VLSM and network ID

[Kn1ghtR1d3rOfD00m]

hi friends, 

Im quite confusing about this topic, I have seen many videos, many techniques and even cisco documents but they seem to be obscure when teaching you, 

in the exam you dont have time to make a bunch of charts, just the basic which from time to time, and practice, you start memorizing the bits and dotted decimal and binary as well to check the increments and all that, 

so, my question is this, 

one of the instructors gave us this address: 10.16.158.0/11

and we are studying VLSM, 

so the request is as follows: 

a subnet of 800 host

a subnet of 300

a subnet of 115

a subnet of 105

a subnet of 80

and a subnet of 65

the first thing he stated is that we need to check if the IP address given is a broadcast, network ID or host.

so after a bit of discussion with the team, he started asking us if this was a host or network id, 

IP address in question: 
10.16.158.0/11

I said network id, but at the end he said it was a host, how come?

and at the end of the excercise he started subnetting with VLSM from 
10.0.0.0/22 

I know where the /22 comes from, cause its from the first subnet requirement for 800 bits, but why from 10.0.0.0 and not from 10.16.X.X something?

does anyone can clarify if Im mis understanding the concept cause its 2 in 1 here, 

first I need to know if its a broadcast, network or host

and second of all, I need to do the systematic process of VLSM which I quite understand, but it confuses me the part where I ned to know the network or host or broadcast in this particular example.

can you please explain ?

im trying to do the best of my abilities to understand but its very hard and Im not asking to make the example, all the subnets, just clarify me why from 10.0.0.0 

regards, 

[Jon Marshall · Accepted solution]

/11 means 255 for the first octet (all 8 bits) + 3 from the second octet so the mask is 255.224.0.0 

A quick way to work out what the subnet increments are is to subtract the first non 255 octet from 256 so - 

256 - 224 = 32 so your subnets go up in 32's eg - 

10.0.0.0/11
10.32.0.0/11
10.64.0.0/11
etc ...

looking at the above you can see that 10.16.158.0/11 falls between the first two subnets so it has to be a host address. 

In addition you can see the first subnet is indeed 10.0.0.0/11 which can the be further subnetted down using VLSM if that is what you need. 

Jon

[Kn1ghtR1d3rOfD00m]

hthank you so much, 

really, I was out of my mind and could not see it, the way you put it, I get it now, 

very strange, but I see it now, 

I will keep practicing and focus on not to read a lot of resources that might be more confusing to me

thanks so much for your help,