Cisco 15327 - Manual (Page 101)

6-5
Ethernet Card Software Feature and Configuration Guide, R7.2
Chapter 6 Configuring Bridges
Transparent Bridging Modes of Operation
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0005.9a39.6634
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0 Desg FWD 19 128.3 P2p
PO0 Desg FWD 9 128.20 P2p
Transparent Bridging Modes of Operation
The transparent bridging feature in the Cisco IOS software combines bridge-groups and IP routing. This
combination provides the speed of an adaptive spanning-tree bridge, along with the functionality,
reliability, and security of a router. The ML-Series card supports transparent bridging in the same general
manner as other Cisco IOS platforms.
Transparent bridging processes IP frames in four distinct modes, each with different rules and
configuration options. The modes are IP routing, no IP routing, bridge crb, and bridge irb. This section
covers the configuration and operation of these four modes on the ML-Series card.
For additional general Cisco IOS user documentation on configuring transparent bridging, see the
“Configuring Transparent Bridging” chapter of the Cisco IOS Bridging and IBM Networking
Configuration Guide, Release 12.2
at:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter0918
6a00800ca767.html
IP Routing Mode
IP routing mode is the default mode. It disables the other modes (no IP routing, bridge crb, and bridge
irb). The global command ip routing enables IP routing mode.
In IP routing mode, the bridge-groups do not process IP packets. The IP packets are either routed or
discarded.
The following rules help describe packet handling in this mode:
• An input interface or subinterface configured with only a bridge-group will bridge non-IP packets
and discard IP packets (
Example 6-4 ).
• An input interface or subinterface configured with only an IP address will route IP packets and
discard non-IP packets (
Example 6-5 ).
• An input interface or subinterface configured with both an IP address and a bridge-group routes IP
packets and bridges non-IP packets (
Example 6-6 ). This configuration is sometimes referred to as
fallback bridging. If a protocol cannot be routed, then the interface falls back to bridging.
• All of the interfaces or subinterfaces belonging to a specific bridge-group need consistent
configuration with regards to configuring or not configuring IP addresses. Mixing interfaces
configured with IP addresses and interfaces not configured with IP addresses in the same bridge
group can cause inconsistent or unpredictable routing at the network level.