup</primary></indexterm>
842 From the top of the packets captured, scan down to locate the first packet that has
843 interpreted as <constant>Session Setup AndX Request, NTLMSSP_AUTH</constant>.
844 </para></step>
846 <step><para>
847 <indexterm><primary>GSS-API</primary></indexterm>
848 <indexterm><primary>SPNEGO</primary></indexterm>
849 <indexterm><primary>NTLMSSP</primary></indexterm>
850 In the dissection (analysis) panel, expand the <constant>SMB, Session Setup AndX Request</constant>.
851 Expand the packet decode information, beginning at the <constant>Security Blob:</constant>
852 entry. Expand the <constant>GSS-API -> SPNEGO -> netTokenTarg -> responseToken -> NTLMSSP</constant>
853 keys. This should reveal that this is a <constant>NULL</constant> session setup packet.
854 The <constant>User name: NULL</constant> indicates this. An example decode is shown in
855 <link linkend="XPCap01"/>.
856 </para></step>
858 <step><para>
859 Return to the packet capture sequence. There will be a number of packets that have been
860 decoded of the type <constant>Session Setup AndX Request</constant>. Click the last such packet that
861 has been decoded as <constant>Session Setup AndX Request, NTLMSSP_AUTH</constant>.
862 </para></step>
864 <step><para>
865 <indexterm><primary>encrypted password</primary></indexterm>
866 In the dissection (analysis) panel, expand the <constant>SMB, Session Setup AndX Request</constant>.
867 Expand the packet decode information, beginning at the <constant>Security Blob:</constant>
868 entry. Expand the <constant>GSS-API -> SPNEGO -> netTokenTarg -> responseToken -> NTLMSSP</constant>
869 keys. This should reveal that this is a <constant>User Mode</constant> session setup packet.
870 The <constant>User name: jht</constant> indicates this. An example decode is shown in
871 <link linkend="XPCap02"/>. In this case the user name was <constant>jht</constant>. This packet
872 decode includes the <constant>Lan Manager Response:</constant> and the <constant>NTLM Response:</constant>.
873 The value of these two parameters is the Microsoft encrypted password hashes, respectively, the LanMan
874 password and then the NT (case-preserving) password hash.
875 </para></step>
877 <step><para>
878 <indexterm><primary>password length</primary></indexterm>
879 <indexterm><primary>User Mode</primary></indexterm>
880 The passwords are 24 characters long hexadecimal numbers. This packet confirms that this is a User Mode
881 session setup packet.
882 </para></step>
884 </procedure>
886 <image id="XPCap01">
887 <imagedescription>Typical Windows XP NULL Session Setup AndX Request</imagedescription>
888 <imagefile scale="50">WindowsXP-NullConnection</imagefile>
889 </image>
891 <image id="XPCap02">
892 <imagedescription>Typical Windows XP User Session Setup AndX Request</imagedescription>
893 <imagefile scale="50">WindowsXP-UserConnection</imagefile>
894 </image>
896 <sect3>
897 <title>Discussion</title>
899 <para><indexterm>
900 <primary>NULL-Session</primary>
901 </indexterm>
902 This exercise demonstrates that, while the specific protocol for the Session Setup AndX is handled
903 in a more sophisticated manner by recent MS Windows clients, the underlying rules or principles
904 remain the same. Thus it is demonstrated that MS Windows XP Professional clients still use a
905 <constant>NULL-Session</constant> connection to query and locate resources on an advanced network
906 technology server (one using Windows NT4/200x or Samba). It also demonstrates that an authenticated
907 connection must be made before resources can be used.
908 </para>
910 </sect3>
912 </sect2>
914 <sect2>
915 <title>Conclusions to Exercises</title>
917 <para>
918 In summary, the following points have been established in this chapter:
919 </para>
921 <itemizedlist>
922 <listitem><para>
923 When NetBIOS over TCP/IP protocols are enabled, MS Windows networking employs broadcast
924 oriented messaging protocols to provide knowledge of network services.
925 </para></listitem>
927 <listitem><para>
928 Network browsing protocols query information stored on Browse Masters that manage
929 information provided by NetBIOS Name Registrations and by way of on-going Host
930 Announcements and Workgroup Announcements.
931 </para></listitem>
933 <listitem><para>
934 All Samba servers must be configured with a mechanism for mapping the <constant>NULL-Session</constant>
935 to a valid but non-privileged UNIX system account.
936 </para></listitem>
938 <listitem><para>
939 The use of Microsoft encrypted passwords is built right into the fabric of Windows
940 networking operations. Such passwords cannot be provided from the UNIX <filename>/etc/passwd</filename>
941 database and thus must be stored elsewhere on the UNIX system in a manner that Samba can
942 use. Samba-2.x permitted such encrypted passwords to be stored in the <constant>smbpasswd</constant>
943 file or in an LDAP database. Samba-3 permits that use of multiple different <parameter>passdb backend</parameter>
944 databases, in concurrent deploy. Refer to <emphasis>TOSHARG</emphasis>, Chapter 10, <quote>Account Information Databases.</quote>
945 </para></listitem>
946 </itemizedlist>
948 </sect2>
950 </sect1>
952 <sect1 id="chap01conc">
953 <title>Dissection and Discussion</title>
955 <para>
956 <indexterm><primary>guest account</primary></indexterm>
957 The exercises demonstrate the use of the <constant>guest</constant> account, the way that
958 MS Windows clients and servers resolve computer names to a TCP/IP address, and how connections
959 between a client and a server are established.
960 </para>
962 <para>
963 Those wishing background information regarding NetBIOS name types should refer to
964 the Microsoft Knowledge Base Article
965 <ulink url="http://support.microsoft.com/support/kb/articles/Q102/78/8.asp">Q102878.</ulink>
966 </para>
968 <sect2>
969 <title>Technical Issues</title>
971 <para>
972 <indexterm><primary>guest account</primary></indexterm>
973 Network browsing involves SMB broadcast announcements, SMB enumeration requests,
974 connections to the <constant>IPC$</constant> share, share enumerations, and SMB connection
975 setup processes. The use of anonymous connections to a Samba server involve the use of
976 the <parameter>guest account</parameter> that must map to a valid UNIX UID.
977 </para>
979 </sect2>
981 </sect1>
983 <sect1 id="chap01qa">
984 <title>Questions and Answers</title>
986 <para>
987 The questions and answers given in this section are designed to highlight important aspects of Microsoft
988 Windows networking.
989 </para>
991 <qandaset defaultlabel="chap01qa">
992 <qandaentry>
993 <question>
995 <para>
996 What is the significance of the MIDEARTH<1b> type query?
997 </para>
999 </question>
1000 <answer>
1002 <para>
1003 <indexterm><primary>Domain Master Browser</primary><see>DMB</see></indexterm>
1004 <indexterm><primary>DMB</primary></indexterm>
1005 This is a broadcast announcement by which the Windows machine is attempting to
1006 locate a Domain Master Browser (DMB) in the event that it might exist on the network.
1007 Refer to <emphasis>TOSHARG</emphasis> Chapter 9, Section 9.7, <quote>Technical Overview of Browsing</quote>
1008 for details regarding the function of the DMB and its role in network browsing.
1009 </para>
1011 </answer>
1012 </qandaentry>
1014 <qandaentry>
1015 <question>
1017 <para>
1018 What is the significance of the MIDEARTH<1d> type name registration?
1019 </para>
1021 </question>
1022 <answer>
1024 <para>
1025 <indexterm><primary>Local Master Browser</primary><see>LMB</see></indexterm>
1026 <indexterm><primary>LMB</primary></indexterm>
1027 This name registration records the machine IP addresses of the Local Master Browsers (LMBs).
1028 Network clients can query this name type to obtain a list of browser servers from the
1029 Master Browser.
1030 </para>
1032 <para>
1033 The LMB is responsible for monitoring all host announcements on the local network and for
1034 collating the information contained within them. Using this information, it can provide answers to other Windows
1035 network clients that request information such as:
1036 </para>
1038 <itemizedlist>
1039 <listitem><para>
1040 The list of machines known to the LMB (i.e., the browse list)
1041 </para></listitem>
1043 <listitem><para>
1044 The IP addresses of all Domain Controllers known for the Domain
1045 </para></listitem>
1047 <listitem><para>
1048 The IP addresses of LMBs
1049 </para></listitem>
1051 <listitem><para>
1052 The IP address of the DMB (if one exists)
1053 </para></listitem>
1055 <listitem><para>
1056 The IP address of the LMB on the local segment
1057 </para></listitem>
1058 </itemizedlist>
1060 </answer>
1061 </qandaentry>
1063 <qandaentry>
1064 <question>
1066 <para>
1067 What is the role and significance of the <01><02>__MSBROWSE__<02><01>
1068 name registration?
1069 </para>
1071 </question>
1072 <answer>
1074 <para>
1075 <indexterm><primary>Browse Master</primary></indexterm>
1076 This name is registered by the Browse Master to broadcast and receive domain announcements.
1077 Its scope is limited to the local network segment, or subnet. By querying this name type,
1078 Master Browsers on networks that have multiple domains can find the names of Master Browsers
1079 for each domain.
1080 </para>
1082 </answer>
1083 </qandaentry>
1085 <qandaentry>
1086 <question>
1088 <para>
1089 What is the significance of the MIDEARTH<1e> type name registration?
1090 </para>
1092 </question>
1093 <answer>
1095 <para>
1096 <indexterm><primary>Browser Election Service</primary></indexterm>
1097 This name is registered by all Browse Masters in a domain or workgroup. The registration
1098 name type is known as the Browser Election Service. Master Browsers register themselves
1099 with this name type so that Domain Master Browsers can locate them to perform cross-subnet
1100 browse list updates. This name type is also used to initiate elections for Master Browsers.
1101 </para>
1103 </answer>
1104 </qandaentry>
1106 <qandaentry>
1107 <question>
1109 <para>
1110 <indexterm><primary>guest account</primary></indexterm>
1111 What is the significance of the <parameter>guest account</parameter> in smb.conf?
1112 </para>
1114 </question>
1115 <answer>
1117 <para>
1118 This parameter specifies the default UNIX account to which MS Windows networking
1119 NULL session connections are mapped. The default name for the UNIX account used for
1120 this mapping is called <constant>nobody</constant>. If the UNIX/Linux system that
1121 is hosting Samba does not have a <constant>nobody</constant> account and an alternate
1122 mapping has not been specified, network browsing will not work at all.
1123 </para>
1125 <para>
1126 It should be noted that the <parameter>guest account</parameter> is essential to
1127 Samba operation. Either the operating system must have an account called <constant>nobody</constant>
1128 or there must be an entry in the &smb.conf; file with a valid UNIX account. For example,
1129 <smbconfoption name="guest account">ftp</smbconfoption>.
1130 </para>
1132 </answer>
1133 </qandaentry>
1135 <qandaentry>
1136 <question>
1138 <para>
1139 Is it possible to reduce network broadcast activity with Samba-3?
1140 </para>
1142 </question>
1143 <answer>
1145 <para>
1146 <indexterm><primary>WINS</primary></indexterm>
1147 <indexterm><primary>NetBIOS</primary></indexterm>
1148 Yes, there are two ways to do this. The first involves use of WINS (See <emphasis>TOSHARG</emphasis>, Chapter 9,
1149 Section 9.5, <quote>WINS &smbmdash; The Windows Inter-networking Name Server</quote>), the
1150 alternate method involves disabling the use of NetBIOS over TCP/IP. This second method requires
1151 a correctly configured DNS server (see <emphasis>TOSHARG</emphasis>, Chapter 9, Section 9.3, <quote>Discussion</quote>).
1152 </para>
1154 <para>
1155 <indexterm><primary>broadcast</primary></indexterm>
1156 <indexterm><primary>NetBIOS</primary><secondary>Node Type</secondary></indexterm>
1157 <indexterm><primary>Hybrid</primary></indexterm>
1158 The use of WINS reduces network broadcast traffic. The reduction is greatest when all network
1159 clients are configured to operate in <parameter>Hybrid Mode</parameter>. This can be effected through
1160 use of DHCP to set the NetBIOS node type to type 8 for all network clients. Additionally, it is
1161 beneficial to configure Samba to use <smbconfoption name="name resolve order">wins host cast</smbconfoption>.
1162 </para>
1164 <note><para>
1165 Use of SMB without NetBIOS is possible only on Windows 200x/XP Professional clients and servers, as
1166 well as with Samba-3.
1167 </para></note>
1169 </answer>
1170 </qandaentry>
1172 <qandaentry>
1173 <question>
1175 <para>
1176 Can I just use plain-text passwords with Samba?
1177 </para>
1179 </question>
1180 <answer>
1182 <para>
1183 Yes, you can configure Samba to use plain-text passwords, though this does create a few problems.
1184 </para>
1186 <para>
1187 First, the use of <filename>/etc/passwd</filename> based plain-text passwords requires that registry
1188 modifications be made on all MS Windows client machines to enable plain-text passwords support. This
1189 significantly diminishes the security of MS Windows client operation. Many network administrators
1190 are bitterly opposed to doing this.
1191 </para>
1193 <para>
1194 Second, Microsoft has not maintained plain-text password support since the default setting was made
1195 disabling this. When network connections are dropped by the client it is not be possible to re-establish
1196 the connection automatically. Users need to log off and then log on again. Plain-text password support
1197 may interfere with recent enhancements that are part of the Microsoft move toward a more secure computing
1198 environment.
1199 </para>
1201 <para>
1202 Samba-3 supports Microsoft encrypted passwords. Be advised not to reintroduce plain-text password handling.
1203 Just create user accounts by running: <command>smbpasswd -a 'username'</command>
1204 </para>
1206 <para>
1207 It is not possible to add a user to the <parameter>passdb backend</parameter> database unless there is
1208 a UNIX system account for that user. On systems that run <command>winbindd</command> to access the Samba
1209 PDC/BDC to provide Windows user and group accounts, the <parameter>idmap uid, idmap gid</parameter> ranges
1210 set in the &smb.conf; file provide the local UID/GIDs needed for local identity management purposes.
1211 </para>
1213 </answer>
1214 </qandaentry>
1216 <qandaentry>
1217 <question>
1219 <para>
1220 What parameter in the &smb.conf; file is used to enable the use of encrypted passwords?
1221 </para>
1223 </question>
1224 <answer>
1226 <para>
1227 The parameter in the &smb.conf; file that controls this behavior is known as <parameter>encrypt
1228 passwords</parameter>. The default setting for this in Samba-3 is <constant>Yes (Enabled)</constant>.
1229 </para>
1231 </answer>
1232 </qandaentry>
1234 <qandaentry>
1235 <question>
1237 <para>
1238 Is it necessary to specify <smbconfoption name="encrypt passwords">Yes</smbconfoption>
1239 when Samba-3 is configured as a Domain Member?
1240 </para>
1242 </question>
1243 <answer>
1245 <para>
1246 No. This is the default behavior.
1247 </para>
1249 </answer>
1250 </qandaentry>
1252 <qandaentry>
1253 <question>
1255 <para>
1256 Is it necessary to specify a <parameter>guest account</parameter> when Samba-3 is configured
1257 as a Domain Member server?
1258 </para>
1260 </question>
1261 <answer>
1263 <para>
1264 Yes. This is a local function on the server. The default setting is to use the UNIX account
1265 <constant>nobody</constant>. If this account does not exist on the UNIX server, then it is
1266 necessary to provide a <smbconfoption name="guest account">an_account</smbconfoption>,
1267 where <constant>an_account</constant> is a valid local UNIX user account.
1268 </para>
1270 </answer>
1271 </qandaentry>
1272 </qandaset>
1274 </sect1>
1276 </appendix>