Switches

Antonio González Torres

Hierarchical Network Design

The design of larger LANs includes identifying the following: An access layer that connects end users into the LAN A distribution layer that provides policy-based

connectivity between end-user LANs A core layer that provides the fastest connection

between the distribution points

LAN design goals

Functionality Scalability Adaptability Manageability

Functionality

The network must work. The network must allow users to meet their job requirements. The network must provide user-to-user and user-to-application connectivity with reasonable speed and reliability.

Scalability

The network must be able to grow. The initial design should grow without any major changes to the overall design.

Adaptability

The network must be designed with a vision toward future technologies. The network should include no element that would limit implementation of new technologies as they become available.

Manageability

The network should be designed to facilitate network monitoring and management to ensure ongoing stability of operation.

LAN design considerations

LAN design considerations The function and

placement of servers

Collision detection issues

Segmentation issues

Broadcast domain issues

Enterprise servers support all the users should be placed in the

main distribution facility (MDF).

Workgroup servers support a specific set of

users should be placed in the

intermediate distribution facility (IDF).

Server Placement

Segmentation

the process of splitting a single collision domain into smaller collision domains reduces the number of collisions allows for greater utilization of bandwidth Using Layer 2 devices such as bridges and

switches Routers reduce the size of the collision

domain and the size of the broadcast domain at Layer 3

LAN design methodology

Gather requirements and expectations

Analyze requirements and data

Design the Layer 1, 2, and 3 LAN structure, or topology 

Document the logical and physical network implementation

Availability measures

Availability measures the usefulness of the network.

things that affect availability: Throughput Response time Access to resources

Every customer has a different definition of availability.

Design LAN Structure

The most common LAN topologies are star and extended star

The topology structure can be broken into OSI layers to determine devices to use

LAN design documentation

OSI layer topology map

LAN logical map LAN physical map Cut sheets VLAN logical map Layer 3 logical map Addressing maps

Document Logical Diagram

the flow of data in a network

A snapshot view of all LAN implementation

OSI layer topology map

This diagram shows how the devices and telecommunication closets are connected

Cut sheets

Cut sheets store detail information about the different connections in the network

VLAN logical map

VLAN logical maps show the inter VLAN and Intra VLAN interconnection using a router or trunking ports

Layer 3 logical map

These diagrams show the logical addresses different devices use to send and receive information

Addressing maps

Addressing maps show the logical addresses configured for each network device

Layers design

Layer 1 Design

•One of the most important components to consider when designing a network is the physical cabling.

Layer 1 Design Issue: Type of Cabling

copper or fiber-optic?

the overall structure of the cabling

Some rules on Cabling

Fiber-optic cable should be used in the backbone and risers in all cable designs.

Category 5e UTP cable should be used in the horizontal runs.

The cable upgrade should take priority over any other necessary changes.

Enterprises should also make certain that these systems conform to well-defined industry standards, such as the TIA/EIA-568-A specifications.

Star Topology Using Cat. 5 UTP

Typical MDF in Star Topology

In a simple star topology with only one wiring closet, the MDF includes one or more horizontal cross-connect (HCC) patch panels.

HCC patch cables are used to connect the Layer 1 horizontal cabling with the Layer 2 LAN switch ports.

The uplink port of the LAN switch, depending on the model, is connected to the Ethernet port of the Layer 3 router using a patch cable. At this point, the end host has a complete physical connection to the router port.

Multi-Building Campus

When hosts in larger networks exceed the 100-meter limitation for Cat. 5e UTP, more than one wiring closet is required.

Multiple wiring closets mean multiple catchment areas.

The secondary wiring closets are referred to as IDFs.

Extended-Star Topology in a Multi-Building Campus

Fiber-optic cable is normally used because the vertical cable lengths are typically longer than 100 meters

VCC is used to interconnect the various IDFs to the central MDF.

IDFs should be connected to the MDF by vertical cabling, also called backbone cabling.

Logical Diagram

the network topology model without all the details of the exact installation paths of the cables

the basic road map of the LAN

the locations and identification of the MDF and IDF wiring closets

the type and quantity of cables used to interconnect the IDFs with the MDF

the number of spare cables

detailed documentation of all cable runs, the identification numbers, and the port the run is terminated on at the HCC or VCC.

Layer 2 Design

Devices at Layer 2 determine the size of the collision domains. 

Asymmetric Switching

provides more bandwidth to vertical cabling, uplinks, and servers

The desired capacity of a vertical cable run is greater than that of a horizontal cable run.

Determine the number of 10 Mbps and 100 Mbps ports

review of the user requirements for the number of horizontal cable drops per room and the number of total drops in any catchment area.

This includes the number of vertical cable runs. E.g.: four horizontal cable runs per room;

total 18 rooms; require 72 LAN switch ports

Collision Domain Size with Hubs

Layer 2 Switch Collision Domains

An Acceptable Solution Using Hubs

Must make sure bandwidth to the host is provided in accordance to the specifications gathered in the requirements phase of the network design process

Layer 3 Design

Layer 3 Router for Segmentation

All data traffic from Network 1 destined for Network 2 has to go through the router.

There are two broadcast domains

Logical Addressing Mapped to the Physical Network

A standard convention should be set for addresses of important hosts on the network.

Address Map and Logical Network Map

Logical Network Map Address Mapprovides a snapshot of the network

Physical Network Map

helps to troubleshoot the network

VLAN Environment

combines Layer 2 switching and Layer 3 routing technologies

limits both collision domains and broadcast domains

provides security with the creation of VLAN groups

Hierarchical LAN Designeasier to make changes to the network as the organization grows

Access layer switches

the entry point for user workstations and servers to the network

provides services such as VLAN membership. Access layer functions also include MAC layer

filtering and microsegmentation

Distribution layer

Networks are segmented into broadcast domains

Policies are applied and ACLs can filter packets.

Switches in this layer operate at Layer 2 and Layer 3

Distribution layer functions: Aggregation of the wiring closet connections Broadcast/multicast domain definition Virtual LAN (VLAN) routing Any media transitions that need to occur Security

Distribution layer

The following Cisco switches are suitable for the distribution layer:  Catalyst 2926G Catalyst 5000 family Catalyst 6000 family

Core layer

The core layer is a high-speed switching backbone.

If the switch does not have a router module, an external router is used for the Layer 3 function.

This layer should not perform any packet manipulation.

A core infrastructure with redundant alternate paths gives stability to the network

Asynchronous Transfer Mode (ATM) or Ethernet switches can be used.

Core layer

The following Cisco switches are suitable for the core layer: Catalyst 6500 series Catalyst 8500 series IGX 8400 series Lightstream 1010