6-7
Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
Chapter 6 Configuring Bridges
Bridge CRB Mode
• An input interface or subinterface configured with only an IP address discards all packets, except
packets with the destination MAC and IP address of the input interface, which are processed by
Cisco IOS. This is not a valid configuration.
• An input interface or subinterface configured with both an IP address and a bridge group bridges all
packets, except packets sent to the input interface M AC address. Packets sent to the input interface
MAC address and the interface IP address are processed by Cisco IOS. Other packets sent to the
input interface MAC address are discarded. This is not a valid configuration for the IP addresses.
• All of the interfaces or subinterfaces belonging to a specific bridge-group need consistent
configuration in 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.
Example 6-7 shows ML-Series card interfaces configured in a bridge group with no IP addresses.
Example 6-7 Bridge Group with No IP Address
no ip routing
bridge 1 proto rstp
int f0
bridge-group 1
int pos 0
bridge-group 1
Bridge CRB Mode
In bridge crb mode, the default sub-mode for every bridge group is to bridge but not route the IP packets.
This is similar to the no ip routing mode behavior. But with bridge crb, packet handling is configured
not globally but for the specific bridge group. You can selectively disable bridge groups to block IP
packets or configure fallback bridging for a group of routed interfaces.
Concurrent routing and bridging is enabled with the g lobal command bridge crb. Enabling bridge crb
disables the other modes.
The following rules help describe packet handling in this mode:
• The command bridge x bridge ip (where x is a bridge-group number) configures a bridge-group to
bridge IP packets. Input interfaces and sub-interfaces belonging to the bridge-group will follow the
rules for no IP routing mode.
• The command bridge x route IP (where x is a bridge-group number) configures a bridge-gr oup to
ignore IP packets. Input interfaces and sub-interfaces belonging to this bridge-group will follow the
rules for IP routing mode (Example 6-8).
• When you enable bridge crb with pre-existing bridge groups, it will generate a bridge x route IP
configuration command for any pre-existing bridge groups with an interface configured for routing
(configured with an IP address). This is a precaution when crb is first enabled.
• All of the interfaces or subinterfaces belonging to a specific bridge-group need consistent
configuration in 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.
• Routing between interfaces or subinterfaces that do not belong to the same b ridge group could result
in inconsistent network behavior. This mode is for routing between member s of a bridge-group, but
never for routing into or out of a bridge group.