draft-ietf-ntp-ntpv4-proto-10.txt   draft-ietf-ntp-ntpv4-proto-11.txt 
NTP WG J. Burbank, Ed. NTP WG J. Burbank, Ed.
Internet-Draft W. Kasch, Ed. Internet-Draft W. Kasch, Ed.
Obsoletes: RFC 4330, RFC 1305 JHU/APL Obsoletes: RFC 4330, RFC 1305 JHU/APL
(if approved) J. Martin, Ed. (if approved) J. Martin, Ed.
Intended status: Standards Track Woven Intended status: Standards Track Woven
Expires: January 15, 2009 D. Mills Expires: March 9, 2009 D. Mills
U. Delaware U. Delaware
July 14, 2008 September 5, 2008
Network Time Protocol Version 4 Protocol And Algorithms Specification Network Time Protocol Version 4 Protocol And Algorithms Specification
draft-ietf-ntp-ntpv4-proto-10 draft-ietf-ntp-ntpv4-proto-11
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on January 15, 2009. This Internet-Draft will expire on March 9, 2009.
Abstract Abstract
The Network Time Protocol (NTP) is widely used to synchronize The Network Time Protocol (NTP) is widely used to synchronize
computer clocks in the Internet. This document describes NTP Version computer clocks in the Internet. This document describes NTP Version
4 (NTPv4), which is backwards compatible with NTP Version 3 (NTPv3) 4 (NTPv4), which is backwards compatible with NTP Version 3 (NTPv3)
described in RFC 1305, as well as previous versions of the protocol. described in RFC 1305, as well as previous versions of the protocol.
NTPv4 includes a modified protocol header to accommodate the Internet NTPv4 includes a modified protocol header to accommodate the Internet
Protocol Version 6 address family. NTPv4 includes fundamental Protocol Version 6 address family. NTPv4 includes fundamental
improvements in the mitigation and discipline algorithms which extend improvements in the mitigation and discipline algorithms which extend
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7.2. Global Parameters 7.2. Global Parameters
In addition to the variable classes a number of global parameters are In addition to the variable classes a number of global parameters are
defined in this document, including those shown with values in defined in this document, including those shown with values in
Figure 6. Figure 6.
+-----------+-------+----------------------------------+ +-----------+-------+----------------------------------+
| Name | Value | Description | | Name | Value | Description |
+-----------+-------+----------------------------------+ +-----------+-------+----------------------------------+
| PORT | 123 | NTP port number | | PORT | 123 | NTP port number |
| VERSION | 4 | version number | | VERSION | 4 | NTP version number |
| TOLERANCE | 15e-6 | frequency tolerance PHI (s/s) | | TOLERANCE | 15e-6 | frequency tolerance PHI (s/s) |
| MINPOLL | 4 | minimum poll exponent (16 s) | | MINPOLL | 4 | minimum poll exponent (16 s) |
| MAXPOLL | 17 | maximum poll exponent (36 h) | | MAXPOLL | 17 | maximum poll exponent (36 h) |
| MAXDISP | 16 | maximum dispersion (16 s) | | MAXDISP | 16 | maximum dispersion (16 s) |
| MINDISP | .005 | minimum dispersion increment (s) | | MINDISP | .005 | minimum dispersion increment (s) |
| MAXDIST | 1 | distance threshold (1 s) | | MAXDIST | 1 | distance threshold (1 s) |
| MAXSTRAT | 16 | maximum stratum number | | MAXSTRAT | 16 | maximum stratum number |
+-----------+-------+----------------------------------+ +-----------+-------+----------------------------------+
Figure 6: Global Parameters Figure 6: Global Parameters
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The most important state variables from an external point of view are The most important state variables from an external point of view are
the packet header variables described in Figure 7 and below. The NTP the packet header variables described in Figure 7 and below. The NTP
packet header consists of an integral number of 32-bit (4 octet) packet header consists of an integral number of 32-bit (4 octet)
words in network byte order. The packet format consists of three words in network byte order. The packet format consists of three
components, the header itself, one or more optional extension fields components, the header itself, one or more optional extension fields
and an optional message authentication code (MAC). The header and an optional message authentication code (MAC). The header
component is identical to the NTPv3 header and previous versions. component is identical to the NTPv3 header and previous versions.
The optional extension fields are used by the Autokey public key The optional extension fields are used by the Autokey public key
cryptographic algorithms described in [ref3]. The optional MAC is cryptographic algorithms described in [ref3]. The optional MAC is
used by both Autokey and the symmetric key cryptographic algorithm used by both Autokey and the symmetric key cryptographic algorithm
described in this report. described in this RFC.
+-----------+------------+-----------------------+ +-----------+------------+-----------------------+
| Name | Formula | Description | | Name | Formula | Description |
+-----------+------------+-----------------------+ +-----------+------------+-----------------------+
| leap | leap | leap indicator (LI) | | leap | leap | leap indicator (LI) |
| version | version | version number (VN) | | version | version | version number (VN) |
| mode | mode | mode | | mode | mode | mode |
| stratum | stratum | stratum | | stratum | stratum | stratum |
| poll | poll | poll exponent | | poll | poll | poll exponent |
| precision | rho | precision exponent | | precision | rho | precision exponent |
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level retransmission and corrected for the time to compute a MAC on level retransmission and corrected for the time to compute a MAC on
transmit. transmit.
NTP messages make use of two different communication modes, one-to- NTP messages make use of two different communication modes, one-to-
one and one-to-many, commonly referred to as unicast and broadcast. one and one-to-many, commonly referred to as unicast and broadcast.
For the purposes of this document, the term broadcast is interpreted For the purposes of this document, the term broadcast is interpreted
as any available one-to-many mechanism. For IPv4 this equates to as any available one-to-many mechanism. For IPv4 this equates to
either IPv4 broadcast or IPv4 multicast. For IPv6 this equates to either IPv4 broadcast or IPv4 multicast. For IPv6 this equates to
IPv6 multicast. For this purpose, IANA has allocated the IPv4 IPv6 multicast. For this purpose, IANA has allocated the IPv4
multicast address 224.0.1.1 and the IPv6 multicast address ending multicast address 224.0.1.1 and the IPv6 multicast address ending
:101, with prefix determined by scoping rules. :101, with prefix determined by scoping rules. Any other non-
allocated multicast address may also be used in addition to these
allocated multicast addresses.
The on-wire protocol uses four timestamps numbered t1 through t4 and The on-wire protocol uses four timestamps numbered t1 through t4 and
three state variables org, rec and xmt, as shown in Figure 15. This three state variables org, rec and xmt, as shown in Figure 15. This
figure shows the most general case where each of two peers, A and B, figure shows the most general case where each of two peers, A and B,
independently measure the offset and delay relative to the other. independently measure the offset and delay relative to the other.
For purposes of illustration the packet timestamps are shown in lower For purposes of illustration the packet timestamps are shown in lower
case, while the state variables are shown in upper case. The state case, while the state variables are shown in upper case. The state
variables are copied from the packet timestamps upon arrival or variables are copied from the packet timestamps upon arrival or
departure of a packet. departure of a packet.
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