All right, let's go ahead and go through these challenge questions. It's important for us to
be able to do DSCP translation because as we'll see when it comes to SD-WAN configurations,
there are places where we actually have to enter decimal values. So it is actually important for
us studying SD-WAN to be able to look at a per-hop behavior and be able to figure out what
those decimal values are and vice versa. So first of all, what are the decimal equivalents here,
number one, of AF31 as well as AF43. All right, so remember our equation. This is very important.
It's 8x plus 2y is going to give us the decimal value. We also have x and y in this order.
So with AF31, it's going to be 3 times 8 plus 1 times 2. So that's 24 plus 2, and that would be
26. AF43 is 4 times 8 plus 3 times 2. So that's going to be 32 plus 6. That would be 38. It's as
simple as that. If we can remember this formula, yeah, we're going to have to do some algebra,
plug in some values in, but we don't have to like try to remember the bits or anything like that.
It's just remember the equation and we'll be good to go. Now number two, there's no equation for
this. What's the decimal equivalent of DSCPEF? This is simply going to be the highest value we
can use before we get to 48 and above. Now I didn't specifically talk about that. I just said
there are reasons for this, but that is the reason. It's essentially saying, hey, remember AF values
only use even values. We lock that last bit into zero. So it's the highest even value we can get to.
Whereas in traditional networking, 6 and 7 are reserved for network control traffic,
and if we multiply that out by 8, that means it starts at 48. So that's why we can't use 48,
but we want to use the highest even value. So if that helps us remember, then so be it.
Otherwise, just remember that EF is 46. Now three, we're asked to work backwards here. What AF value
applies to DSCP18? Well, remember what we said. We're going to pull out as many 8s as possible.
So what's the X value? What's the Y value? Pull out as many 8s. How many 8s are in here? I would
say there's two 8s. So X is 2. That's the number of 8s in there. If I subtract two 8s, that leaves
me with 2. How many 2s are in there? Just one. So this applies to AF21. That is how we can work our
way backwards. Now next, this starts to get interesting. Which packet is given higher priority,
AF11 or AF41? First and foremost, we always pay attention to the priority value, and remember,
higher numbers are better when it comes to priority. So AF41 will always be given higher
priority, and also remember that as important as EF is, AF4X is right behind it, and this is why we
apply video, especially like video conferencing, into this category. But 5 gets a little more
interesting because now we're asking about AF21 versus AF22, and we'd say, well, look at the
priority value. Well, the priority value is the same, so now what? Well, we might also just assume that
the higher number is the higher priority or given the higher treatment level, but in this case, AF21
is given better treatment. Why is that? Well, we have to remember what Y represents. Y represents
droppability, and so the higher the value, the higher the droppability or the higher the drop
rate. So AF22 will get dropped at a higher rate than AF21, and therefore AF21 is given
better treatment. Now lastly, number 6, I already answered part of this, which PHBs are typically
assigned. Actually, I already answered all of this. VoIP and video traffic, voice over IP traffic is given
to EF, video right there is given to AF4X. So that was a very quick overview of some really
important questions, so these will really help cement our understanding of DSCP tags, and again,
it's going to be important as we get into configuration and we start looking at how
exactly to configure this in SD-WAN, we might actually need to know that, hey, if I want to
assign AF43, that I have to plug in decimal 38. So it's very important we can do all of these
challenge questions. If any of these tripped us up, then just, you know, give ourselves some examples.
Calculate out AF42, for example, and see if we can get there, and then do a quick search to make
sure that we got those values correct. I hope this has been informative for you, and I'd like to thank
you for viewing.