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Basically a layer 2 switch operates utilizing Mac addresses in it's caching table to quickly pass information from port to port. A layer 3 switch utilizes IP addresses to do the same.

While the previous explanation is the "What", for folks in networking the following "How" is far more interesting.

Essentially, A layer 2 switch is essentially a multiport transparent bridge. A layer 2 switch will learn about MAC addresses connected to each port and passes frames marked for those ports. It also knows that if a frame is sent out a port but is looking for the MAC address of the port it is connected to and drop that frame. Whereas a single CPU Bridge runs in serial, todays hardware based switches run in parallel, translating to extremly fast switching.

Layer 3 switching is a hybrid, as one can imagine, of a router and a switch. There are different types of layer 3 switching, route caching andtopology-based. In route caching the switch required both a Route Processor (RP) and a Switch Engine (SE). The RP must listen to the first packet to determine the destination. At that point the Switch Engine makes a shortcut entry in the caching table for the rest of the packets to follow. Due to advancement in processing power and drastic reductions in the cost of memory, today's higher end layer 3 switches implement a topology-based switching which builds a lookup table and and poputlates it with the entire network's topology. The database is held in hardware and is referenced there to maintain high throughput. It utilizes the longest address match as the layer 3 destination.

Now when and why would one use a l2 vs l3 vs a router? Simply put, a router will generally sit at the gateway between a private and a public network. A router can perform NAT whereas an l3 switch cannot (imagine a switch that had the topology entries for the ENTIRE internet!!). In a small very flat network (meaning only one private network range for the whole site) a L2 switch to connect all the servers and clients to the internet is probably going to suffice. Larger networks, or those with the need to contain broadcast traffic or those utilizing VOIP, a multi network approach utilizing VLANs is appropriate, and when one is utilizing VLANs, L3 switches are a natural fit. While a router on a stick scenario can work, it can quickly overtax a router if there is any significant intervlan traffic since the router must make complicated routing decisions for every packet that it recieves.

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Q: What is the difference between Layer 2 switch and Layer 3 switch?
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What is the difference between a layer 2 and a layer 3 switch?

The difference between Layer 2 and Layer 3 switching is the type of information inside the frame that is used to determine the correct output interface. With Layer 2 switching, frames are switched based on MAC address information. With Layer 3 switching, frames are switched based on network-layer information.

What is difference between L3 switch and router?

A layer 3 switch has routing capability like a router. However, it also has layer 2 switching capabilities like a switch. To fulfill both functions, layer 3 switches will generally have a greater number of ports than most routers.

What is the difference between Layer 2 switch and modem?

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Which layer device is a switch?

A Switch is a Layer 2 device as they operate in the data link layer

Ws-c3560-24ps-e is layer 2 switch or layer3 switch?

It is a layer 3 switch

This device serves as a gateway between two subnets It sends and receives packets between networks?

I believe it's a router. I have this question on a test the choices are. router, hub, layer 2 switch or firewall. I answered layer 2 switch. It was wrong.

Will a Cisco 4000 switch automatically switch from layer 3 to layer 2?

I believe there is no such thing as switching "from layer 3 to layer 2". Switching is either done within layer 3, or within layer 2.

Why is a switch called as layer 2 device?

because one layer is the electrical part, and the other layer is the place where the switch is on.

Difference between layer 2 and layer 3?

Layer 2 switches are working based up on the MAC address and layer 3 switches are working based up on the ip address

What does a layer 2 switch use to decide where to forward a received frame?

A layer 2 switch uses the MAC address to determine which port to switch the frame out of.

Switch operates at which osi layer?

A switch is mainly a layer 2 device (because it switches on the MAC address)

What is the difference between switch and router?

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