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Cisco 3 - Switches
Perrine - Brierley Page 204/18/23
Module 5
LAN Design - Servers
Workgroup– Provide file/print/application services to groups of users
– Placed in IDF close to users
Enterprise– Provide enterprise services such as DNS, email, applications
– Increasing trend to enterprise servers in organisations
– Should be placed in MDF
Cisco 3 - Switches
Perrine - Brierley Page 304/18/23
Module 5
LAN Design - Availability
Goal to maximise availability
• Throughput
• Response time
• Access to resources
Cisco 3 - Switches
Perrine - Brierley Page 404/18/23
Module 5
Layer 1 Design
• Copper medium? – CAT5, CAT5e, CAT6 UTP/STP
• Fibre?
• Position of MDF/IDF to create appropriate catchment areas
Cisco 3 - Switches
Perrine - Brierley Page 504/18/23
Module 5
Layer 2 Design
• Flow control, error detection & correction, reduce congestion
• Reduce collision domain size & effects of collisions
• Keep collision domains small – ideally fully switched full-duplex environment
Cisco 3 - Switches
Perrine - Brierley Page 604/18/23
Module 5
Layer 3 Design
• Controls traffic flow between network segments
• Logical addressing scheme to separate different network/workgroup functions
• Broadcast control
Cisco 3 - Switches
Perrine - Brierley Page 704/18/23
Module 5
Hierarchical Design Model
• Core layer – backbone – no packet manipulation
• Distribution layer – packet manipulation, interconnecting workgroups, Layer 3 switches, enterprise servers
• Access layer – closest to user/workgroup – hosts, switches, workgroup servers
Cisco 3 - Switches
Perrine - Brierley Page 904/18/23
Module 5
NOTE:
The following is Cisco’s logical idea of planning a LAN.
Their design is an approach but not the only one.
Medium & smaller companies will depend on the ideas of their people to come up with design criteria – this is where the Cisco planning criteria can be used.
This chapter will give additional requirements & suggestions for your LAN design.
Cisco 3 - Switches
Perrine - Brierley Page 1004/18/23
Module 5
First step in designing a LAN
• establish & document the goals of the design. It is based on:
• functionality –design must meet the job requirement – must work; connectivity with reasonable speed & reliability
• scalability – initial design should grow without any major chances to overall design
• adaptability – design toward the future (Frame Relay over ATM; SMDS, Switched Multi-megabit Data Service, to ATM)
• manageability – design to facilitate network monitoring & management
Inter-network design seeks to provide the greatest availability for the least cost.
Cisco 3 - Switches
Perrine - Brierley Page 1104/18/23
Module 5
One needs to consider the following in overall LAN design:
• function & placement of servers
• collision detection
• place devices to reduce the collision
• contention refers to excessive collisions on Ethernet caused by too many devices
• segmentation
• use bridges, switches & routers to separate collision domains
• note for bridges & switches; don’t forward collisions, but still belong to the broadcast domain
• bandwidth vs. broadcast domains
• bandwidth domain is everything associated with one port on a bridge /switch. All workstations within one bandwidth domain compete for the same LAN bandwidth resource.
Cisco 3 - Switches
Perrine - Brierley Page 1204/18/23
Module 5
Under segmentation: bridges & switches are used
• results in multiple collision domains
• still a single broadcast domain
Bandwidth domain is everything associated with one port on a bridge or switch.
For Ethernet switches, a bandwidth domain is also known as a collision domain.
Cisco 3 - Switches
Perrine - Brierley Page 1304/18/23
Module 5
Cisco’s design methodology:
1) Gather the users’ requirements & expectations
• organization’s history• operational policies• what their business is• who has the authority to make decisions on network changes
2) Analyze requirements
• what are the voice & data requirements; which is in more demand; affects bandwidth
• requirements of the users
3) Design the layer 1,2,3 i.e. topology• type of topology – star, extended star (most common; 802.3)• cabling ( TIA/EIA-568-A); UTP; FIBER• type of cabling determines the distance of the catchment area
4) Document the logical & physical network implementation
Cisco 3 - Switches
Perrine - Brierley Page 1404/18/23
Module 5
Servers:
Two distinct classes:
• enterprise server –
• supports all the users on the network by offering services (e-mail, DNS)
• placed in the MDF
• workgroup server –
• applications for users
• placed in the IDF
Cisco 3 - Switches
Perrine - Brierley Page 1504/18/23
Module 5
Cisco: between the MDF and IDF, the layer 2 LAN switches should have 100 Mbps or more allocated for these servers.
Intranet versus the internet is that the public does not have access to the organization intranet.
When layer 2 bridges or switches are used for segmentation, they create separate collision domains, and hence increase bandwidth to individual stations.
A bandwidth domain is everything associated with one port on a bridge or switch.
Cisco 3 - Switches
Perrine - Brierley Page 1604/18/23
Module 5
MDF – Main Distribution Facility
• HCC – Horizontal cross-connect
Wiring closet where the horizontal cabling connects to a patch panel that is connected by backbone cabling to the MDF
IDF – Intermediate Distribution Facility
Used when a second wiring closed is needed because the hosts are outside of the 100 meter limit. Multiple catchment areas are formed. The IDF is connected to the MDF.
IDF is connected to the MDF by using vertical cabling, also called the backbone cabling
• VCC – Vertical cross-connect
Is used to interconnect the various IDFs to the central MDF.
Fast Ethernet, cooper wire ( 100Base-TX) & fiber-optic (100Base-FX) is used to connect the MDF to the IDF.
Cisco 3 - Switches
Perrine - Brierley Page 1704/18/23
Module 5
Layer 2 devices, bridges/switches purposes in the network is to provide:
• flow control
• error detection
• error correction
• reduce congestion
Cisco 3 - Switches
Perrine - Brierley Page 1804/18/23
Module 5
Asymmetric Switching / Symmetric Switching
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Macintosh SE¾
Macintosh SE¾
10 Mbps
10 Mbps
10 Mbpsswitch
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Macintosh SE¾
Macintosh SE¾
10 Mbps
100 Mbps
10 Mbpsswitch
Cisco 3 - Switches
Perrine - Brierley Page 1904/18/23
Module 5
In a pure switched LAN environment, the size of the collision domain is two hosts.
Routers allows for segmentation of the LAN into unique physical & logical networks. Routers provide scalability because they can serve as firewalls for broadcasts.
Cisco 3 - Switches
Perrine - Brierley Page 2004/18/23
Module 5
3-layer Model
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Macintosh SE¾
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Core
Distribution
Access
Other sites/Internet
Campus Backbone
BuildingBackbone
Cisco 3 - Switches
Perrine - Brierley Page 2104/18/23
Module 5
3-layer Model Core
Core
• implemented as WAN
• doesn’t perform any packet manipulation
• no ACLs, nor filtering
• were redundant paths are established
• load sharing & rapid convergence of routing protocols
• efficient use of bandwidth
Other sites/Internet
Cisco 3 - Switches
Perrine - Brierley Page 2204/18/23
Module 5
3-layer Model Distribution
Core
Distribution
• demarc between access & core layers
• ACLs are added; filtering; packet manipulation
• VLAN routing
• workgroup access to the core layer
• broadcast/multicast domain definition
• policy-based connectivity (what is acceptable traffic)
• where remote sites have access
• security
Building backbone
Campus backbone
Cisco 3 - Switches
Perrine - Brierley Page 2304/18/23
Module 5
3-layer Model Access
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Macintosh SE¾
Macintosh SE¾ Macintosh SE¾ Macintosh SE¾
Access
• where local end users have access to network
• shared bandwidth
• switched bandwidth
• MAC-layer filtering
• microsegmentation
• isolate broadcast traffic from the workgroup
• ACLs & filtering
• LAN
• logical segmentation into functions
Cisco 3 - Switches
Perrine - Brierley Page 2404/18/23
Module 5
Server Placement
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Macintosh SE¾
Macintosh SE¾ Macintosh SE¾ Macintosh SE¾
Enterprise Server
Too much traffic for router 1 when enterprise server placed at access layer.
1
Core
Distribution
Access
Cisco 3 - Switches
Perrine - Brierley Page 2504/18/23
Module 5
Server Placement
Macintosh SE¾ Macintosh SE¾Macintosh SE¾Macintosh SE¾
Macintosh SE¾
Macintosh SE¾ Macintosh SE¾ Macintosh SE¾
Enterprise Server
Less traffic for router 1 when enterprise server placed at distribution layer.
1
Core
Distribution
Access
Cisco 3 - Switches
Perrine - Brierley Page 2604/18/23
Module 5
Server Placement
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Macintosh SE¾
Macintosh SE¾ Macintosh SE¾ Macintosh SE¾
Workgroup Server
Workgroup server is placed at access layer of site where the largest concentration of users are located.
1
Cisco 3 - Switches
Perrine - Brierley Page 2704/18/23
Module 5
Enterprise servers are placed at the highest layer in the hierarchy.
Workgroup servers are placed nearest to the group that is using it.