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:
- The MLS-RP sends MLSP hello
packets.
- The MLS-SE identifies candidate
packets.
- The MLS-SE identifies enable
packets.
- 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.
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