Subnetting Question

gabrielbtoledo

Question: What is the last valid host on the subnetwork 172.19.138.0 255.255.254.0?

Got this question from an online practice test and would like to know why the answer. (I have the answer, just wanna know why. Won't post the answer now, so others learning can try at home).

Many thanks in advance.

NeonNoodle

gabrielbtoledo wrote:

Question: What is the last valid host on the subnetwork 172.19.138.0 255.255.254.0?

Got this question from an online practice test and would like to know why the answer. (I have the answer, just wanna know why. Won't post the answer now, so others learning can try at home).

Many thanks in advance.

172.19.139.254 is the last valid host.

gabrielbtoledo

Thanks for the quick reply, but that wasn't my question.
I wanna know why and I didn't want to post the answer, so other people learning could try it at home.

networker050184

Do the binary you will see why. The binary always clarifys it for me!

NeonNoodle

gabrielbtoledo wrote:

Thanks for the quick reply, but that wasn't my question.
I wanna know why and I didn't want to post the answer, so other people learning could try it at home.

Well, I and others here have posted before on how to figure out the subnet address, the broadcast address, the first host address and last host address. networker050184 just mentioned looking at the binary. That's where you should always look when trying to understand subnetting.

This thread will help you understand why

Netstudent

gabrielbtoledo wrote:

Thanks for the quick reply, but that wasn't my question.
I wanna know why and I didn't want to post the answer, so other people learning could try it at home.

255.255.254.0

254-256=2

3rd OCTET = 2,4,6,8,10..........138. Next subnet would be 140. That means that the last usable is 139.254

no brainer

gabrielbtoledo

Yeah, I always do by the binary form.
What I was actually looking for was a quicker way to find a network range without having to write down all the ranges till I get to the one I want.

See what I am saying now?

Netstudent

I learned to subnet the binary way. But after a while it gets tedious and pointless. I see the binary in my mind now so theres no real reason to write it out. Plus if you are trying to answer 55-60 questions in 90minutes, it would be advantageous to learn a quick way. But I believe one shouldn't do quick ways untill they understans what the binary logic is doing.

gabrielbtoledo

Thanks, but again. I did all 4 semesters of cisco and learned using binary, however it's been a while since I took those classes and I'm reviewing the material to take the cert test, but without a teacher.
So I did the binary form and got the answer doing range by range till I finally got to the range in question. Like this range example wasn't too difficult to guess the next range without having to do all the ranges.

Maybe I'm not seeing the big picture here. Maybe I should find the number that the subs go by and then find the next sub after the one being in question, and finally subtract 2 from the next sub. Am I in the right direction?

networker050184

Are you talking about a good way to find the subnet closest to that address? Like, you know it goes in increments of 2 but want to know how to get to the 138 faster without having to count by twos? Is that what you are asking???

gabrielbtoledo

networker050184 wrote:

Are you talking about a good way to find the subnet closest to that address? Like, you know it goes in increments of 2 but want to know how to get to the 138 faster without having to count by twos? Is that what you are asking???

You got it.

Maybe I'm doing something wrong.
I know how to find the network ID doing the ANDing. My problem is when I get a range in the middle of the subnets and have to go subnet by subnet till I get into the range.

Netstudent

gabrielbtoledo wrote:

Thanks, but again. I did all 4 semesters of cisco and learned using binary, however it's been a while since I took those classes and I'm reviewing the material to take the cert test, but without a teacher.
So I did the binary form and got the answer doing range by range till I finally got to the range in question. Like this range example wasn't too difficult to guess the next range without having to do all the ranges.

Maybe I'm not seeing the big picture here. Maybe I should find the number that the subs go by and then find the next sub after the one being in question, and finally subtract 2 from the next sub. Am I in the right direction?

Yes thats kinda how I do it. After a while you will be able to count by 2's 4's 8's 16's ect....and you will start remembering all multiples and divisors of binary numbers. It just math man. Just keep hacking away at it and things will start to open up.

networker050184

Well, unless you memorize the increments of 2, 4, 8, 16, 32....... and so on I don't really see another way. I just do it in my head for short ones, or on paper for the long ones. Usually I just use a subnet calculator in real life

gabrielbtoledo

Let me see if I get this right.
If I have to find something in some range, then:
First find by what number the subnet goes (IE 2, or 16, or 64, or ...)
Second find the network ID for that IP given
Third add the number found in step one to the network ID found in step two and you got your range.

I hope I got this right. It seems the quicker way to find the network ID, range, valid hosts and broadcast.

Netstudent

thats right. like if you had 10.10.10.202 /30 whats the broadcast address?

well /30 is 255.255.255.252

256-252 = 4

now you know 4 goes evenly into 200 because it does evenly into 100. So 200 must be a subnet number because it is a even mulitple of 4.

Next subnet is 204 so the boradcast address for 200 must be 203.

networker050184

Netstudent wrote:

thats right. like if you had 10.10.10.202 /30 whats the broadcast address?

well /30 is 255.255.255.252

256-252 = 4

now you know 4 goes evenly into 200 because it does evenly into 100. So 200 must be a subnet number because it is a even mulitple of 4.

Next subnet is 204 so the boradcast address for 200 must be 203.

You should change your name to Netteacher

gabrielbtoledo

Thanks a lot. Now it is in my head.

Netstudent

networker050184 wrote:

Netstudent wrote:

thats right. like if you had 10.10.10.202 /30 whats the broadcast address?

well /30 is 255.255.255.252

256-252 = 4

now you know 4 goes evenly into 200 because it does evenly into 100. So 200 must be a subnet number because it is a even mulitple of 4.

Next subnet is 204 so the boradcast address for 200 must be 203.

You should change your name to Netteacher

thast what my classmates say as well. I just love this stuff and I work hard. Everyone at school thinks I'm this really smart person. I'm like man, I'm no smarter than you(well maybe a a little ), I just work harder than you do.

And helping others helps me keep thigns fresh in my head. Also typing facts, is another sense that your brain uses so it helps you remember thigns. Lots of people learn by hearing, others by seeing. The more senses you can add, the more you can learn and retain.

networker050184

Everyone at work thinks I'm some kind of genious. I'm like yeah I'm good, but in reality I just google it or look it up in a book if I don't know how to do it. Ah the joys of the internet!

Netstudent

Theres nothing wrong with being resourceful. Same thing happened to me not to long ago. We were trying to get a 15 year old PBX (Meridian Option 11C) to interface with a IAD2400 router for VoIP. Well we tried DMS100 signalling and NI2 yatta yatta. OUr voice guy and our service providor technicians could not get these devices to interface. So i'm sittin there, not knowing much about Voice and PBX's, and I google it. Sure enough it comes right up on how to use S100 signalling as well as the voice switch configs. I print it out fax it to the technicians, 30 minutes later its working great.

networker050184

I use Redcom and Avya PBX. They are pretty simple to set up with T1 conects if you know what you are doing. Well, we are getting off topic here!

wait2dominate

networker050184 wrote:

You should change your name to Netteacher

Sounds like what I get in my class. I've taught VSLM to many a people

gabrielbtoledo

That means we have a great team here. One help another and vice verse.
Good job ya'll.