Configuration Guide User guide

FastIron Configuration Guide 759
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VLAN overview
It is possible that STP will block one or more ports in a protocol VLAN that uses a virtual routing
interface to route to other VLANs. For IP protocol and IP subnet VLANs, even though some of the
physical ports of the virtual routing interface are blocked, the virtual routing interface can still route
so long as at least one port in the virtual routing interface protocol VLAN is not blocked by STP.
If you enable Single STP (SSTP) on the device, the ports in all VLANs on which STP is enabled
become members of a single spanning tree. The ports in VLANs on which STP is disabled are
excluded from the single spanning tree.
For more information, refer to Chapter 27, “Spanning Tree Protocol”.
Virtual routing interfaces
A virtual routing interface is a logical routing interface that Brocade Layer 3 switches use to route
Layer 3 protocol traffic between protocol VLANs.
Brocade devices 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 routing interface on each protocol VLAN, then configure routing
parameters on the virtual routing interfaces. For example, to enable a Layer 3 switch to route IP
traffic from one IP subnet VLAN to another, you must configure a virtual routing interface on each IP
subnet VLAN, then configure the appropriate IP routing parameters on each of the virtual routing
interfaces.
Figure 78 shows an example of Layer 3 protocol VLANs that use virtual routing interfaces for
routing.