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Introduction - Understanding Basic Cisco Switching and Routing IT Part I

In many organizations maters regarding LAN/ WAN can get very complicated. There are various systems and protocols to be used as solutions for network services. Network service resources can include virtualization, DNS, storage, email, printer, client/ server, and Active directory just to name a few.

In this introduction we will focus on fundamental basic Cisco switching and routing information technology. Network concepts, configuration and environment details can be simplified into categories. A way to visualize these systems and understand their use is by using a network model.

The OSI model

A good model to use is the Open Systems Interconnection OSI model. There are many other network models available. For the information included here, the OSI model will be primarily used to understand where the systems and services fit into a contemporary network model.

The OSI model is divided into seven layers. These layers divide network hardware and software into organized groups. These are the seven OSI layers, listed in order from software to hardware with some examples of elements from the associated layer.

  • 1. Physical ( Wiring, cables, Rj-45, physical ports )
  • 2. Data Link ( Mac addresses, switching functions )
  • 3. Network ( TCP/IP, routing functions )
  • 4. Transport
  • 5. Session
  • 6. Presentation
  • 7. Application

On further examination we can easily see the routing and switching elements and what layers they are associated. There are some exceptions to some systems and what layer they are really on. Sometime there will be layer crossover. For example, a standard switch will likely be present only at layer 2, but if it's a more advanced switch it may combine layers of functionality therefore producing a multilayer system ( layer 2-3 switch ).

In the real World we know it is impossible to not have layer crossover somewhere on the network. Modern systems often integrate systems into each other and this is how we can end up with devices on more than one network layer. This introduction theory assumes all systems and elements of a computer network remain on there associated layer and do not crossover.

Once the OSI model is learned, it’s easy to see basic switching and routing concepts in the different network layers. Cisco systems is a leading provider of switching and routing technology. Most brands of switches and routers are very Cisco like, especially command line syntax from the console. So learning from a Cisco point of view is a great place to start.

For basic Cisco switching and routing theory its best to keep things simple. Switching and routing are complex subjects. When learning the basics it is a good idea not to get involved with too many details, because for some it can quickly become overwhelming. Move forward in understanding basic concepts, and how they are organized in the OSI model.

Switching and routing category concepts

These next switching and routing concepts are a great way to categorize more specific switching and routing network elements. The network concepts listed here are based on the Cisco networking standard and can be customized and adapted to different switching and routing platforms.

  • Switching - OSI layer 2

- Configuration files - MAC address table - VLAN - STP

  • Routing - OSI layer 3

- Configuration files - Routing table ( TCP/IP, etc. ) - Routing protocols ( RIP, RIP2, OSPF, EIGRP, etc. ) - WAN - Wide area networks - MPLS - Frame relay - VPN

After analyzing the network systems and elements, then it's time to consider how these pieces fit together in the network architecture. One may consider organizing the network systems together using the Cisco Hierarchical Model. This is a 3 layer network model more detailing the functional roles of the switching and routing systems.

Cisco Hierarchical Model

1) Access layer - This layer connects users to the network. Users systems connect to access switches. A example of this from a switching point of view could be wall jacks in a office are tied to cables connected to a access switch located in a switching room or wiring closet. In modern networks it is also popular to use WI-FI wireless access points to allow wireless device connections. Often these wireless access points need to be wired in a optimized manner for best network performance, so in these cases they would be using fiber optic cabling to the access switches they establish connections to.

2) Distribution layer - Access layer devices or switches connected to a router or layer 3 switch so traffic can be routed to other networks using a gateway like function. WAN routing functions are usually done at this layer. Depending on how old the technology is in use on the network, the wide area network may be using something like frame relay for WAN connectivity or might use a newer solution like MPLS ( Multi protocol label switching ) Firewalls may be critical at this layer to filter unknown traffic from outside the local area network.

3) Core layer - The fastest layer in this model. Function here might include fast switches moving data from the distribution layer to centralized system resources and services like email servers, or database servers for example. Data storage may be a critical aspect to consider in the network design. General data of all types will need to be stored and retrieved quickly, efficiently and reliably, therefore using the fastest core switches available in this layer of the network would be a wise choice to achieve those objectives.

Keep in mind here that some networks may have a combination layer distribution and core. These layers might be combined together in an integrated fashion. It may be the network designer’s choice in this regard, a configuration requirement, or just simplification in network design to facilitate reliability.

Interpretation and views regarding the Cisco Hierarchical Model vary among network designers and architects. Also best practice differences can occur when applying this model to specific brand systems combination's. One must be aware unknowns can come into play.

When analyzing the network it is also best to be flexible and keep in mind no two networks are the same. Every company’s network design will be dependent on what makes sense to them and what is important to them to fulfill their network switching and routing objectives.

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