Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 47)

Brocade Virtual ADX Switch and Router Guide 33
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Routing between VLANs
3
Bridging and routing the same protocol simultaneously
on the same device
Some configurations may require simultaneous switching and routing of the same single protocol
across different sets of ports on the same router. When IP routing is enabled on a Brocade 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 at the same time these protocols are being routed, you need to configure an IP subnet
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
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 subnet VLANs.
To create any type of VLAN on a Brocade 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 your backbone is consisted 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. Full backbone routing can be achieved by configuring routing on each
physical interface that connects to the backbone.
If your ISR design requires that you switch IP at Layer 2 while simultaneously routing the same
protocol 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.
There is a separate STP domain for each port-based VLAN. Routing occurs independently across
port-based VLANs or STP domains. You can define each end of each backbone link as a separate
tagged port-based VLAN. Routing will occur independently across the port-based VLANs.
Dynamic port assignment
All switch ports are dynamically assigned to any non-routable VLAN on Brocade Layer 3 Switches.
To maintain explicit control of the VLAN, you can explicitly exclude ports when configuring any
non-routable Layer 3 VLAN on a Brocade Layer 3 Switch.