In a traditional network, broadcast domains consist of either physical ports connected to a single switch or logical ports connected to one or more switches through virtual local area network (VLAN) configurations. Switches send traffic to hosts that are part of the same broadcast domain, but routers are needed to route traffic from one broadcast domain to another and to perform other Layer 3 functions such as traffic engineering.
With integrated routing and bridging (IRB), routers can switch traffic, route traffic, and perform other Layer 3 capabilities.
The interface that routes data to other Layer 3 interfaces is called the IRB interface. It performs the same functions as other Layer 3 interfaces. The IRB interface must be configured as part of a bridge domain or VPLS routing instance in order for Layer 3 traffic to be routed out of it. The IRB interface supports IPv4, IPv6, MPLS, and ISIS traffic. At least one Layer 2 logical interface should be operationally up in order for the IRB interface to be operationally up.
You must configure a bridge domain or VPLS routing instance just as you would configure a VLAN on a switch. Multicast data, broadcast data, or unicast data is switched between ports within the same IRB bridge domain or VPLS routing instance. The IRB interface routes data that is destined for the router’s media access control (MAC) address.
To learn more about configuring routing protocols and policies, see the JUNOS Routing Protocols Configuration Guide.