Cisco Systems CL-28826-01 Bridging on Cisco IOS Routers

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User Guide for Cisco Security Manager 4.4

OL-28826-01

Chapter 60 Router Device Administration

Bridging on Cisco IOS Routers

Bridging on Cisco IOS Routers

Bridging policies enable you to perform transparent bridging (as specified in RFC 1286) on selected

interfaces that you have configured to function as a bridge group. Security Manager supports integrated

routing and bridging, which makes it possible to route a specific protocol between routed interfaces and

bridge groups, or route a specific protocol between bridge groups. Local or unroutable traffic can be

bridged among the bridged interfaces in the same bridge group, while routable traffic can be routed to

other routed interfaces or bridge groups, as shown in Figure 60-1.

Using integrated routing and bridging, you can:

•Switch packets from a bridged interface to a routed interface.

•Switch packets from a routed interface to a bridged interface.

•Switch packets within the same bridge group.

Figure 60-1 Transparent Bridging

Because bridging takes places at the data link layer and routing takes place at 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. As shown in Figure 60-2, the interface number assigned to the BVI corresponds to the bridge

group that the BVI represents. This number serves as the link between the virtual interface and the bridge

group.

Bridged

interfaces

Router

Bridge group 1

Routed

interface

180109

10.0.0.1