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Synchronize and Coordinate Time Distribution Using NTP

You can use NTP to synchronize and coordinate time distribution in a large network.

Using NTP to synchronize and coordinate time distribution in a large network involves these tasks:

Configure NTP

To configure NTP on the switch, include the ntp statement at the [edit system] hierarchy level:

Configure NTP Boot Server

When you boot the switch, it issues an ntpdate request, which polls a network server to determine the local date and time. You need to configure a server that the switch uses to determine the time when the switch boots. Otherwise, NTP will not be able to synchronize to a time server if the server’s time appears to be very far off of the local switch’s time.

  • To configure the NTP boot server, include the set ntp server statement at the [edit system ntp] hierarchy level. Specify either the IP address or the hostname of the network server:

  • Prior to Junos OS Release 15.1, to configure the NTP boot server, include the boot-server statement at the [edit system ntp] hierarchy level:

Note:

The boot-server option is deprecated starting in Junos OS Release 20.4R1.

Specify a Source Address for NTP Server

For IP version 4 (IPv4), you can specify that if the NTP server configured at the [edit system ntp] hierarchy level is contacted on one of the loopback interface addresses, the reply always uses a specific source address. This is useful for controlling which source address NTP will use to access your network when it is either responding to an NTP client request from your network or when it itself is sending NTP requests to your network.

To configure the specific source address that the reply will always use, and the source address that requests initiated by NTP server will use, include the source-address statement at the [edit system ntp] hierarchy level. The source-address is a valid IP address configured on one of the router or switch interfaces.

For example:

Starting in Junos OS Release 13.3, and Junos OS Evolved Release 20.2R1 you can configure the source address using the routing-instance statement at the [edit system ntp source-address source-address] hierarchy level:

As a result, while sending NTP message through any interface in the ntp-source-test routing instance, the source address 12.12.12.12 is used.

Note:

The routing-instance statement is optional and if not configured, the primary address of the interface will be used.

Specify one source address per family for each routing instance,

For example:

When configuring the NTP service in the management VRF (mgmt_junos), you must configure at least one IP address on a physical or logical interface within the default routing instance and ensure that this interface is up in order for the NTP service to work with the mgmt_junos VRF.

Note:

If a firewall filter is applied on the loopback interface, ensure that the source-address specified for the NTP server at the [edit system ntp] hierarchy level is explicitly included as one of the match criteria in the firewall filter. This enables the Junos OS to accept traffic on the loopback interface from the specified source address.

The following example shows a firewall filter with the source address 10.1.4.3 specified in the from statement included at the [edit firewall filter firewall-filter-name] hierarchy:

If no source-address statement is configured for the NTP server, include the primary address of the loopback interface in the firewall filter.