Chapter 4 Configuring Interfaces

Configuring the POS OC-12c Uplink Interface (Catalyst 8540)

Additional Configurations

To configure additional properties to match those of the interface at the far end, perform the following steps, beginning in global configuration mode:

 

 

 

Command

Purpose

Step 1

 

 

Router(config-if)# no keepalive

Turns off keepalive messages. Keepalive messages, though not

 

 

 

 

required, are recommended.

Step 2

 

 

Router(config-if)# no cdp enable

Turns off CDP, which is not required.

Step 3

 

 

Router(config-if)# crc {16 32}

Sets the CRC value. If the device to which the POS module is

 

 

 

 

connected does not support the default CRC value of 32, set both

 

 

 

 

devices to use a value of 16.

 

 

 

 

 

 

 

 

 

 

Note

The above steps apply both to the POS OC-12c uplink interface on the switch router and

 

 

 

to the interface to which it connects at the far end.

 

 

 

 

 

 

Customizing the Configuration

This section describe how to customize the configuration of the POS OC-12c uplink interface to match your network environment.

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 pos

Enters interface configuration mode and specifies the POS

 

 

 

slot/subslot/interface

interface to configure.

 

 

 

Router(config-if)#

 

 

Step 2

 

 

Router(config-if)# mtu bytes

Configures the MTU size up to a maximum of 9188 bytes. Default

 

 

 

 

MTU size is 4470 bytes.

 

 

 

 

 

 

 

 

 

 

Note

The POS OC-12c uplink interface supports IP unicast and IP multicast fragmentation. For

 

 

 

IP unicast fragmentation, the packet must ingress on a POS interface and egress on any

 

 

 

interface. For IP multicast fragmentation, IP multicast data packets greater than

 

 

 

1500 bytes are fragmented to 1500 bytes on the ingress POS interface before being

 

 

 

switched to other members in the multicast group. All the members in the multicast group

 

 

 

must have a MTU equal to or greater than 1500 bytes.

 

 

 

 

 

 

 

 

Layer 3 Switching Software Feature and Configuration Guide

 

 

 

 

 

 

 

78-6235-04, Cisco IOS Release 12.0(10)W5(18)

 

 

4-17

 

 

 

 

 

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Cisco Systems 8510 CSR, 8540 CSR appendix Customizing the Configuration, Additional Configurations, Setting the MTU Size