OSI Model Hardware

taco_thunder · 06-12-2009, 03:45 PM

I know that depending on how the hardware is being used, (NICs, routers, hubs, etc) they can be thrown into either the Physical, Data Link, or Network layer of the OSI model. The practice questions ask what layer this hardware is related to, but on your study guides it has the hardware in a couple layers. Was wondering if anyone can help me out, thanks in advance guys!

Leo

Morty3 · 06-12-2009, 05:49 PM

A hub works in the physical layer, a switch at the datalink layer and a router at the network layer.

You have to know what each device does and what happends at each layer to get this.
For example: A hub regenerates the signal and sends it out all the ports as is. A switch reads the frame (how much depends of switching mode) and makes a decision of where to send the frame based on layer 2 addressing (datalink layer). A router reads the layer 3 information and makes its decision from that.

taco_thunder · 06:24 PM

I know how each one works. It's more the OSI model and how it's referenced to the hardware in the practice exams, at least on this website, that is confusing me. TechNotes state:

Physical
Examples of devices that operate on this layer are hubs/concentrators, repeaters, NICs, WAPs, and LAN and WAN interfaces such as RS-232, OC-3, BRI, and antennas.

Data Link
Examples of devices that operate on this layer are switches, bridges, WAPs, and NICs.

Network
Examples of devices that operate on this layer are layer-3 switches and routers.

I have several books from CompTIA, have searched the internets endlessly, and have downloaded numerous e-books... all giving various results of the OSI model >.<

dynamik · 06-12-2009, 06:39 PM

What specifically are you having trouble with?

taco_thunder · 06-12-2009, 06:58 PM

Finding out where routers, switches, hubs, repeaters, and bridges fall on the OSI model. Everyone I look at says something different.

dynamik · 06-12-2009, 07:12 PM

There's not always a single correct answer. For example, WAPs use eletrical signals, radio waves, etc. at layer-1. They also use layer-2 addressing like switches do. Basic switches operate on the second layer, but more advanced ones provide routing functionality, so they can operate at layer-3 as well.

taco_thunder · 06-12-2009, 07:15 PM

I was afraid of that, time to hit the books again

Morty3 · 06-12-2009, 09:15 PM

You just have to, as I stated before, understand what each device does. A router configuered as a NAT (with PAT) will work at:
Layer 1, since it will use something to send the signals (RF/optical signal/electricity).
Layer 2, since it will put a layer 2 header on each packet it processes.
Layer 3, since it reads and makes decisions based on this data.
Layer 4, since it will also read this header to track sessions between private and public IP:s (You can ofc translate any address but you get me :P)

It takes a while to fully understand this, and I dont think that I fully learned it either.

taco_thunder · 06-17-2009, 08:35 PM

Ethernet: The Definitive Guide | O'Reilly Media

This book really helped me understand detailed features of network devices, and in turn, the OSI model

TravR1 · 06-18-2009, 12:12 AM

Remember NIC's operate on layers 1 and 2. But for testing purposes the correct answer will be layer 2, data link.

Clio · 06-20-2009, 03:31 AM

this is my first post--advanced apologies it's wrong in some way!

is the OSI model covered on A+ Essentials (601) or Remote tech (603) exams? I didn't see it listed on the objectives?

rsutton · 06-20-2009, 03:32 PM

I usually see things referred to in the context of the highest OSI layer that they perform on, even though they can perform lower layer functions as well.

gravyjoe · 06-21-2009, 04:33 AM

I guess different devices can fall on different layers depending on what is mentioned about the device. For example, if you can't get to the Internet because your router is unplugged, then it would be labeled as a layer 1 issue because there's no electricity there. For the most part, hubs and repeaters are at layer 1, switches and bridges at layer 2, and routers at layer 3.

taco_thunder · 06-23-2009, 05:00 PM

Quote:

Originally Posted by rsutton

I usually see things referred to in the context of the highest OSI layer that they perform on, even though they can perform lower layer functions as well.

You answered my question, thanks!

TravR1 · 07-18-2009, 11:52 PM

Yeah don't worry about it. On your test it will be very straight forward. Just know the general rules that were discussed above and on test day know hub is layer 1, switch is layer 2, and a router is layer 3. It will not go into any further depth and it just wants to make sure you understand the basic principles.