Configuring VLANs

Layer 2 traffic is bridged within a port-based VLAN and Layer 2 broadcasts are sent to all the ports within the VLAN.

Layer 3 Protocol-Based VLANs

If you want some or all of the ports within a port-based VLAN to be organized according to Layer 3 protocol, you must configure a Layer 3 protocol-based VLAN within the port-based VLAN.

You can configure each of the following types of protocol-based VLAN within a port-based VLAN. All the ports in the Layer 3 VLAN must be in the same Layer 2 VLAN.

•AppleTalk – The device sends AppleTalk broadcasts to all ports within the AppleTalk protocol VLAN.

•IP – The device sends IP broadcasts to all ports within the IP protocol VLAN.

•IPX – The device sends IPX broadcasts to all ports within the IPX protocol VLAN.

•DECnet – The device sends DECnet broadcasts to all ports within the DECnet protocol VLAN.

•NetBIOS – The device sends NetBIOS broadcasts to all ports within the NetBIOS protocol VLAN.

•Other – The device sends broadcasts for all protocol types other than those listed above to all ports within the VLAN.

Figure 16.2 shows an example of Layer 3 protocol VLANs configured within a Layer 2 port-based VLAN.

Default VLAN

User-configured port-based VLAN

Protocol VLAN, IP sub-net VLAN,

IPX network VLANor AppleTalk VLAN

Figure 16.2 Layer 3 protocol VLANs within a Layer 2 port-based VLAN

Integrated Switch Routing (ISR)

The Integrated Switch Routing (ISR) feature enables VLANs configured on routing switches to route Layer 3 traffic from one protocol VLAN or IP sub-net, IPX network, or AppleTalk cable VLAN to another. Normally, to route traffic from one IP sub-net, IPX network, or AppleTalk cable VLAN to another, you would need to forward the traffic to an external router. The VLANs provide Layer 3 broadcast domains for these protocols but do not in themselves provide routing services for these protocols. This is true even of the source and destination IP sub-nets, IPX networks, or AppleTalk cable ranges are on the same device.

ISR eliminates the need for the external router by allowing you to route between the VLANs, on the same device,

using virtual interfaces (VEs).1 A virtual interface is a logical port on which you can configure Layer 3 routing parameters. You configure a separate virtual interface on each VLAN that you want to be able to route from or to.

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