General terms

Hi,

Im reading the BCMSN material and would like clarification on a few terms, maybe because im not a native english speaker

A router performs path determination and switching (ie. routing and switching). When the material mentions layer-3 switching and layer-3 forwarding, how are you to understand that?

My best guess is that switching is putting a frame from one interface onto another interface, and that routing is the path determination function..

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Comments

roswald

The big difference between a router and a Layer 3 switch is the way that they physically handle traffic.

Routers must pass traffic to the processor to determine a path, while a L3 switch doesn't typically pass traffic to the CPU. L3 switches forward traffic at "line speed" which is much faster than if that traffic has to be processed.

It boils down to this: A typical router is routing in software, while L3 switching is routing in hardware.

Plazma

To help you understand it.. do some reading on Cisco's Website about Process switched, fast switched, and CEF switched methodologies.. it really helps put some things into perspective.

bighornsheep

Your question probably belong more in the CCNA forum....but I'll give you the benefit of English being your 2nd language.

Switching can mean a few things, but Cisco generally refer switching as to the process of layer 2 switching or multilayer switching.

Routing is the process of forwarding packets. A router will participate in routing by advertising its local routing table to other routers, a router in order to process incoming traffic will perform route lookup and forward packets to another router or host. This process where packets are forwarded from one router to another based on routing information is collectively known as packet switching. The name can be confusing but comes down to us from the traditional circuit switching networks.

In terms of how the router will pick the path for a packet to go (how the packet is forwarded), you can see what plazma talked about, there are essentially the following 3 ways:

Plazma wrote:

To help you understand it.. do some reading on Cisco's Website about Process switched, fast switched, and CEF switched methodologies.. it really helps put some things into perspective.

Layer 2 switching is the process by which an L2 packet data unit called a frame will be forwarded. A switch will decide the port(s) to forward the frame based on MAC address.

Layer 3 switching or multilayer switching in general is performing the routing process in hardware using ASIC vs. traditional routing which is software algorithm-based.