Virtual Routing Interfaces; Bridging And Routing The Same Protocol Simultaneously On The Same Device; Routing Between Vlans Using Virtual Routing Interfaces - HP ProCurve 9304M Installation And Configuration Manual

Installation and Basic Configuration Guide

Virtual Routing Interfaces

You need to configure virtual routing interfaces if an IP, IPX, or Appletalk protocol VLAN, IP sub-net 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.

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, IPX, or Appletalk routing is enabled on an HP Routing 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 sub-net, 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

HP 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 sub-net, IPX protocol, IPX network,
AppleTalk protocol, and AppleTalk cable VLANs.
To create any type of VLAN on an HP Routing Switch, Layer 2 forwarding must be enabled. When Layer 2
forwarding is enabled, the Routing 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 is comprised 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.
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. Because each port-based VLAN's STP domain is
a single point-to-point backbone connection, you are guaranteed to never have an STP loop. STP will never block
the virtual router interfaces within the tagged port-based VLAN, and you will have a fully routed backbone.
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