Layer 3 Switches.ppt


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Layer 3 Switches.ppt

  1. 1.     Layer 3 Switches
  2. 2. Topics Covered <ul><li>Definitions </li></ul><ul><li>Characteristics </li></ul><ul><li>Comparison between Routers and Layer 3 Switches </li></ul><ul><li>Functionality </li></ul><ul><li>The Benefits of Layer 3 Switching </li></ul><ul><li>Cost </li></ul>
  3. 3. Router <ul><li>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. </li></ul><ul><li>Routing occurs at layer 3 (Network layer ) </li></ul>
  4. 4. Network Switches <ul><li>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. </li></ul>
  5. 5. Layer 3 Switches <ul><li>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). </li></ul><ul><li>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. </li></ul>
  6. 6. Characteristic <ul><li>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. </li></ul><ul><li>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 </li></ul><ul><li>a Layer 3 switch can reprogram the hardware dynamically with the current Layer 3 routing information. This is what allows much faster packet processing. </li></ul>
  7. 7. Similarities <ul><li>A Layer 3 switch does everything to a packet that a traditional router does: </li></ul><ul><li>Determines forwarding path based on Layer 3 information </li></ul><ul><li>Validates the integrity of the Layer 3 header via checksum </li></ul><ul><li>Verifies packet expiration and updates accordingly </li></ul><ul><li>Processes and responds to any option information </li></ul><ul><li>Updates forwarding statistics in the Management Information Base (MIB) </li></ul><ul><li>Applies security controls if required </li></ul><ul><li>Both types of boxes share a similar appearance </li></ul>
  8. 8. Differences <ul><li>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. </li></ul><ul><ul><li>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. </li></ul></ul><ul><ul><li>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. </li></ul></ul><ul><li>Layer 3 switches often cost less than traditional routers </li></ul>
  9. 9. Functionality <ul><li>The principle of a Layer 3 is &quot;route once, switch many&quot;. </li></ul><ul><ul><li>A Layer 3 switch can actually store MAC to IP Address associations for the source and destination of the packet. </li></ul></ul><ul><ul><li>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. </li></ul></ul><ul><ul><li>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). </li></ul></ul>
  10. 10. The benefits of Layer 3 switching <ul><li>The benefits of layer 3 switching include the following: </li></ul><ul><li>Hardware-based packet forwarding </li></ul><ul><li>High-performance packet switching </li></ul><ul><li>High-speed scalability </li></ul><ul><li>Low latency </li></ul><ul><ul><li>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. </li></ul></ul><ul><li>Lower per-port cost </li></ul>
  11. 11. Cont… <ul><li>Flow accounting </li></ul><ul><li>Security </li></ul><ul><li>Quality of service </li></ul><ul><ul><li>( 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 </li></ul></ul>
  12. 12. $$$ Cost $$$ <ul><li>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. </li></ul><ul><ul><li>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 </li></ul></ul>
  13. 13. What is VLAN <ul><li>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 </li></ul>
  14. 15. Do Layer 3 Switches Completely Eliminate Need for the Traditional Router <ul><li>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. </li></ul><ul><li>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 . </li></ul>
  15. 16. <ul><li>Routers perform numerous other functions like </li></ul><ul><ul><li>filtering with access lists, </li></ul></ul><ul><ul><li>inter-Autonomous System (AS) routing with protocols such as the Border Gateway Protocol (BGP) </li></ul></ul><ul><li>Some Layer 3 switches may completely replace the need for a router if they can provide all these functions </li></ul>
  16. 17. <ul><li>The End </li></ul>