Troubleshooting guide

12-13
ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Chapter 12 Troubleshooting Layer 2 Interfaces
Troubleshooting Integrated Routing and Bridging
Troubleshooting Integrated Routing and Bridging
This section describes troubleshooting Integrated Routing and Bridging (IRB) on the
Catalyst 8510 MSR and Catalyst 8540 MSR and Catalyst 8510 CSR and Catalyst 8540 CSR switches.
Your network may require you to bridge local traffic within several segments while having hosts on the
bridged segments reach the hosts or routers on routed networks. For example, if you are migrating
bridged topologies into routed topologies, you may want to start by connecting some of the bridged
segments to the routed networks.
IP Switching with IRB Overview
Using the IRB feature, you can route a given protocol between routed interfaces and bridge groups
within a single switch router. Specifically, local or unroutable traffic will be bridged among the bridged
interfaces in the same bridge group, while routable traffic will be routed to other routed interfaces or
bridge groups.
Because bridging is in the data-link layer (Layer 2) and routing is in the network layer (Layer 3), they
have different protocol configuration models. With IP, for example, bridge group interfaces belong to the
same network and have a collective IP network address. In contrast, each routed interface represents a
distinct network and has its own IP network address. Integrated routing and bridging uses the concept of
a Bridge-Group Virtual Interface (BVI) to enable these interfaces to exchange packets for a given
protocol.
A BVI is a virtual interface within the campus switch router that acts like a normal routed interface.
A BVI does not support bridging, but it actually represents the corresponding bridge group to routed
interfaces within the switch router. The interface number is the link between the BVI and the bridge
group.
Layer 3 switching software supports the routing of IP and IPX between routed interfaces and bridged
interfaces in the same router, in both fast-switching and process-switching paths.
Note BVIs do not support IP multicast routing.
Before Configuring IRB
Consider the following before configuring IRB:
• The default route/bridge behavior in a bridge group (when IRB is enabled) is to bridge all packets.
Make sure you explicitly configure routing on the BVI for protocols that you want routed.
• Packets of nonroutable protocols such as local-area transport (LAT) are always bridged. You cannot
disable bridging for the nonroutable traffic.
show bridge number Displays the status of the bridge group.
show epc patricia interface {fastethernet |
gigabitethernet} slot/subslot/port mac detail
Displays the MAC patricia tree for the specified
interface physical interface in the bridge group
with a problem.
Command Purpose