System Testing

In addition to the sophisticated debugging option, a huge variety of show commands are available
to allow you to take snapshot views of everything from the configuration to information
about the frame flow on an interface. In the absence of a photographic memory, the contextsensitive
help is the first step in determining which command you need. This can best be demonstrated
by using the show help command.
Terry_3550#show ?
access-expression List access expression
access-lists List access lists
accounting Accounting data for active sessions
adjacency Adjacent nodes
aliases Display alias commands
arp ARP table
auto Show Automation Template
boot show boot attributes
One command you may wish to familiarize yourself with is the show processes command.
In addition to providing an (almost indecipherable) list of the processes running, it provides a
very valuable snapshot of the processor overhead. (The underlines are mine.)
Terry_3550#show processes ?
cpu Show CPU use per process
memory Show memory use per process
| Output modifiers

<cr>
Terry_3550#show processes cpu
CPU utilization for five seconds: 20%/20%; one minute: 16%; five minutes: 10%
PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process
1 0 1 0 0.00% 0.00% 0.00% 0 Chunk Manager
2 4 105887 0 0.00% 0.00% 0.00% 0 Load Meter
3 0 72 0 0.00% 0.00% 0.00% 0 SpanTree Helper
4 0 2 0 0.00% 0.00% 0.00% 0 IpSecMibTopN
5 106752 53797 1984 0.00% 0.01% 0.00% 0 Check heaps
6 4 477 8 0.00% 0.00%
[output cut]

One additional module that can be implemented with the 6500 series switches is the Network
Analysis Module (NAM), which constitutes an integrated traffic monitoring solution,
enabling network managers to gain “application-level visibility” into network traffic. The
NAM supplies an embedded, web-based traffic analyzer, providing remote monitoring and
troubleshooting through a browser. NAM’s Main features include
 Integrated monitoring
 Real-time and historical data gathering
 Performance management
 Fault isolation
 QoS and VoIP monitoring
 Capacity planning


The architecture of modern switches does not conform to a single model. Vendors, in competition
with each other, devise their own mechanisms to create faster, more scalable switches to
suit every niche in the modern network. Cisco is no exception; in fact, they are probably among
the world’s greatest innovators.
New technologies such as the Content Addressable Memory (CAM) lookup system are
used in the entry-level 2950 series switches, and CAM’s big brother, the Ternary CAM
(TCAM), is used in the 3550, 4000, and 6500 series. This provides the speedy lookup
required for fast decision-making. In turn, this decision-making is itself speeded up by the
use of processors external to the memory tables. In the 3550, these are satellite ASICs, and
in the 6500 they are provided by the Distributed Forwarding Card.
All of this is bound together by the selection of the most appropriate switching fabric.
Whether it is the shared memory of the 2950 and the 4000, the distributed shared memory of
the 3550, or the crossbar of the 6500, each switch has a fabric that matches its needs and position
in the network. In addition, a range of software options is currently available, with the biggest
decisions centering around whether to purchase SI or EI for the 2950, and whether to use
hybrid IOS or native IOS on the 4000 and 6500.
Finally, switch management has never been more difficult. With the range of newer technologies
such as voice and video demanding newer QoS options, we find ourselves with an almost
bewildering array of configuration options. To manage this environment, we have the legacy
range of show and debug commands, although debug will be new to many of you without a
router background. But we also have the Cisco Cluster Management Suite (CMS), which allows
us to manage up to 16 switches using a single front end.

Exam Essentials
Understand what switching architecture is. Switches have come a long way in the last few
years. From simple systems using shared buses and interrupt-driven access, we have arrived
at the crossbar switch�"a truly non-blocking architecture suitable for building the largest
switches in the busiest environments. But the crossbar is expensive, and other mechanisms
exist that are suitable for lesser needs. These include the shared memory and distributed
shared memory fabrics. And you need to understand how they work, and remember which
Cisco switch uses which.
Understand CAM and TCAM. Storing addressing information in memory is quite easy. The
difficult part is referencing it and accessing it quickly. A number of different techniques have
emerged in the past to carry out this task, including simple pointing and hash referencing, but
all have been slow. A modern, more intelligent process is called a Content Addressable Memory
(CAM). In the CAM, the location of the data in the memory block is somehow related to the
type of data that is stored, making for a much faster lookup.
Exam Essentials 701
Even so, the CAM is limited by the fact that there are only two binary numbers, and that means
checking every bit. By adding a third bit (the “don’t care” bit) in a mask, the resulting Ternary
CAM (TCAM) can provide even faster lookups by ignoring unnecessary bits of information.
Understand switch types. Cisco switches come in a variety of shapes and sizes. As the range
changes and becomes more modern, some new switches have appeared. Some of them, such as
the fixed-configuration 3550 series, are almost multi-port routers, running native IOS. Others,
such as the 4000 and 6500 series, are modular, running updated versions of the IOS. You need
to know which switches have which features, and know how to upgrade the CatOS to IOS.
Understand switch management. Switches need to be managed, and in an increasingly complex
network topology, that task also becomes more complex. Cisco has the Cluster Management
Suite (CMS) to help, and there is a range of show and debug commands that you need to
learn, practice, and remember. 746