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
|
Network Working Group V. Kalusivalingam
Request for Comments: 4075 Cisco Systems (India) Private Limited
Category: Standards Track May 2005
Simple Network Time Protocol (SNTP) Configuration Option for DHCPv6
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document describes a new DHCPv6 option for passing a list of
Simple Network Time Protocol (SNTP) server addresses to a client.
1. Introduction
This document describes a new option, called the SNTP [3] servers
option, for passing information about SNTP servers in DHCPv6 [1].
2. Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in RFC 2119 [2].
3. Terminology
This document uses terminology specific to IPv6 and DHCPv6 as defined
in the "Terminology" section of the DHCPv6 specification [1].
4. Simple Network Time Protocol (SNTP) Servers Option
The Simple Network Time Protocol servers option provides a list of
one or more IPv6 addresses of SNTP [3] servers available to the
client for synchronization. The clients use these SNTP servers to
synchronize their system time to that of the standard time servers.
Clients MUST treat the list of SNTP servers as an ordered list. The
server MAY list the SNTP servers in decreasing order of preference.
Kalusivalingam Standards Track [Page 1]
^L
RFC 4075 SNTP Configuration Option for DHCPv6 May 2005
The option defined in this document can only be used to configure
information about SNTP servers that can be reached using IPv6. The
DHCP option to configure information about IPv4 SNTP servers can be
found in RFC 2132 [4]. Mechanisms for configuring IPv4/IPv6 dual-
stack applications are being considered, but are not specified in
this document.
The format of the Simple Network Time Protocol servers option is as
shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_SNTP_SERVERS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SNTP server (IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SNTP server (IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_SNTP_SERVERS (31)
option-len: Length of the 'SNTP server' fields, in octets;
it must be a multiple of 16
SNTP server: IPv6 address of SNTP server
5. Appearance of This Option
The SNTP servers option MUST NOT appear in messages other than the
following: Solicit, Advertise, Request, Renew, Rebind, Information-
Request, and Reply. If this option appears in messages other than
those specified above, the receiver SHOULD ignore it.
The option number for this option MAY appear in the Option Request
Option [1] in the following messages: Solicit, Request, Renew,
Rebind, Information-Request, and Reconfigure. If this option number
appears in the Option Request Option in messages other than those
specified above, the receiver SHOULD ignore it.
Kalusivalingam Standards Track [Page 2]
^L
RFC 4075 SNTP Configuration Option for DHCPv6 May 2005
6. Security Considerations
The SNTP servers option may be used by an intruder DHCPv6 server to
cause DHCPv6 clients to contact a rogue SNTP server, resulting in
invalid synchronization of time in the client, finally leading to
time-critical applications running inaccurately in the client
machine. Time accuracy can be crucial to some security algorithms.
For example, expired certificates may gain a new life, making the
applications running on the client machine less secure. The
inaccuracy can even cause clients to set their time incorrectly,
making them vulnerable to replay attacks in protocols that use time
stamps to detect replays.
To avoid attacks through these options, the DHCPv6 client SHOULD use
authenticated DHCPv6 (see the "Authentication of DHCP messages"
section in the DHCPv6 specification [1]).
7. IANA Considerations
The IANA has assigned an option code to the following from the
option-code space defined in the "DHCPv6 Options" section of the
DHCPv6 specification [1].
Option Name Value Described in
OPTION_SNTP_SERVERS 31 Section 4.
8. Acknowledgements
Thanks to the DHC Working Group for their time and input on the
specification. In particular, thanks to (in alphabetical order)
Bernie Volz, Jim Bound, Margaret Wasserman, Pekka Savola, Ralph
Droms, Robert Elz, and Thomas Narten for their thorough review.
Kalusivalingam Standards Track [Page 3]
^L
RFC 4075 SNTP Configuration Option for DHCPv6 May 2005
9. Normative References
[1] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
10. Informative References
[3] Mills, D., "Simple Network Time Protocol (SNTP) Version 4 for
IPv4, IPv6 and OSI", RFC 2030, October 1996.
[4] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
Author's Address
Vijayabhaskar A. Kalusivalingam
Cisco Systems (India) Private Limited,
No: 9, Brunton Road,
Bangalore - 560025
India
Phone: +91-80-51036615
EMail: vibhaska@cisco.com
Kalusivalingam Standards Track [Page 4]
^L
RFC 4075 SNTP Configuration Option for DHCPv6 May 2005
Full Copyright Statement
Copyright (C) The Internet Society (2005).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Kalusivalingam Standards Track [Page 5]
^L
|
