Chapter_01_3

LAN Design

About Hierarchical Network Design:

Hierarchical network design involves dividing the network into discrete layers. Each layer provides specific functions that define its role within the overall network. By separating the various functions that exist on a network, the network design becomes modular, which facilitates scalability and performance.

The typical hierarchical design model is broken up in to three layers:

• access
• distribution
• core

Access Layer

The access layer interfaces with end devices, such as PCs, printers, and IP phones, to provide access to the rest of the network. The access layer can include routers, switches, bridges, hubs, and wireless access points (AP).

The main purpose of the access layer is to provide a means of connecting devices to the network and controlling which devices are allowed to communicate on the network.

Distribution Layer

The distribution layer aggregates the data received from the access layer switches before it is transmitted to the core layer for routing to its final destination.

The distribution layer:

• controls the flow of network traffic using policies
• delineates broadcast domains by performing routing functions between virtual LANs (VLANs) defined at the access layer.

Distribution layer switches are typically high-performance devices that have high availability and redundancy to ensure reliability.

The Core Layer

The core layer of the hierarchical design is the high-speed backbone of the internetwork. The core layer is critical for interconnectivity between distribution layer devices, so it is important for the core to be

• highly available
• redundant

The core area can also connect to Internet resources. The core aggregates the traffic from all the distribution layer devices, so it must be capable of forwarding large amounts of data quickly.

Advantages of Hirarchial Design:

• Security
• Managabilty
• Administration
• Reduntancy
• Performance
• Scalabiltiy
• Maintainability

Network Diameter:

When designing a hierarchical network topology, the first thing to consider is network diameter. Diameter is usually a measure of distance, but in this case, we are using the term to measure the number of devices. Network diameter is the number of devices that a packet has to cross before it reaches its destination. Keeping the network diameter low ensures low and predictable latency between devices.

Convergence is the process of combining voice and video communications on a data network.

A converged Network is unifying:

• voice,
• video,
• and data networks

To decide for the right switches and network design:

1. Study Network Traffic Analysis
2. Think about Future Growth
3. Check User Community Data Flow patterns

There are 3 types of switches:

• Fixed Configuration Switches
• Modular Switches
• Stackable

Port Density:

Port density is the number of ports available on a single switch.

Forwarding Rates:

Forwarding rates define the processing capabilities of a switch by rating how much data the switch can process per second. Switch product lines are classified by forwarding rates.

Link Aggregation (or EtherChannel):

Link aggregation helps to reduce these bottlenecks of traffic by allowing up to eight switch ports to be bound together for data communications, providing up to 8 Gb/s of data throughput when Gigabit Ethernet ports are used. With the addition of multiple 10 Gigabit Ethernet (10GbE) uplinks on some enterprise-layer switches, very high throughput rates can be achieved. Cisco uses the term EtherChannel when describing aggregated switch ports.

Power over Ethernet:

Power over Ethernet (PoE) allows the switch to deliver power to a device over the existing Ethernet cabling. As you can see in the figure, this feature can be used by IP phones and some wireless access points. PoE allows you more flexibility when installing wireless access points and IP phones because you can install them anywhere you can run an Ethernet cable. You do not need to consider how to run ordinary power to the device. You should only select a switch that supports PoE if you are actually going to take advantage of the feature, because it adds considerable cost to the switch.

Access Layer Switch need to support the following features:

Access layer switches:

• as port security,
• VLANs,
• Fast Ethernet/Gigabit Ethernet,
• PoE,
• and link aggregation
• QoS ( for a converged network supporting voice, video and data network traffic)

Distribution Layer Switch need to support the following features:

• Because inter-VLAN routing is performed at the distribution layer, the switches at this layer need to support Layer 3 functions.
• advanced security policies that can be applied to network traffic. Access lists are used to control how traffic flows through the network. An Access Control List (ACL) allows the switch to prevent certain types of traffic and permit others.
• Quality of Service
• distribution switches support redundancy for adequate availability.
• It is also recommended that distribution layer switches support multiple, hot swappable power supplies. Having more than one power supply allows the switch to continue operating even if one of the power supplies failed during operation.
• Finally, distribution layer switches need to support link aggregation.

Core Layer Switch Switch need to support the following features:

The core layer of a hierarchical topology is the high-speed backbone of the network and requires switches that can handle very high forwarding rates.

• Link Aggregation
• Redundancy
• QoS

Cisco Stackwise Technology:

Cisco StackWise is a technology offered by Cisco Systems that allows for up to 9 Catalyst switch 3750 series switches to operate as though they were one 32-Gbit/s switch. This allows for greater resiliency, and performance.