Specifications

Multilayer Switching Overview
Introduction to IPX MLS
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• The router is configured as a member of the IP multicast group (using the ip igmp join-group
interface command) on the RPF interface of the multicast source.
• The router is the first-hop router to the source in PIM sparse mode (in this case, the router must send
PIM-register messages to the rendezvous point [RP]).
• Multicast TTL threshold or multicast boundary is configured on an outgoing interface for the flow.
• Multicast helper is configured on the RPF interface for the flow and multicast to broadcast
translation is required.
• Access list restrictions are configured on an outgoing interface (see the “Access List Restrictions
and Guidelines” section in the “Configuring Multicast Multilayer Switching” chapter).
• Integrated routing and bridging (IRB) is configured on the ingress interface.
• An output rate limit is configured on an outgoing interface.
• Multicast tag switching is configured on an outgoing interface.
When all the outgoing router interfaces for a given flow are multilayer switched, and none of the
situations described applies to the flow, that flow is considered completely switched. When a completely
switched flow is created, the MMLS-SE prevents multicast traffic bridged on the source VLAN for that
flow from reaching the MMLS-RP interface in that VLAN, reducing the load on the router.
One consequence of a completely switched flow is that the router cannot record multicast statistics for
that flow. Therefore, the MMLS-SE periodically sends multicast packet and byte count statistics for all
completely switched flows to the router using multicast MLSP. The router updates the corresponding
multicast routing table entry and resets the expiration timer for that multicast route.
Introduction to IPX MLS
The IPX MLS feature provides high-performance, hardware-based, Layer 3 switching for LAN switches.
IPX data packet flows are switched between networks, off loading processor-intensive packet routing
from network routers.
Whenever a partial or complete switched path exists between two hosts, packet forwarding occurs on
Layer 3 switches. Packets without such a partial or complete switched path are still forwarded by routers
to their destinations. Standard routing protocols such as RIP, Enhanced IGRP, and NetWare Link
Services Protocol (NLSP) are used for route determination.
IPX MLS also allows you to debug and trace flows in your network. Use MLS explorer packets to
identify which switch is handling a particular flow. These packets aid you in path detection and
troubleshooting.
IPX MLS Components
An IPX MLS network topology has the following components:
• MLS-SE—For example, a Catalyst 5000 series switch with the Netflow Feature Card (NFFC II).
The MLS-SE provides Layer 3 LAN-switching services.
• MLS-RP—For example, a Catalyst 5000 series RSM or an externally connected Cisco 4500, 4700,
7200, or 7500 series router with software that supports MLS. The MLS-RP provides Cisco
IOS-based multiprotocol routing, network services, and central configuration and control for the
switches.
• MLSP—The protocol running between the MLS-SE and MLS-RP that enables MLS.