Overview of Layer 2 Bridging Interfaces

Bridging operates at Layer 2 of the OSI reference model while routing operates at Layer 3. A set of logical ports configured for bridging can be said to constitute a bridging domain.

A bridging domain can be created by configuring a routing instance and specifying the instance-type as bridge.

Integrated routing and bridging (IRB) is the ability to:

• Route a packet if the destination MAC address is the MAC address of the router and the packet ethertype is IPv4, IPv6, or MPLS.
• Switch all multicast and broadcast packets within a bridging domain at layer 2.
• Route a copy of the packet if the destination MAC address is a multicast address and the ethertype is IPv4 or IPv6.
• Switch all other unicast packets at Layer 2.
• Handle supported Layer 2 control packets such as STP and LACP.
• Handle supported Layer 3 control packets such as OSPF and RIP.

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