12-2
Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
Chapter 12 Configuring IRB
Configuring IRB
• 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.
• Packets of unroutable protocols such as local-area transport (LAT) are always bridged. You cannot
disable bridging for the unroutable traffic.
• Protocol attributes should not be configured on the bridged interfaces when you are using IRB to
bridge and route a given protocol. You can configure protocol attributes on the BVI, but you cannot
configure bridging attributes on the BVI.
• A bridge links several network segments into one large, flat network. To bridge a packet co ming
from a routed interface among bridged interfaces, the bridge group should be represented by one
interface.
• All ports in a BVI group must have matching maximum transmission unit (MUTT) settings.
Configuring IRB
The process of configuring integrated routing and bridging consists of the following tasks:
1. Configure bridge groups and routed interfaces.
a. Enable bridging.
b. Assign interfaces to the bridge groups.
c. Configure the routing.
2. Enable IRB.
3. Configure the BVI.
a. Enable the BVI to accept routed packets.
b. Enable routing on the BVI.
4. Configure IP addresses on the routed interfaces.
5. Verify the IRB configuration.
When you configure the BVI and enable routing on it, packets that come in on a ro uted interface destined
for a host on a segment that is in a bridge group are routed to the BVI and forwarded to the bridging
engine. From the bridging engine, the packet exits through a bridged interface. Similarly, packets that
come in on a bridged interface but are destined for a host on a routed interface go first to the BVI. The
BVI forwards the packets to the routing engine that sends them out on the routed interface.
To configure a bridge group and an interface in the bridge group, perform th e following procedure,
beginning in global configuration mode:
Command Purpose
Step 1 Router(config)# bridge
bridge-group
protocol {ieee | rstp}
Defines one or more bridge groups.
Step 2 Router(config)# interface
type number
Enters interface configuration mode.
Step 3 Router(config-if)# bridge-group
bridge-group
Assigns the interface to the specified bridge
group.
Step 4 Router(config-if)# end Returns to privileged EXEC mode.