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S3C2 – LAN Switching. Addressing LAN Problems. Congestion is Caused By. Multitasking, Faster operating systems, More Web-based applications Client-Server client/server applications allow administrators to centralize information, thus making it easy to maintain and protect.

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S3C2 – LAN Switching

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s3c2 lan switching

S3C2 – LAN Switching

Addressing LAN Problems

congestion is caused by
Congestion is Caused By
  • Multitasking,
  • Faster operating systems,
  • More Web-based applications
  • Client-Server
    • client/server applications allow administrators to centralize information, thus making it easy to maintain and protect.
  • Point-to-point (host to host) connection is collision free
lans impacted by
LANS Impacted By:
  • The data frame broadcast delivery nature of Ethernet/802.3 LANs
  • Carrier sense multiple access collision detect (CSMA/CD) access methods allowing only one station to transmit at a time
  • Multimedia applications with higher bandwidth demand such as video and the Internet, coupled with the broadcast nature of Ethernet, can create network congestion.
impact issues continued
Impact Issues Continued
  • Normal latency as the frames travel across the Layer 1 medium and through Layer 1, 2, and 3 networking devices, and the latency added by the extension of Ethernet/802.3 LANs by adding repeaters
  • Extending the distances of the Ethernet/802.3 LANs by using Layer 1 repeaters
  • Latency is caused by:
    • the time it takes the source NIC to place voltage pulses on the wire and the time it takes the receiving NIC to interpret these pulses. This is sometimes called NIC delay (it is typically around 1 microsecond for10BASE-T NICs).
    • A byte takes a minimum of 800 ns to transmit
latency continued
Latency Continued
  • Second, there is the actual propagation delay as the signal takes time -- albeit a very short time -- to actually travel down the cable (it is typically about .556 microseconds per 100 m for Cat 5 UTP). The longer the cable, the more propagation delay; the slower the nominal velocity of propagation (NVP) of the cable, the more the propagation delay.
  • Third, latency is added according to which networking devices -- whether they be Layer 1, 2, or 3 (and how they are configured) -- are added in the path between the two communicating computers. The actual transmission time (the duration of the host actually sending bits) must also be included in understanding timing on networks.
half duplex or duplex
Half Duplex or Duplex
  • Ethernet LANs are half-duplex technology
  • Full-duplex Ethernet allows the transmission of a packet and the reception of a different packet at the same time – requires full duplex NIC card
    • This simultaneous transmission and reception requires the use of two pairs of wires in the cable and a switched connection between each node. This connection is considered point-to-point and is collision free.
    • Because both nodes can transmit and receive at the same time, there are no negotiations for bandwidth. Full-duplex Ethernet can use an existing shared medium as long as the medium meets minimum Ethernet standards. Requires 2 pairs of wires and switched connection
benefit of full duplex
Benefit of Full Duplex
  • Ethernet usually can only use 50%-60% of the 10-Mbps available bandwidth because of collisions and latency.
  • Full-duplex Ethernet offers 100% of the bandwidth in both directions.
  • This produces a potential 20-Mbps throughput- 10-Mbps TX and 10-Mbps RX.
  • Remember – Transmit connects to Receive
    • Think SIMPLE LAN
why segment
Why Segment
  • Isolates certain traffic
  • Creates smaller collision domains
  • Data are passed between segments using bridges, switches, or routers
    • Decreasing size of collision domains increases the number of collision domains
  • Create tables to match segments and MAC addresses
  • Layer 3 protocol independent
  • Stores and then forwards based on MAC address
  • Increases latency on network (10-30%)
  • Creates smaller collision domains but increases number of collision domains
  • Operate at Layer 3 using IP addresses
  • More manageable, greater functionality, multiple paths
  • Smaller collision domains
  • Introduce latency
    • Protocols that provide acknowledgements introduce 30-40% delays
    • Protocols that provide minimal acknowledgements have 20%-30% loss in throughput
    • So routers introduce 20-40% delay depending on protocol
switches switched ethernet
Switches/Switched Ethernet
  • Low latency and high frame-forwarding rates
  • Eliminates impact of collisions through micro-segmentation
  • Works with existing 802.3 standards
  • Create dedicated network segments (point to point) with full bandwidth – virtual circuits
  • Create collision free domains
  • Cost more than bridges or routers
bridges vs switches
Bridges vs Switches
  • Both bridges and switches connect LAN segments, use a table of MAC addresses to determine the segment on which a datagram needs to be transmitted, and reduce traffic.
  • Switches are more functional in today’s networks than bridges because they operate at much higher speeds than bridges and can support new functionality, such as virtual LANs (VLANs).
  • Bridges typically switch using hardware; switches typically switch using software.
layer 2 switching
Layer 2 Switching
  • With Layer 2 switching, frames are switched based on MAC address information.
  • If the Layer 2 switch does not know where to send the frame, it broadcasts the frame out all its ports to the network to learn the correct destination
  • the switch learns the location of the new address and adds the information to the switching table
    • MAC Address and ports
virtual lans
Virtual LANs
  • dedicated paths between sending and receiving hosts within the switch are temporary. The switch’s power comes from the fact that it can rapidly make and break these 1 to 1 connections through its various ports, depending upon the data in its switching table.
how a switch learns addresses
How A Switch Learns Addresses
  • Examines source address
  • Sends out all ports except incoming port when address is unknown, multicast, or broadcast
  • Forwards when the destination is at a different interface
  • Filters when the destination is on the same interface
  • Date stamps each address– discards after a certain time period
  • Addresses stored in CAM – Content Addressable Memory
benefits of switching
Benefits of Switching
  • Number of collisions reduced
  • Simultaneous multiple communications
  • High speed uplinks
  • Improved network response
  • Increased user productivity
symmetric asymmetric switching
Symmetric/Asymmetric Switching
  • Symmetric switching provides switching between like bandwidths
    • Multiple simultaneous conversations increase throughput
  • Asymmetric provides switching between unlike bandwidths
    • Requires the switch to use memory buffering
spanning tree protocol
Spanning Tree Protocol
  • Switches forward broadcast frames
  • Prevents loops
    • Loops can cause broadcast storms and exponentially proliferate fragments
  • Allows redundant links
  • Prunes topology to a minimal spanning tree
  • Resilient to topology changes and device failures
  • Spanning Tree Frames are called bridge
  • protocol data units (BPDUs)
  • Spanning Tree enabled by default on catalyst switch
spanning tree states
Spanning Tree States
  • States are initially set and then modified by STP
    • Blocking
    • Listening
    • Learning
    • Forwarding
    • Disabled
  • Server ports can be configured to immediately enter SPT forwarding mode
  • You can determine the status, cost, and priority of ports and VLANs by using the show spantree command
  • Listening and learning create latency
switching modes
Switching Modes
  • Store and Forward
    • Entire frame received before forwarding takes place – causes more latency but error detection is high
  • Cut Though (Read first 6 bytes)
    • Switch reads destination address before receiving entire frame and it is forwarded – decreases latency but higher error rate
      • Fast forward immediately forwards
      • Fragment Free filters out collision fragments
  • Fragment Free (Read first 64 bytes)
    • Ensures frame is not a runt and probably not an error
  • Two methods
    • Port-based
      • Packets stored in queues that are linked to incoming ports – packets forwarded when queue is clear
    • Shared Memory buffering
      • Deposits all packets into common memory buffer shared by all ports
        • Dynamic location assigns port areas
    • Switch maintains a map of ports and clears when packet is switched
virtual lan
Virtual LAN
  • Logical network independent of their members’ physical locations
  • Administratively defined broadcast domain
  • Users reassigned to different VLAN using software
  • Can be grouped by function, department, application
  • Creates a single broadcast domain that is not restricted to physical segment