Data Sheet
© 2009 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information. Page 16 of 26
dedicated forwarding engine complete with the full forwarding tables. Distributed Cisco Express
Forwarding (Figure 6) works like this:
●
As in standard Cisco Express Forwarding, the central PFCx located on the supervisor
engine and the DFC engines located on the interface modules are loaded with the same
Cisco Express Forwarding information derived from the forwarding table before any user
traffic arrives at the switch.
●
As a packet arrives at an interface module, its DFC engine inspects the packet and uses
the information in the Cisco Express Forwarding table (including Layer 2, Layer 3, ACLs,
and QoS) to make a completely hardware-based forwarding decision for that packet.
●
The Distributed Cisco Express Forwarding engine manages all hardware-based forwarding
for traffic on that module, including Layer 2 and Layer 3 forwarding, ACLs, QoS policing
and marking, and NetFlow.
●
Because the DFCs make all the switching decisions locally, the central PFCx can dedicate
more hardware-forwarding resources to any modules not equipped with a DFC.
Figure 6. Distributed Cisco Express Forwarding Packet Flow
Distributed Cisco Express Forwarding Requirements
Requires a Cisco Catalyst 6500 Series Supervisor Engine 720 for the dCEF720 interface module;
requires either a Cisco Catalyst Supervisor Engine 720 or a Catalyst Supervisor Engine 2
multilayer switch feature card (MSFC) and a switch fabric module (SFM) for the dCEF256 interface
module.
Cisco IOS Software and Cisco Catalyst Operating System Software
Cisco Catalyst 6500 Series switches offer two software operating modes—the Cisco Catalyst
Operating System Software with optional Cisco IOS Software on the MSFC, and Cisco IOS
Software for the supervisor engines. Each operating mode can be deployed at different hierarchies
of the network, depending on the network’s requirements. These software solutions for Cisco
Catalyst 6500 Series switches provide full, high-performance Layer 2 through 4 switching and
routing functions.
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