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L3 switch for vlan

foxbatreco
Level 3
Level 3

Hi guys,

Can anyone clarify how do i justify the use of an L3 switch as compared to a Router( Say 1841 )for vlan purpose?? i mean what advantage will an l3 give me in real network over a router.expecting your techie reply as this is my first string. thnks in adv...

1 Accepted Solution

Accepted Solutions

minumathur
Level 1
Level 1

Hi.

Search: Browse the index

Definition of: layer 3 switch

A network device that forwards traffic based on layer 3 information at very high speeds. Traditionally, routers, which inspect layer 3, were considerably slower than layer 2 switches. In order to increase routing speeds, many "cut-through" techniques were used, which perform an "inspect the first packet at layer 3 and send the rest at layer 2" type of processing. Ipsilon's IP Switch and Cabletron's SecureFast switches were pioneers in cut-through switching.

As more routing lookup functions were moved from software into the ASIC chips, layer 3 switches could inspect each packet just like a router at high speed without using proprietary cut-through methods. If a layer 3 switch supports packet-by-packet inspection and supports routing protocols, it is called a "routing switch" or "switch router," which simply means "fast router." For example, Cisco calls its high-end routers Gigabit Switch Routers.

The more deeply a packet is examined, the more forwarding decisions can be made based upon type of traffic, quality of service and so on. To get to this information means digging into the packet's headers to ferret out the data, which takes processing time. To understand how the packets are formed, see TCP/IP abc's. The following shows what is examined at each layer. See layer 3, layer 2 switch, Web switch and virtual LAN.

Forwarding

Decision

Layer Based on Examples

2 MAC address Ethernet, Token Ring, etc.

3 Network address IP, IPX, etc.

3 Service quality IP, IPX, etc.

3 Application IPX socket

4 Application IP socket

If you want more infomation, http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_1-2/switch_evolution.html

this will clear all the doubt.

-Minu

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1 Reply 1

minumathur
Level 1
Level 1

Hi.

Search: Browse the index

Definition of: layer 3 switch

A network device that forwards traffic based on layer 3 information at very high speeds. Traditionally, routers, which inspect layer 3, were considerably slower than layer 2 switches. In order to increase routing speeds, many "cut-through" techniques were used, which perform an "inspect the first packet at layer 3 and send the rest at layer 2" type of processing. Ipsilon's IP Switch and Cabletron's SecureFast switches were pioneers in cut-through switching.

As more routing lookup functions were moved from software into the ASIC chips, layer 3 switches could inspect each packet just like a router at high speed without using proprietary cut-through methods. If a layer 3 switch supports packet-by-packet inspection and supports routing protocols, it is called a "routing switch" or "switch router," which simply means "fast router." For example, Cisco calls its high-end routers Gigabit Switch Routers.

The more deeply a packet is examined, the more forwarding decisions can be made based upon type of traffic, quality of service and so on. To get to this information means digging into the packet's headers to ferret out the data, which takes processing time. To understand how the packets are formed, see TCP/IP abc's. The following shows what is examined at each layer. See layer 3, layer 2 switch, Web switch and virtual LAN.

Forwarding

Decision

Layer Based on Examples

2 MAC address Ethernet, Token Ring, etc.

3 Network address IP, IPX, etc.

3 Service quality IP, IPX, etc.

3 Application IPX socket

4 Application IP socket

If you want more infomation, http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_1-2/switch_evolution.html

this will clear all the doubt.

-Minu

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