Network Time

OPNsense ships with a standard NTPd server, which synchronizes time with upstream servers and provides time to connected clients.

A newly installed firewall comes with NTP enabled on all interfaces (firewall blocks all non LAN access in this case), forwarding queries to one of the upstreams (X is any of 0,1,2,3).

General settings

In most cases the default setup is ready to use, below you will find some of the general options which can be configured.


NTPd syncs the local clock to remote NTP servers and listens for incoming client queries using the selected interfaces. The interface selection must therefore include a WAN type interface so that normal routing to the internet can take place. Only selecting a LAN type interface will likely work due to outbound NAT rules, however, if CARP is configured, it is possible that such NAT rules will translate to the address of the CARP VIP, causing asymmetric routing for secondary nodes.

Unless you are sure that you want to use a specific interface, it is recommended to keep the default of listening on all interfaces and use the firewall rules to constrain access to the NTP service. See Listen interfaces for more information.


Interfaces to listen on. This interface selection is also used for outgoing queries. when no interfaces are selected it listens on all interfaces with a wildcard. Selecting all interfaces will explicitly listen on only the interfaces/IPs specified. Interfaces without an IP address will not be shown.

Time servers

Servers to use, comes with two toggles:

  • Prefer

    Marks the server as preferred.

  • Do not use

    Marks the server as unused, except for display purposes. The server is discarded by the selection algorithm.

Orphan mode

Orphan mode allows the system clock to be used when no other clocks are available. The number here specifies the stratum reported during orphan mode and should normally be set to a number high enough to insure that any other servers available to clients are preferred over this server.

NTP graphs

Enable RRD graphs of NTP statistics, which can be viewed in Reporting ‣ Health

Syslog logging

Extend logging with peer and/or system messages

Statistics logging

Enable statistical logging in /var/log/ntp, doesn’t come with a user interface

Access restrictions

Within the access restriction row, you can set various options which limit the use of ntpd and in some cases instruct ntpd how to handle rejected clients.

Leap seconds

You can manually supply ntpd with a leap seconds file, more detailed info on the contents of those files can be found here


NTPs is disabled if no Time servers are configured. There is no separate enable/disable toggle.


If you own a gps receiver, which supports NMEA, you can use it as a reference clock and configure it in this section. For some brands settings are preconfigured, you can also use custom settings.


If your GPS receiver supports PPS (Pulse Per Second) output or you have a separate PPS signal available, you can configure the serial port to use along with some other settings here.


The status page can be used to query the health of the upstream time sources, it shows the following characteristics.


Human readable status of the upstream


Upstream source

Ref ID

Source IP address or kiss code:


NTP uses a hierarchical, semi-layered system of time sources (wikipedia) This field shows the stratum of the upstream source (lower usually means closer to the actual time source)


Type of time source, one of:

  • u: unicast or manycast client

  • b: broadcast or multicast client

  • p: pool source

  • l: local (reference clock)

  • s: symmetric (peer)

  • A: manycast server

  • B: broadcast server

  • M: multicast server


time in seconds, minutes, hours, or days since the last packet was received, or ‘-‘ if a packet has never been received


poll interval in seconds


reach shift register (octal), when set to 377 all 8 bits are set and thus no responses have been lost. Convert to bits to inspect which tries failed. (e.g. 257 –> 10101111 means the last four responses where received and two where lost within the last 8 tries)


roundtrip delay in milliseconds


offset time in milliseconds of the server relative to this host


indicates the difference, in milliseconds, between two samples