Difference between revisions of "Time Synchronisation"

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(explain that default is NT5DS)
m (/* Remove most mentions of the PDC emulator role, it seems this isn't the windows default.)
 
(5 intermediate revisions by 2 users not shown)
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In an Active Directory (AD) you must have an accurate time synchronisation. For example, Kerberos requires correct time stamps to prevent replay attacks and the AD uses the time to resolve replication conflicts. The default maximum allowed time deviation in an AD is 5 minutes. If a domain member or domain controller (DC) has a higher or lower time difference, the access is denied. As a result, a user cannot access shares or query the directory.
 
In an Active Directory (AD) you must have an accurate time synchronisation. For example, Kerberos requires correct time stamps to prevent replay attacks and the AD uses the time to resolve replication conflicts. The default maximum allowed time deviation in an AD is 5 minutes. If a domain member or domain controller (DC) has a higher or lower time difference, the access is denied. As a result, a user cannot access shares or query the directory.
  
Samba supports the <code>ntpd</code> from http://ntp.org. The daemon synchronises the time with external sources and enables clients to retrieve the time from the server running the daemon.
+
Samba supports the <code>ntpd</code> from http://ntp.org and <code>chrony</code> from https://chrony.tuxfamily.org/ . The daemon synchronises the time with external sources and enables clients to retrieve the time from the server running the daemon.
  
By default domain joined Windows clients synchronize their clock via NT5DS with the AD-DC which holds the PDC-emulator FSMO role.
+
 
The NT5DS protocol uses digital signatures. These can be provided by Samba if ntp runs on the same server, and is configured as described on this page (with options mssntp and ntpsigndsocket).
+
'''Recommended best practise'''
 +
 
 +
internet time server
 +
          ^
 +
          |
 +
          |
 +
  PDC Emulator DC
 +
    ^        ^
 +
    |        |
 +
    |        |
 +
Other DC <----Workstation 
 +
 
 +
From the above, you can see that only the PDC emulator DC gets its time from external time servers, all other DC's get their time from the PDC emulator, all other workstations get their time from any DC.
 +
There is however a problem with this, Windows clients get their time from the PDC emulator DC and if this goes offline, they will not use the other DC's and the other DC's will be looking for the PDC emulator DC.
 +
As a workaround for this, set the same external time servers on all DC's, then if the PDC emulator goes offline and cannot easily be restarted, transfer or seize the PDC emulator role to another DC.
 +
 
 +
By default domain joined Windows clients synchronize their clock via NT5DS with AD-DC's.
 +
The NT5DS protocol uses digital signatures. These can be provided by Samba if the time server runs on the same server, and is configured as described on this page (with options mssntp and ntpsigndsocket).
 
Alternatively you could configure all machines to do standard ntp, but NT5DS is recommended.
 
Alternatively you could configure all machines to do standard ntp, but NT5DS is recommended.
  
Note that <code>ntpd</code> does not support authenticated time synchronisation with Windows 2000 clients.
+
Note that authenticated time synchronisation with Windows 2000 clients is not supported.
 +
 
 +
Before deciding which time server software to install, You can see a comparison of ntp and chrony here https://chrony.tuxfamily.org/comparison.html
 +
 
 +
For example, the NTP modes table.  (last date checked 7 June 2018.)
 +
 
 +
:{| class="wikitable"
 +
!
 +
!chrony
 +
!ntp
 +
!openntpd
 +
|-
 +
|Broadcast server
 +
|Yes
 +
|Yes
 +
|No
 +
|-
 +
|Broadcast client
 +
|No
 +
|Yes
 +
|No
 +
|-
 +
|Multicast server
 +
|No
 +
|Yes
 +
|No
 +
|-
 +
|Multicast client
 +
|No
 +
|Yes
 +
|No
 +
|-
 +
|Manycast server
 +
|No
 +
|Yes
 +
|No
 +
|-
 +
|Manycast client
 +
|No
 +
|Yes
 +
|No
 +
|}
 +
 
  
 
= Configuring Time Synchronisation on a DC =
 
= Configuring Time Synchronisation on a DC =
Line 17: Line 76:
 
* ntpd >= 4.2.6 from http://www.ntp.org, compiled with enabled signed ntp support (<code>--enable-ntp-signd</code>)
 
* ntpd >= 4.2.6 from http://www.ntp.org, compiled with enabled signed ntp support (<code>--enable-ntp-signd</code>)
  
* Verify the socket permissions on your domain controller (DC). The <code>ntpd</code> daemon must have read permissions in the <code>ntp_signed</code> directory. To list the permissions, enter:
+
Or
 +
 
 +
* chrony >= 3.0 from https://chrony.tuxfamily.org, compiled with enabled signed ntp support (<code>--enable-ntp-signd</code>)
 +
 
 +
 
 +
 
 +
= NTP =
 +
 
 +
* Verify the socket permissions on your domain controller (DC). The time daemon must have read permissions in the <code>ntp_signed</code> directory. To list the permissions, enter:
  
 
  # ls -ld /usr/local/samba/var/lib/ntp_signd/
 
  # ls -ld /usr/local/samba/var/lib/ntp_signd/
Line 25: Line 92:
 
  # chown root:ntp /usr/local/samba/var/lib/ntp_signd/
 
  # chown root:ntp /usr/local/samba/var/lib/ntp_signd/
 
  # chmod 750 /usr/local/samba/var/lib/ntp_signd/
 
  # chmod 750 /usr/local/samba/var/lib/ntp_signd/
 
  
  
Line 58: Line 124:
 
  restrict 1.pool.ntp.org  mask 255.255.255.255    nomodify notrap nopeer noquery
 
  restrict 1.pool.ntp.org  mask 255.255.255.255    nomodify notrap nopeer noquery
 
  restrict 2.pool.ntp.org  mask 255.255.255.255    nomodify notrap nopeer noquery
 
  restrict 2.pool.ntp.org  mask 255.255.255.255    nomodify notrap nopeer noquery
 +
 +
If you are running the DC in a VM, you should consider adding <code>tinker panic 0</code> to the end of the <code>ntp.conf</code>. This tells NTP not to panic and exit, no matter what the time offset is. This is recommended because
 +
virtual machines have no physical clock and can be paused at anytime and started back up hours later.
 +
For further information see: https://www.redhat.com/en/blog/avoiding-clock-drift-vms
  
 
For further information about the <code>ntpd</code> access control, see http://support.ntp.org/bin/view/Support/AccessRestrictions.
 
For further information about the <code>ntpd</code> access control, see http://support.ntp.org/bin/view/Support/AccessRestrictions.
Line 63: Line 133:
 
If you have SELinux enabled on your server, see [[Time_Synchronisation_-_SELinux_Labeling_and_Policy|Time Synchronisation - SELinux Labeling and Policy]].
 
If you have SELinux enabled on your server, see [[Time_Synchronisation_-_SELinux_Labeling_and_Policy|Time Synchronisation - SELinux Labeling and Policy]].
  
 +
 +
 +
= CHRONY =
 +
 +
* Verify the socket permissions on your domain controller (DC). The time daemon must have read permissions in the <code>ntp_signed</code> directory. To list the permissions, enter:
 +
 +
# ls -ld /usr/local/samba/var/lib/ntp_signd/
 +
drwxr-x--- 2 root _chrony 4096  1. May 09:30 /usr/local/samba/var/lib/ntp_signd/
 +
 +
: To set the permissions, run:
 +
# chown root:_chrony /usr/local/samba/var/lib/ntp_signd/
 +
# chmod 750 /usr/local/samba/var/lib/ntp_signd/
 +
 +
 +
== Set up the chrony.conf File on a DC ==
 +
 +
Typically, the <code>chrony</code> daemon read its configuration from the <code>/etc/chrony/chrony.conf</code> file.
 +
 +
The following is a minimum <code>chrony.conf</code> file that synchronises the time with three external NTP servers and enables clients to query the time using signed NTP requests:
 +
 +
# Welcome to the chrony configuration file. See chrony.conf(5) for more
 +
# information about usuable directives.
 +
 +
# This directive specify the location of the file containing ID/key pairs for
 +
# NTP authentication.
 +
keyfile /etc/chrony/chrony.keys
 +
 +
# This directive specify the file into which chronyd will store the rate
 +
# information.
 +
driftfile /var/lib/chrony/chrony.drift
 +
 +
# Uncomment the following line to turn logging on.
 +
#log tracking measurements statistics
 +
 +
# Log files location.
 +
logdir /var/log/chrony
 +
 +
# Stop bad estimates upsetting machine clock.
 +
maxupdateskew 100.0
 +
 +
# This directive tells 'chronyd' to parse the 'adjtime' file to find out if the
 +
# real-time clock keeps local time or UTC. It overrides the 'rtconutc' directive.
 +
hwclockfile /etc/adjtime
 +
 +
# This directive enables kernel synchronisation (every 11 minutes) of the
 +
# real-time clock. Note that it can’t be used along with the 'rtcfile' directive.
 +
rtcsync
 +
 +
# Step the system clock instead of slewing it if the adjustment is larger than
 +
# one second, but only in the first three clock updates.
 +
makestep 1 3
 +
 +
bindcmdaddress 192.168.0.2 # ipaddress of this DC
 +
 +
# The source, where we are receiving the time from
 +
server 0.pool.ntp.org    iburst
 +
server 1.pool.ntp.org    iburst
 +
server 2.pool.ntp.org    iburst
 +
 +
allow 192.168.0.0/24 # dns netmask
 +
 +
ntpsigndsocket  /usr/local/samba/var/lib/ntp_signd
  
  
Line 72: Line 204:
  
 
* ntpd from http://www.ntp.org.
 
* ntpd from http://www.ntp.org.
 +
 +
Or
 +
 +
* chrony >= 3.0 from https://chrony.tuxfamily.org
  
  
Line 77: Line 213:
 
== Set up the ntpd.conf File on a Unix Domain Member ==
 
== Set up the ntpd.conf File on a Unix Domain Member ==
  
Typically, the <code>ntpd</code> daemon reads its configuration, depending on the operating system, from the <code>/etc/ntpd.conf</code> or <code>/etc/ntp.conf</code> file.
+
Typically, the <code>ntpd</code> daemon read its configuration from the <code>/etc/ntpd.conf</code> file.
  
 
The following is a minimum conf file that synchronises the time with the Samba Active Directory (AD) domain controllers (DC) <code>DC1</code> and <code>DC2</code> and does not provide time services for other hosts.
 
The following is a minimum conf file that synchronises the time with the Samba Active Directory (AD) domain controllers (DC) <code>DC1</code> and <code>DC2</code> and does not provide time services for other hosts.
Line 84: Line 220:
 
  server 127.127.1.0
 
  server 127.127.1.0
 
  fudge  127.127.1.0 stratum 10
 
  fudge  127.127.1.0 stratum 10
+
 
 
  # Where to retrieve the time from
 
  # Where to retrieve the time from
 
  server DC1.samdom.example.com    iburst prefer
 
  server DC1.samdom.example.com    iburst prefer
Line 102: Line 238:
 
  restrict DC1.samdom.example.com  mask 255.255.255.255    nomodify notrap nopeer noquery
 
  restrict DC1.samdom.example.com  mask 255.255.255.255    nomodify notrap nopeer noquery
 
  restrict DC2.samdom.example.com  mask 255.255.255.255    nomodify notrap nopeer noquery
 
  restrict DC2.samdom.example.com  mask 255.255.255.255    nomodify notrap nopeer noquery
 +
 +
If you are running the Unix Domain Member in a VM, you should consider adding <code>tinker panic 0</code> to the end of the <code>ntp.conf</code>. This tells NTP not to panic and exit, no matter what the time offset is. This is recommended because virtual machines have no physical clock and can be paused at any time and started back up hours later.
 +
For further information see: https://www.redhat.com/en/blog/avoiding-clock-drift-vms
  
 
For further information about the <code>ntpd</code> access control, see http://support.ntp.org/bin/view/Support/AccessRestrictions.
 
For further information about the <code>ntpd</code> access control, see http://support.ntp.org/bin/view/Support/AccessRestrictions.
 +
 +
 +
 +
 +
 +
== Set up the chrony.conf File on a Unix Domain Member ==
 +
 +
Typically, the <code>chrony</code> daemon read its configuration from the <code>/etc/chrony/chrony.conf</code> file.
 +
 +
The following is a minimum conf file that synchronises the time with the Samba Active Directory (AD) domain controllers (DC) <code>DC1</code> and <code>DC2</code> and does not provide time services for other hosts.
 +
 +
# Welcome to the chrony configuration file. See chrony.conf(5) for more
 +
# information about usuable directives.
 +
 +
# This directive specify the location of the file containing ID/key pairs for
 +
# NTP authentication.
 +
keyfile /etc/chrony/chrony.keys
 +
 +
# This directive specify the file into which chronyd will store the rate
 +
# information.
 +
driftfile /var/lib/chrony/chrony.drift
 +
 +
# Uncomment the following line to turn logging on.
 +
#log tracking measurements statistics
 +
 +
# Log files location.
 +
logdir /var/log/chrony
 +
 +
# Stop bad estimates upsetting machine clock.
 +
maxupdateskew 100.0
 +
 +
# This directive tells 'chronyd' to parse the 'adjtime' file to find out if the
 +
# real-time clock keeps local time or UTC. It overrides the 'rtconutc' directive.
 +
hwclockfile /etc/adjtime
 +
 +
# This directive enables kernel synchronisation (every 11 minutes) of the
 +
# real-time clock. Note that it can’t be used along with the 'rtcfile' directive.
 +
rtcsync
 +
 +
# Step the system clock instead of slewing it if the adjustment is larger than
 +
# one second, but only in the first three clock updates.
 +
makestep 1 3
 +
 +
bindcmdaddress 192.168.0.6 # ipaddress of this Unix domain member
 +
 +
# The source, where we are receiving the time from
 +
server DC1.samdom.example.com    iburst
 +
server DC2.samdom.example.com    iburst
 +
  
  
Line 111: Line 299:
 
= Configuring Time Synchronisation on a Windows Domain Member =
 
= Configuring Time Synchronisation on a Windows Domain Member =
  
The following describes the basics of how to configure time synchronizsation on a Windows domain member. For further details, see your Microsoft Windows documentation.
+
The following describes the basics of how to configure time synchronisation on a Windows domain member. For further details, see your Microsoft Windows documentation.
  
  
Line 117: Line 305:
 
== Default Time Source ==
 
== Default Time Source ==
  
Windows AD domain members use the DC holding the [[Flexible_Single-Master_Operations_(FSMO)_Roles#PDC_Emulator|PDC emulator FSMO role]] as default time source. For more information about the time synchronisation and hierarchy in an AD, see http://technet.microsoft.com/en-us/library/cc773013%28v=ws.10%29.aspx#w2k3tr_times_how_izcr.
+
Windows AD domain members will use any DC as their default time source. If you have set up ntp on the DC as described on this page, you usually do not need to reconfigure the clients. Alternative configuration options for the clients are described below.
 
 
  
 +
For more information about the time synchronisation and hierarchy in an AD, see http://technet.microsoft.com/en-us/library/cc773013%28v=ws.10%29.aspx#w2k3tr_times_how_izcr.
  
 
== Setting User Defined Time Sources and Options  ==
 
== Setting User Defined Time Sources and Options  ==
Line 153: Line 341:
  
  
 +
Notes:
  
 +
* The default Type NT5DS ignores the parameter NtpServer, and syncs with the DC.
  
 +
* If ntpd on your DC is not configured for mssntp with ntpsigndsocket, use Type NTP.
  
----
+
* If a client will not be able to connect to the DC for a long time (for example a laptop), use Type AllSync and set NtpServer to "time.windows.com,0x9". This will cause the client to try both NT5DS to your DC, and NTP to NtpServer.
[[Category:Active Directory]]
 

Latest revision as of 08:04, 22 June 2018

Introduction

In an Active Directory (AD) you must have an accurate time synchronisation. For example, Kerberos requires correct time stamps to prevent replay attacks and the AD uses the time to resolve replication conflicts. The default maximum allowed time deviation in an AD is 5 minutes. If a domain member or domain controller (DC) has a higher or lower time difference, the access is denied. As a result, a user cannot access shares or query the directory.

Samba supports the ntpd from http://ntp.org and chrony from https://chrony.tuxfamily.org/ . The daemon synchronises the time with external sources and enables clients to retrieve the time from the server running the daemon.


Recommended best practise

internet time server
          ^
          |
          |
  PDC Emulator DC
   ^         ^
   |         |
   |         | 
Other DC <----Workstation  

From the above, you can see that only the PDC emulator DC gets its time from external time servers, all other DC's get their time from the PDC emulator, all other workstations get their time from any DC. There is however a problem with this, Windows clients get their time from the PDC emulator DC and if this goes offline, they will not use the other DC's and the other DC's will be looking for the PDC emulator DC. As a workaround for this, set the same external time servers on all DC's, then if the PDC emulator goes offline and cannot easily be restarted, transfer or seize the PDC emulator role to another DC.

By default domain joined Windows clients synchronize their clock via NT5DS with AD-DC's. The NT5DS protocol uses digital signatures. These can be provided by Samba if the time server runs on the same server, and is configured as described on this page (with options mssntp and ntpsigndsocket). Alternatively you could configure all machines to do standard ntp, but NT5DS is recommended.

Note that authenticated time synchronisation with Windows 2000 clients is not supported.

Before deciding which time server software to install, You can see a comparison of ntp and chrony here https://chrony.tuxfamily.org/comparison.html

For example, the NTP modes table. (last date checked 7 June 2018.)

chrony ntp openntpd
Broadcast server Yes Yes No
Broadcast client No Yes No
Multicast server No Yes No
Multicast client No Yes No
Manycast server No Yes No
Manycast client No Yes No


Configuring Time Synchronisation on a DC

Requirements

  • ntpd >= 4.2.6 from http://www.ntp.org, compiled with enabled signed ntp support (--enable-ntp-signd)

Or


NTP

  • Verify the socket permissions on your domain controller (DC). The time daemon must have read permissions in the ntp_signed directory. To list the permissions, enter:
# ls -ld /usr/local/samba/var/lib/ntp_signd/
drwxr-x--- 2 root ntp 4096  1. May 09:30 /usr/local/samba/var/lib/ntp_signd/
To set the permissions, run:
# chown root:ntp /usr/local/samba/var/lib/ntp_signd/
# chmod 750 /usr/local/samba/var/lib/ntp_signd/


Set up the ntpd.conf File on a DC

Typically, the ntpd daemon read its configuration from the /etc/ntpd.conf file.

The following is a minimum ntpd.conf file that synchronises the time with three external NTP server and enables clients to query the time using signed NTP requests:

# Local clock. Note that is not the "localhost" address!
server 127.127.1.0
fudge  127.127.1.0 stratum 10

# Where to retrieve the time from
server 0.pool.ntp.org     iburst prefer
server 1.pool.ntp.org     iburst prefer
server 2.pool.ntp.org     iburst prefer

driftfile       /var/lib/ntp/ntp.drift
logfile         /var/log/ntp
ntpsigndsocket  /usr/local/samba/var/lib/ntp_signd/

# Access control
# Default restriction: Allow clients only to query the time
restrict default kod nomodify notrap nopeer mssntp

# No restrictions for "localhost"
restrict 127.0.0.1

# Enable the time sources to only provide time to this host
restrict 0.pool.ntp.org   mask 255.255.255.255    nomodify notrap nopeer noquery
restrict 1.pool.ntp.org   mask 255.255.255.255    nomodify notrap nopeer noquery
restrict 2.pool.ntp.org   mask 255.255.255.255    nomodify notrap nopeer noquery

If you are running the DC in a VM, you should consider adding tinker panic 0 to the end of the ntp.conf. This tells NTP not to panic and exit, no matter what the time offset is. This is recommended because virtual machines have no physical clock and can be paused at anytime and started back up hours later. For further information see: https://www.redhat.com/en/blog/avoiding-clock-drift-vms

For further information about the ntpd access control, see http://support.ntp.org/bin/view/Support/AccessRestrictions.

If you have SELinux enabled on your server, see Time Synchronisation - SELinux Labeling and Policy.


CHRONY

  • Verify the socket permissions on your domain controller (DC). The time daemon must have read permissions in the ntp_signed directory. To list the permissions, enter:
# ls -ld /usr/local/samba/var/lib/ntp_signd/
drwxr-x--- 2 root _chrony 4096  1. May 09:30 /usr/local/samba/var/lib/ntp_signd/
To set the permissions, run:
# chown root:_chrony /usr/local/samba/var/lib/ntp_signd/
# chmod 750 /usr/local/samba/var/lib/ntp_signd/


Set up the chrony.conf File on a DC

Typically, the chrony daemon read its configuration from the /etc/chrony/chrony.conf file.

The following is a minimum chrony.conf file that synchronises the time with three external NTP servers and enables clients to query the time using signed NTP requests:

# Welcome to the chrony configuration file. See chrony.conf(5) for more
# information about usuable directives.

# This directive specify the location of the file containing ID/key pairs for
# NTP authentication.
keyfile /etc/chrony/chrony.keys

# This directive specify the file into which chronyd will store the rate
# information.
driftfile /var/lib/chrony/chrony.drift

# Uncomment the following line to turn logging on.
#log tracking measurements statistics

# Log files location.
logdir /var/log/chrony

# Stop bad estimates upsetting machine clock.
maxupdateskew 100.0

# This directive tells 'chronyd' to parse the 'adjtime' file to find out if the
# real-time clock keeps local time or UTC. It overrides the 'rtconutc' directive.
hwclockfile /etc/adjtime

# This directive enables kernel synchronisation (every 11 minutes) of the
# real-time clock. Note that it can’t be used along with the 'rtcfile' directive.
rtcsync

# Step the system clock instead of slewing it if the adjustment is larger than
# one second, but only in the first three clock updates.
makestep 1 3

bindcmdaddress 192.168.0.2 # ipaddress of this DC

# The source, where we are receiving the time from
server 0.pool.ntp.org     iburst
server 1.pool.ntp.org     iburst
server 2.pool.ntp.org     iburst

allow 192.168.0.0/24 # dns netmask

ntpsigndsocket  /usr/local/samba/var/lib/ntp_signd



Configuring Time Synchronisation on a Unix Domain Member

Requirements

Or


Set up the ntpd.conf File on a Unix Domain Member

Typically, the ntpd daemon read its configuration from the /etc/ntpd.conf file.

The following is a minimum conf file that synchronises the time with the Samba Active Directory (AD) domain controllers (DC) DC1 and DC2 and does not provide time services for other hosts.

# Local clock. Note that is not the "localhost" address!
server 127.127.1.0
fudge  127.127.1.0 stratum 10
 
# Where to retrieve the time from
server DC1.samdom.example.com     iburst prefer
server DC2.samdom.example.com     iburst

driftfile /var/lib/ntp/ntp.drift
logfile   /var/log/ntp

# Access control
# Default restriction: Disallow everything
restrict default ignore

# No restrictions for "localhost"
restrict 127.0.0.1

# Enable the time sources only to only provide time to this host
restrict DC1.samdom.example.com   mask 255.255.255.255    nomodify notrap nopeer noquery
restrict DC2.samdom.example.com   mask 255.255.255.255    nomodify notrap nopeer noquery

If you are running the Unix Domain Member in a VM, you should consider adding tinker panic 0 to the end of the ntp.conf. This tells NTP not to panic and exit, no matter what the time offset is. This is recommended because virtual machines have no physical clock and can be paused at any time and started back up hours later. For further information see: https://www.redhat.com/en/blog/avoiding-clock-drift-vms

For further information about the ntpd access control, see http://support.ntp.org/bin/view/Support/AccessRestrictions.



Set up the chrony.conf File on a Unix Domain Member

Typically, the chrony daemon read its configuration from the /etc/chrony/chrony.conf file.

The following is a minimum conf file that synchronises the time with the Samba Active Directory (AD) domain controllers (DC) DC1 and DC2 and does not provide time services for other hosts.

# Welcome to the chrony configuration file. See chrony.conf(5) for more
# information about usuable directives.

# This directive specify the location of the file containing ID/key pairs for
# NTP authentication.
keyfile /etc/chrony/chrony.keys

# This directive specify the file into which chronyd will store the rate
# information.
driftfile /var/lib/chrony/chrony.drift

# Uncomment the following line to turn logging on.
#log tracking measurements statistics

# Log files location.
logdir /var/log/chrony

# Stop bad estimates upsetting machine clock.
maxupdateskew 100.0

# This directive tells 'chronyd' to parse the 'adjtime' file to find out if the
# real-time clock keeps local time or UTC. It overrides the 'rtconutc' directive.
hwclockfile /etc/adjtime

# This directive enables kernel synchronisation (every 11 minutes) of the
# real-time clock. Note that it can’t be used along with the 'rtcfile' directive.
rtcsync

# Step the system clock instead of slewing it if the adjustment is larger than
# one second, but only in the first three clock updates.
makestep 1 3

bindcmdaddress 192.168.0.6 # ipaddress of this Unix domain member

# The source, where we are receiving the time from
server DC1.samdom.example.com    iburst
server DC2.samdom.example.com    iburst




Configuring Time Synchronisation on a Windows Domain Member

The following describes the basics of how to configure time synchronisation on a Windows domain member. For further details, see your Microsoft Windows documentation.


Default Time Source

Windows AD domain members will use any DC as their default time source. If you have set up ntp on the DC as described on this page, you usually do not need to reconfigure the clients. Alternative configuration options for the clients are described below.

For more information about the time synchronisation and hierarchy in an AD, see http://technet.microsoft.com/en-us/library/cc773013%28v=ws.10%29.aspx#w2k3tr_times_how_izcr.

Setting User Defined Time Sources and Options

To create a group policy object (GPO) to for setting a user defined NTP time source and options:

  • Log in to a computer using an account that is allowed you to edit group policies, such as the AD domain Administrator account.
  • Open the Group Policy Management Console. If you are not having the Remote Server Administration Tools (RSAT) installed on this computer, see Installing RSAT.
  • Right-click to your AD domain and select Create a GPO in this domain, and Link it here.
  • Enter a name for the GPO, such as Time Sources. The new GPO is shown below the domain entry.
  • Right-click to the newly-created GPO and select Edit to open the Group Policy Management Editor.
  • Navigate to the Computer ConfigurationPoliciesAdministrative TemplatesSystemWindows Time ServiceTime Providers entry, and double-click Configure Windows NTP Client to configure the policy:
  • Enable the policy and set the following options:
  • Enter the fully-quallified domain name (FQDN) of the NTP server to the NtpServer field and and append the 0x9 flag. For example:
GPO Windows NTP Client Options.png
To enter multiple server, separate the individual entries using a space.
  • Keep the NT5DS type setting.
  • Update the additional parameters, if necessary.
  • Click OK to save the settings.
  • Navigate to the Computer ConfigurationPoliciesAdministrative TemplatesSystemWindows Time ServiceTime Providers entry, and double-click Enable Windows NTP Client to configure the policy:
  • Enable the policy.
  • Click OK to save the settings.
  • Close the Group Policy Management Editor.
  • Close the Group Policy Management Console.


Notes:

  • The default Type NT5DS ignores the parameter NtpServer, and syncs with the DC.
  • If ntpd on your DC is not configured for mssntp with ntpsigndsocket, use Type NTP.
  • If a client will not be able to connect to the DC for a long time (for example a laptop), use Type AllSync and set NtpServer to "time.windows.com,0x9". This will cause the client to try both NT5DS to your DC, and NTP to NtpServer.