false positives that result from the different tools that we use. Monitoring and valida‐
tion are essential to make sure that what you are presenting to your employer or cus‐
tomer is valid as well as actionable. Remember, you are trying to help them improve
their security posture, not just point out where things are broken.
Layers
As Donkey in the movie
Shrek
suggests, layers are important. Actually, Shrek says that
ogres have layers, and Donkey says cakes have layers, but Shrek likens ogres to
onions, and cake is better than onions. Plus, I still hear Eddie Murphy as Donkey say‐
ing cakes have layers. None of which is really the point, of course. Except for cake.
Cake may be the point—because when we talk about networks and communications
between systems, we usually talk about layers. If you think about a seven-layer cake,
with thin layers of cake, you may be able to envision the way we think about net‐
works. Plus, in order to envision the best process, you’d need to envision two slices of
cake. Two slices of cake have to be better than one slice of cake, right?
Figure 2-3
shows a simple representation of the seven layers of the OSI model and
how each layer communicates with the same layer on remote systems. You can imag‐
ine that the lines between each of the layers is really icing and maybe jam, just to
make it more interesting. Plus, the jam will help the layers adhere to one another
since it’s sticky. Each layer on every system you are communicating with is exactly the
same, so when you are sending a message from one slice of cake to the other slice of
cake, it’s the same layer that receives it.
Figure 2-3. OSI model showing system-to-system communication
Let’s think about it this way. Our first layer at the very bottom is the
physical layer
, so
we can think of that as pistachio. Our pistachio (physical) layer is where we connect
to the network or, in this case, the plate that the cake sits on. As with cake, nothing is
