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
|
Network Working Group R. Austein
draft-ietf-dnsext-dnsmib-historical-00.txt InterNetShare.com, Inc.
October 2000
Applicability Statement for DNS MIB Extensions
Status of this document
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
<http://www.ietf.org/ietf/1id-abstracts.txt>
The list of Internet-Draft Shadow Directories can be accessed at
<http://www.ietf.org/shadow.html>
Distribution of this document is unlimited. Please send comments to
the Namedroppers mailing list <namedroppers@ops.ietf.org>.
Abstract
More than six years after the DNS Server and Resolver MIB extensions
became proposed standards, there still has not been any significant
deployment of these MIB extensions. This note examines the reasons
why these MIB extensions were never deployed, and recommends retiring
these MIB extensions by moving them to Historical status.
History
The road to the DNS MIB extensions was paved with good intentions.
In retrospect, it's obvious that the working group never had much
agreement on what belonged in the MIB extensions, just that we should
have some. This happened during the height of the craze for MIB
extensions in virtually every protocol that the IETF was working on
Austein Expires 2 May 2001 [Page 1]
draft-ietf-dnsext-dnsmib-historical-00.txt October 2000
at the time, so the question of why we were doing this in the first
place never got a lot of scrutiny. Very late in the development
cycle we discovered that much of the support for writing the MIB
extensions in the first place had come from people who wanted to use
SNMP SET operations to update DNS zones on the fly. Examination of
the security model involved, however, led us to conclude that this
was not a good way to do dynamic update and that a separate DNS
Dynamic Update protocol would be necessary.
The MIB extensions started out being fairly specific to one
particular DNS implementation (BIND-4.8.3); as work progressed, the
BIND-specific portions were rewritten to be as implementation-neutral
as we knew how to make them, but somehow every revision of the MIB
extensions managed to accrete new counters that just happened to
closely match statistics kept by some version of BIND. As a result,
the MIB extensions ended up being much too big, which raised a number
of concerns with the network management directorate, but the WG
resisted every attempt to remove any of these variables. In the end,
large portions of the MIB extensions were moved into optional groups
in an attempt to get the required subset down to a manageable size.
The DNS Server and Resolver MIB extensions were one of the first
attempts to write MIB extensions for a protocol usually considered to
be at the application layer. Fairly early on it became clear that,
while it was certainly possible to write MIB extensions for DNS, the
SMI was not really designed with this sort of thing in mind. A case
in point was the attempt to provide direct indexing into the caches
in the resolver MIB extensions: while arguably the only sane way to
do this for a large cache, this required much more complex indexing
clauses than is usual, and ended up running into known length limits
for object identifiers in some SNMP implementations.
Furthermore, the lack of either real proxy MIB support in SNMP
managers or a standard subagent protocol meant that there was no
reasonable way to implement the MIB extensions in the dominant
implementation (BIND). When the AgentX subagent protocol was
developed a few years later, we initially hoped that this would
finally clear the way for an implementation of the DNS MIB
extensions, but by the time AgentX was a viable protocol it had
become clear that nobody really wanted to implement these MIB
extensions.
Finally, the MIB extensions took much too long to produce. In
retrospect, this should have been a clear warning sigh, particularly
when the WG had clearly become so tired of the project that the
authors found it impossible to elicit any comments whatsoever on the
documents.
Austein Expires 2 May 2001 [Page 2]
draft-ietf-dnsext-dnsmib-historical-00.txt October 2000
Lessons
Observations based on the preceding list of mistakes, for the benefit
of anyone else who ever attempts to write DNS MIB extensions again:
- Define a clear set of goals before writing any MIB extensions.
Know who the constituency is and make sure that what you write
solves their problem.
- Keep the MIB extensions short, and don't add variables just because
somebody in the WG thinks they'd be a cool thing to measure.
- If some portion of the task seems to be very hard to do within the
SMI, that's a strong hint that SNMP is not the right tool for
whatever it is that you're trying to do.
- If the entire project is taking too long, perhaps that's a hint
too.
Recommendation
In view of the community's apparent total lack of interest in
deploying these MIB extensions, we recommend that RFCs 1611 and 1612
be reclassified as Historical documents.
Security Considerations
Getting rid of the DNS MIB extensions undoubtedly closes a few
security holes, or would if anybody had ever implemented them.
IANA Considerations
Getting rid of the DNS MIB extensions should not impose any new work
on IANA.
Acknowledgments
The author would like to thank all the people who were involved in
this silly project over the years for their optimism and patience,
misguided though it may have been.
References
[DNS-SERVER-MIB] Austein, R., and Saperia, J., "DNS Server MIB
Extensions", RFC 1611, May 1994.
Austein Expires 2 May 2001 [Page 3]
draft-ietf-dnsext-dnsmib-historical-00.txt October 2000
[DNS-RESOLVER-MIB] Austein, R., and Saperia, J., "DNS Resolver MIB
Extensions", RFC 1612, May 1994.
[DNS-DYNAMIC-UPDATE] Vixie, P., Ed., Thomson, S., Rekhter, Y., and
Bound, J., "Dynamic Updates in the Domain Name System (DNS
UPDATE)", RFC 2136, April 1997.
[AGENTX] Daniele, M., Wijnen, B., Ellison, M., and Francisco, D.,
"Agent Extensibility (AgentX) Protocol Version 1", RFC 2741,
January 2000.
Author's addresses:
Rob Austein
InterNetShare.com, Inc.
505 West Olive Ave., Suite 321
Sunnyvale, CA 94086
USA
sra@hactrn.net
Austein Expires 2 May 2001 [Page 4]
|
