Cisco Systems 8540 CSR, 8510 CSR appendix Configuring the Clock Source, Example

Chapter 4 Configuring Interfaces

Configuring the ATM Uplink Interface (Catalyst 8540)

Example

The following configuration is an example of the tasks in the preceding table:

Router(config)# interface atm 2/0/0

Router(config-if)#ip address 10.1.2.4 255.0.0.0

Router(config-if)# atm clock internal

Router(config-if)# no shutdown

Configuring the Clock Source

The ATM uplink interfaces support internal and line clock source. The default mode for the clock is no internal, which is the same as the line clock. If your system clock source is set to line clock, it uses the recovered received clock to transmit.

When two ATM uplink interfaces are connected and set to line clock, both interfaces at each end of the link cannot accurately synchronize the clock. This causes transfer of corrupt data, which might cause the line protocol on both interfaces to go down. To prevent this situation, make sure you configure one end of the connection with internal clock and the other end with no internal clock.

When your system is configured to use the line clock, the following conditions cause the clock to automatically revert to internal:

•SLOS (section loss of signal)

•SLOF (section loss of frame)

•AIS-L (line alarm indication signal)

•S1 (synchronizing status) byte in the SONET line overhead is equal to 0xF When these conditions clear, the clock automatically restores to line clock.

Customizing the Configuration

This section describes how to configure your ATM uplink interface to match your network configuration.

Setting the MTU Size

To set the maximum transmission unit (MTU), perform the following steps, beginning in global configuration mode:

	Command	Purpose
Step 1
	Router(config)# interface atm	Enters interface configuration mode and specifies the ATM
	slot/subslot/interface	interface to configure.
	Router(config-if)#
Step 2
	Router(config-if)# mtu bytes	Configures the MTU size with a value from 64 to 9188 bytes. The
		default MTU size is 4478 bytes.
Step 3
	Router(config-if)# no shutdown	Enables the interface with the previous configuration.

	Layer 3 Switching Software Feature and Configuration Guide
4-30	78-6235-04, Cisco IOS Release 12.0(10)W5(18)