Time Synchronisation: Difference between revisions

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= Introduction =
= Introduction =


In an Active Directory, an accurate time synchronisation is absolutely necessary. E. g. Kerberos relies on correct timestamps to prevent replay attacks and AD needs it for resolving replication conflicts. The maximum time tolerance in an Active Directory is 5 minutes per default. If e. g. your domain members (clients, Member Servers, DCs) clock differs more than that to your servers clock, accessing the server is denied. As the default time source in an Active Directory forest, is the Domain Controller with the [[Flexible_Single-Master_Operations_(FSMO)_roles#PDC_Emulator|PDC emulator FSMO role]]. See http://technet.microsoft.com/en-us/library/cc773013%28v=ws.10%29.aspx#w2k3tr_times_how_izcr for information about time synchronisation in an AD DS hierarchy.
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.
ntpd from http://ntp.org allows time synchronisation with external sources and can also be configured to be a time source for others. Please note, that ntpd does not support authenticated time to Windows 2000 clients! This is due to these clients not behaving as the ntpd server expects. As these clients are now very old and unsupported, you may need to find another way to keep these clocks in sync.


By default domain joined Windows clients synchronize their clock via NT5DS with the AD-DC which holds the PDC-emulator FSMO role.
'''See the [[Host_information_used_in_documentation|host information used in documentation]] page for used paths, hostnames, etc.'''
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).
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.


= Configuring Time Synchronisation on a DC =



= Configuring time synchronisation on a DC =


== Requirements ==
== Requirements ==


* ntpd >= 4.2.6 from [http://www.ntp.org/ ntp.org], with enabled signed ntp support ("--enable-ntp-signd"), installed via package or self compiled
* ntpd >= 4.2.6 from http://www.ntp.org, compiled with enabled signed ntp support (<code>--enable-ntp-signd</code>)


* Make sure, that the socket permissions are set correct. It must be readable by the account your ntpd uses and should not be accessible by other
* 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:


# chown root:ntp /usr/local/samba/var/lib/ntp_signd/
# chmod 750 /usr/local/samba/var/lib/ntp_signd/
# ls -ld /usr/local/samba/var/lib/ntp_signd/
# 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/
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/




== Setup ntpd.conf ==


== Set up the ntpd.conf File on a DC ==
Typically ntpd's configuration file is /etc/ntpd.conf in most distributions. In the following, you see a working minimum ntpd.conf, that retrieves its time from an external NTP server and provides time via signed NTP for others.


Typically, the <code>ntpd</code> daemon read its configuration from the <code>/etc/ntpd.conf</code> file.
# Local clock (Note: This is not the localhost address!)

The following is a minimum <code>ntpd.conf</code> 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
server 127.127.1.0
fudge 127.127.1.0 stratum 10
fudge 127.127.1.0 stratum 10
# The source, where we are receiving the time from
# Where to retrieve the time from
server 0.pool.ntp.org iburst prefer
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
driftfile /var/lib/ntp/ntp.drift
Line 43: Line 48:
# Access control
# Access control
# Default restriction: Only allow querying time (incl. ms-sntp) from this machine
# Default restriction: Allow clients only to query the time
restrict default kod nomodify notrap nopeer mssntp
restrict default kod nomodify notrap nopeer mssntp
# Allow everything from localhost
# No restrictions for "localhost"
restrict 127.0.0.1
restrict 127.0.0.1
# Allow that our time source can only provide time and do nothing else
# 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 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


For further information about ntpd 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.
Examples about ntpd SELinux labeling and policy you will find [[Time_syncronisation_SELinux_labeling_and_policy|here]].


If you have SELinux enabled on your server, see [[Time_Synchronisation_-_SELinux_Labeling_and_Policy|Time Synchronisation - SELinux Labeling and Policy]].









= Configuring time synchronisation on Samba Domain Members =
= Configuring Time Synchronisation on a Unix Domain Member =


== Requirements ==
== Requirements ==


* ntpd from [http://www.ntp.org/ ntp.org], installed via package or self compiled
* ntpd from http://www.ntp.org.






== Setup ntpd.conf ==
== 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 ntpd's configuration file is /etc/ntpd.conf in most distributions. In the following, you see a working minimum ntpd.conf, that retrieves its time from an Samba AD Domain Controller and doesn't provide NTP for others.


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.
# Local clock (this is not the localhost address!)

# Local clock. Note that is not the "localhost" address!
server 127.127.1.0
server 127.127.1.0
fudge 127.127.1.0 stratum 10
fudge 127.127.1.0 stratum 10
# The source, where we are receiving the time from
# Where to retrieve the time from
server DC1.samdom.example.com iburst prefer
server DC1.samdom.example.com iburst prefer
server DC2.samdom.example.com iburst
driftfile /var/lib/ntp/ntp.drift
driftfile /var/lib/ntp/ntp.drift
Line 82: Line 93:
# Access control
# Access control
# Default restriction
# Default restriction: Disallow everything
restrict default ignore
restrict default ignore
# Allow everything from localhost
# No restrictions for "localhost"
restrict 127.0.0.1
restrict 127.0.0.1
# Allow that our time source can only provide time and do nothing else
# 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 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

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





= 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.




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


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. 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 <code>Administrator</code> account.
= Configuring time synchronisation on Windows clients =


* Open the <code>Group Policy Management Console</code>. If you are not having the Remote Server Administration Tools (RSAT) installed on this computer, see [[Installing RSAT|Installing RSAT]].
Per default, Windows clients in an Active Directory, automatically synchronize their time with the DC, owning the PDC emulator role. If you don't want to use a different source or to configure multiple time server, etc. you don't have to take any action.


* Right-click to your AD domain and select <code>Create a GPO in this domain, and Link it here</code>.


* Enter a name for the GPO, such as <code>Time Sources</code>. The new GPO is shown below the domain entry.


* Right-click to the newly-created GPO and select <code>Edit</code> to open the <code>Group Policy Management Editor</code>.
== Setting user defined time source(s) and options ==


* Navigate to the <code>Computer Configuration</code> &rarr; <code>Policies</code> &rarr; <code>Administrative Templates</code> &rarr; <code>System</code> &rarr; <code>Windows Time Service</code> &rarr; <code>Time Providers</code> entry, and double-click <code>Configure Windows NTP Client</code> to configure the policy:
If you require your Windows clients to synchronize time with a different server than your DC owning the PDC role, you can configure this via Group Policies. Using the following way, you can define multiple time servers and adjust time synchronisation related options:
:* Enable the policy and set the following options:
::* Enter the fully-quallified domain name (FQDN) of the NTP server to the <code>NtpServer</code> field and and append the <code>0x9</code> flag. For example:
:::[[Image:GPO_Windows_NTP_Client_Options.png]]
::: To enter multiple server, separate the individual entries using a space.
::* Keep the <code>NT5DS</code> type setting.
::* Update the additional parameters, if necessary.
:* Click <code>OK</code> to save the settings.


* Navigate to the <code>Computer Configuration</code> &rarr; <code>Policies</code> &rarr; <code>Administrative Templates</code> &rarr; <code>System</code> &rarr; <code>Windows Time Service</code> &rarr; <code>Time Providers</code> entry, and double-click <code>Enable Windows NTP Client</code> to configure the policy:
* Create a new Group Policy Object in the Group Policy Management Console (part of the [[Installing_RSAT|Remote Server Administration Tools]]) and edit it.
:* Enable the policy.
:* Click <code>OK</code> to save the settings.


* In the Group Policy Management Editor, go to "Computer Configuration" / "Administrative Templates" / "System" / "Windows Time Service" / "Time Providers".
* Close the <code>Group Policy Management Editor</code>.


* Close the <code>Group Policy Management Console</code>.
* Edit the "Configure Windows NTP Client" policy:


:[[Image:GPO_Windows_NTP_Client_Options.png]]


Notes:
:This example changes the NTP server setting to a DC that provides time, but is not owner of the PDC role. For further explanations on the possible options, see the description in the policy and, visit http://technet.microsoft.com/de-de/library/cc779145%28v=ws.10%29.aspx.


* Save the GPO and link it to the desired OU.
* 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:Configuration]]
[[Category:Active Directory]]
[[Category:Active Directory]]

Revision as of 11:32, 26 April 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. 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). Alternatively you could configure all machines to do standard ntp, but NT5DS is recommended.

Note that ntpd does not support authenticated time synchronisation with Windows 2000 clients.

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)
  • Verify the socket permissions on your domain controller (DC). The ntpd 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

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.



Configuring Time Synchronisation on a Unix Domain Member

Requirements


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

Typically, the ntpd daemon reads its configuration, depending on the operating system, from the /etc/ntpd.conf or /etc/ntp.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

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



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.


Default Time Source

Windows AD domain members use the DC holding the PDC emulator FSMO role as 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.