We start with 3 basic layers:

1. Physical - (Cables, radio waves, binary 1’s and 0’s, etc).
2. Data Link - (Switch/Bridge devices/MAC address)
3. Network - (Routers)

Routers are the devices which are given the most focus. Here is the back of an example router:
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I was going to write a bunch of stuff in here about Access Control Lists and the Cisco IOS image files, but Wordpress deleted all of my draft work I had saved up, and I’m not in the mood to retype it all. You probably weren’t gonna read that Greek nonsense anyway….


Here’s some good reading though:


* Backing up and restoring an IOS image file
* Cisco IOS access lists: 10 things you should know
* Q and A: Wildcard Masks in ACL’s

For some f—ed up reason, Wordpress would give me a 403 error every time I tried to post something about access control lists. That last failed attempt at a post for this CCNA series was caused by the same problem: IOS command syntax in the writing. Really, I think that’s the problem. I can’t prove it for certain, but I can point to another Wordpress bug that would do the same thing to people who wrote posts that included a couple of very common Linux commands.

So, yesterday after losing over half of what I wrote AGAIN, I copied and pasted my text to a word file first before producing that damn 403 error again. I reinstalled my whole blog twice, and the same error was being produced by that specific text. I didn’t have a problem posting other test blogs, or that other super long one I put up yesterday.

Anyway, enough ranting. Without further a due, here’s a link to the word file I wrote my notes into. Topics touched on are Advanced ACL’s and the Cisco Discovery Protocol.

Now….back to the mystery that is my day of trying to remember where I put that f—ing thumb drive!! Don’t you just hate it when you lose tiny stuff like that?

Today we’re going to learn about the OSI 7-Layer Reference Model. Here’s a great link for reading about it (more links below too). This model exists for the purpose of simplifying the complex task of thinking about how data is transported over a network, and is used to help networking professionals troubleshoot problems. Here are the layers:
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Today we’re going to talk about Layers 2 and 3 of the OSI reference model.First layer 2, the Data Link Layer.

Strait from Wikipedia:
Logical Link Control Sublayer
The uppermost sublayer is Logical Link Control (LLC). This sublayer multiplexes protocols running atop the data link layer, and optionally provides flow control, acknowledgment, and error recovery. The LLC provides addressing and control of the data link. It specifies which mechanisms are to be used for addressing stations over the transmission medium and for controlling the data exchanged between the originator and recipient machines .Read more

Today we’re going to talk about Layer 4 of the OSI model, also known as the Transport Layer. The transport layer is responsible for establishing either “connectionless” or “connection oriented” conversations between two nodes. It is also responsible for flow control, congestion avoidance, and error recovery. Read more