1. LAN Design Goals Frequent goals of network design:
Functionality - the network must work
Scalability - the network must be able to grow
Adaptability - network must be able to adapt to new technologies
Manageability - network must facilitate network monitoring and management
These goals are typical of most networks
·         Functionality-The network must work. That is, it 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. That is, the initial design should grow without any major changes to the overall design.
·         Adaptability-The network must be designed with an eye toward future technologies, and it 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.

2. Components of LAN Design
Critical factors when designing a LAN
Function and placement of servers
Contention
Segmentation
Bandwidth vs. broadcast domains
These are things an administrator has control over that will effect how efficiently network resources are to be used
Slides below look at each of these components

3. Function and Placement of Servers
Servers categorised as Enterprise or Workgroup
Enterprise servers
Support all users on a network (e.g. , DNS)
Should be placed at the MDF
Workgroup servers
Support specific group of employees
Should be placed at IDF nearest workgroup
Idea is to minimise distance (in terms of networks) data needs to cross in order to get to/from user
Explain MDF and IDF

4. Function and Placement of Servers
enterprise server located in MDF
Sales, marketing, accounting, engineering workgroup servers located in closest IDF to users (for sales and marketing, that is the MDF)
High-speed, dedicated access for servers (e.g. 100mbps), lower speed or shared access for users (e.g. 10mbps dedicated or 100mbps shared).

5. LAN design considerations
IDF
MDF: Main Distribution Facility
IDF: Intermediate Distribution Facility
To maximize available LAN bandwidth and performance:
The function and placement of servers
Collision detection issues
Segmentation issues
Broadcast domain issues

6. Cabrillo College – MDF/IDF Map
MDF: Main Distribution Facility
IDF: Intermediate Distribution Facility

7. LAN design considerations
Server Placement
Servers can be categorized into two distinct classes:
Enterprise servers (located in a Data Centre)
Workgroup servers (Located in specific departments within the intranet)
An enterprise server supports all the users on the network by offering services, such as or Domain Name System (DNS) that everyone in an organization would need because it is a centralized function.
A workgroup server supports a specific set of users, offering services such as word processing and file sharing. Other examples might include applications that are specific to a group of users.

8. LAN design considerations
Server Placement
Enterprise servers should be placed in the main distribution facility (MDF).
Traffic to the enterprise servers travels only to the MDF and is not transmitted across other networks.
Ideally, workgroup servers should be placed in the intermediate distribution facilities (IDFs) closest to the users accessing the applications on these servers.
By placing workgroup servers close to the users, traffic only has to travel the network infrastructure to an IDF, and does not affect other users on that intranet network segment.
Layer 2 LAN switches located in the MDF and IDFs should have at least 100 Mbps or more allocated to these servers.

9. Contention on an Ethernet Network
Contention refers to excessive collisions on Ethernet, caused by too many devices, each with a great demand, on a single network segment
Collisions are overhead on Ethernet – more collisions means less data gets through
Contention solved by segmentation
Collisions an integral part of shared Ethernet, but mean that it does not scale well
Segmentation done using bridges, switches & routers

10. Segmentation & Broadcast Domains
Bridges and switches split collision domains but not broadcast domains – they filter or forward based on MAC address, but always forward MAC broadcasts

11. Bandwidth Domain vs. Broadcast Domain
A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcastat the data link layer A broadcast domain can be within the same LAN segment or it can be bridged to other LAN segments.
In terms of current popular technologies: Any computer connected to the same Ethernet repeater or switch is a member of the same broadcast domain. Further, any computer connected to the same set of inter-connected switches/repeaters is a member of the same broadcast domain. Routers and other higher-layer devices form boundaries between broadcast domains.

12. A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcastat the data link layer A broadcast domain can be within the same LAN segment or it can be bridged to other LAN segments.
In terms of current popular technologies: Any computer connected to the same Ethernet repeater or switch is a member of the same broadcast domain.
Further, any computer connected to the same set of inter-connected switches/repeaters is a member of the same broadcast domain.
Routers and other higher-layer devices form boundaries between broadcast domains.

13. A Bandwidth or collision domain is a section of a network where data packets can collide with one another when being sent on a shared medium or through repeaters, in particular, when using early versions of Ethernet.
A network collision occurs when more than one device attempts to send a packet on a network segment at the same time.
Collisions are resolved using carrier sense multiple access with collision detection in which the competing packets are discarded and re-sent one at a time. This becomes a source of inefficiency in the network

14. Network Design Methodology
A systematic, step-by-step approach:
Gathering the users’ requirements and expectations
Analysing requirements
Designing the Layer 1, 2 and 3 structure
Documenting the logical and physical network implementation
Layer 1, 2, 3 structure – i.e. topology

15. Gathering & Analysing Requirements
Gather and analyse info firstly on organisation structure (projected growth, operating policies / management procedures, staff skill levels)
e.g. mission critical data or operations? Restrictions on network protocols? What resources to support LAN? What hardware / software currently in use and projected for future?

16. Factors Affecting Network Availability
Availability = usefulness of network
Availability affected by throughput, response time, access to resources…
Traffic-intensive applications can be catered for through the layout of the network and the provisioning of extra bandwidth where required
Note that web-services are more bandwidth intensive than traditional network services – voice and video more bandwidth intensive again

17. Developing a LAN Topology in 3 stages
We focus on the physical topology because that’s the most commonly used in industry
Within the boundaries set by that topology, we then design the network by focusing on physical layer, data link layer and network layer in turn – i.e. using the OSI model to guide the design.

18. Layer 1 Design Issues: Type of cabling to be used Layout of cable
Distance limitations
Use fibre-optic for backbones / vertical runs, UTP for horizontal runs
Most problems caused by Layer 1 issues
Cable installation must meet standards

19. Structured Cabling HCC is the patch panel
Point out modularity of connections

20. Designing the Layer 1 Topology
Diagram shows star topology and distance limitation for Cat 5 UTP

21. Extended Star Topology

22. Characteristics of Cable Types
10BASE-T and 10BASE-FL – Standard Ethernet
100BASE-TX and 100BASE-FX – Fast Ethernet
1000BASE-TX and 1000BASE-FX – Gigabit Ethernet

23. Extended Star Topology in a Multi-Building Campus (1)
If hosts are outside the 100-metre limitation for Cat 5 UTP, multiple wiring closets are the best solution
This creates multiple catchment areas
Standard Ethernet might connect workstations to IDF, Fast Ethernet connect IDF to MDF (because traffic aggregated)

24. Extended Star Topology in a Multi-Building Campus (2)
IDFs are connected to the MDF via vertical cable which runs from a Vertical Cross Connect (VCC) in IDF to a VCC in the MDF
Note that the vertical cable is fibre optic, since this allow for greater bandwidth in the long-run (even if greater bandwidth is not necessary now)
Also, more runs of fibre are laid than are immediately necessary, for cost reasons and to provide for the future
Note how more than one fibre is in use between MDF and IDF, and traffic is distributed over the fibres
Point out how the bandwidth is limited by the cable type/technology, but is defined (within the limit) by the equipment you pay for. But you can also get greater bandwidth across a connection by aggregating the bandwidth of several cables
Note the WAN connection from the MDF, since this is where the POP is (the location to where telecoms services are run into the building by a PTT)

25. Layer 1 Logical Diagram & Cut Sheet
Showing logical diagram – leaves out detail of exact installation path of cabling
Shows:
Locations of MDF/IDFs
Type/quantity of cable interconnecting MDF and IDFs, how many spare cables
Cut sheet (right picture) has information to identify each specific cable based on an ID (labelled on the cable at both ends). Helps with trouble-shooting

26. Layer 1 Physical Diagram
Incomplete physical diagram of cabling for multi-building campus – just shows backbone cable.

27. Layer 2 Design Common Layer 2 Devices:
Layer 2 devices: bridges, switches, NIC cards – switches most relevant for Ethernet network design
Switches used to split collision domains

28. Layer 2 design
Collisions and collision domain size are two factors that negatively affect the performance of a network.
Micro-segmentation of the network reduces the size of collision domains and reduces collisions. 
Micro-segmentation is implemented through the use of bridges and switches.
The goal is to boost performance for a workgroup or a backbone.
Switches can be used with hubs to provide the appropriate level of performance for different users and servers.

29. Layer 3 design
Routers can be used to create unique LAN segments and also allow for connectivity to wide-area networks (WANs), such as the Internet.
Layer 3 routing determines traffic flow between unique physical network segments based on Layer 3 addressing.
Routers provide scalability because they serve as firewalls for broadcasts.
They can also provide scalability by dividing networks into subnetworks, or subnets, based on Layer 3 addresses.
VLAN implementation combines Layer 2 switching and Layer 3 routing technologies to limit both collision domains and broadcast domains.
VLANs can also be used to provide security by creating the VLAN groups according to function and by using routers to communicate between VLANs.

30. Switched LANs, access layer overview
The hierarchical design model includes the following three layers:
The access layer provides users in workgroups access to the network.
The distribution layer provides policy-based connectivity.
The core layer provides optimal transport between sites.
The core layer is often referred to as the backbone.

31. Access layer switches
Access layer switches operate at Layer 2 of the OSI model and provide services such as VLAN membership.
The main purpose of an access layer switch is to allow and connect end-users into the network.
An access layer switch should provide this functionality with low cost and high port density.
Catalyst 1900 series
Catalyst 2820 series
Catalyst 2950 series
Catalyst 4000 series
Catalyst 5000 series

32. Distribution Layer
The purpose of this layer is to provide a boundary definition in which packet manipulation can take place.
Networks are segmented into broadcast domains by this layer.
Policies can be applied and access control lists can filter packets.
The distribution layer also prevents problems from affecting the core layer.
Switches in this layer operate at Layer 2 and Layer 3.
The distribution layer includes several functions such as the following:
Aggregation of the wiring closet connections
Broadcast/multicast domain definition
Virtual LAN (VLAN) routing
Any media transitions that need to occur
Security

33. Distribution layer switches
6500
2926G
Distribution layer switches are the aggregation points for multiple access layer switches.
The switch must be able to accommodate the total amount of traffic from the access layer devices.
The distribution layer combines VLAN traffic and is a focal point for policy decisions about traffic flow.
For these reasons distribution layer switches operate at both Layer 2 and Layer 3.
The following Cisco switches are suitable for the distribution layer: 
Catalyst 2926G
Catalyst 5000 family
Catalyst 6000 family

34. Core Layer The core layer is a high-speed switching backbone.
If they do not have an associated router module, an external router is used for the Layer 3 function.
This layer of the network design should not perform any packet manipulation.
Packet manipulation, such as access list filtering, would slow down the switching of packets.
Providing a core infrastructure with redundant alternate paths gives stability to the network in the event of a single device failure.

35. Core Layer Switches 8540 Lightstream 1010
In a network design, the core layer can be a routed, or Layer 3, core.
Core layer switches are designed to provide efficient Layer 3 functionality when needed.
Factors such as need, cost, and performance should be considered before a choice is made.
The following Cisco switches are suitable for the core layer:
Catalyst 6500 series
Catalyst 8500 series
IGX 8400 series
Lightstream 1010

36. Asymmetric Switching
LAN switch can allocate bandwidth on a per port basis – e.g. to allow more bandwidth to vertical connections, servers.
Assymetric switching is providing connections between ports of unequal bandwidth
Symmetric switching provides switched connections between ports with the same bandwidth, such as all 100 Mb/s ports or all 1000 Mb/s ports. An asymmetric LAN switch provides switched connections between ports of unlike bandwidth, such as a combination of 10 Mb/s, 100 Mb/s, and 1000 Mb/s ports

37. Microsegmentation
Microsegmentation allows concurrent paths through the switch so that many pairs of devices can talk to each other at the same time
Switches can be used to give dedicated bandwidth to a device, or used with hubs to control the bandwidth available to a group of devices
If one device is connected to a switch port, and full duplex communication is used, then collisions won’t occur

38. Determining the Number of Cable Runs and Drops
Two horizontal runs per work area (according to standard), then number of vertical runs depends on current and future requirements
And at the same time figuring out how many switch ports you need, and at what speed (e.g. how many 10Mbps ports, how many 100Mbps ports?), so you can then work out the cost

39. Determining Collision Domain Size
How many hosts are physically connected to any single port on a switch?
That affects how much network bandwidth is available to any host
Ideally, one host connected to each switch port, but expensive!
So more normal to have a bunch of machines connected to a hub, then connecting the hub to a switch port. But is enough bandwidth allowed per host then? Back of envelope calculation.

40. Diagramming Hub Placement
Diagram shows hub at the end of a horizontal cable run to create more connection points (Give Microsoft example).

41. Migrating a Network from 10Mbps to 100Mbps
May require replacing NICs, hubs, switches – but not cable or patch panels or wall outlets.
Cost of migrating may be less if 10/100 NICs originally bought, and if enough 100mbps ports originally speced on switch

42. Routers as the Basis for Layer 3 Design
Routers can be used to divide networks logically based on layer 3 addressing (e.g. IP addressing)
A router can connect two (or more) physical segments. Each segment is a broadcast domain, the router routes directed traffic between them as appropriate, but not [data-link/undirected] broadcasts.
Segments could be different IP networks, or subnets of the one IP network
The router is required for an WAN connections (e.g. connection to the Internet)

43. Using VLANs to Create Smaller Broadcast Domains
Example of how a router can be used to reduce the amount of broadcast traffic on a network without changing the physical layout of the network – VLANs implemented on MathComp part of CIT network to reduce traffic
VLANs provide extra flexibility in designing a network
A number of ways of implementing VLANs – e.g. based on port number (as in handout), or based on IP address
More slides later covering VLANs

44. Routers Provide Structure to a Network
Scalability – can the network grow without being crippled by some limiting factor inherent in its design (e.g. broadcast traffic)?
Also, admin policy on assignment of IP addresses can promote scaleability of the network. Bottom Diagram shows class B network subnetted into up to 254 subnets (by borrowing entire 3rd octet)
Table shows somebody’s attempt at scaleability. A few things wrong, what are they?
Better solution:
First 10 addresses for router ports
Next 10 reserved for LAN switches
Next 10 for workgroup servers
Remainder for hosts
Reserve first subnet (or a number of subnets if necessary) for enterprise servers:
Remainder for enterprise servers
This allows for a very large, complex network
Deciding whether to use routers or switches: switches to split collision domains, routers to split broadcast domains, filter protocols, implement security, other network-layer addressing problems.

45. Diagramming a LAN with Routers
Router used in this diagram to create two logical networks
Network 1 is one subnet, network 2 another, WAN connection is a different network
How many collision domains (I.e. physical segments) on this internetwork, how many broadcast domains (I.e. logical networks)? How many subnets?
Diagram above a a logical diagram, although it also includes some physical details.

46. Addressing Maps
Layer 3 documentation: logical address list in textual form, logical address maps in diagrammatic form
List first shows range of addresses in one logical area, subnet mask, then devices in order of ascending IP address.
For each IP address (or group of IP addresses):
what device (and maybe port) is address assigned to?
or is address unused?

47. Logical Network Maps & Addressing Maps
Diagram shows interconnection of devices that have layer 3 addresses; for routers diagram shows port ID as well as IP address, for other devices should show device label (e.g. machine name) with IP address

48. Physical Network Maps
Remember to show routers on physical diagrams as well as layer 2 devices and layer 1 media
This diagram doesn’t show all physical detail – i.e. path
All of the diagrams shown so far are just one way of documenting – different companies have different conventions, just important to be consistent within one company.

49. VLANs A VLAN is a logical grouping of devices or users
Devices or users can be grouped by function, department, or application, regardless of their physical segment location
VLAN configuration is done at the switch and/or router via software
VLANs are not standardized and require the use of proprietary software from the switch vendor

50. VLANs vs. Typical LANs
A typical LAN is configured according to the physical infrastructure it is connecting
Users are grouped based on their location in relation to the hub they are plugged in to and how the cable is run to the wiring closet
The router interconnecting each shared hub typically provides segmentation and can act as a broadcast firewall
The segments created by switches do not split broadcast domains
Traditional LAN segmentation does not group users according to their workgroup association or need for bandwidth. Therefore, they share the same segment and contend for the same bandwidth, although the bandwidth requirements may vary greatly by workgroup or department.

51. VLANs and Physical Boundaries

52. VLANs
A VLAN comprises a group of ports or users in the same broadcast domain
Grouping can be based on port ID, MAC address, protocol or application
LAN switches and management software provide a mechanism to create VLANs
In order to allow users connected to different switches to be part of the same VLAN, frames are tagged with a VLAN ID
The VLAN actually is how the grouping is implemented
Static VLAN based on port, dynamic VLAN based on MAC address / protocol / application – dynamic because, e.g., if based on MAC address, then if user moves machine to different location then is still automatically recognised as being part of the same VLAN.
VLANs can even span across WANs

53. Benefits of VLANs Make additions/moves/changes easier
Allow splitting of broadcast domains to be done by switches
Improve security, e.g. by basing VLAN membership on application
Other things to do with security on a VLAN:
Restrict the number of users in a VLAN group
Prevent another user from joining without first receiving approval from the VLAN network management application
Configure all unused ports to a default low-service VLAN