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test doc from neel

  1. 1. Layer 3 Switches10/08/12 Nariman Mohammed 1
  2. 2. Topics Covered► Definitions► Characteristics► Comparison between Routers and Layer 3 Switches► Functionality► The Benefits of Layer 3 Switching► Cost10/08/12 Nariman Mohammed 2
  3. 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 ) 10/08/12 Nariman Mohammed 3
  4. 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.10/08/12 Nariman Mohammed 4
  5. 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.10/08/12 Nariman Mohammed 5
  6. 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.10/08/12 Nariman Mohammed 6
  7. 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 appearance10/08/12 Nariman Mohammed 7
  8. 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 routers 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 routers10/08/12 Nariman Mohammed 8
  9. 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).10/08/12 Nariman Mohammed 9
  10. 10. The benefits of Layer 3 switchingThe 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 cost10/08/12 Nariman Mohammed 10
  11. 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 program10/08/12 Nariman Mohammed 11
  12. 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 densities10/08/12 Nariman Mohammed 12
  13. 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 LAN10/08/12 Nariman Mohammed 13
  14. 14. 10/08/12 Nariman Mohammed 14
  15. 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 .10/08/12 Nariman Mohammed 15
  16. 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 functions10/08/12 Nariman Mohammed 16
  17. 17. The End10/08/12 Nariman Mohammed 17

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