test doc from neel

05/03/2305/03/23 Nariman MohammedNariman Mohammed 11

Layer 3 Switches Layer 3 Switches

05/03/23 Nariman Mohammed 2

Topics CoveredTopics Covered► DefinitionsDefinitions► Characteristics Characteristics ► Comparison between Routers and Layer 3 Comparison between Routers and Layer 3

SwitchesSwitches► FunctionalityFunctionality► The Benefits of Layer 3 SwitchingThe Benefits of Layer 3 Switching► Cost Cost


RouterRouter► A A routerrouter is a computer is a computer

networking device that networking device that buffers and forwards buffers and forwards data packets across an data packets across an internetwork toward internetwork toward their destinations, their destinations, through a process through a process known as routing.known as routing.

► Routing occurs at layer Routing occurs at layer 3 (Network layer )3 (Network layer )


Network SwitchesNetwork Switches► A A network switch network switch

is a networking is a networking device that device that performs performs transparent transparent connection of connection of multiple network multiple network segments with segments with forwarding based forwarding based on MAC addresses on MAC addresses at up to the speed at up to the speed of the hardware. of the hardware.


Layer 3 SwitchesLayer 3 Switches► A Layer 3 switch is a high-performance device for network A Layer 3 switch is a high-performance device for network

routing. It is relatively new term, was conceived as a routing. It is relatively new term, was conceived as a technology to improve on the performance of routers used in technology to improve on the performance of routers used in large local area networks (LANs).large local area networks (LANs).

► It can support the same routing protocols as network routers It can support the same routing protocols as network routers do. Both inspect incoming packets and make dynamic routing do. Both inspect incoming packets and make dynamic routing decisions based on the source and destination addresses inside. decisions based on the source and destination addresses inside.


CharacteristicCharacteristic

► It is designed to handle high-performance LAN traffic, It is designed to handle high-performance LAN traffic, so Layer 3 switch can be placed anywhere within a so Layer 3 switch can be placed anywhere within a network core or backbone, easily and cost-effectively network core or backbone, easily and cost-effectively replacing the traditional backbone router. replacing the traditional backbone router.

► The switches run routing protocols, such as open The switches run routing protocols, such as open shortest path first (OSPF) or routing information shortest path first (OSPF) or routing information protocol (RIP), to communicate with other Layer 3 protocol (RIP), to communicate with other Layer 3 switches or routers and to build their switches or routers and to build their routing/forwarding tables. These tables are looked up routing/forwarding tables. These tables are looked up to determine the route for an incoming packetto determine the route for an incoming packet

► a Layer 3 switch can reprogram the hardware a Layer 3 switch can reprogram the hardware dynamically with the current Layer 3 routing dynamically with the current Layer 3 routing information. This is what allows much faster packet information. This is what allows much faster packet processing.processing.


Similarities Similarities A Layer 3 switch does everything to a packet that a A Layer 3 switch does everything to a packet that a

traditional router does: traditional router does: ► Determines forwarding path based on Layer 3 Determines forwarding path based on Layer 3

information information ► Validates the integrity of the Layer 3 header via Validates the integrity of the Layer 3 header via

checksum checksum ► Verifies packet expiration and updates Verifies packet expiration and updates

accordingly accordingly ► Processes and responds to any option Processes and responds to any option

information information ► Updates forwarding statistics in the Management Updates forwarding statistics in the Management

Information Base (MIB) Information Base (MIB) ► Applies security controls if requiredApplies security controls if required► Both types of boxes share a similar appearanceBoth types of boxes share a similar appearance


DifferencesDifferences► The key difference between Layer 3 switches and routers The key difference between Layer 3 switches and routers

lies in the hardware technology used to build the unit. lies in the hardware technology used to build the unit. The hardware inside a Layer 3 switch merges that of The hardware inside a Layer 3 switch merges that of traditional switches and routers, replacing some of a traditional switches and routers, replacing some of a router's software logic with hardware to offer better router's software logic with hardware to offer better performance in some situations. performance in some situations. In general-purpose routers, packet switching takes In general-purpose routers, packet switching takes

place using a microprocessor, whereas a Layer 3 place using a microprocessor, whereas a Layer 3 switch performs this using application-specific switch performs this using application-specific integrated circuit (ASIC) hardware. integrated circuit (ASIC) hardware.

Another differentiating feature between a router and a Another differentiating feature between a router and a Layer 3 switch is the number of ports to which Layer 3 switch is the number of ports to which individual terminal devices can be connected. A Layer individual terminal devices can be connected. A Layer 3 switch usually has a significantly greater port 3 switch usually has a significantly greater port density.density.

► Layer 3 switches often cost less than traditional routersLayer 3 switches often cost less than traditional routers


FunctionalityFunctionality► The principle of a Layer 3 is "route once, switch many". The principle of a Layer 3 is "route once, switch many".

A Layer 3 switch can actually store MAC to IP A Layer 3 switch can actually store MAC to IP Address associations for the source and destination of Address associations for the source and destination of the packet.the packet.

when there is a packet with a new source destination when there is a packet with a new source destination pair, it is routed (which means that the routing table pair, it is routed (which means that the routing table is referred to for determining the best path ) which is is referred to for determining the best path ) which is time consuming, and this source destination pair time consuming, and this source destination pair information is stored in the router cache. information is stored in the router cache.

when the next packet arrives with the same source when the next packet arrives with the same source destination pair, no routing lookup is needed and the destination pair, no routing lookup is needed and the packet is directly switched (which is much faster). packet is directly switched (which is much faster).


The benefits of Layer 3 The benefits of Layer 3 switchingswitching

The benefits of layer 3 switching include the The benefits of layer 3 switching include the following:following:

► Hardware-based packet forwarding Hardware-based packet forwarding ► High-performance packet switching High-performance packet switching ► High-speed scalability High-speed scalability ► Low latencyLow latency

Latency is the time taken for a packet of data Latency is the time taken for a packet of data from the sending application to the receiving from the sending application to the receiving application. This includes both transit time over application. This includes both transit time over the network, and computer processing time at the network, and computer processing time at both the source and destination computers. both the source and destination computers.

► Lower per-port cost Lower per-port cost


Cont…Cont…► Flow accounting Flow accounting ► Security Security ► Quality of serviceQuality of service

( ( QoSQoS) refers to control mechanisms that can ) refers to control mechanisms that can provide different priority to different users or provide different priority to different users or data flows, or guarantee a certain level of data flows, or guarantee a certain level of performance to a data flow in accordance with performance to a data flow in accordance with requests from the application program requests from the application program


$$$ Cost $$$$$$ Cost $$$► Cost SavingsCost Savings

A traditional router may run U.S. $8,000 to A traditional router may run U.S. $8,000 to $10,000 per Fast Ethernet interface, while a Layer $10,000 per Fast Ethernet interface, while a Layer 3 switch costs less than U.S. $1,000 per port. 3 switch costs less than U.S. $1,000 per port. Layer 3 switching is cheap because Layer 3 Layer 3 switching is cheap because Layer 3

switches are targeted specifically for inter-VLAN switches are targeted specifically for inter-VLAN routing, where only Ethernet access routing, where only Ethernet access technologies are used in high densities technologies are used in high densities


What is VLANWhat is VLAN

► A A virtual LAN, virtual LAN, is a method of creating independent logical networks is a method of creating independent logical networks within a physical network. Several VLANs can co-exist within such a within a physical network. Several VLANs can co-exist within such a network. This helps in reducing the broadcast domain and aids in network. This helps in reducing the broadcast domain and aids in network administration by separating logical segments of a LAN (like network administration by separating logical segments of a LAN (like company departments) that should not exchange data using a LANcompany departments) that should not exchange data using a LAN


Do Layer 3 Switches Completely Do Layer 3 Switches Completely Eliminate Need for the Traditional Eliminate Need for the Traditional

RouterRouter

► Routers are still needed, especially where connections Routers are still needed, especially where connections to the wide area are required. Layer 3 switches may to the wide area are required. Layer 3 switches may still connect to such routers to learn their tables and still connect to such routers to learn their tables and route packets to them when these packets need to be route packets to them when these packets need to be sent over the WAN.sent over the WAN.

► The switches will be very effective on the workgroup The switches will be very effective on the workgroup and the backbone within an enterprise, but most likely and the backbone within an enterprise, but most likely will not replace the router at the edge of the WAN .will not replace the router at the edge of the WAN .


► Routers perform numerous other functions like Routers perform numerous other functions like filtering with access lists, filtering with access lists, inter-Autonomous System (AS) routing with inter-Autonomous System (AS) routing with

protocols such as the Border Gateway Protocol protocols such as the Border Gateway Protocol (BGP)(BGP)

Some Layer 3 switches may completely replace the Some Layer 3 switches may completely replace the need for a router if they can provide all these need for a router if they can provide all these functions functions


The EndThe End

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