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The fundamental difference between a router and a Layer3 switch is that Layer3 switches have optimized hardware to pass data as fast as Layer2 switches, yet they make decisions on how to transmit traffic at Layer3, just like a router. Within the LAN environment, a Layer3 switch is usually faster than a router because it is built on switching hardware. In fact, many of Cisco's Layer3 switches are actually routers that operate faster because they are built on "switching" hardware with customized chips inside the box.
The pattern matching and Caching on Layer3 switches is similar to the pattern matching and caching on a router. Both use a routing protocol and routing table to determine the best path. However, a Layer3 switch has the ability to reprogram the hardware dynamically with the current Layer3 routing information. This is what allows for faster packet processing.
On current Layer3 switches, the information received from the routing protocols is used to update the hardware caching tables.
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echnically, the differences are:
1- L3 Switch do switching at layer3 by preserving the source and destination mac and preserving the TTL value of the IP header of the1st routed packet, so the first packet is routed using normal routing lookup, but after that all packet are switched.
2- router do normal routing lookup, but by introducing fast switching and CEF, packets are also now switched on a router.
3- Switches doesnt support some QoS features.
4- Switches doesnt support NAT.
5- The forwarding on switches is done on ASIC (Application Specific Integrated Circuits) which is done in hardware rather than a software.
6- Forwarding on routers are done in a software.
7- router supports different WAN technologies (modules) unlike switches.
A router uses IP addresses -- ISO Layer3 addresses -- to determine which of typically a few attached interfaces a packet should be routed to. A switch uses Ethernet MAC address -- ISO Layer2 addresses -- to "learn" which devices are attached to a port, and route packets to that port. A router is a device used to connect different networks, while a switch is the backbone of a network.
The major difference between Layer3 switches and routers is the CPU and hardware/software performance.
Routers use more general-purpose CPUs to provide raw power. All of their functions must be performed in software, and since their processors aren't specialized. They can do more complex things like QoS policies.
Also routers have expansion slots and cards that allow them to use different media types, like serial connections for T1 and T3 circuits.
On the other hand, Layer3 switches are both a switch and a router which use Application-Specific Integrated Circuits (ASICs) to perform their tasks.
These purpose-built chips are fast on their jobs, but very specific to their role. An ASIC designed do packet forwarding really can't do QoS for example.
ASICs allow layer3 switches to forward packets quickly, but at the cost of not providing more advanced services that must be done in software. Layer3 switches are usually Ethernet connection type only.
L3 switches do not have WAN interfaces.
You can connect Ethernet circuits to a switch so you only need a router if you want to connect traditional circuits such as E1 E1 SDH or old technology such as X21 V35 or async circuits.
As far as I know Call Manager Express does not run on a switch but does on a router.
Switches support WiFi controller, Firewall so are quite powerfull.
So you need to understand the business requirement before deciding router or switch.
Also routers can include switch modules.
both do the same functions, except router do conversion between two different network types, like Frame Relay to Ethernet.
L3 switches do not have WAN interfaces.
Switches have optimized hardware to pass data as fast as Layer2 switches.
Both use a routing protocol and routing table to determine the best path.
The basic difference between layer3 switches and routers is that; routers are software based and switches are hardware based. Hence swithces conclude with faster data rate. As well as router doesn't switch data, they actually route data; where L3 switch does both.
Normally routers are designed to configure at the edge of the network where L3 can be configured at the edge of the network as well as within it. It depends upon the scenario which you wish to impliment over.It's just a short description, can be elaborated more.Hope this helps.Thanks.
The primary difference between switches and routers at layer3 is the CPU and hardware/software performance.L3 switches do not have WAN interfaces.From a software perspective, L3 switches are not capable of the extra services that routers typically provide, such as NAT, and Quality of Service (QOS).
