Exam Essentials

Know the components of MLS. Multilayer Switching is made of three components. The first is the MLS-SE, the switch. The second is the MLS-RP, the router that makes the changes to the initial packet. The third is MLSP, the communication protocol that is used between the router and any switches.

Understand what a flow is and how a switch uses them. A flow is nothing more than a conversation, a stream of packets between two devices. A switch caches information about the conversation and information about how the packets are supposed to be manipulated. When a packet arrives that matches a packet stream that the switch has already seen, the switch makes the necessary changes.

Know what information a switch can use to identify flows. A switch can use various pieces of information to identify flows, but only three broad configurations are allowed. The first tells the switch to identify flows based only on the destination IP address. The second says to use both source and destination IP addresses. The third uses the protocol as well as the source and destination IP addresses and ports.

Understand how access control lists on the router affect MLS. Outbound access control lists have always been supported and are the primary way of telling the switch what information to use to identify the flow. Inbound access control lists are supported with additional configuration. Reflexive lists and IP security on the interface disable the MLS process for that interface.