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08_LAN Design


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08_LAN Design

  1. 1. Local Area Network Design
  2. 2. Contents <ul><li>Components of a LAN </li></ul><ul><li>Cabling </li></ul><ul><li>Active Components </li></ul><ul><li>Ethernet Switching </li></ul><ul><li>Virtual LANs </li></ul><ul><li>Switched LAN Design </li></ul>
  3. 3. The Components of LAN <ul><li>The cabling system : media </li></ul><ul><li>The active components : </li></ul><ul><li>* hub: distributes the bus capacity among equipment </li></ul><ul><li>* switch: gives dedicated bandwidth to the LAN </li></ul><ul><li>equipment and connections </li></ul><ul><li>* router: provides logical segmenting </li></ul><ul><li>The servers : provide shared resources for the hosts </li></ul><ul><li>The workstations : use the network resources </li></ul><ul><li>The network interface card+driver software : adapts </li></ul><ul><li>the equipment and the programs to the network </li></ul><ul><li>The networking software : </li></ul><ul><li>* Networked operating system, e.g. Windows2000 </li></ul><ul><li>* Communication software: e.g. TCP/IP </li></ul>
  4. 4. The Structured LAN Cabling CD BD BD BD FD FD FD FD TO TO TO Horizontal cabling Vertical cabling Campus cabling CD Campus Distributor = aluejakamo BD Building Distributor = talojakamo FD Floor Distributor = kerrosjakamo TO (To Office) = työpiste
  5. 5. The Principles of Design Floor distributor patch panel equipment cable horizontal cabling equipment cable active component jack terminal equipment P 2 P 3 P 4 P 1 <ul><li>Cabling recommendations : twisted pair : 100 Ω UTP- or STP cable </li></ul><ul><li>fiber : MM-fiber (GK or GI) </li></ul><ul><li>Horizontal cabling: </li></ul>
  6. 6. <ul><li>Campus and vertical cabling </li></ul>Floor distributor Building distributor Campus distributor fiber panel fiber panel patch panel patch cable Equipment cable twisted pair fiber Campus cable A 1 A 4 A 1 A 1 A 2 A 3 Vertical cable <ul><li>Cable recommendations : </li></ul><ul><li>- vertical cabling : GK –multimode fiber </li></ul><ul><li> Cat 5 twisted pair </li></ul><ul><li>- Campus cabling : GK-multimode fiber </li></ul><ul><li> SM-singlemode fiber </li></ul>
  7. 7. The Active Components <ul><li>Functions of the active c omponents </li></ul><ul><ul><li>the end equipment access </li></ul></ul><ul><ul><li>(hubs, switches) </li></ul></ul><ul><ul><li>extending the physical network </li></ul></ul><ul><ul><li>enhance the performance of the network (switches, routers) </li></ul></ul><ul><ul><li>interconnect different types of </li></ul></ul><ul><ul><li>networks (bridges, switches, routers, gateways) </li></ul></ul>Application Presentation Session Transport Network Data Link Physical REPEATER BRIDGE ROUTER GATEWAY SWITCH
  8. 8. The Concentrator = Hub <ul><li>Shared media operation : the incoming frames are copied to all </li></ul><ul><li>other ports </li></ul><ul><li>A hub is a repeater: the signals are regenerated </li></ul><ul><li>Maximum distance between hub and workstation is 100 m </li></ul><ul><li>(twisted pair), catchment area 210 m </li></ul><ul><li>Used as the ”backbone ” of small offices </li></ul>repeater MAU MAU MAU MAU
  9. 9. Characteristics of a hub network collision domain A <ul><li>All the equipment in a hub network are in the same collision domain </li></ul><ul><li>- all traffic can be monitored from any port with an analyzer </li></ul><ul><li>- hubs may filter errored frames (runts, giants) </li></ul>
  10. 10. Bridge <ul><li>If a hub-extension is not sufficient, the span of the LAN can be extended with a bridge </li></ul><ul><ul><li>local bridge (adjacent LANs) </li></ul></ul><ul><ul><li>remote bridge (far away LANs) </li></ul></ul>B another LAN, or remote bridge <ul><li>Multiport bridge is a LAN switch </li></ul>B
  11. 11. The Operation of a bridge <ul><li>Works on layer 2 of the OSI-model </li></ul><ul><li>- self-learning : MAC - addresses </li></ul><ul><li>LAN segmentation and traffic filtering </li></ul><ul><li>- the LAN is split into two collision domains </li></ul><ul><li>Transparent </li></ul>Collision domain 1 Collision domain 2 A B
  12. 12. Ethernet Switching <ul><li>A switch is a multiport bridge, whose task is to switch frames </li></ul><ul><li>as fast as possible from the input port to the output port </li></ul><ul><li>- the idea is to provide wire-speed capacity to simultaneous </li></ul><ul><li>connections (10, 100 or 1000 Mbit/s) </li></ul><ul><li>- a switch needs to have a fast internal backplane bus and </li></ul><ul><li>efficient ASIC- circuits </li></ul>Bus 10 Gbit/s 1 2 3 4 5 6 7 8 12 10 10 …… 100
  13. 13. Benefits of Switching <ul><li>The connections speeds increase (throughput) </li></ul><ul><li>Better security : unicast-traffic is confined to the ports of the </li></ul><ul><li>communicating parties </li></ul>10 MB/s 10 MB/s 10 MB/s 10 MB/s 10 MB/s 100 MB/s 100 MB/s
  14. 14. Basic Operation of an Ethernet Switch <ul><li>The switch learns the layer 2 (MAC) addresses from each port ; </li></ul><ul><li>there can be several addresses (hub or another switch in a port) </li></ul><ul><li>The switch builds a MAC-address table based on the addresses it has </li></ul><ul><li>learned </li></ul><ul><li>Broadcast-messages are copied to every port </li></ul><ul><li>A switch has two operation modes: cut-through and store-and-forward </li></ul><ul><li>Higher speed can be used on trunk ports (between switches) or on </li></ul><ul><li>server ports (100 or 1000 Mbit/s) </li></ul>Port MAC-address 00:a0:24:d6;b7:c8 1 00:a0:24:12:d5:a1 2 00:a0:24:c1:e2:b6 3
  15. 15. Collision Domains in a Switch Network Broadcast domain Collision domain <ul><li>Each switch port forms a collision domain (half-duplex, HD) </li></ul><ul><li>A switch does not limit the spreading of broadcast-messages </li></ul><ul><li>(unless virtual LANs are used) </li></ul><ul><li>A port can be set to full-duplex (FD) operation, where there are no </li></ul><ul><li>collisions </li></ul>A
  16. 16. Half Duplex and Full Duplex port HD : FD : <ul><li>Benefits of bidirectional operation: </li></ul><ul><li>- the capacity increases (max about 20/200 Mbit/s) </li></ul><ul><li>maximum distance between equipment increases (only media </li></ul><ul><li>restriction) </li></ul>
  17. 17. The Switching Modes <ul><li>The store-and-forward mode: </li></ul><ul><li>- the switch is a fast multiport bridge: the whole frame is copied to the </li></ul><ul><li>input buffer before switching decision </li></ul><ul><li>- frames with errors can be discarded </li></ul><ul><li>- networks of different types and speeds can be interconnected </li></ul><ul><li>- added delay (almost 100 μs ) </li></ul><ul><li>The cut-through: </li></ul><ul><li>- bit by bit switching starts after reading the destination address </li></ul><ul><li>from the incoming frame </li></ul><ul><li>- small delay (in the order of 10 μs) </li></ul><ul><li>- frames with errors are forwarded </li></ul>BER threshold cut-through store-and-forward
  18. 18. The Performance of a Switch <ul><li>Filtering rate : the ability to interpret the destination addresses </li></ul><ul><li>in the incoming frames within a specified time period </li></ul><ul><li>Forwarding rate : the ability to forward frames through the switch </li></ul><ul><li>within a specified time period </li></ul>preamble actual frame IFG = Interframe gap (0.96 μs at 100 M speed) <ul><li>The theoretical maximum forwarding rates in Ethernet : </li></ul>Rate (Mbit/s Minimum frames Maximum frames 10 14880 812 100 148800 8120 1000 235000 81200 Minimum frame : 64 + 8 bytes Maximum : 1526 + 8 bytes
  19. 19. The Spanning Tree Protocol <ul><li>A switch network can be pruned to be loopless by using the STP </li></ul><ul><li>protocol </li></ul><ul><li>The main functions of STP: </li></ul><ul><li>- loop detection and elimination </li></ul><ul><li>- media fault detection and reconfiguration </li></ul><ul><li>- fine tuning of parameters by manual configuration </li></ul>
  20. 20. The Spanning Tree Operation <ul><li>The protocol sets the trunk ports of the switches to blocking or </li></ul><ul><li>forwarding state using 3 parameters: </li></ul><ul><li>- bridge identifier : switch priority and MAC-address </li></ul><ul><li>- path cost : each port has a cost value, which is usually inversely </li></ul><ul><li>proportional to the port speed </li></ul><ul><li>- port priority : each port has a default priority : lower value means </li></ul><ul><li>higher priority </li></ul><ul><li>The spanning tree information is transferred using periodical </li></ul><ul><li>BPDU-multicast frames (1 - 3 s period) </li></ul><ul><li>- distribution of topology information </li></ul><ul><li>- election of the root switch </li></ul><ul><li>- pruning the redundant links </li></ul>
  21. 21. Election of the Root Switch and Root Ports <ul><li>The root switch will the switch with the lowest bridge identifier </li></ul><ul><li>value </li></ul><ul><li>- the default value is 32768 </li></ul><ul><li>- the lowest MAC-address value will ”win” </li></ul><ul><li>The root port: it has the lowest cost path to the root bridge </li></ul><ul><li>- low cost is preferred </li></ul>Switch 1 (ROOT) Switch 2 Switch 3 Switch 4 Switch 5 10 20 10 10 40 10 30 20 10 10 R R R R
  22. 22. Election of the Designated Bridge and Port Switch 1 (ROOT) Switch 2 Switch 3 Switch 4 Switch 5 10 20 10 10 40 10 30 20 10 10 R R R R LAN segment A LAN segment B LAN segment C LAN segment D <ul><li>After election of the root ports, the designated switch and the </li></ul><ul><li>designated port are chosen: the lowest cost from a certain LAN </li></ul><ul><li>segment to the root switch </li></ul>D D D D <ul><li>The designated ports are set to forwarding state, the other ports </li></ul><ul><li>are set to blocking state (except root ports): loops have been eliminated </li></ul>
  23. 23. Virtual LANs <ul><li>Virtual local area networks (VLANs) are logical LANs, which are </li></ul><ul><li>using the same physical LAN as a “platform” </li></ul><ul><li>Benefits of VLANs: </li></ul><ul><li>They make it easier to add, move, or change users in a network </li></ul><ul><li>(reduced cost of administration) </li></ul><ul><li>They enhance network security by means of logical segmentation </li></ul><ul><li>of users and groups </li></ul><ul><li>- They help to control the spreading of broadcast-messages </li></ul>
  24. 24. <ul><li>Effect of the number of broadcasts on the computer performance </li></ul>
  25. 25. <ul><li>Logical grouping of users based on services </li></ul><ul><li>Creating isolated broadcast domains not dependent on location </li></ul><ul><li>VLANs are created on switches </li></ul><ul><li>The traffic between VLANs should be minimized </li></ul>The Basic Ideas of VLANs Sales Engineering Logistics The traffic of different departments is logically separated Server of Sales and Engineering Server of Logistics Enterprise switch
  26. 26. <ul><li>VLANs can be created on basis of several parameters: </li></ul><ul><li>- Switch port </li></ul><ul><li>- MAC-address </li></ul><ul><li>- Protocol </li></ul><ul><li>- IP subnet </li></ul><ul><li>- Application </li></ul><ul><li>…… . </li></ul>VLAN types VLAN Components <ul><li>Switches for logical segmentation </li></ul><ul><li>A protocol to separate the different VLANs on trunk lines </li></ul><ul><li>A server and a protocol for distributing the VLAN information </li></ul><ul><li>in a dynamic environment </li></ul><ul><li>VLAN management system </li></ul><ul><li>A router to forward the traffic between VLANs </li></ul>
  27. 27. Port based VLANs <ul><li>A common VLAN-implementation in workgroup switches: </li></ul><ul><li>layer 1 VLAN </li></ul><ul><li>A port is configured statically to a VLAN </li></ul><ul><li>VLAN ports are location independent </li></ul><ul><li>An easy implementation </li></ul>Port 1 VLAN1 Port 2 VLAN3 Port 3 VLAN1 Port 4 VLAN2 Port 5 VLAN3
  28. 28. Routing Between VLANs Router VLAN1 = subnet 1 VLAN2 = subnet 2
  29. 29. <ul><li>Standard IEEE 802.1Q </li></ul><ul><li>The standard specifies the method how to tag the frames of different </li></ul><ul><li>VLANs on trunk lines </li></ul><ul><li>12 bits are used for VLAN identification : 4094 VLANs </li></ul>DA SA P CFI VLANID Type data ... 12 bits 802.1Q P = priority CFI = Canonical Format Identifier VLANID = VLAN identification
  30. 30. Switched LAN Design <ul><li>Basic concepts : </li></ul>LAN Core equipment Edge equipment uplink downlink 10/100 Mbit/s 100 Mbit/s 1 Gbit/s Servers End equipment Users Services
  31. 31. A very small LAN Basis of Design <ul><li>Amount of traffic/user (Mbit/s) </li></ul><ul><li>Amount of traffic/server (Mbit/s) </li></ul><ul><li>Number of users (ports needed) </li></ul><ul><li>Need for routing </li></ul><ul><li>The nature of applications (bursty/flat) </li></ul>hub UTP
  32. 32. A small LAN <ul><li>If the number users is in the order of 10-20: a switched LAN </li></ul><ul><li>- e.g. 12 - 24 port switch (10/100 Mbit/s) </li></ul><ul><li>- 20 - 40 workstations : a stackable switch (e.g. 48 ports) </li></ul>
  33. 33. Core switch Edge switch 1 Gbit/s 1 Gbit/s <ul><li>E.g. 200 - 100 workstations </li></ul><ul><li>Fault tolerant fast trunk lines and server ports </li></ul>An Enterprise LAN