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
