Switches

1
Switches

• LAN Design
• LAN Switches

2
Congestion and Bandwidth

• As more people utilize a network to share large
  files, access file servers and connect to the
  Internet, network congestion occurs.
• To relieve network congestion, more bandwidth is
  needed or the available bandwidth must be used
  more efficiently.

3
LAN Design Goals

• General requirements of network design
• Functionality -- It must work
• Scalability -- It must be able to grow
• Adaptability -- It must work with future
  technologies
• Manageability -- It must be monitored

4
LAN Design Methodology

• Three steps describe a simple model that could be
  used in network design
• Analyze requirements
• Develop a LAN structure (topology)
• Set up addressing and routing

5
LAN Design - Availability

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

6
What Problem are you Trying to Solve?

• The decision to use an internetworking device
  depends on which problems you are trying to solve
  for your client.

7
Types of Problems

• Media contention
• Excessive broadcasts
• Need to transport new payloads
• Need for more bandwidth
• Overloaded backbone
• Network addressing issues

8
Developing a LAN Topology

• The topology design can be broken into three OSI
  categories
• Layer 1 - Physical Layer (wire media type)
• Layer 2 - Data Link Layer (bridges switches)
• Layer 3 - Network Layer (routers and network
  addressing)

9
Developing Layer 1 LAN Topology

• The Physical layer
• - controls the way data is transmitted between
  nodes.
• - type of media and topology selected will
  determine how much and how fast data can travel
  across the network.

10
Layer 1 Design

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

11
Extended Star Topology

• In larger networks it is not unusual to have more
  than one wiring closet.
• By creating multiple wiring closets, multiple
  catchment areas are created.
• The secondary wiring closets are referred to as
  Intermediate Distribution Facilities.

12
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

13
Why Segment LANs?

• using segments in a network
• - less users devices sharing total
  bandwidth
• greater communication within the segment.
• segmentation
• process of creating smaller collision
  broadcast domains.

14
Layer 2 Switching

• Installing LAN switching at the MDF and IDFs
• - we can start to look at the size of the
  collision domains
• - review the speed for each horizontal cable and
  vertical cable run.

15
Layer 3 Design

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

16
Layer 3 Segmentation

• With multiple physical networks
• all data traffic from Network 1 destined for
  Network 2 has to go through the route.
• the route is the central point in the LAN for
  traffic destined for the WAN port.

17
Server Placement

• If servers are to be distributed around the
  network topology according to function
• the networks Layer 2 and 3 must be designed to
  accommodate this.
• The Layer 2 LAN switches must have high speed
  ports allocated for these servers.

18
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

19
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

20
Layer 3 Routing

• Only differences between Switches and Routers are
  the way Administrator creates the physical
  implementation.
• Traditional routers use microprocessors to make
  forwarding decisions.
• Some traditional routers CAN have other hardware
  functions as well as high-end models

21
Layer 3 Switching

• Switch performs only hardware-based packet
  switching.
• Layer 3 switches can be placed anywhere in the
  network .
• Layer 3 switches can handle high performance LAN
  traffic.
• Can cost effectively replace routers.

22
Layer 3 Switching

• All hardware based packet forwarding.
• All packet forwarding is handled by the hardware
  ASICs

23
Layer 3 Switching Functions

• Determine paths based on logic addressing.
• Run layer 3 checksums (header only).
• Use Time To Live (TTL).
• Process respond to option information.
• Can update SNMP with Management. Information Base
  (MIB) information.
• Provide security.

24
Layer 3 Switching Benefits

• Hardware-based packet forwarding
• High-performance packet switching
• High speed scalability
• Low latency
• Lower per port cost
• Flow accounting
• Security
• Quality of Service (QoS)

25
Layer 4 Switching

• Considered hardware based layer 3 switching with
  consideration for the application used (IE FTP,
  Telnet)
• Uses port s found in Transport Layer to make
  routing decisions.
• Port numbers are found in RFC 1700 and reference
  the upper layer protocol, program or application.

26
Layer 4 Switching

• Extended access lists can filter packets based on
  layer 4 port numbers
• Another example is accounting information
  gathered by Netflow switching in Ciscos higher
  end routers.

27
Layer 4 Switching

• Largest benefit is network administrator can
  configure to prioritize data traffic by
  application.
• Means a QoS can be defined per user.
• Must be able to provide a huge filter table or
  response time will suffer. (user/multi-groups)
• Filter tables must be much larger than any layer
  2 or 3 switch

28
Layer 4 Switching

• Layer 2 switch may only require a filter table as
  large as of users connected to this LAN
• Possibly less if hubs are used in the switched
  fabric
• Layer 4 switch might have 5 or 6 entries per.
• If the layer 4 switch does not have a filter
  table to include all information it will not be
  able to produce wire speed results!

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Version 3.0 Semester 3 Essential Labs