Need Help pls

mustafa86m · February 2015

How can I find the network ID for an ip address fast. I use this method be counting the block size , but sometimes it takes time to find the network ID for a specific IP address

Example
219.141.101.108 /29

I have to count by 8 till i get the netork ID for 108 which is 104

Is there a faster way to do that ?

Thank you

chantt · February 2015

Well if you know your block sizes you just need to memorize your 8 and 16 multiplication tables.

mustafa86m · February 2015

Thnx , but I also need to memorize 32 . 64 ... kinda hard

siggnation · February 2015

musta--

chantt is right. Memorize those multiplication tables. I wish I dedicated more time to that because I encountered the same issues during my ICND1 exam. This is one mistake I don't intend to make again, especially on ICND2.

Cheers.

chantt · February 2015

mustafa,

maybe some online tools will help you get them down to memory. maybe look into one of these free tools?

Simple free learning tools for students and teachers | Quizlet

https://www.studyblue.com/online-flashcards

You can customize this one to fit your needs, Learn: Network port number (by benzart) - Memorize.com - Remember and Understand

mustafa86m · February 2015

Thnx guys

sagarmistry · February 2015

128

64

32

16

8

4

2

1

25

26

27

28

29

30

31

32

128

192

224

240

248

252

254

255

17

18

19

20

21

22

23

24

Here is the easiest way, this way I calculated the question in under a minute.

/29 means 8 bits, and 6 usable hosts.

now about calculating to 104:

multiply by 10s, so 8 times 10 is 80, then 12 times is 96 then 13 times is 96 + 8 = 104.

So, if you get a question like this where the end octet is 108, try multiplying by 10 so u can jump start!

Jon_Cisco · February 2015

Practice is what works. You need to memorize some basic charts then just practice applying them. If you are going to take the Cisco exams you must be able to do this in your head. If you need to write it out you will most likely be pressed for time.

practice at subnetting.net don't go for speed go for accuracy the speed will come later.

HAMP · February 2015

Lol, you guys are hilarious with this memorizing chart. To the OP here is a formula I made for myself. I took part of it from somewhere and continued with my own.

The only part that I memorize is: 8.16.24.32
219.141.101.108 /29

Whatever the /## you subtract that from the next block higher than the “ .block “.
(If /23, you would subtract from .24) (if /13, you would subtract from .16)

In your example, its /29, so we subtract from .32

32 – 29 = 3
2 ^ 3 = 8
Whichever block you used to subtract from, you use that number from the IP address. In our example, you subtracted from the last block, which was 108.

Take the IP number and divide it by the answer from ( 2 ^ 3 = 8 )
108 / 8 = 13.5

BUT, you don’t have to do the complete division, just stop before the .5, and only use the full number before the “.” And multiply it by what you divide it by, which was the “8”
13 * 8 = 104

Sounds long because I was explaining but it is something you can do in your head without paper and pen, and it only take seconds to do.

8.16.24.32

192.168.56.25 /20
(24 - 20=4)
(2 ^ 4=16 ) <-- Block size is 16
(56 / 16=3.5 ) <-- we don’t need the .5
(16 * 3=48 ) Our network is 192.168.48.0 /20

Forget memorizing(pun intended), do the math!!!

Heero · February 2015

mustafa86m wrote: »

Example
219.141.101.108 /29

I have to count by 8 till i get the network ID for 108 which is 104

Is there a faster way to do that ?

108 divided by 8, rounded down is 13. 8 multiplied by 13 is 104.

jamthat · February 2015

HAMP wrote: »

Lol, you guys are hilarious with this memorizing chart. To the OP here is a formula I made for myself. I took part of it from somewhere and continued with my own.

The only part that I memorize is: 8.16.24.32
219.141.101.108 /29

Whatever the /## you subtract that from the next block higher than the “ .block “.
(If /23, you would subtract from .24) (if /13, you would subtract from .16)

In your example, its /29, so we subtract from .32

32 – 29 = 3
2 ^ 3 = 8
Whichever block you used to subtract from, you use that number from the IP address. In our example, you subtracted from the last block, which was 108.

Take the IP number and divide it by the answer from ( 2 ^ 3 = 8 )
108 / 8 = 13.5

BUT, you don’t have to do the complete division, just stop before the .5, and only use the full number before the “.” And multiply it by what you divide it by, which was the “8”
13 * 8 = 104

Sounds long because I was explaining but it is something you can do in your head without paper and pen, and it only take seconds to do.

8.16.24.32

192.168.56.25 /20
(24 - 20=4)
(2 ^ 4=16 ) <-- Block size is 16
(56 / 16=3.5 ) <-- we don’t need the .5
(16 * 3=48 ) Our network is 192.168.48.0 /20

Forget memorizing(pun intended), do the math!!!

This is how I've done it as well..it's amazingly simple once you get the hang of it. Subnetting pretty much anything in a matter of seconds in your head is oddly impressive to a lot of people..learn this method!

mikeybinec · February 2015

mustafa86m wrote: »

How can I find the network ID for an ip address fast. I use this method be counting the block size , but sometimes it takes time to find the network ID for a specific IP address

Example
219.141.101.108 /29

I have to count by 8 till i get the netork ID for 108 which is 104

Is there a faster way to do that ?

Thank you

my thing is 256 - (the block size). In your case it's a /29 = 248. 256 - 248 = 8.. How many 8s can i fit in 108 without going over?.. as you said the club or gang ID is 104. The suggestions that you memorize the block sizes is spot on. I guarantee you, you will be able to subnet in 15 seconds once you recall block sizes.

But here's a curveball for future digestion: Let's say the setup is you have to find the 4th or 5th subnet but the router is set for no subnet zero.. YIKES!~!

HAMP · February 2015

mikeybinec wrote: »

my thing is 256 - (the block size). In your case it's a /29 = 248. 256 - 248 = 8.. How many 8s can i fit in 108 without going over?.. as you said the club or gang ID is 104. The suggestions that you memorize the block sizes is spot on. I guarantee you, you will be able to subnet in 15 seconds once you recall block sizes.

But here's a curveball for future digestion: Let's say the setup is you have to find the 4th or 5th subnet but the router is set for no subnet zero.. YIKES!~!

That doesn't sound like a curve ball it sounds like a different question. lol

Still do the math, Multiple the block size by which subnet you are asking about, which is just as easy.

Need Help pls

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