(20170504 — The steps in this post were amended to address changes in recent versions of software — iceflatline)
In a previous post, I described how to install and setup pfSense in a home network. In this post I will describe how to configure pfSense to act as an Network Time Protocol (“NTP”) server, as well as how to configure various hosts in your network to synchronize their local clock to this server.
pfSense is a customized version of FreeBSD tailored specifically for use as a perimeter firewall and router. It can be managed almost entirely from a web-based GUI. In addition to being a firewall and routing platform, pfSense includes a long list of other features, as well as a package system allowing its capabilities to be expanded even further. pfSense is free, open source software distributed under the BSD license.
Originally designed by David L. Mills of the University of Delaware circa 1985, NTP is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks, and one of the oldest Internet protocols still in use. NTP uses User Datagram Protocol (UDP) port number 123. pfSense uses OpenNTPD, a free, easy to use implementation of NTP.
The versions for the software used in this post were as follows:
- FreeBSD 11.0-RELEASE
- pfSense 2.3.3-RELEASE-p1
- Ubuntu 16.04.2 LTS
- Windows 7 Professional (x64)
Configure OpenNTPD in pfSense
Before configuring the OpenNTP server, it’s a good idea to ensure that pfSense itself is keeping accurate time. The best way to do that is to have it synchronize its clock with one or more remote NTP servers. First though, you should make sure that the clock in the machine hosting pfSense is set to something close to accurate – if the difference is too great, pfSense will not synchronize properly with the remote NTP server.
Login to the pfSense machine using its “webConfigurator” (webGUI) interface. Navigate to System->General Setup and select the timezone that matches the physical location of the pfSense machine from among the options under “Timezone.” Next, enter the host name or IP address for the remote NTP server under “Timeservers” (Remember to add at least one DNS server under “DNS Servers” if you decide to use a host name instead of an IP address). Most likely you’ll find this field is already populated with one or more default remote NTP server(s) such as 0.pfsense.pool.ntp.org, 1.pfsense.pool.ntp.org, etc. These servers will work just fine in most cases, however you may get more accurate results if you use one of the continental zone servers (e.g., europe., north-america., oceania., or asia.pool.ntp.org), and even more accurate time if you choose to use one of the country zone servers (e.g., us.pool.ntp.org in the United States). For all of these zones, you can use the 0, 1 or 2 prefix, like 0.us.pool.ntp.org, to distinguish between servers from a particular region or country. (See the NTP Pool Project web site for more information on how to use pool.ntp.org servers). Like 0.pfsense.pool.ntp.org, these server entries will pick random NTP servers from a pool of known good ones. Also, while one NTP server is sufficient, you can improve reliability by adding more. Just make sure their host names or IP addresses are separated by a space.
Now that the pfSense machine is on its way to keeping accurate time, let’s configure its OpenNTPD server. Navigate to Services->NTP and pick which interface OpenNTPD should listen on. This will typically be the “LAN” interface. When complete select “Save.” The OpenNTPD server will start immediately, however there may a delay of several minutes before it is ready to service NTP requests as it must first ensure that its own time is accurate. That’s all there is to it. You’ll find the OpenNTPD logs under by selecting the ‘NTP” tab under Status->System Logs->NTP.
Configure Hosts
- Windows
After configuring the OpenNTPD server in pfSense, let’s configure a Windows host to synchronize its local clock to this server. Right-click on the time (usually located in the lower right corner of the desktop) and select “Adjust date/time.” Select the “Internet Time” tab, then select “Change settings.” Check the “Synchronize with an Internet time server” box, enter the host name or IP address of the pfSense machine, then select “Update now.” It’s not uncommon to get error message the first time you attempt to update. Wait a few seconds and try again; you should receive a “The clock was successfully synchronized…” message.
- Linux
Many Linux distributions feature two utilities to help the local clock maintain its accuracy: ntpdate and/or ntpd (Note: Linux systems using systemd-timesyncd are discussed below). The ntpdate utility is typically included in Linux distributions as a default package, but if yours does not you can install it using your distribution’s package manager, for example:
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sudo apt-get install ntpdate |
ntpdate typically runs once at boot time and will synchronize the local clock with a default NTP server defined by the distribution. However what if this machine isn’t rebooted often, say in the case of a server for example? And what about using the OpenNTPD server in the pfSense machine? We can address both of those issues by occasionally running ntpdate using the following command. For this and subsequent examples we’ll assume the IP address assigned to the LAN interface in the pfSense machine is 192.168.1.1:
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sudo ntpdate 192.168.1.1 |
Perhaps a more effective approach though is to use cron, a utility that allows tasks to be automatically run in the background at regular intervals by the cron daemon. These tasks are typically referred to as “cron jobs.” A “crontab” is a file which contains one or more cron job entries to be run at specified times. You can create a new crontab (or edit an exiting one) using the command crontab -e under your user account. Because ntpdate needs to be run by the system’s root user we’ll create the crontab using the command sudo crontab -e. Here’s some example cron job entries using the ntpdate command. Note that cron will attempt to email to the user the output of the commands it runs. To silence this, you can redirect the command output to /dev/null:
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#Run ntpdate every 15 minutes #*/15 * * * * /usr/sbin/ntpdate 192.168.1.1 >> /dev/null 2>&1 #Run ntpdate every 30 minutes #*/30 * * * * /usr/sbin/ntpdate 192.168.1.1 >> /dev/null 2>&1 #Run ntpdate at the top of every hour # 0 * * * * /usr/sbin/ntpdate 192.168.1.1 >> /dev/null 2>&1 #Run ntpdate every three hours at the top of each hour 0 */3 * * * /usr/sbin/ntpdate 192.168.1.1 >> /dev/null 2>&1 #Run ntpdate every six hours at the top of each hour #0 */6 * * * /usr/sbin/ntpdate 192.168.1.1 >> /dev/null 2>&1 |
While using ntpdate will certainly work well, the utility ntpd on the other hand is considerably more sophisticated. It continually runs, calculating the drift of the local clock and then adjusting its time on an ongoing basis by synchronizing with one or more NTP servers. By default ntpd acts as a NTP client, querying NTP servers to set the local clock, however it also can act as a NTP server, providing time service to other clients. Alas though, nothing is free, and using ntpd will result in yet one more system process that may not otherwise be running in your system, consuming both CPU and memory resources, albeit modestly.
Like ntpdate many Linux distributions include ntpd by default. If yours does not, you can install it using your distribution’s package manager, for example:
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sudo apt-get install ntp |
The installation process should add ntpd to the requisite run levels and start its daemon automatically. Now we need to configure it so that it acts as a NTP client only and not as a NTP server. After all, that’s what we’re going to use the pfSense machine for right?
ntpd is configured using the file /etc/ntp.conf. Open this file and comment out the existing ntp pool servers, then add the IP address assigned to the LAN interface on the pfSense machine. Again, we’ll assume this address is 192.168.1.1. Appending the “iburst” option to the address will provide for faster initial synchronisation. We’ll also want to comment out the NTP server-related options that allow the local machine to exchange time with other host devices on the network and interrogate the local NTP server. The remaining options can remain at their default settings:
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# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help driftfile /var/lib/ntp/ntp.drift # Enable this if you want statistics to be logged. #statsdir /var/log/ntpstats/ statistics loopstats peerstats clockstats filegen loopstats file loopstats type day enable filegen peerstats file peerstats type day enable filegen clockstats file clockstats type day enable # Specify one or more NTP servers. # Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board # on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for # more information. #server 0.ubuntu.pool.ntp.org #server 1.ubuntu.pool.ntp.org #server 2.ubuntu.pool.ntp.org #server 3.ubuntu.pool.ntp.org server 192.168.1.1 iburst # Use Ubuntu's ntp server as a fallback. #server ntp.ubuntu.com # Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for # details. The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions> # might also be helpful. # # Note that "restrict" applies to both servers and clients, so a configuration # that might be intended to block requests from certain clients could also end # up blocking replies from your own upstream servers. # By default, exchange time with everybody, but don't allow configuration. #restrict -4 default kod notrap nomodify nopeer noquery #restrict -6 default kod notrap nomodify nopeer noquery # Local users may interrogate the ntp server more closely. #restrict 127.0.0.1 #restrict ::1 # Clients from this (example!) subnet have unlimited access, but only if # cryptographically authenticated. #restrict 192.168.123.0 mask 255.255.255.0 notrust # If you want to provide time to your local subnet, change the next line. # (Again, the address is an example only.) #broadcast 192.168.123.255 # If you want to listen to time broadcasts on your local subnet, de-comment the # next lines. Please do this only if you trust everybody on the network! #disable auth #broadcastclient |
A comment about the driftfile option: this file is used to store the local clock’s frequency offset. ntpd uses this file to automatically compensate for the local clock’s natural time drift, allowing it to maintain reasonably accurate time even if it cannot communicate with the pfSense machine for some period of time.
While not required, you can run the ntpdate command one time to fully synchronize the local clock with the OpenNTPD server in pfSense, then restart ntpd.
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sudo /etc/init.d/ntp stop sudo ntpdate 192.168.1.1 sudo /etc/init.d/ntp start |
In recent Linux releases using systemd-timesyncd, timedatectl replaces ntpdate and timesyncd replaces the client portion of ntpd. By default timedatectl syncs the time by querying one or more NTP servers once on boot and later on uses socket activation to recheck once network connections become active. timesyncd on the other hand regularly queries the NTP server(s) to keep the time in sync. It also stores time updates locally, so that after reboots monotonically advances if applicable.
The NTP server(s) used to sync time for timedatectl and timesyncd from can be specified in /etc/systemd/timesyncd.conf. By default the system will rely upon the default NTP server(s) defined by the distribution and specified by FallbackNTP= in the “[Time]” section of the file. To use the OpenNTPD server in the pfSense machine, uncomment NTP= and append the IP address assigned to the LAN interface on the pfSense machine. Again, assuming this address is 192.168.1.1:
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[Time] NTP=192.168.1.1 #FallbackNTP=ntp.ubuntu.com |
You can specify additional NTP servers by listing their host names or IP addresses separated by a space on these lines. Now run the following command:
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timedatectl set-ntp yes |
The current status of time and time configuration via timedatectl and timesyncd can be checked with the command timedatectl status:
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$ timedatectl status Local time: Tue 2017-04-25 17:41:04 EDT Universal time: Tue 2017-04-25 21:41:04 UTC RTC time: Tue 2017-04-25 21:41:04 Time zone: America/New_York (EDT, -0400) Network time on: yes NTP synchronized: yes RTC in local TZ: no |
- FreeBSD
ntpdate and ntpd are installed in FreeBSD by default, however ntpd is not configured to start at boot time.
Similar to Linux, we can run ntpdate manually as root to synchronize with the OpenNTP server running in the pfSense machine. Again, we’ll assume 192.168.1.1 is the IP address assigned to the LAN interface on the pfSense machine.
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ntpdate 192.168.1.1 |
ntpdate can also be made to run at boot time in FreeBSD by using the sysrc command to add the following lines to /etc/rc.conf:
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sysrc ntpdate_enable=YES sysrc ntpdate_hosts=192.168.1.1 |
We can also use cron under FreeBSD to run ntpdate. You can create a new crontab (or edit an exiting one) using the command crontab -e as root. The example cron job entries provided above under Linux will also work under FreeBSD.
To enable ntpd under FreeBSD, open /etc/ntp.conf and comment out the existing ntp pool servers and add the IP address assigned to the LAN interface on the pfSense machine. The remaining options can remain at their default settings:
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# # The following three servers will give you a random set of three # NTP servers geographically close to you. # See http://www.pool.ntp.org/ for details. Note, the pool encourages # users with a static IP and good upstream NTP servers to add a server # to the pool. See http://www.pool.ntp.org/join.html if you are interested. # # The option `iburst' is used for faster initial synchronisation. # #server 0.freebsd.pool.ntp.org iburst #server 1.freebsd.pool.ntp.org iburst #server 2.freebsd.pool.ntp.org iburst #server 3.freebsd.pool.ntp.org iburst server 192.168.1.1 iburst # # If you want to pick yourself which country's public NTP server # you want sync against, comment out the above servers, uncomment # the next ones and replace CC with the country's abbreviation. # Make sure that the hostnames resolve to a proper IP address! # # server 0.CC.pool.ntp.org iburst # server 1.CC.pool.ntp.org iburst # server 2.CC.pool.ntp.org iburst # # Security: Only accept NTP traffic from the following hosts. # The following configuration example only accepts traffic from the # above defined servers. # # Please note that this example doesn't work for the servers in # the pool.ntp.org domain since they return multiple A records. # (This is the reason that by default they are commented out) # #restrict default ignore #restrict 0.pool.ntp.org nomodify nopeer noquery notrap #restrict 1.pool.ntp.org nomodify nopeer noquery notrap #restrict 2.pool.ntp.org nomodify nopeer noquery notrap #restrict 127.0.0.1 #restrict -6 ::1 #restrict 127.127.1.0 # # If a server loses sync with all upstream servers, NTP clients # no longer follow that server. The local clock can be configured # to provide a time source when this happens, but it should usually # be configured on just one server on a network. For more details see # http://support.ntp.org/bin/view/Support/UndisciplinedLocalClock # The use of Orphan Mode may be preferable. # #server 127.127.1.0 #fudge 127.127.1.0 stratum 10 |
Now use sysrc to add the following two lines to /etc/rc.conf. The first line enables ntpd. The second tells the system to perform a one time sync at boot time:
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sysrc ntpd_enable=YES sysrc ntpd_sync_on_start=YES |
Run the ntpdate command one time to synchronize the local clock with the OpenNTPD server in pfSense, then start ntpd.
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ntpdate 192.168.1.1 service ntpd start |
Conclusion
This concludes the post on how to how to configure your pfSense machine to also act as a NTP server. The OpenNTPD service in pfSense will listen for requests from FreeBSD, Linux and Windows hosts and allow them to synchronize their local clock with that of the OpenNTPD server in pfsense. Using pfSense as a NTP server in your network ensures that your hosts always have consistent accurate time and reduces the load on the Internet’s NTP servers. Configuring Windows hosts to utilize this server is straightforward, while configuration under FreeBSD and Linux requires a bit more work.
References
Buechler, C.M. & Pingle, J. (2009). pfSense: The definitive guide. USA: Reed Media
http://www.ntp.org/documentation.html
http://support.ntp.org/bin/view/Support/WebHome
http://www.marksanborn.net/linux/learning-cron-by-example/
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