7.1 MLS Processes
7.1.3 MLS operations
MLS makes use of three components:
  • MLS Route Processor (MLS-RP)
  • MLS Switching Engine (MLS-SE)
  • MultiLayer Switching Protocol (MLSP)

The MLS-RP acts as the router in the network (note that more than one can be used). This device handles the first packet in every flow, allowing the MLS-SE to build shortcut entries in a Layer 3 content-addressable memory (CAM) table. The MLSP is a lightweight protocol used by the MLS-RP to initialize the MLS-SE and notify it of changes in the Layer 3 topology or security requirements. For simplicity, at times, this chapter may refer to the MLS-RP as the router and the MLS-SE as the NFFC. The NFFC and NFFC II are exclusively used on the Catalyst 5000 series switches.

MLS uses a four-step process:

  1. The MLS-RP sends MLSP hello packets.
  2. The MLS-SE identifies candidate packets.
  3. The MLS-SE identifies enable packets.
  4. The MLS-SE shortcuts future packets.

The following sections describe each of these steps using the sample network shown in the Figure.

This network consists of two virtual LANs (VLANs), VLAN 1 (red) and VLAN 2 (blue). Two end stations are shown. Host-A has been assigned to the blue VLAN, and Host-B has been assigned to the red VLAN. An ISL-attached router has also been included. Its single Fast Ethernet interface (Fast Ethernet1/0) has been logically partitioned into two subinterfaces, one per VLAN. The IP and Media Access Control (MAC) addresses for all devices and subinterfaces are shown.

The Figure also portrays the router as an ISL-attached external device using the router-on-a-stick configuration. Other possibilities include an RSM or a one-interface-per-VLAN attached router.