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Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
Layer 3 Switches.ppt
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Layer 3 Switches.ppt


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  • 1.     Layer 3 Switches
  • 2. Topics Covered
    • Definitions
    • Characteristics
    • Comparison between Routers and Layer 3 Switches
    • Functionality
    • The Benefits of Layer 3 Switching
    • Cost
  • 3. Router
    • A router is a computer networking device that buffers and forwards data packets across an internetwork toward their destinations, through a process known as routing.
    • Routing occurs at layer 3 (Network layer )
  • 4. Network Switches
    • A network switch is a networking device that performs transparent connection of multiple network segments with forwarding based on MAC addresses at up to the speed of the hardware.
  • 5. Layer 3 Switches
    • A Layer 3 switch is a high-performance device for network routing. It is relatively new term, was conceived as a technology to improve on the performance of routers used in large local area networks (LANs).
    • It can support the same routing protocols as network routers do. Both inspect incoming packets and make dynamic routing decisions based on the source and destination addresses inside.
  • 6. Characteristic
    • It is designed to handle high-performance LAN traffic, so Layer 3 switch can be placed anywhere within a network core or backbone, easily and cost-effectively replacing the traditional backbone router.
    • The switches run routing protocols, such as open shortest path first (OSPF) or routing information protocol (RIP), to communicate with other Layer 3 switches or routers and to build their routing/forwarding tables. These tables are looked up to determine the route for an incoming packet
    • a Layer 3 switch can reprogram the hardware dynamically with the current Layer 3 routing information. This is what allows much faster packet processing.
  • 7. Similarities
    • A Layer 3 switch does everything to a packet that a traditional router does:
    • Determines forwarding path based on Layer 3 information
    • Validates the integrity of the Layer 3 header via checksum
    • Verifies packet expiration and updates accordingly
    • Processes and responds to any option information
    • Updates forwarding statistics in the Management Information Base (MIB)
    • Applies security controls if required
    • Both types of boxes share a similar appearance
  • 8. Differences
    • The key difference between Layer 3 switches and routers lies in the hardware technology used to build the unit. The hardware inside a Layer 3 switch merges that of traditional switches and routers, replacing some of a router's software logic with hardware to offer better performance in some situations.
      • In general-purpose routers, packet switching takes place using a microprocessor, whereas a Layer 3 switch performs this using application-specific integrated circuit (ASIC) hardware.
      • Another differentiating feature between a router and a Layer 3 switch is the number of ports to which individual terminal devices can be connected. A Layer 3 switch usually has a significantly greater port density.
    • Layer 3 switches often cost less than traditional routers
  • 9. Functionality
    • The principle of a Layer 3 is "route once, switch many".
      • A Layer 3 switch can actually store MAC to IP Address associations for the source and destination of the packet.
      • when there is a packet with a new source destination pair, it is routed (which means that the routing table is referred to for determining the best path ) which is time consuming, and this source destination pair information is stored in the router cache.
      • when the next packet arrives with the same source destination pair, no routing lookup is needed and the packet is directly switched (which is much faster).
  • 10. The benefits of Layer 3 switching
    • The benefits of layer 3 switching include the following:
    • Hardware-based packet forwarding
    • High-performance packet switching
    • High-speed scalability
    • Low latency
      • Latency is the time taken for a packet of data from the sending application to the receiving application. This includes both transit time over the network, and computer processing time at both the source and destination computers.
    • Lower per-port cost
  • 11. Cont…
    • Flow accounting
    • Security
    • Quality of service
      • ( QoS ) refers to control mechanisms that can provide different priority to different users or data flows, or guarantee a certain level of performance to a data flow in accordance with requests from the application program
  • 12. $$$ Cost $$$
    • Cost Savings A traditional router may run U.S. $8,000 to $10,000 per Fast Ethernet interface, while a Layer 3 switch costs less than U.S. $1,000 per port.
      • Layer 3 switching is cheap because Layer 3 switches are targeted specifically for inter-VLAN routing, where only Ethernet access technologies are used in high densities
  • 13. What is VLAN
    • A virtual LAN, is a method of creating independent logical networks within a physical network. Several VLANs can co-exist within such a network. This helps in reducing the broadcast domain and aids in network administration by separating logical segments of a LAN (like company departments) that should not exchange data using a LAN
  • 14.  
  • 15. Do Layer 3 Switches Completely Eliminate Need for the Traditional Router
    • Routers are still needed, especially where connections to the wide area are required. Layer 3 switches may still connect to such routers to learn their tables and route packets to them when these packets need to be sent over the WAN.
    • The switches will be very effective on the workgroup and the backbone within an enterprise, but most likely will not replace the router at the edge of the WAN .
  • 16.
    • Routers perform numerous other functions like
      • filtering with access lists,
      • inter-Autonomous System (AS) routing with protocols such as the Border Gateway Protocol (BGP)
    • Some Layer 3 switches may completely replace the need for a router if they can provide all these functions
  • 17.
    • The End