Brocade TurboIron 24X Series Configuration Guide - Manual (Page 409)

Brocade TurboIron 24X Series Configuration Guide 375
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Routing between VLANs
If you do not need to further partition the port-based VLAN by defining separate Layer 3 VLANs, you
can define a single virtual routing interface at the port-based VLAN level and enable IP, IPX, and
Appletalk routing on a single virtual routing interface.
Some configurations may require simultaneous switching and routing of the same single protocol
across different sets of ports on the same router. When IP, IPX, or Appletalk routing is enabled on a
Layer 3 Switch, you can route these protocols on specific interfaces while bridging them on other
interfaces. In this scenario, you can create two separate backbones for the same protocol, one
bridged and one routed.
To bridge IP, IPX, or Appletalk at the same time these protocols are being routed, you need to
configure an IP protocol, IP subnet, IPX protocol, IPX network, or Appletalk protocol VLAN and not
assign a virtual routing interface to the VLAN. Packets for these protocols are bridged or switched
at Layer 2 across ports on the router that are included in the Layer 3 VLAN. If these VLANs are built
within port-based VLANs, they can be tagged across a single set of backbone fibers to create
separate Layer 2 switched and Layer 3 routed backbones for the same protocol on a single physical
backbone.
Routing between VLANs using virtual routing
interfaces (Layer 3 Switches only)
Brocade calls the ability to route between VLANs with virtual routing interfaces Integrated Switch
Routing (ISR). There are some important concepts to understand before designing an ISR
backbone.
Virtual router interfaces can be defined on port-based, IP protocol, IP subnet, IPX protocol, IPX
network, AppleTalk protocol, and AppleTalk cable VLANs.
To create any type of VLAN on a Layer 3 Switch, Layer 2 forwarding must be enabled. When Layer 2
forwarding is enabled, the Layer 3 Switch becomes a Switch on all ports for all non-routable
protocols.
If the router interfaces for IP, IPX, or AppleTalk are configured on physical ports, then routing occurs
independent of the Spanning Tree Protocol (STP). However, if the router interfaces are defined for
any type VLAN, they are virtual routing interfaces and are subject to the rules of STP.
If your backbone consists of virtual routing interfaces all within the same STP domain, it is a
bridged backbone, not a routed one. This means that the set of backbone interfaces that are
blocked by STP will be blocked for routed protocols as well. The routed protocols will be able to
cross these paths only when the STP state of the link is FORWARDING. This problem is easily
avoided by proper network design.
When designing an ISR network, pay attention to your use of virtual routing interfaces and the
spanning-tree domain. If Layer 2 switching of your routed protocols (IP, IPX, AppleTalk) is not
required across the backbone, then the use of virtual routing interfaces can be limited to edge
switch ports within each router. Full backbone routing can be achieved by configuring routing on
each physical interface that connects to the backbone. Routing is independent of STP when
configured on a physical interface.
If your ISR design requires that you switch IP, IPX, or Appletalk at Layer 2 while simultaneously
routing the same protocols over a single backbone, then create multiple port-based VLANs and use
VLAN tagging on the backbone links to separate your Layer 2 switched and Layer 3 routed
networks.