Describing Routing Between VLANs
Inter-VLAN routing using multiple interfaces on an external router

On a single VLAN on a single switch all frames are processed and passed between ports based upon inspection of Layer 2 headers. Once packets must be passed between VLANs, this requires packet forwarding based upon inspection of the Layer 3 header, specifically the destination IP address.

In a multilayer switch, Layer 2 and Layer 3 processing occur on the same device. However, if a switch supports multiple VLANs but has no Layer 3 capability to route packets between those VLANs, the switch must be connected to a router external to the switch. This can be accomplished by setting up one router interface for each VLAN on the switch. The router then provides all Layer 3 routing functionality between VLANs on the switch.

In Figure , the clients on VLAN10 need to establish sessions with a server that is in VLAN20. This will require that traffic be routed between the VLANs as described in Figure .

External Router with Multiple Interface: Advantages and Disadvantages
Figure describes the advantages and disadvantages of using an external router with multiple interfaces for the purpose of inter-VLAN routing.


Demonstration Activity

Demonstration Activity: Cisco Secure ACS for Windows NT or Windows 2000

This demonstration activity presents an introduction to the Cisco Secure ACS for Windows NT or Windows 2000.

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