Advanced Configuration and Management Guide

blocked, the virtual interface can still route so long as at least one port in the virtual interface’s protocol VLAN is not blocked by STP.

NOTE: If you plan to connect the device to networking devices that run only a single instance of STP on all ports, you can configure the device to run a single instance of STP on all ports. However, doing so causes the device to stop using the individual VLANs you have configured and instead places all ports in a single logical VLAN, which is VLAN 4094. See the addendum or release notes shipped with your product for information.

Virtual Interfaces

A virtual interface is a logical routing interface that routing switches use to route Layer 3 protocol traffic between protocol VLANs.

The routing switches send Layer 3 traffic at Layer 2 within a protocol VLAN. However, Layer 3 traffic from one protocol VLAN to another must be routed.

If you want the device to be able to send Layer 3 traffic from one protocol VLAN to another, you must configure a virtual interface on each protocol VLAN, then configure routing parameters on the virtual interfaces. For example, to enable a routing switch to route IP traffic from one IP sub-net VLAN to another, you must configure a virtual interface on each IP sub-net VLAN, then configure the appropriate IP routing parameters on each of the virtual interfaces.

Figure 16.6 shows an example of Layer 3 protocol VLANs that use virtual interfaces for routing.

 

 

 

 

 

 

 

 

 

 

VE 1

 

 

 

 

 

 

 

 

 

 

VE 3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VE 2

VE 4

User-configured port-based VLAN

Protocol VLAN, IP sub-net VLAN,

IPX network VLANor AppleTalk VLAN

Figure 16.6 Use virtual interfaces for routing between Layer 3 protocol VLANs

VLAN and Virtual Interface Groups

To simplify configuration, you can configure VLAN groups and virtual interface groups. When you create a VLAN group, the VLAN parameters you configure for the group apply to all the VLANs within the group. Additionally, you can easily associate the same IP sub-net interface with all the VLANs in a group by configuring a virtual interface group with the same ID as the VLAN group.

For configuration information, see “Configuring VLAN Groups and Virtual Interface Groups” on page 16-39.

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