Configuring Transparent Bridging
Transparent and SRT Bridging Configuration Task List
BC-42
Cisco IOS Bridging and IBM Networking Configuration Guide
Note When a bridge group contains Token Ring interfaces, the Token Ring packets must not
include RIF. The IEEE 802.1d transparent bridge standard specifies that frames with source
routing information are to be dropped by transparent bridges; therefore, if Token Ring
traffic includes RIF, it will be dropped. RIF is designated by the RII, which is the first bit
of the MAC address. RII=1 indicates that the packet comes with RIF, RII=0 indicates that
the frame does not come with RIF.
For example, to bridge AppleTalk, bridge and route IPX, and route IP in the same bridge group, you
would do the following:
•Bridge AppleTalk—Because integrated routing and bridging bridges everything by default, no
configuration is required to bridge AppleTalk.
•Bridge and route IPX—After using the bridge irb command to enable integrated routing and
bridging, and the interface bvi command to create the bridge-group virtual interface for the bridge
group, you would use the bridge route command to both bridge and route IPX (bridging is already
enabled by default; the bridge route command enables routing).
•Route IP—Use the bridge route command to enable routing, and then use the no bridge bridge
command to disable bridging.
Note When integrated routing and bridging is not enabled, routing a given protocol means that
protocol is not bridged, and bridging a protocol means that protocol is not routed. When
integrated routing and bridging is enabled, the disjunct relationship between routing and
bridging is broken down, and a given protocol can be switched between routed and bridged
interfaces on a selective, independent basis.
Configuring Transparent Bridging Options
You can configure one or more transparent bridging options. To configure transparent bridging options,
perform one or more of the tasks in the following sections:
•Disabling IP Routing, page 42
•Enabling Autonomous Bridging, page 43
•Configuring LAT Compression, page43
•Establishing Multiple Spanning-Tree Domains, page44
•Preventing the Forwarding of Dynamically Determined Stations, page45
•Forwarding Multicast Addresses, page 45
•Configuring Bridge Table Aging Time, page45

Disabling IP Routing

If you want to bridge IP, you must disable IP routing because IP routing is enabled by default on the
Cisco IOS software. You can enable IP routing when you decide to route IP packets. To disable or enable
IP routing, use one of the following commands in global configuration mode: