Our next topic is variable length subnet masking
even though it sounds challenging and complicated. It's very simple.
It does require an understanding of the material we've discussed in previous sections of this chapter.
It's just submitting based on number of hosts or on number of subnets
were either submitting to steal additional ones or additional zeros.
Variable length subnet masking means each subnet. It can use its own sub net mask.
If you have a larger departments within your organization,
you don't have to have a one size fits all mask for your whole company.
If you have 2000 hosts to support in one sub net and 15 and another, it doesn't make sense to use the same sub net.
This goes back to the days where routers only understood the classical add dressing scheme we discussed
when we didn't have a lot of flexibility with R. I. P addresses.
That was a long time ago.
Variable length subnet masking allows us to figure out what's necessary at each network and use the appropriate mask.
In this instance, we started off with an I P address on the 172.30 point 232.0 network,
I'm making a mental note of that.
We can also see here how many devices each network needs to support.
And I'm thinking of binary zeros.
I need 57 devices in the binary zeros.
I know that in order to make this happen, I'll need to use a sub net mask.
So let's jump over to the answers.
I'll need to steal 40 sat six bits to zero
for HR. I only need 23 devices,
so I'll set five bits to zero to the power of five. Minus two
30 to minus two means 30 devices would be supported.
I need 12 devices in it and to support 12. I'll steal four bits and four bits will be set to zero.
The remaining would be set to one, so I have 28 ones
then. Our Finance department has 32 devices.
We use the slash 26 mask again.
Marketing uses nine devices and also the 20 bit mask.
In this case, each department gets their own mask. Nothing too exciting
for the next question. It's assuming we want to contain all of these on a single network and forget about submitting.
We'll bring them back into the fold without sacrificing any more host addresses than we have to.
The idea here is if you go with slash 26 were choosing the smallest number of binary ones because it's going to encompass the greatest number of host addresses.
If you have an environment where there is a variable length subnet masking, then the question arises that says, Incorporate all of them on the same network.
Choose the lowest address.