7.1 MLS Processes
7.1.1 MLS overview
MultiLayer Switching (MLS) provides high-performance hardware-based Layer 3 switching for Catalyst® Switches. MLS switches IP and/or IPX data packet flows between subnets using advanced application-specific integrated circuit (ASIC) switching hardware.  MLS offloads processor-intensive packet routing from network routers.

Layer 3 protocols, such as IP, are connectionless, delivering each packet independently of each other. However, actual network traffic consists of many end-to-end conversations, or flows, between users or applications.

A flow is a specific conversation, consisting of many packets, between a network source and destination within a specific time interval. For example, Hypertext Transfer Protocol (HTTP) packets from a particular source to a particular destination are a separate flow from File Transfer Protocol (FTP) file transfer packets between the same pair of hosts. Flows may consist of unicast or multicast traffic.

MLS is a technique used to increase IP routing performance by handling the packet-switching and rewrite functions in hardware. The Cisco implementation of MLS supports all the traditional routing protocols; however, the frame forwarding and rewrite process functions previously handled by a router have now been moved into switch hardware. MLS moves the packet-forwarding function traditionally handled by the router to Layer 3 switches whenever a switched path exists.