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13-2

Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7

OL-8978-04

Chapter 13 Configuring CEF for PFC2 and PFC3A

Understanding How Layer 3 Switching Works

These sections describe Layer 3 switching with PFC2:

• Layer 3 Switching Overview, page 13-2

• Understanding Layer 3-Switched Packet Rewrite, page 13-2

• Understanding CEF for PFC2/PFC3A, page 13-5

• Understanding the NetFlow Statistics, page 13-11

Layer 3 Switching Overview

Note With Supervisor Engine 720 (MSFC3), IPX routing is done through the software.

Layer 3 switching allows a switch, instead of a router, to forward the IP and IPX unicast traffic and the

IP multicast traffic between the VLANs. Layer 3 switching is implemented in the hardware and provides

wire-speed interVLAN forwarding on the switch, rather than on MSFC2/MSFC3. Layer 3 switching

requires minimal support from MSFC2/MSFC3. MSFC2/MSFC3 routes any traffic that cannot be

Layer 3 switched.

Note Layer 3 switching supports the routing protocols that are configured on MSFC2/MSFC3. Layer 3

switching does not replace the routing protocols that are configured on MSFC2/MSFC3. Layer 3

switching uses Protocol Independent Multicast (PIM) for multicast route determination.

Layer 3 switching on Catalyst 6500 series switches provides flow statistics that you can use to identify

the traffic characteristics for administration, planning, and troubleshooting. Layer 3 switching uses

NetFlow Data Export (NDE) to export the flow statistics. See Chapter 16, “Configuring NDE”

for more

information about NDE.

Note Traffic is Layer 3 switched after being processed by the VLAN access control list (VACL) feature and

the quality of service (QoS) feature.

Understanding Layer 3-Switched Packet Rewrite

Note With Supervisor Engine 720 (MSFC3), IPX routing is done through the software.

When a packet is Layer 3 switched from a source in one VLAN to a destination in another VLAN, the

switch performs a packet rewrite at the egress port that is based on information learned from

MSFC2/MSFC3 so that the packets appear to have been routed by MSFC2/MSFC3.

Note Rather than just forwarding IP multicast packets, the PFC2/PFC3A replicates them as necessary on the

appropriate VLANs.

Cisco WS-C6506 User Manual

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