RFC 4075

Simple Network Time Protocol (SNTP) Configuration Option for DHCPv6

📅 published May 2005, from ietf

RFC 4075: Simple Network Time Protocol (SNTP) Configuration Option for DHCPv6 🎀

okay bestie, here's the header info 📋✨ This is RFC 4075, from the Network Working Group, and it's a Standards Track doc, so it's an actual protocol spec 💅. It was written by V. Kalusivalingam (full name Vijayabhaskar A. Kalusivalingam) at Cisco Systems (India) Private Limited, and it came out in May 2005 🌸. The header doesn't list any RFCs it obsoletes or updates, so it's standing on its own 🦋

Status of This Memo 🧾

okay so this doc is an Internet standards track protocol for the Internet community, and the authors are literally asking for discussion and suggestions for improvements 🫶 If you want the current standardization state of this protocol, check the "Internet Official Protocol Standards" (STD 1) 📚 The distribution of this memo is unlimited, so share it with everyone 💖

Copyright Notice ©️

Abstract ✨

this doc describes a brand new DHCPv6 option 🎀 Its job is passing a list of Simple Network Time Protocol (SNTP) server addresses over to a client, so the client knows where to get the time 🧚

1. Introduction 🌈

so the new option is called the SNTP [3] servers option, and it's how you pass info about SNTP servers in DHCPv6 [1] 💜 That's the whole plot!

2. Requirements 📝

the keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they show up in this doc, are to be read the way RFC 2119 [2] describes 🔥

3. Terminology 📖

this doc uses IPv6 and DHCPv6 terminology, as defined in the "Terminology" section of the DHCPv6 specification [1] 🍓 no new vocab, just the usual suspects

4. Simple Network Time Protocol (SNTP) Servers Option ⏰

the SNTP servers option gives the client a list of one or more IPv6 addresses of SNTP [3] servers it can use for synchronization 🫧 Clients use these servers to sync their system time to the standard time servers, and honestly it's giving precision 💅

Here's the vibe check on the list: Clients MUST treat the list of SNTP servers as an ordered list. The server MAY list the SNTP servers in decreasing order of preference. So the order matters, and the server gets to decide how it's sorted 👑

this option can ONLY configure SNTP servers you can reach over IPv6. The DHCP option for IPv4 SNTP servers is in RFC 2132 [4] 🙈 And mechanisms for IPv4/IPv6 dual-stack apps are being considered, but this doc doesn't specify them yet

The format of the SNTP servers option looks like this 🧚‍♀️

    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)                   |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

the fields, bestie 🎀

option-code: OPTION_SNTP_SERVERS (31)
option-len: the length of the 'SNTP server' fields, in octets. It must be a multiple of 16 🔢
SNTP server: the IPv6 address of the SNTP server 🌐

5. Appearance of This Option 🚦

the SNTP servers option MUST NOT show up in messages other than these: Solicit, Advertise, Request, Renew, Rebind, Information-Request, and Reply. If it does appear in any other messages, the receiver SHOULD ignore it 🙅‍♀️

the option number for this option MAY appear in the Option Request Option [1] in these messages: Solicit, Request, Renew, Rebind, Information-Request, and Reconfigure. If the option number shows up in the Option Request Option in any other messages, the receiver SHOULD ignore it 💀

6. Security Considerations 🔐

okay this section is serious, so listen up 🚨 The SNTP servers option could be abused by an intruder DHCPv6 server to make DHCPv6 clients contact a rogue SNTP server. That leads to invalid time synchronization on the client, and then time-critical apps on that machine run inaccurately 😱 Time accuracy can be crucial for some security algorithms. For example, expired certificates may gain a new life, which makes the apps on the client machine less secure. The inaccuracy can even make clients set their time incorrectly, leaving them open to replay attacks in protocols that use timestamps to detect replays 🥀

so to avoid attacks through this option, the DHCPv6 client SHOULD use authenticated DHCPv6 (see the "Authentication of DHCP messages" section in the DHCPv6 specification [1]) 🔒 this is a must-do, no cap 🫶

7. IANA Considerations 🗂️

the IANA has assigned an option code 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 💌

big thank yous to the DHC Working Group for their time and input on the spec 🥰 Specifically, thanks in alphabetical order to Bernie Volz, Jim Bound, Margaret Wasserman, Pekka Savola, Ralph Droms, Robert Elz, and Thomas Narten for their thorough review 👑

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

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Intellectual Property 💼

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Acknowledgement 🫶

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📦 where this page comes from

ietf: rfc4075 2005-05
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