CCNP SWITCH Analyzing Campus Network Designs

CCNP SWITCH Comparing CatOS and Cisco IOS (Native Mode) 


Everywhere you look in Cisco’s documentation you’ll find that famous phrase “consistency is the key”.  Well throw that out the window!  Inconsistency is the key when it comes to Cisco switches and their operating systems.  Yes, there is a logical explanation.  Just because the label says Cisco doesn’t mean they were actually “born” at Cisco.  There are a number of different vendors who built a box, called it a switch, and sold it to Cisco.  So there you have it.  No fancy algorithms or complex notations needed to explain that one.

So how do you know which commands to use on each switch?  Well, the more familiar you become with the different operating systems, the more it make sense.  There essentially are two main operating systems usually referred to as the “Set Based” switch and the “IOS Based” switch.  We will explore both of them throughout this course.

CCNP SWITCH Switching Benefits


In  non-switched flat topology networks of today, when one PC wants to talk to another every PC hears and tries to process the communication to decide if they are the destination.

This is bad because:

The CPU on every PC must Process the data frames.

Collisions of data occur more frequently.

As more users use the network less bandwidth is available.

High bandwidth applications suck up the available bandwidth.

In  a switched network, switches learn the MAC addresses of every device attached to each port.  Once the mac address is learned, the switch can now forward the frames from the source interface directly to the port of the destination interface.  This virtually eliminates collisions, eliminates broadcast storms and frees valuable bandwidth.

CCNP SWITCH Benefits Of Layer 3 Devices


Ok, we are already familiar with Routing and the benefits of routing so why are we mentioning it here in a switching module?  Well because routing will always play an important part in all networking functionality.  Within this switching course we will identify that some switches have built in or modular routing functionality.  The hardware platforms that do not have built in or modular routing functionality still have a default gateway.  It is that default gateway, the router, that completes the building blocks of a network.


CCNP SWITCH Customer Network Requirements


When we combine the benefits of switching and routing we achieve the following:

  • • Fast convergence
  • • Deterministic paths
  • • Deterministic failover
  • • Scalable
  • • Centralized applications
  • • The new 20/80 rule (Traffic is 20% Local and 80% Remote)
  • • Multiprotocol support
  • • Multicasting

CCNP SWITCH Emerging Campus Structure


Local Services

  • • Layer 2 devices connected by switches
  • • Traffic within the same subnet/VLAN/Color
  • • Traffic does not cross the backbone 

Remote Services

  • • Devices connected by routers
  • • Traffic crosses subnet/VLAN
  • • Traffic may/may not cross the backbone

Enterprise Services

  • • Common to all users
  • • Traffic crosses subnet/VLAN
  • • Traffic must cross backbone
  • • Segregated by Layer 3
  • • May be grouped by Layer 2

CCNP SWITCH The Hierarchical Model


Cisco recommends that we build our networks with some logic behind our placement of each device.  Cisco’s Hierarchical Module consists of 3 separate layers; Core, Distribution and Access layer.  The Access Layer of the network is the point at where end-users are allowed into the network.  The key function of this layer is to provide access for end-users into the network.  In the campus environment, some of the functions performed by this layer are as follows:

Shared bandwidth

Switched bandwidth

Layer 2 services, such as VLAN membership and traffic filtering based on broadcast or MAC addresses.

The Distribution layer is located between the Access and Core Layer.  It  provides a boundary definition and designates where potentially “expensive” or processor intensive  packet manipulations such as filtering are handled.

The functions are represented in the Distribution Layer are as follows:

Broadcast or multicast domain definition.

InterVLAN routing

Media translations


Filtering and policy based connectivity.

The sole purpose of the Core Layer of the network is to move traffic as fast as possible.  This layer of the network should not be involved in time consuming packet manipulation or any processing that slows down the traffic switching. Functions such as access lists and packet filtering should be avoided in the Core Layer.

CCNP SWITCH Enterprise Composite Network Model



CCNP SWITCH Modules in the Enterprise Campus



CCNP SWITCH Campus Infrastructure Module


The Cisco three layer model network model with a Core, Distribution and Access Layer is a typical model for larger campus networks.  Having redundant connections within and between layers aids with designing and robust network.

CCNP SWITCH A Collapsed Core


A collapsed core might sound like a bad situation, but its not!  A collapsed core is a term used to identify that you are using a device that operates in the Distribution layer and also in the Core layer.  This is when the Core layer gets “shoved” up into the Distribution layer.

CCNP SWITCH Increasing FE Performance with Full Duplex


There are a number of different types of mediums that you can choose to use in your network.  The deciding factor on what type of medium you use will depend mainly on the type of medium that switch supports.  Fastethernet standards allow your medium to operate 10times faster than 10Mbps and operating in fullduplex your medium can offer up to 200Mbps thoughput, but it doesn’t stop there.  Can you say gigabit. Gigabit speeds enhances client/server performance across the enterprise and is used mainly to connect distribution-layer switches in each building with a central campus core.  Here is a quick peek at the different characteristics each type of switching medium covered in this section.


Standard          Cable   Mode   Pairs     Distance

10BaseT          3,4,5    Half      2          100

100BaseTX      5          Half/Full           2          100

100BaseT4      3          Half                  4          100

100BaseT2      3,4,5    Half/Full           2          100

100BaseFX      multimode         Half/Full           1          400/half  2000/full

100BaseFX      Singlemode       Half/Full           1          10 km


GIG Standard   Cable Size        BW                 Distance

1000BaseSX    62.5um 160                  200

1000BaseSX    62.5     200                  275

1000BaseSX    50        400                  500

1000BaseSX    50        500                  550

1000BaseLX    62.5     500                  550

1000BaseLX    50        400                  550