1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
|
<!--
- Copyright (C) 2004-2006 Internet Systems Consortium, Inc. ("ISC")
- Copyright (C) 2000-2003 Internet Software Consortium.
-
- Permission to use, copy, modify, and distribute this software for any
- purpose with or without fee is hereby granted, provided that the above
- copyright notice and this permission notice appear in all copies.
-
- THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
- AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
- LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
- OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
- PERFORMANCE OF THIS SOFTWARE.
-->
<!-- $Id: Bv9ARM.ch04.html,v 1.30.2.6.2.24 2006/11/15 04:33:41 marka Exp $ -->
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Chapter 4. Advanced DNS Features</title>
<meta name="generator" content="DocBook XSL Stylesheets V1.70.1">
<link rel="start" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual">
<link rel="up" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual">
<link rel="prev" href="Bv9ARM.ch03.html" title="Chapter 3. Name Server Configuration">
<link rel="next" href="Bv9ARM.ch05.html" title="Chapter 5. The BIND 9 Lightweight Resolver">
</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 4. Advanced DNS Features</th></tr>
<tr>
<td width="20%" align="left">
<a accesskey="p" href="Bv9ARM.ch03.html">Prev</a> </td>
<th width="60%" align="center"> </th>
<td width="20%" align="right"> <a accesskey="n" href="Bv9ARM.ch05.html">Next</a>
</td>
</tr>
</table>
<hr>
</div>
<div class="chapter" lang="en">
<div class="titlepage"><div><div><h2 class="title">
<a name="Bv9ARM.ch04"></a>Chapter 4. Advanced DNS Features</h2></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#notify">Notify</a></span></dt>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#dynamic_update">Dynamic Update</a></span></dt>
<dd><dl><dt><span class="sect2"><a href="Bv9ARM.ch04.html#journal">The journal file</a></span></dt></dl></dd>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#incremental_zone_transfers">Incremental Zone Transfers (IXFR)</a></span></dt>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2573147">Split DNS</a></span></dt>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#tsig">TSIG</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2573709">Generate Shared Keys for Each Pair of Hosts</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2573776">Copying the Shared Secret to Both Machines</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2573784">Informing the Servers of the Key's Existence</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2573824">Instructing the Server to Use the Key</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2573876">TSIG Key Based Access Control</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2573920">Errors</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2573933">TKEY</a></span></dt>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2573982">SIG(0)</a></span></dt>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#DNSSEC">DNSSEC</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2574049">Generating Keys</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2574116">Signing the Zone</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2574259">Configuring Servers</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2574396">IPv6 Support in <acronym class="acronym">BIND</acronym> 9</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2574455">Address Lookups Using AAAA Records</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2574475">Address to Name Lookups Using Nibble Format</a></span></dt>
</dl></dd>
</dl>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="notify"></a>Notify</h2></div></div></div>
<p><acronym class="acronym">DNS</acronym> NOTIFY is a mechanism that allows master
servers to notify their slave servers of changes to a zone's data. In
response to a <span><strong class="command">NOTIFY</strong></span> from a master server, the
slave will check to see that its version of the zone is the
current version and, if not, initiate a zone transfer.</p>
<p><acronym class="acronym">DNS</acronym>
For more information about
<span><strong class="command">NOTIFY</strong></span>, see the description of the
<span><strong class="command">notify</strong></span> option in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a> and
the description of the zone option <span><strong class="command">also-notify</strong></span> in
<a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>. The <span><strong class="command">NOTIFY</strong></span>
protocol is specified in RFC 1996.
</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="dynamic_update"></a>Dynamic Update</h2></div></div></div>
<p>Dynamic Update is a method for adding, replacing or deleting
records in a master server by sending it a special form of DNS
messages. The format and meaning of these messages is specified
in RFC 2136.</p>
<p>Dynamic update is enabled on a zone-by-zone basis, by
including an <span><strong class="command">allow-update</strong></span> or
<span><strong class="command">update-policy</strong></span> clause in the
<span><strong class="command">zone</strong></span> statement.</p>
<p>Updating of secure zones (zones using DNSSEC) follows
RFC 3007: RRSIG and NSEC records affected by updates are automatically
regenerated by the server using an online zone key.
Update authorization is based
on transaction signatures and an explicit server policy.</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="journal"></a>The journal file</h3></div></div></div>
<p>All changes made to a zone using dynamic update are stored in the
zone's journal file. This file is automatically created by the
server when the first dynamic update takes place. The name of
the journal file is formed by appending the
extension <code class="filename">.jnl</code> to the
name of the corresponding zone file. The journal file is in a
binary format and should not be edited manually.</p>
<p>The server will also occasionally write ("dump")
the complete contents of the updated zone to its zone file.
This is not done immediately after
each dynamic update, because that would be too slow when a large
zone is updated frequently. Instead, the dump is delayed by
up to 15 minutes, allowing additional updates to take place.</p>
<p>When a server is restarted after a shutdown or crash, it will replay
the journal file to incorporate into the zone any updates that took
place after the last zone dump.</p>
<p>Changes that result from incoming incremental zone transfers are also
journalled in a similar way.</p>
<p>The zone files of dynamic zones cannot normally be edited by
hand because they are not guaranteed to contain the most recent
dynamic changes — those are only in the journal file.
The only way to ensure that the zone file of a dynamic zone
is up to date is to run <span><strong class="command">rndc stop</strong></span>.</p>
<p>If you have to make changes to a dynamic zone
manually, the following procedure will work: Disable dynamic updates
to the zone using
<span><strong class="command">rndc freeze <em class="replaceable"><code>zone</code></em></strong></span>.
This will also remove the zone's <code class="filename">.jnl</code> file
and update the master file. Edit the zone file. Run
<span><strong class="command">rndc thaw <em class="replaceable"><code>zone</code></em></strong></span>
to reload the changed zone and re-enable dynamic updates.</p>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="incremental_zone_transfers"></a>Incremental Zone Transfers (IXFR)</h2></div></div></div>
<p>The incremental zone transfer (IXFR) protocol is a way for
slave servers to transfer only changed data, instead of having to
transfer the entire zone. The IXFR protocol is specified in RFC
1995. See <a href="Bv9ARM.ch09.html#proposed_standards">Proposed Standards</a>.</p>
<p>When acting as a master, <acronym class="acronym">BIND</acronym> 9
supports IXFR for those zones
where the necessary change history information is available. These
include master zones maintained by dynamic update and slave zones
whose data was obtained by IXFR. For manually maintained master
zones, and for slave zones obtained by performing a full zone
transfer (AXFR), IXFR is supported only if the option
<span><strong class="command">ixfr-from-differences</strong></span> is set
to <strong class="userinput"><code>yes</code></strong>.
</p>
<p>When acting as a slave, <acronym class="acronym">BIND</acronym> 9 will
attempt to use IXFR unless
it is explicitly disabled. For more information about disabling
IXFR, see the description of the <span><strong class="command">request-ixfr</strong></span> clause
of the <span><strong class="command">server</strong></span> statement.</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2573147"></a>Split DNS</h2></div></div></div>
<p>Setting up different views, or visibility, of the DNS space to
internal and external resolvers is usually referred to as a <span class="emphasis"><em>Split
DNS</em></span> setup. There are several reasons an organization
would want to set up its DNS this way.</p>
<p>One common reason for setting up a DNS system this way is
to hide "internal" DNS information from "external" clients on the
Internet. There is some debate as to whether or not this is actually useful.
Internal DNS information leaks out in many ways (via email headers,
for example) and most savvy "attackers" can find the information
they need using other means.</p>
<p>Another common reason for setting up a Split DNS system is
to allow internal networks that are behind filters or in RFC 1918
space (reserved IP space, as documented in RFC 1918) to resolve DNS
on the Internet. Split DNS can also be used to allow mail from outside
back in to the internal network.</p>
<p>Here is an example of a split DNS setup:</p>
<p>Let's say a company named <span class="emphasis"><em>Example, Inc.</em></span>
(<code class="literal">example.com</code>)
has several corporate sites that have an internal network with reserved
Internet Protocol (IP) space and an external demilitarized zone (DMZ),
or "outside" section of a network, that is available to the public.</p>
<p><span class="emphasis"><em>Example, Inc.</em></span> wants its internal clients
to be able to resolve external hostnames and to exchange mail with
people on the outside. The company also wants its internal resolvers
to have access to certain internal-only zones that are not available
at all outside of the internal network.</p>
<p>In order to accomplish this, the company will set up two sets
of name servers. One set will be on the inside network (in the reserved
IP space) and the other set will be on bastion hosts, which are "proxy"
hosts that can talk to both sides of its network, in the DMZ.</p>
<p>The internal servers will be configured to forward all queries,
except queries for <code class="filename">site1.internal</code>, <code class="filename">site2.internal</code>, <code class="filename">site1.example.com</code>,
and <code class="filename">site2.example.com</code>, to the servers in the
DMZ. These internal servers will have complete sets of information
for <code class="filename">site1.example.com</code>, <code class="filename">site2.example.com</code>,<span class="emphasis"><em> </em></span><code class="filename">site1.internal</code>,
and <code class="filename">site2.internal</code>.</p>
<p>To protect the <code class="filename">site1.internal</code> and <code class="filename">site2.internal</code> domains,
the internal name servers must be configured to disallow all queries
to these domains from any external hosts, including the bastion
hosts.</p>
<p>The external servers, which are on the bastion hosts, will
be configured to serve the "public" version of the <code class="filename">site1</code> and <code class="filename">site2.example.com</code> zones.
This could include things such as the host records for public servers
(<code class="filename">www.example.com</code> and <code class="filename">ftp.example.com</code>),
and mail exchange (MX) records (<code class="filename">a.mx.example.com</code> and <code class="filename">b.mx.example.com</code>).</p>
<p>In addition, the public <code class="filename">site1</code> and <code class="filename">site2.example.com</code> zones
should have special MX records that contain wildcard (`*') records
pointing to the bastion hosts. This is needed because external mail
servers do not have any other way of looking up how to deliver mail
to those internal hosts. With the wildcard records, the mail will
be delivered to the bastion host, which can then forward it on to
internal hosts.</p>
<p>Here's an example of a wildcard MX record:</p>
<pre class="programlisting">* IN MX 10 external1.example.com.</pre>
<p>Now that they accept mail on behalf of anything in the internal
network, the bastion hosts will need to know how to deliver mail
to internal hosts. In order for this to work properly, the resolvers on
the bastion hosts will need to be configured to point to the internal
name servers for DNS resolution.</p>
<p>Queries for internal hostnames will be answered by the internal
servers, and queries for external hostnames will be forwarded back
out to the DNS servers on the bastion hosts.</p>
<p>In order for all this to work properly, internal clients will
need to be configured to query <span class="emphasis"><em>only</em></span> the internal
name servers for DNS queries. This could also be enforced via selective
filtering on the network.</p>
<p>If everything has been set properly, <span class="emphasis"><em>Example, Inc.</em></span>'s
internal clients will now be able to:</p>
<div class="itemizedlist"><ul type="disc">
<li>Look up any hostnames in the <code class="literal">site1</code> and
<code class="literal">site2.example.com</code> zones.</li>
<li>Look up any hostnames in the <code class="literal">site1.internal</code> and
<code class="literal">site2.internal</code> domains.</li>
<li>Look up any hostnames on the Internet.</li>
<li>Exchange mail with both internal AND external people.</li>
</ul></div>
<p>Hosts on the Internet will be able to:</p>
<div class="itemizedlist"><ul type="disc">
<li>Look up any hostnames in the <code class="literal">site1</code> and
<code class="literal">site2.example.com</code> zones.</li>
<li>Exchange mail with anyone in the <code class="literal">site1</code> and
<code class="literal">site2.example.com</code> zones.</li>
</ul></div>
<p>Here is an example configuration for the setup we just
described above. Note that this is only configuration information;
for information on how to configure your zone files, see <a href="Bv9ARM.ch03.html#sample_configuration" title="Sample Configurations">the section called “Sample Configurations”</a>.</p>
<p>Internal DNS server config:</p>
<pre class="programlisting">
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { <code class="varname">bastion-ips-go-here</code>; };
options {
...
...
forward only;
forwarders { // forward to external servers
<code class="varname">bastion-ips-go-here</code>;
};
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { internals; externals; }; // restrict query access
allow-recursion { internals; }; // restrict recursion
...
...
};
zone "site1.example.com" { // sample master zone
type master;
file "m/site1.example.com";
forwarders { }; // do normal iterative
// resolution (do not forward)
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site2.example.com" { // sample slave zone
type slave;
file "s/site2.example.com";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site1.internal" {
type master;
file "m/site1.internal";
forwarders { };
allow-query { internals; };
allow-transfer { internals; }
};
zone "site2.internal" {
type slave;
file "s/site2.internal";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals };
allow-transfer { internals; }
};
</pre>
<p>External (bastion host) DNS server config:</p>
<pre class="programlisting">
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { bastion-ips-go-here; };
options {
...
...
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { internals; externals; }; // restrict query access
allow-recursion { internals; externals; }; // restrict recursion
...
...
};
zone "site1.example.com" { // sample slave zone
type master;
file "m/site1.foo.com";
allow-query { any; };
allow-transfer { internals; externals; };
};
zone "site2.example.com" {
type slave;
file "s/site2.foo.com";
masters { another_bastion_host_maybe; };
allow-query { any; };
allow-transfer { internals; externals; }
};
</pre>
<p>In the <code class="filename">resolv.conf</code> (or equivalent) on
the bastion host(s):</p>
<pre class="programlisting">
search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4
</pre>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="tsig"></a>TSIG</h2></div></div></div>
<p>This is a short guide to setting up Transaction SIGnatures
(TSIG) based transaction security in <acronym class="acronym">BIND</acronym>. It describes changes
to the configuration file as well as what changes are required for
different features, including the process of creating transaction
keys and using transaction signatures with <acronym class="acronym">BIND</acronym>.</p>
<p><acronym class="acronym">BIND</acronym> primarily supports TSIG for server to server communication.
This includes zone transfer, notify, and recursive query messages.
Resolvers based on newer versions of <acronym class="acronym">BIND</acronym> 8 have limited support
for TSIG.</p>
<p>TSIG might be most useful for dynamic update. A primary
server for a dynamic zone should use access control to control
updates, but IP-based access control is insufficient.
The cryptographic access control provided by TSIG
is far superior. The <span><strong class="command">nsupdate</strong></span>
program supports TSIG via the <code class="option">-k</code> and
<code class="option">-y</code> command line options.</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573709"></a>Generate Shared Keys for Each Pair of Hosts</h3></div></div></div>
<p>A shared secret is generated to be shared between <span class="emphasis"><em>host1</em></span> and <span class="emphasis"><em>host2</em></span>.
An arbitrary key name is chosen: "host1-host2.". The key name must
be the same on both hosts.</p>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2573725"></a>Automatic Generation</h4></div></div></div>
<p>The following command will generate a 128-bit (16 byte) HMAC-MD5
key as described above. Longer keys are better, but shorter keys
are easier to read. Note that the maximum key length is 512 bits;
keys longer than that will be digested with MD5 to produce a
128-bit key.</p>
<p><strong class="userinput"><code>dnssec-keygen -a hmac-md5 -b 128 -n HOST host1-host2.</code></strong></p>
<p>The key is in the file <code class="filename">Khost1-host2.+157+00000.private</code>.
Nothing directly uses this file, but the base-64 encoded string
following "<code class="literal">Key:</code>"
can be extracted from the file and used as a shared secret:</p>
<pre class="programlisting">Key: La/E5CjG9O+os1jq0a2jdA==</pre>
<p>The string "<code class="literal">La/E5CjG9O+os1jq0a2jdA==</code>" can
be used as the shared secret.</p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2573760"></a>Manual Generation</h4></div></div></div>
<p>The shared secret is simply a random sequence of bits, encoded
in base-64. Most ASCII strings are valid base-64 strings (assuming
the length is a multiple of 4 and only valid characters are used),
so the shared secret can be manually generated.</p>
<p>Also, a known string can be run through <span><strong class="command">mmencode</strong></span> or
a similar program to generate base-64 encoded data.</p>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573776"></a>Copying the Shared Secret to Both Machines</h3></div></div></div>
<p>This is beyond the scope of DNS. A secure transport mechanism
should be used. This could be secure FTP, ssh, telephone, etc.</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573784"></a>Informing the Servers of the Key's Existence</h3></div></div></div>
<p>Imagine <span class="emphasis"><em>host1</em></span> and <span class="emphasis"><em>host 2</em></span> are
both servers. The following is added to each server's <code class="filename">named.conf</code> file:</p>
<pre class="programlisting">
key host1-host2. {
algorithm hmac-md5;
secret "La/E5CjG9O+os1jq0a2jdA==";
};
</pre>
<p>The algorithm, hmac-md5, is the only one supported by <acronym class="acronym">BIND</acronym>.
The secret is the one generated above. Since this is a secret, it
is recommended that either <code class="filename">named.conf</code> be non-world
readable, or the key directive be added to a non-world readable
file that is included by <code class="filename">named.conf</code>.</p>
<p>At this point, the key is recognized. This means that if the
server receives a message signed by this key, it can verify the
signature. If the signature is successfully verified, the
response is signed by the same key.</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573824"></a>Instructing the Server to Use the Key</h3></div></div></div>
<p>Since keys are shared between two hosts only, the server must
be told when keys are to be used. The following is added to the <code class="filename">named.conf</code> file
for <span class="emphasis"><em>host1</em></span>, if the IP address of <span class="emphasis"><em>host2</em></span> is
10.1.2.3:</p>
<pre class="programlisting">
server 10.1.2.3 {
keys { host1-host2. ;};
};
</pre>
<p>Multiple keys may be present, but only the first is used.
This directive does not contain any secrets, so it may be in a world-readable
file.</p>
<p>If <span class="emphasis"><em>host1</em></span> sends a message that is a request
to that address, the message will be signed with the specified key. <span class="emphasis"><em>host1</em></span> will
expect any responses to signed messages to be signed with the same
key.</p>
<p>A similar statement must be present in <span class="emphasis"><em>host2</em></span>'s
configuration file (with <span class="emphasis"><em>host1</em></span>'s address) for <span class="emphasis"><em>host2</em></span> to
sign request messages to <span class="emphasis"><em>host1</em></span>.</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573876"></a>TSIG Key Based Access Control</h3></div></div></div>
<p><acronym class="acronym">BIND</acronym> allows IP addresses and ranges to be specified in ACL
definitions and
<span><strong class="command">allow-{ query | transfer | update }</strong></span> directives.
This has been extended to allow TSIG keys also. The above key would
be denoted <span><strong class="command">key host1-host2.</strong></span></p>
<p>An example of an allow-update directive would be:</p>
<pre class="programlisting">
allow-update { key host1-host2. ;};
</pre>
<p>This allows dynamic updates to succeed only if the request
was signed by a key named
"<span><strong class="command">host1-host2.</strong></span>".</p>
<p>You may want to read about the more
powerful <span><strong class="command">update-policy</strong></span> statement in <a href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called “Dynamic Update Policies”</a>.</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573920"></a>Errors</h3></div></div></div>
<p>The processing of TSIG signed messages can result in
several errors. If a signed message is sent to a non-TSIG
aware server, a FORMERR (format error) will be returned, since
the server will not understand the record. This is a result
of misconfiguration, since the server must be explicitly
configured to send a TSIG signed message to a specific
server.</p>
<p>If a TSIG aware server receives a message signed by an
unknown key, the response will be unsigned with the TSIG
extended error code set to BADKEY. If a TSIG aware server
receives a message with a signature that does not validate, the
response will be unsigned with the TSIG extended error code set
to BADSIG. If a TSIG aware server receives a message with a time
outside of the allowed range, the response will be signed with
the TSIG extended error code set to BADTIME, and the time values
will be adjusted so that the response can be successfully
verified. In any of these cases, the message's rcode is set to
NOTAUTH (not authenticated).</p>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2573933"></a>TKEY</h2></div></div></div>
<p><span><strong class="command">TKEY</strong></span> is a mechanism for automatically
generating a shared secret between two hosts. There are several
"modes" of <span><strong class="command">TKEY</strong></span> that specify how the key is
generated or assigned. <acronym class="acronym">BIND</acronym> 9
implements only one of these modes,
the Diffie-Hellman key exchange. Both hosts are required to have
a Diffie-Hellman KEY record (although this record is not required
to be present in a zone). The <span><strong class="command">TKEY</strong></span> process
must use signed messages, signed either by TSIG or SIG(0). The
result of <span><strong class="command">TKEY</strong></span> is a shared secret that can be
used to sign messages with TSIG. <span><strong class="command">TKEY</strong></span> can also
be used to delete shared secrets that it had previously
generated.</p>
<p>The <span><strong class="command">TKEY</strong></span> process is initiated by a client
or server by sending a signed <span><strong class="command">TKEY</strong></span> query
(including any appropriate KEYs) to a TKEY-aware server. The
server response, if it indicates success, will contain a
<span><strong class="command">TKEY</strong></span> record and any appropriate keys. After
this exchange, both participants have enough information to
determine the shared secret; the exact process depends on the
<span><strong class="command">TKEY</strong></span> mode. When using the Diffie-Hellman
<span><strong class="command">TKEY</strong></span> mode, Diffie-Hellman keys are exchanged,
and the shared secret is derived by both participants.</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2573982"></a>SIG(0)</h2></div></div></div>
<p><acronym class="acronym">BIND</acronym> 9 partially supports DNSSEC SIG(0)
transaction signatures as specified in RFC 2535 and RFC2931. SIG(0)
uses public/private keys to authenticate messages. Access control
is performed in the same manner as TSIG keys; privileges can be
granted or denied based on the key name.</p>
<p>When a SIG(0) signed message is received, it will only be
verified if the key is known and trusted by the server; the server
will not attempt to locate and / or validate the key.</p>
<p>SIG(0) signing of multiple-message TCP streams is not
supported.</p>
<p>The only tool shipped with <acronym class="acronym">BIND</acronym> 9 that
generates SIG(0) signed messages is <span><strong class="command">nsupdate</strong></span>.</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="DNSSEC"></a>DNSSEC</h2></div></div></div>
<p>Cryptographic authentication of DNS information is possible
through the DNS Security (<span class="emphasis"><em>DNSSEC-bis</em></span>)
extensions, defined in RFC 4033, RFC4034 and RFC4035. This
section describes the creation and use of DNSSEC signed
zones.</p>
<p>In order to set up a DNSSEC secure zone, there are a series
of steps which must be followed. <acronym class="acronym">BIND</acronym> 9 ships
with several tools
that are used in this process, which are explained in more detail
below. In all cases, the <code class="option">-h</code> option prints a
full list of parameters. Note that the DNSSEC tools require the
keyset files to be in the working directory or the
directory specified by the <code class="option">-h</code> option, and
that the tools shipped with BIND 9.2.x and earlier are not compatible
with the current ones.</p>
<p>There must also be communication with the administrators of
the parent and/or child zone to transmit keys. A zone's security
status must be indicated by the parent zone for a DNSSEC capable
resolver to trust its data. This is done through the presence
or absence of a <code class="literal">DS</code> record at the delegation
point.</p>
<p>For other servers to trust data in this zone, they must
either be statically configured with this zone's zone key or the
zone key of another zone above this one in the DNS tree.</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574049"></a>Generating Keys</h3></div></div></div>
<p>The <span><strong class="command">dnssec-keygen</strong></span> program is used to
generate keys.</p>
<p>A secure zone must contain one or more zone keys. The
zone keys will sign all other records in the zone, as well as
the zone keys of any secure delegated zones. Zone keys must
have the same name as the zone, a name type of
<span><strong class="command">ZONE</strong></span>, and must be usable for authentication.
It is recommended that zone keys use a cryptographic algorithm
designated as "mandatory to implement" by the IETF; currently
the only one is RSASHA1.</p>
<p>The following command will generate a 768-bit RSASHA1 key for
the <code class="filename">child.example</code> zone:</p>
<p><strong class="userinput"><code>dnssec-keygen -a RSASHA1 -b 768 -n ZONE child.example.</code></strong></p>
<p>Two output files will be produced:
<code class="filename">Kchild.example.+005+12345.key</code> and
<code class="filename">Kchild.example.+005+12345.private</code> (where
12345 is an example of a key tag). The key file names contain
the key name (<code class="filename">child.example.</code>), algorithm (3
is DSA, 1 is RSAMD5, 5 is RSASHA1, etc.), and the key tag (12345 in this case).
The private key (in the <code class="filename">.private</code> file) is
used to generate signatures, and the public key (in the
<code class="filename">.key</code> file) is used for signature
verification.</p>
<p>To generate another key with the same properties (but with
a different key tag), repeat the above command.</p>
<p>The public keys should be inserted into the zone file by
including the <code class="filename">.key</code> files using
<span><strong class="command">$INCLUDE</strong></span> statements.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574116"></a>Signing the Zone</h3></div></div></div>
<p>The <span><strong class="command">dnssec-signzone</strong></span> program is used to
sign a zone.</p>
<p>Any <code class="filename">keyset</code> files corresponding
to secure subzones should be present. The zone signer will
generate <code class="literal">NSEC</code> and <code class="literal">RRSIG</code>
records for the zone, as well as <code class="literal">DS</code> for
the child zones if <code class="literal">'-d'</code> is specified.
If <code class="literal">'-d'</code> is not specified, then DS RRsets for
the secure child zones need to be added manually.</p>
<p>The following command signs the zone, assuming it is in a
file called <code class="filename">zone.child.example</code>. By
default, all zone keys which have an available private key are
used to generate signatures.</p>
<p><strong class="userinput"><code>dnssec-signzone -o child.example zone.child.example</code></strong></p>
<p>One output file is produced:
<code class="filename">zone.child.example.signed</code>. This file
should be referenced by <code class="filename">named.conf</code> as the
input file for the zone.</p>
<p><span><strong class="command">dnssec-signzone</strong></span> will also produce a
keyset and dsset files and optionally a dlvset file. These
are used to provide the parent zone administators with the
<code class="literal">DNSKEYs</code> (or their corresponding <code class="literal">DS</code>
records) that are the secure entry point to the zone.</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574259"></a>Configuring Servers</h3></div></div></div>
<p>
To enable <span><strong class="command">named</strong></span> to respond appropriately
to DNS requests from DNSSEC aware clients,
<span><strong class="command">dnssec-enable</strong></span> must be set to yes.
</p>
<p>
To enable <span><strong class="command">named</strong></span> to validate answers from
other servers <span><strong class="command">dnssec-enable</strong></span> and
some <span><strong class="command">trusted-keys</strong></span> must be configured
into <code class="filename">named.conf</code>.
</p>
<p>
<span><strong class="command">trusted-keys</strong></span> are copies of DNSKEY RRs
for zones that are used to form the first link in the
cryptographic chain of trust. All keys listed in
<span><strong class="command">trusted-keys</strong></span> (and corresponding zones)
are deemed to exist and only the listed keys will be used
to validated the DNSKEY RRset that they are from.
</p>
<p>
<span><strong class="command">trusted-keys</strong></span> are described in more detail
later in this document.
</p>
<p>
Unlike <acronym class="acronym">BIND</acronym> 8, <acronym class="acronym">BIND</acronym>
9 does not verify signatures on load, so zone keys for
authoritative zones do not need to be specified in the
configuration file.
</p>
<p>
After DNSSEC gets established, a typical DNSSEC configuration
will look something like the following. It has a one or
more public keys for the root. This allows answers from
outside the organization to be validated. It will also
have several keys for parts of the namespace the organization
controls. These are here to ensure that named is immune
to compromises in the DNSSEC components of the security
of parent zones.
</p>
<pre class="programlisting">
trusted-keys {
/* Root Key */
"." 257 3 3 "BNY4wrWM1nCfJ+CXd0rVXyYmobt7sEEfK3clRbGaTwSJxrGkxJWoZu6I7PzJu/
E9gx4UC1zGAHlXKdE4zYIpRhaBKnvcC2U9mZhkdUpd1Vso/HAdjNe8LmMlnzY3
zy2Xy4klWOADTPzSv9eamj8V18PHGjBLaVtYvk/ln5ZApjYghf+6fElrmLkdaz
MQ2OCnACR817DF4BBa7UR/beDHyp5iWTXWSi6XmoJLbG9Scqc7l70KDqlvXR3M
/lUUVRbkeg1IPJSidmK3ZyCllh4XSKbje/45SKucHgnwU5jefMtq66gKodQj+M
iA21AfUVe7u99WzTLzY3qlxDhxYQQ20FQ97S+LKUTpQcq27R7AT3/V5hRQxScI
Nqwcz4jYqZD2fQdgxbcDTClU0CRBdiieyLMNzXG3";
/* Key for our organization's forward zone */
example.com. 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM65KbhTjrW1ZaARmPhEZZe
3Y9ifgEuq7vZ/zGZUdEGNWy+JZzus0lUptwgjGwhUS1558Hb4JKUbb
OTcM8pwXlj0EiX3oDFVmjHO444gLkBO UKUf/mC7HvfwYH/Be22GnC
lrinKJp1Og4ywzO9WglMk7jbfW33gUKvirTHr25GL7STQUzBb5Usxt
8lgnyTUHs1t3JwCY5hKZ6CqFxmAVZP20igTixin/1LcrgX/KMEGd/b
iuvF4qJCyduieHukuY3H4XMAcR+xia2 nIUPvm/oyWR8BW/hWdzOvn
SCThlHf3xiYleDbt/o1OTQ09A0=";
/* Key for our reverse zone. */
2.0.192.IN-ADDRPA.NET. 257 3 5 "AQOnS4xn/IgOUpBPJ3bogzwcxOdNax071L18QqZnQQQA
VVr+iLhGTnNGp3HoWQLUIzKrJVZ3zggy3WwNT6kZo6c0
tszYqbtvchmgQC8CzKojM/W16i6MG/ea fGU3siaOdS0
yOI6BgPsw+YZdzlYMaIJGf4M4dyoKIhzdZyQ2bYQrjyQ
4LB0lC7aOnsMyYKHHYeRv PxjIQXmdqgOJGq+vsevG06
zW+1xgYJh9rCIfnm1GX/KMgxLPG2vXTD/RnLX+D3T3UL
7HJYHJhAZD5L59VvjSPsZJHeDCUyWYrvPZesZDIRvhDD
52SKvbheeTJUm6EhkzytNN2SN96QRk8j/iI8ib";
};
options {
...
dnssec-enable yes;
};
</pre>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
None of the keys listed in this example are valid. In particular,
the root key is not valid.
</div>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2574396"></a>IPv6 Support in <acronym class="acronym">BIND</acronym> 9</h2></div></div></div>
<p><acronym class="acronym">BIND</acronym> 9 fully supports all currently defined forms of IPv6
name to address and address to name lookups. It will also use
IPv6 addresses to make queries when running on an IPv6 capable
system.</p>
<p>For forward lookups, <acronym class="acronym">BIND</acronym> 9 supports only AAAA
records. The use of A6 records is deprecated by RFC 3363, and the
support for forward lookups in <acronym class="acronym">BIND</acronym> 9 is
removed accordingly.
However, authoritative <acronym class="acronym">BIND</acronym> 9 name servers still
load zone files containing A6 records correctly, answer queries
for A6 records, and accept zone transfer for a zone containing A6
records.</p>
<p>For IPv6 reverse lookups, <acronym class="acronym">BIND</acronym> 9 supports
the traditional "nibble" format used in the
<span class="emphasis"><em>ip6.arpa</em></span> domain, as well as the older, deprecated
<span class="emphasis"><em>ip6.int</em></span> domain.
<acronym class="acronym">BIND</acronym> 9 formerly
supported the "binary label" (also known as "bitstring") format.
The support of binary labels, however, is now completely removed
according to the changes in RFC 3363.
Any applications in <acronym class="acronym">BIND</acronym> 9 do not understand
the format any more, and will return an error if given.
In particular, an authoritative <acronym class="acronym">BIND</acronym> 9 name
server rejects to load a zone file containing binary labels.</p>
<p>For an overview of the format and structure of IPv6 addresses,
see <a href="Bv9ARM.ch09.html#ipv6addresses" title="IPv6 addresses (AAAA)">the section called “IPv6 addresses (AAAA)”</a>.</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574455"></a>Address Lookups Using AAAA Records</h3></div></div></div>
<p>The AAAA record is a parallel to the IPv4 A record. It
specifies the entire address in a single record. For
example,</p>
<pre class="programlisting">
$ORIGIN example.com.
host 3600 IN AAAA 2001:db8::1
</pre>
<p>It is recommended that IPv4-in-IPv6 mapped addresses not
be used. If a host has an IPv4 address, use an A record, not
a AAAA, with <code class="literal">::ffff:192.168.42.1</code> as the
address.</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2574475"></a>Address to Name Lookups Using Nibble Format</h3></div></div></div>
<p>When looking up an address in nibble format, the address
components are simply reversed, just as in IPv4, and
<code class="literal">ip6.arpa.</code> is appended to the resulting name.
For example, the following would provide reverse name lookup for
a host with address
<code class="literal">2001:db8::1</code>.</p>
<pre class="programlisting">
$ORIGIN 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 14400 IN PTR host.example.com.
</pre>
</div>
</div>
</div>
<div class="navfooter">
<hr>
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left">
<a accesskey="p" href="Bv9ARM.ch03.html">Prev</a> </td>
<td width="20%" align="center"> </td>
<td width="40%" align="right"> <a accesskey="n" href="Bv9ARM.ch05.html">Next</a>
</td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Chapter 3. Name Server Configuration </td>
<td width="20%" align="center"><a accesskey="h" href="Bv9ARM.html">Home</a></td>
<td width="40%" align="right" valign="top"> Chapter 5. The <acronym class="acronym">BIND</acronym> 9 Lightweight Resolver</td>
</tr>
</table>
</div>
</body>
</html>
|
