Dell FCX624-S Laptop User Manual


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PowerConnect B-Series FCX Configuration Guide 443
53-1002266-01
Routing between VLANs
13
Routing between VLANs
Layer 3 Switches can locally route IP, IPX, and Appletalk between VLANs defined within a single
router. All other routable protocols or protocol VLANs (for example, DecNet) must be routed by
another external router capable of routing the protocol.
Virtual routing interfaces (Layer 3 Switches only)
You need to configure virtual routing interfaces if an IP, IPX, or Appletalk protocol VLAN, IP subnet
VLAN, AppleTalk cable VLAN, or IPX network VLAN needs to route protocols to another port-based
VLAN on the same router. A virtual routing interface can be associated with the ports in only a
single port-based VLAN. Virtual router interfaces must be defined at the highest level of the VLAN
hierarchy.
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)
Dell 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.