Chapter 11 Configuring Irb; Integrated Routing And Bridging - Cisco ONS 15454 Software Feature And Configuration Manual

Configuring IRB
This chapter describes how to configure integrated routing and bridging (IRB) for the ML-Series card.
For more information about the Cisco IOS commands used in this chapter, refer to the
Cisco IOS Command Reference publication.
This chapter includes the following major sections:
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Cisco Inter-Switch Link (ISL) and Cisco Dynamic Trunking Protocol (DTP) are not supported by the
Caution
ML-Series, but the ML-Series broadcast forwards these formats. Using ISL or DTP on connecting
devices is not recommended. Some Cisco devices attempt to use ISL or DTP by default.

Integrated Routing and Bridging

Your network might require you to bridge local traffic within several segments and have hosts on the
bridged segments reach the hosts or ML-Series card on routed networks. For example, if you are
migrating bridged topologies into routed topologies, you might want to start by connecting some of the
bridged segments to the routed networks.
Using the integrated routing and bridging (IRB) feature, you can route a given protocol between routed
interfaces and bridge groups within a single ML-Series card. Specifically, local or unroutable traffic is
bridged among the bridged interfaces in the same bridge group, while routable traffic is routed to other
routed interfaces or bridge groups.
Because bridging is in the data link layer and routing is in the network layer, 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 ML-Series card that acts like a normal routed interface. A BVI
does not support bridging but actually represents the corresponding bridge group to routed interfaces
within the ML-Series card. The interface number is the link between the BVI and the bridge group.
Before configuring IRB, consider the following:
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Cisco ONS 15454 SONET/SDH ML-Series Multilayer Ethernet Card Software Feature and Configuration Guide, R4.0
78-15224-02
Integrated Routing and Bridging, page 11-1
Configuring IRB, page 11-2
Monitoring and Verifying IRB, page 11-4
The default routing/bridging behavior in a bridge group (when IRB is enabled) is to bridge all
packets. Make sure that you explicitly configure routing on the BVI for IP traffic.
C H A P T E R
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