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Layer 3 Switching Software Feature and Configuration Guide
78-6235-04, Cisco IOS Release 12.0(10)W5(18)
Chapter 4 Configuring Interfaces
Configuring the POS OC-12c Uplink Interface (Catalyst 8540)
To initially configure the POS OC-12c uplink interface, perform the following steps, beginning in
global configuration mode:
Example
The following configuration is an example of the tasks in the preceding table:
Router(config)# interface pos 1/0/0
Router(config-if)# ip address 10.1.2.3 255.0.0.0
Router(config-if)# encapsulation ppp
Router(config-if)# clock source line
Router(config-if)# no shutdown
Automatic Reverting of Clock Source
If your system clock source is set to line clock, it uses the recovered received clock to transmit. Under
some conditions, the received clock is not reliable because of severe degradation of the signal quality.
Because your system software monitors SF (signal failure), it knows when there is severe degradation
in the signal quality and resorts to using the internal clock temporarily. Once the conditions that caused
the signal quality to deteriorate clear, your system reverts to the line clock.
When two POS interface modules are connected and configured with the default line clock, the signal
quality can degrade over time and both POS interfaces revert to the internal clock. As soon as the signal
quality improves, both POS interfaces revert to using the line clock. This cycle repeats itself causing
the line protocol on both interfaces to toggle. You can prevent this situation by configuring one end of
the connection with the default line clock and the other with the internal clock.
In addition, degradation in the signal quality causes an automatic reverting of the clock source under
the following conditions:
• SLOS (section loss of signal)
• SLOF (section loss of frame)
• AIS-L (line alarm indication signal)
• SF (signal failure) due to B2 error rate crossing the SF threshold value
• SF (signal failure) due to B3 error rate crossing the SF threshold value when the pos delay triggers
path command is configured
Command Purpose
Step 1
Router(config)# ip routing Enables IP routing.
Step 2
Router(config)# interface pos
slot/subslot/interface
Router(config-if)#
Enters interface configuration mode and specifies the POS
interface to configure.
Step 3
Router(config-if)# ip address
ip-address subnet-mask
Assigns an IP address and subnet mask to the interface.
Step 4
Router(config-if)# encapsulation
{hdlc | ppp}
Specifies the encapsulation type.
Step 5
Router(config-if)# clock source
{line | internal}
Specifies the clock source for the interface. When clocking is
derived from the received clock, line (the default) is used. When
no line clocking source is available, internal is used.
Step 6
Router(config-if)# no shutdown Enables the interface with the previous configurations.