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Hierarchy Level

Release Information

Statement introduced before Junos OS Release 7.4.

interface option added in Junos OS Release 8.2.

Statement introduced in Junos OS Release 12.2 for the ACX Series Universal Metro Routers.


For interfaces that can use various clock sources, configure the source of the transmit clock on each interface.


On Channelized SONET/SDH PICs, if you set the parent (or the master) controller clock to external, then you must set the child controller clocks to the default value—that is, internal.

For example, on the Channelized STM1 PIC, if the clock on the Channelized STM1 interface (which is the master controller) is set to external, then you must not configure the CE1 interface (which is the child controller) clock to external. Instead you must configure the CE1 interface clock to internal.


external—The clock source is provided by the data communication equipment (DCE).

interface interface-name—Configure clocking for the drop-and insert feature. When configuring this feature, both ports must use the same clock source: either the router’s internal clock or an external clock on one of the interfaces. If an external clock source is required, one interface must specify clocking external and the other must specify the same clock.

internal—Use the internal stratum 3 clock as the reference clock.

Default: internal

Required Privilege Level

interface—To view this statement in the configuration.

interface-control—To add this statement to the configuration.