Switches

1
Switches

• LAN Design
• LAN Switches

2
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

3
LAN Design - Availability

• Goal to maximise availability
• Throughput
• Response time
• Access to resources

4
Layer 1 Design

• Copper medium? CAT5, CAT5e, CAT6 UTP/STP
• Fibre?
• Position of MDF/IDF to create appropriate
  catchment areas

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

6
Layer 3 Design

• Controls traffic flow between network segments
• Logical addressing scheme to separate different
  network/workgroup functions
• Broadcast control

7
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

8
Switches
9
NOTE The following is Ciscos 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.
10

• 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.

11

• 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 dont 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.

12

• 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.

13

• Ciscos design methodology
• Gather the users requirements expectations
• organizations 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

14

• 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

15
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.
16

• 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.

17

• Layer 2 devices, bridges/switches purposes in the
  network is to provide
• flow control
• error detection
• error correction
• reduce congestion

18
Asymmetric Switching / Symmetric Switching
10 Mbps
switch
10 Mbps
10 Mbps
10 Mbps
switch
10 Mbps
100 Mbps
19
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.
20
3-layer Model
Other sites/Internet
Core
Distribution
Campus Backbone
Building Backbone
Access
21
3-layer Model Core
Core
Other sites/Internet

• implemented as WAN
• doesnt perform any packet manipulation
• no ACLs, nor filtering
• were redundant paths are established
• load sharing rapid convergence of routing
  protocols
• efficient use of bandwidth

22
3-layer Model Distribution
Core
Campus backbone
Distribution
Building backbone

• 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

23
3-layer Model 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

Access
24
Server Placement
Core
Distribution
Enterprise Server
Access
1
Too much traffic for router 1 when enterprise
server placed at access layer.
25
Server Placement
Core
Enterprise Server
Distribution
Access
1
Less traffic for router 1 when enterprise server
placed at distribution layer.
26
Server Placement
Workgroup Server
1
Workgroup server is placed at access layer of
site where the largest concentration of users are
located.
27
Enterprise servers are placed at the highest
layer in the hierarchy. Workgroup servers are
placed nearest to the group that is using it.
28

• Cisco suggests the following equipment for
  physical design
• core (routers)
• 12000 7500 7200 7000
• distribution (routers)
• 4500 400 3600
• access (routers)
• 2600 2500 1700 1600