Configuring LAN Interfaces
Configuring a LAN Extender Interface
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
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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
Filters applied by standard
router input filters
LEX Input packet filters
Packet flow
Packet flow Core router LEX Output packet filters
Filters applied by standard
router output filters
LAN Extender
S2982
Cisco IOS Interface Configuration Guide
