IRB interfaces over an MPLS core network

You can configure integrated routing and bridging (IRB) interfaces over an MPLS network on switches. An IRB is a logical Layer 3 VLAN interface used to route traffic between VLANs. By definition, VLANs divide a LAN's broadcast environment into isolated virtual broadcast domains, thereby limiting the amount of traffic flowing across the entire LAN and reducing the possible number of collisions and packet retransmissions within the LAN. To forward packets between different VLANs, you normally need a router that connects the VLANs. Now you can accomplish this forwarding without using a router by simply configuring an IRB interface on the switch. The IRB interface functions as a logical switch on which you can configure a Layer 3 logical interface for each VLAN. The switch relies on its Layer 3 capabilities to provide this basic routing between VLANs. With IRB, you can configure label-switched paths (LSPs) to enable the switch to recognize which packets are being sent to local addresses, so that they are bridged (switched) whenever possible and are routed only when necessary. Whenever packets can be switched instead of routed, several layers of processing are eliminated.