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Configuring LAN Interfaces

Configuring a LAN Extender Interface

IC-51

Cisco IOS Interface Configuration Guide

Note Do not configure the MTU to a value other than the default value when you are configuring

a LAN Extender interface.

Defining Packet Filters

You can configure specific administrative filters that filter frames based on their source MAC address.

The LAN Extender forwards packets between a remote LAN and a core router. It examines frames and

transmits them through the internetwork according to the destination address, and it does not forward a

frame back to its originating network segment.

You define filters on the LAN Extender interface in order to control which packets from the remote

Ethernet LAN are permitted to pass to the core router (see Figure 7). These filters are applied only on

traffic passing from the remote LAN to the core router. Filtering on the LAN Extender interface is

actually performed in the LAN Extender, not on the core router. This means that the filtering is done

using the LAN Extender CPU, thus offloading the function from the core router. This process also saves

bandwidth on the WAN, because only the desired packets are forwarded from the LAN Extender to the

core router. Whenever possible, you should perform packet filtering on the LAN Extender.

Figure 7 Packet Filtering on the LAN Extender

You can also define filters on the core router to control which packets from the LAN Extender interface

are permitted to pass to other interfaces on the core router (see Figure 8). You do this using the standard

filters available on the router. This means that all packets are sent across the WAN before being filtered

and that the filtering is done using the core router’s CPU.

Figure 8 Packet Filtering on the Core Router

Ethernet

Packet filters

LAN Extender

Other

networks

Remote

LAN

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Packet flow

Filters applied by lex

input-address-list and lex

input-type-list commands

Core router

LAN Extender

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Filters applied by standard

router output filters

LEX Output packet filters

LEX Input packet filters

Packet flow

Filters applied by standard

router input filters

Core router

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