Network+ – 4/22/2008

Now that we’ve talked about the OSI model (you do have all seven layers memorized, right??), we talked today about the real-life implementation of that in the most common networking protocol we see today, TCP/IP. To do that, we compared the OSI to the Department of Defense (DoD) model. Doing that we were able to line up various aspects of the TCP/IP protocol to the varying functionalities that the DoD set out to accomplish in their model.

The point of all this talk is to show you specifically what each of these differing technologies do. For example, the TCP/IP ARP tool exists on OSI Level 3 (the Network layer). We know that OSI3 is responsible for directing data packets to the various different destination points they are headed to. Knowing that ARP is responsible for showing us what MAC addresses are assigned to which IP address, it makes sense that ARP would exist on the layer responsible for making sure data gets to where it’s going.

On the OSI 5- 7 layers, we specifically talked about several tools that TCP/IP provide us with and discussed what many of them actually do. In addition, we went over the default port numbers that each of these tools use (FTP uses port 21, DNS uses port 53, etc.). It would do you a lot of good to know which tools use which port numbers (if they aren’t in your book, they are listed in the handout for chapter 3, downloadable on your right).

Homework:

• Chapter 3: Review Questions
• Make sure you know OSI and port numbers for next week!