6500 Series Switches

The 6500 series switches use a crossbar switching fabric. This is good, because as the heart of the
Cisco high-end range, they are widely used as core switches, and need to ensure non-blocking
throughput at very high speeds.
The 6500 series switches have 8 usable slots, with 2 fabric channels per slot and
8 Gigabits/sec per fabric channel, providing an advertised 256 Gigabits/second
(full-duplex) switching fabric.
A TCAM lookup mechanism is applied to the architecture for the fastest possible addressmatching
decision, and the actual forwarding mechanism is assisted by a distributed forwarding
mechanism using the Distributed Forwarding Card. (This is similar to the satellite ASICs in the
3550 series.)
In addition, the 6500 series gains a large increase in throughput speed by using a process
called Demand-Base Switching. This involves updating an ASIC-based cache with information
from the first layer 3 packet forwarded at routing table speeds, and then switching the rest of
the packets along the same path. The use of ASICs to manage this table increases the throughput
by a factor of thousands. This is in addition to standard fast CEF table. The basic architecture
of the 6500 switches is shown in Figure 21.10.
You can select the options you need in this modular architecture, taking into account both
cost and requirements. For example, line cards can be installed with several configuration
options, including the following:
 Classic line cards: bus connectivity only
 Fabric-enabled line cards: switch fabric and bus connectivity
 Fabric-only line cards: dual switch fabric, no bus connectivity
 Switch fabric: line cards that contain the actual 256 Gigabits fabric

6500 switch architecture
Crossbar
Fabric
Routing Tables
Hardware Tables
MSFC 2
PFC2
Forward
Tables
ASICs
Fabric Enabled Card Fabric Only Card
16 Gbps Fabric
ASIC
DFC
ASIC X
32 Gbps Switch Fabric