Interface and Router Clock Sources

When configuring the router, you can configure the transmit clock on each interface; the transmit clock aligns each outgoing packet transmitted over the router's interfaces. For both the router and interfaces, the clock source can be the router's internal stratum 3 clock, which resides on the SCB, SSB, FEB, or MCS (depending on the router model), or an external clock that is received from the interface you are configuring. For example, interface A can transmit on interface A's received clock (external, loop timing) or the stratum 3 clock (internal, line timing). Interface A cannot use a clock from any other source.

By default, each interface uses the router's internal stratum 3 clock. To configure the clock source of each interface, include the clocking statement at the [edit interfaces interface-name] hierarchy level:

[edit interfaces interface-name]

clocking (internal | external);

Figure 2 illustrates the different clock sources.

Figure 2: Clock Sources