Integrated Routing and Bridging (IRB) On 888 Cisco Routers

I used this feature to bridge local interface to ATM as fallowing consideration:

Using the integrated routing and bridging (IRB) feature, you can route a given protocol between routed interfaces and bridge groups within a single switch router.


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.

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.
• The protocol attributes should not be configured on the bridged interfaces when using IRB to bridge
and route a given protocol. Bridging attributes cannot be configured on the BVI.
• A bridge links several network segments into one large, flat network. To bridge a packet coming
from a routed interface among the bridged interfaces, the whole bridge group should be represented
by one interface.
• The BVI has default data-link and network-layer encapsulations. These encapsulations are the same
as on the Ethernet, except that you can configure the BVI with some encapsulations that are not
supported on a normal Ethernet interface.

Configuring IRB

To enable and configure IRB and BVI, perform the following steps, beginning in global configuration
mode:

 To verify the IRB configuration, use the following commands:

show interfaces bvi interface-name
show interfaces irb 

Hesre Is Sample Configuration :

version 15.0
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname *****
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 10
!
!
ip source-route
!
!
ip dhcp excluded-address xxxxxxxx xxxxxxx
!
ip dhcp pool lan
   network xxxxxxx xxxxxxx
   default-router xxxxxxx
   dns-server xxxxxxx
   lease 30
!
!
ip cef
no ipv6 cef
!
!
!
username xxxxxxx privilege 15 secret 5 xxxxxxx
!
!
controller DSL 0
 mode atm
 dsl-mode shdsl symmetric annex B
!
!
!
!
bridge irb
!
!
!
!
interface BRI0
 no ip address
 encapsulation hdlc
 shutdown
 isdn termination multidrop
!
interface ATM0
 no ip address
 no atm ilmi-keepalive
 bridge-group 1
 pvc 0/55
  encapsulation aal5snap
 !
!
interface FastEthernet0
!
interface FastEthernet1
!
interface FastEthernet2
!
interface FastEthernet3
!
interface Vlan1
 ip address xxxxxxx xxxxxxx
!
interface BVI1
 ip address xxxxxxx xxxxxxx
!
ip forward-protocol nd
no ip http server
no ip http secure-server
!
ip route 0.0.0.0 0.0.0.0 xxxxxxx
ip route xxxxxxx 255.240.0.0 xxxxxxx
!
!
!
!
control-plane
!
bridge 1 protocol ieee
bridge 1 route ip
!
line con 0
 logging synchronous
 login local
 no modem enable
line aux 0
line vty 0 4
 logging synchronous
 login local
!
scheduler max-task-time 5000
end