= Differences from NTP Classic =

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|image:pic/clocktower128.png[]|The NTPsec logo

Accept no imitations.
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== Related Links ==

* A list of all links is on the link:sitemap.html[Site Map] page.

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== Table of Contents ==

* link:#intro[Introduction]
* link:#incompatible[Incompatible Changes]
* link:#security[Security Improvements]
* link:#timesync[Time Synchronization Improvements]
* link:#configuration[Configuration Improvements]
* link:#other[Other user-visible changes]

[[intro]]
== Introduction ==

The design objectives of this distribution, NTPsec, are in
many ways a break with NTP's past.  We have deliberately jettisoned
support for ancient legacy hardware and operating systems in order to
ship code that is security-hardened, simpler, drastically less bulky,
easier to understand, and easier to maintain.

We retain, however, almost full compatibility and interoperation with
NTP Classic.  The qualification "almost" is required mainly because we
do not support the Autokey (RFC 5906) public-key encryption scheme. It
had interoperability and exploitable vulnerability issues too severe
to be patched.  We are participating in an IETF effort to develop
better security features.

This project began as an effort to address serious security issues
with NTP Classic, and we intend to keep a particularly strong focus on
code security and code verifiability.

Most of the changes are under the hood, internal to the codebase.  A
few will be user-visible.

[[incompatible]]
== Incompatible Changes ==

Normally NTPsec is a drop-in replacement for legacy versions. We have
tried to hold incompatible changes to a minimum, but there are a
few.  Some can be reverted by building the software in strict
compatibility mode with --enable-classic-mode (note that this is
a build-time switch, not a run-time one).

* The +sntp+ program has been renamed +ntpdig+ in order to make
  NTP installables have a uniform name prefix and take up less
  namespace. Also, +ntp-keygen+ is now +ntpkeygen+, +ntp-wait+
  is ntpwait, and +update-leap+ is now +ntpleapfetch+.

* Log timestamps look a little different; they are now in ISO 8601 format.
  Reverted in the --enable-classic-mode build.

* Clock identifiers in log files are normally the driver shortname
  followed by the unit number in parentheses, rather than the magic IP
  addresses formerly used.  Reverted in the --enable-classic-mode build.

* The -!m, -\>, and -< options of some Classic commands are not
  supported.  (The argument-parsing framework code that implemented
  them in Classic was overcomplicated and buggy and had to be removed.)

* The shortname of --help options is now -h, not -?

* If you had a refclock on a path of the form /dev/palisadeNNN, that
  link needs to change to /dev/trimbleNNN. Reverted in the
  --enable-classic-mode build.

* If you had a refclock on a path of the form /dev/actsNNN, that
  link needs to change to /dev/modemNNN. Reverted in the
  --enable-classic-mode build.

* An instance of +ntpq+ built from the NTPsec code
  querying a legacy NTP daemon will not automatically display
  peers with 127.127.127.t.u addresses as refclocks; that assumption
  has been removed from the NTPsec code as part of
  getting it fully IPv6-ready.

[[security]]
== Security Improvements ==

We have spent more effort than anything else on reducing attack
surface and hardening code.  In toto, more than 70% of the NTP Classic
codebase has been outright removed, with less than 5% new code added.

* The deprecated ntpdc utility, long a chronic locus of security
  vulnerabilities, has been removed.  Its function has been merged
  into +ntpq+.

* Autokey is not supported; that code has been
  removed, as it was chronically prone to security vulnerabilities.

* peer mode has been removed.  The keyword peer in ntp.conf is now
  just an alias for keyword server.

* Broadcast- and multicast client modes, which are impossible to
  secure, have been removed. Broadcast (but not multicast) service can
  still be enabled, though this is a deprecated and unsupported mode
  of operation and may be entirely removed in a future release.

* The authentication requirement for remote configuration commands
  (e.g., via +ntpq+) can no longer be disabled.

* The deprecated and vulnerability-prone ntpdate program has been
  replaced with a shell wrapper around ntpdig.  Its -e and -p
  options are not implemented. It is no longer documented, but can be
  found in the attic/ directory of the source distribution.

* A large number of obsolete refclocks have been removed in order to
  reduce attack surface, code bulk, and documentation complexity.

* Various features related to runtime dumping of the configuration
  state have been removed for security reasons.  These include the
  saveconfig command in ntpq, the --saveconfigquit option of ntpd, and
  the implementation of related config declarations in ntp.conf.

* Likewise, the poorly-documented ntpdsim code has also been removed
  to gain a significant reduction in code complexity.

* The ntpsnmpd daemon, incomplete and not conformant with RFC 5907,
  has been removed.

* The 'trap' feature has been removed.  It was broken by bit-rot in
  recent versions of NTP Classic, and if not broken would have been at
  high risk for bugs that would enable DoS vulnerabilities.

* Interleave mode has been removed.  It didn't work correctly (there
  was an implementation error in the timestamp handling), so no point
  in allowing it to increase attack surface.

* The code has been systematically hardened, with unsafe string
  copy and formatting functions replaced by safe (bounded) ones.

[[timesync]]
== Time-synchronization improvements ==

* Internally, there is more consistent use of nanosecond precision.
  A visible effect of this is that time stepping with sufficiently
  high-precision time sources could be accurate down to nanoseconds
  rather than microseconds; this might actually matter for GPSDOs
  and high-quality radio clocks.

[[clients]]
== Client Tool Improvements ==

* A new tool, +ntpmon+, performs real-time monitoring of your
  peer and MRU status with efficient (least-cost) querying.

* There is a new data-visualization tool,
  link:ntpviz.html[+ntpviz+], which can produce various useful and
  interesting plots from the NTP statistics logs.  These should assist in
  monitoring a time-server's performance, fixing configuration
  problems, and identifying noise sources in network weather and
  elsewhere.

* Because +ntpviz+ exists, a number of ancient and poorly-documented
  scripts in awk, Perl, and S, formerly used for making statistical
  summaries, have been removed from the distribution in order to
  reduce overall maintenance burden and complexity. If you miss any
  of this cruft, the project team will (a) be quite surprised, and (b)
  work with you on better analytics using ntpviz and modern tools.

* The ntpq utility resizes its display to take advantage of wide
  terminal windows, allowing more space for long peer addresses.

* When running as root, the ntpq utility looks in /etc/ntp.conf and
  /usr/local/etc/ntp.keys to find credentials for control requests
  that require authentication. Thus it is not necessary to enter
  them by hand.

* A new utility, +ntpfrob+, collects several small diagnostic functions
  for reading and tweaking the local clock hardware, including reading
  the clock tick rate, precision, and jitter. Part of it formerly
  traveled as +tickadj+.

[[configuration]]
== Configuration Improvements ==

* The notorious collision between pool and nopeer in older
  implementations has been fixed; the pool keyword is now fully
  usable.

* There is a new, simpler syntax for declaring refclocks.  The old
  syntax with the magic 127.127.t.u addresses and fudge command is
  still supported, but no longer documented.  It may be removed in a
  future release.  Relevant examples of the new syntax are included on
  each refclock page.  One major feature of the new syntax is that
  refclock drivers are referred to by names, not numbers.

* For the generic (parse) driver only: Using the new refclock syntax,
  the maximum number of units that can be set up changes from 4
  (numbers 0-3) to unlimited.  However, the old magic-address syntax
  will not work correctly - you _must_ use the new syntax to declare
  generic-driver refclocks.  If the software was compiled with the
  --enable-classic-mode switch, the foregoing is reversed.

* The includefile directive now evaluates relative pathnames not with
  respect to the current working directory but with respect to the
  directory name of the last pushed file in the stack.  This means
  that you can run ntpd from any directory with "includefile foo"
  in /etc/ntp.conf finding /etc/foo rather than looking for foo in
  your current directory.

* It is now possible to set the peer maximum dispersion with "tos
  maxdisp". See RFC 5905 for discussion of this synchronization
  parameter.

* The default baudrate of the NMEA driver has been changed to 9600 to
  match the default speed of almost all modern GPSes.  The code can be
  built in a strict NTP Classic compatibility mode that restores the
  old 4800bps default.

* Most refclock drivers now support configuration options to override the
  default device path, the default PPS device path (if any) and the
  serial baud rate.

[[other]]
== Other user-visible changes ==

* The documentation has been extensively updated and revised.  One
  important change is that manual pages are now generated from the
  same masters as this web documentation, so the two will no longer
  drift out of synchronization.

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