DH Guide: Subnet Masking

***Zardon*** · Sep 28, 2004, 01:22 PM

Forum member Greg "Gutterpunk" Suhr has put together a rather indepth guide detailing subnet masking.

When hearing Subnet Masking, most people just cringe because of the horror stories that are shared throughout networking. In actuality it is fairly simple. The main things you need to understand are:

Binary to decimal conversions, and decimal to binary
Understanding on how to separate network bits to host bits
A brief understanding of the different classifications of IP addresses

In this guide I will cover each of these aspects starting with converting binary to decimal and visa versa. In subnet masking you work with a series of 4 bytes each byte separated by a decimal. This makes up your IP Address. Remember 1 bit = 8 bytes. So each Address contains 8 bytes or 4 bits.

read here

Gardinen · Sep 28, 2004, 01:47 PM

On Cisco 2600 series routers, you can you the [subnet zero] command in order to use the first subnet.

Vidmaster23 · Sep 28, 2004, 02:44 PM

Very good guide.

Some good additions to this guide would be Hexidecimal to binary and Binary to hexidecimal.

No_Style · Sep 28, 2004, 03:22 PM

Nice. Very nice!

I'm taking CISCO now, and a lot of people will benefit from this in my class. I've referred one to your guide. LOL If you could get VLSM/CIDR subnet masking in that would be even better!

Oh, and the 2 subnets not being used aren't really illegal when doing regular subnetting, it's just that one is for broadcasting all the networks and the other is used to ID the network, I believe.

VLSM/CIDR allows you to use those "illegal" subnets. VLSM is basically it's subnetting a subnet. Funky stuff. While CIDR is subnetting a subnet, but also borrowing more than the alotted 8 bits.

Manual subnetting isn't hard, but if you make a mistake it can be brutal which is why subnet calculators are around.

germanjulian · Sep 28, 2004, 04:05 PM

nice read. thank god this semester I am learning TCP/IP fully!!!! fully i mean fully...

Falstaff · Sep 28, 2004, 04:34 PM

looks like gold medal work to me. but then he always paid attention in class. LOL

drakesteakn · Sep 28, 2004, 06:00 PM

he doesn't pay attention in class. he plays vid games. he just learns quick. nice work greg. i really enjoyed reading it

GutterPunk · Sep 28, 2004, 06:14 PM

they are illegal because you cannot use them for an actual network

and thanks for the comments i worked pretty hard on this puppy

Axel Foley · Sep 28, 2004, 06:21 PM

Quote:

In this guide I will cover each of these aspects starting with converting binary to decimal and visa versa. In subnet masking you work with a series of 4 bytes each byte separated by a decimal. This makes up your IP Address. Remember 1 bit = 8 bytes. So each Address contains 8 bytes or 4 bits.

Nice job, just a couple of things:

1. The beginning of the article, which I quoted above, confuses bits and bytes (1 byte=8 bits).

2. An IP address is 4 bytes (32 bits).

A beginner would get confused by reading the rest of the article if these two simple things aren't correctly explained.

Anyway good job Greg, keep it up.

GutterPunk · Sep 28, 2004, 06:35 PM

ooops lol.... 4 bytes or 32 bits... i didnt really get them confused just messed up lol thx for pointing that out

BWX · Sep 28, 2004, 09:16 PM

Wow, nice guide/ info.

...will have to paste it into a text doc and study it, lots of info there.

kbleft · Sep 28, 2004, 09:32 PM

Also, the conversion between binary and decimal is not explained correctly at all. When discussing conversion from binary to decimal, the article has a table on the first page where the values of the binary digits are converted to decimal numbers 0 through 7 and then those numbers are squared. For example, the first line of the table states 1*7^2=128. This explanation is totally wrong.

Each binary digit represents a power of two. The digits correspond to the following powers of two from left to right: 7 6 5 4 3 2 1 0. Thus, on the lefthand side, the digit represents a possible increment of 2^7 or 128. Likewise, the second digit from the left represents a possible increment of 2^6 or 64, and so on. The digit on the right represents a possible increment of 2^0 or 1. The values of binary digits can be either 0 or 1. Accordingly, for the first digit on the lefthand side, a value of 1 represents an increment of 128, while a value of 0 represents no increment of 128. Thus, the proper expression for the decimal value of the Jth digit is either (0*2^J) or (1*2^J). It is never, ever, 1*7^2.

No_Style · Sep 28, 2004, 09:35 PM

Quote:

Originally Posted by GutterPunk

they are illegal because you cannot use them for an actual network

and thanks for the comments i worked pretty hard on this puppy

I would have said "unusable" or "reserved" instead of "illegal" because it makes it sound like some kind of crime if you do.

You can use the first network on a VLSM/CIDR network though or when you enable "ip subnet zero" on a router. With IOS version 12 and up its enabled by default. What semester of CISCO are you at? As you learn more and more, you'll realize how much the Internet was based on a foundation of poor planning.

Again, good work on the whole run down of it

P.S - Here's a nice document for those who want a nice charts relating to subnetting from Cisco! It will compliment Greg's work really really nicely!

Falstaff · Sep 28, 2004, 11:00 PM

I know it sounds cheezy but I used the calculator in windows accessories to do the conversions.

GutterPunk · Sep 28, 2004, 11:51 PM

Quote:

Originally Posted by kbleft

Also, the conversion between binary and decimal is not explained correctly at all. When discussing conversion from binary to decimal, the article has a table on the first page where the values of the binary digits are converted to decimal numbers 0 through 7 and then those numbers are squared. For example, the first line of the table states 1*7^2=128. This explanation is totally wrong.

Each binary digit represents a power of two. The digits correspond to the following powers of two from left to right: 7 6 5 4 3 2 1 0. Thus, on the lefthand side, the digit represents a possible increment of 2^7 or 128. Likewise, the second digit from the left represents a possible increment of 2^6 or 64, and so on. The digit on the right represents a possible increment of 2^0 or 1. The values of binary digits can be either 0 or 1. Accordingly, for the first digit on the lefthand side, a value of 1 represents an increment of 128, while a value of 0 represents no increment of 128. Thus, the proper expression for the decimal value of the Jth digit is either (0*2^J) or (1*2^J). It is never, ever, 1*7^2.

Wow I mustve mixed it up good call, as you are right... i dunno what i was thinking good thing i showed both ways... but I was thinking i had someone try to teach it to me that way thanks will be fixed

Falstaff · Sep 29, 2004, 03:18 AM

You put so much work into that Greg, and you ignored your women, tsk tsk....
more for me, woo hoo

GutterPunk · Sep 29, 2004, 11:19 AM

I proof read it so many times cant believe i didnt catch those

tek · Sep 29, 2004, 11:42 AM

I'm currently in a Cisco class, and we learned about all this stuff (binary to decimal, etc) in Module 1 (chapter 1). Pretty simple stuff... just use the Windows Calculator... lol

GutterPunk · Sep 29, 2004, 01:32 PM

the conversions are easy the stupid address space assigning sucks... it took me awhile to get the hang of it, but once you understand it, your golden

Chaos · Sep 29, 2004, 02:12 PM

excellent guide GutterPunk, takes me back to TCP/IP classes of my MCSE training (shudders)

Falstaff · Sep 30, 2004, 01:50 AM

now you got time for women greg....lol

GutterPunk · Sep 30, 2004, 12:01 PM

Lol, I always have time for a good woman

SiikMiike · Sep 30, 2004, 07:58 PM

do you guys really read all this?

BWX · Sep 30, 2004, 10:10 PM

Quote:

Originally Posted by SiikMiike

do you guys really read all this?

DUDE-- you can't use a sig that big.. read the rules.

mtsaint · Aug 27, 2006, 02:56 PM

wow...im going to eat some cheetoes now

Sep 28, 2004, 01:22 PM	#1
*Zardon* enchanted Join Date: May 2002 Location: Driverheaven Posts: 32,252 Rep Power: 3150	DH Guide: Subnet Masking Forum member Greg "Gutterpunk" Suhr has put together a rather indepth guide detailing subnet masking. When hearing Subnet Masking, most people just cringe because of the horror stories that are shared throughout networking. In actuality it is fairly simple. The main things you need to understand are: Binary to decimal conversions, and decimal to binary Understanding on how to separate network bits to host bits A brief understanding of the different classifications of IP addresses In this guide I will cover each of these aspects starting with converting binary to decimal and visa versa. In subnet masking you work with a series of 4 bytes each byte separated by a decimal. This makes up your IP Address. Remember 1 bit = 8 bytes. So each Address contains 8 bytes or 4 bits. read here

Sep 28, 2004, 02:44 PM	#3
Vidmaster23 DriverHeaven Junior Member Join Date: Dec 2003 Location: Virginia Posts: 77 Rep Power: 0	Very good guide. Some good additions to this guide would be Hexidecimal to binary and Binary to hexidecimal. __________________ My System: Athlon 51-FX @ 2.2ghz Asus SK8N 1 gig of PC3200 Mushkin DDR Radeon 9700 Pro Twin 80gig 7200RPM HD's

Sep 28, 2004, 03:22 PM	#4
No_Style Styleless Wonder Join Date: Jun 2002 Location: Ottawa, Ontario Posts: 6,049 Rep Power: 0	Nice. Very nice! I'm taking CISCO now, and a lot of people will benefit from this in my class. I've referred one to your guide. LOL If you could get VLSM/CIDR subnet masking in that would be even better! Oh, and the 2 subnets not being used aren't really illegal when doing regular subnetting, it's just that one is for broadcasting all the networks and the other is used to ID the network, I believe. VLSM/CIDR allows you to use those "illegal" subnets. VLSM is basically it's subnetting a subnet. Funky stuff. While CIDR is subnetting a subnet, but also borrowing more than the alotted 8 bits. Manual subnetting isn't hard, but if you make a mistake it can be brutal which is why subnet calculators are around. __________________ "The Best Style Is No Style" Specifications Here Last edited by No_Style; Sep 28, 2004 at 03:32 PM.

Sep 28, 2004, 04:05 PM	#5
germanjulian Back in London Join Date: Jul 2003 Location: London Posts: 1,794 Rep Power: 0	nice read. thank god this semester I am learning TCP/IP fully!!!! fully i mean fully... __________________ /\|\ Asus P5W DH Deluxe, Intel C2D E6600, 2GB Corsair XMS2-6400C4 DDR2, E-VGA GeForce 7800 GT, Creative X-Fi Extreme Music, 500GB Seagate 7200.10 SATA, Lian Li PC-V1100 Aluminum Case Black, etc. http://germanjulian.com /\|\

Sep 28, 2004, 04:34 PM	#6
Falstaff Old Codger Join Date: Sep 2002 Location: USAFA Posts: 18,137 Rep Power: 131	looks like gold medal work to me. but then he always paid attention in class. LOL __________________ The tallest blade of grass is the first to be cut by the scythe.

Sep 28, 2004, 01:47 PM	#2
Gardinen DriverHeaven Senior Member Join Date: Feb 2003 Location: Trollhättan, Sweden Posts: 512 Rep Power: 0	On Cisco 2600 series routers, you can you the [subnet zero] command in order to use the first subnet.

Sep 28, 2004, 06:00 PM	#7
drakesteakn boo!!!! Join Date: Aug 2003 Location: Ft. Meyers, FL Posts: 2,042 Rep Power: 44	he doesn't pay attention in class. he plays vid games. he just learns quick. nice work greg. i really enjoyed reading it __________________

Sep 28, 2004, 06:14 PM	#8
GutterPunk I = Greatest Dood Join Date: Nov 2003 Location: Nebraska Posts: 5,945 Rep Power: 54	they are illegal because you cannot use them for an actual network and thanks for the comments i worked pretty hard on this puppy __________________ Rock On \m/ Thank you Mousey for the Sig! --------------- Intel Core2Duo E6660 (3.4GHZ) ~ Tuniq Tower 120 ~ Enermax Galaxy 1000W ~ Corsair Dominator @ 1090MHZ 5-5-5-15 (OCZ XTC Modded Cooler)~ EVGA 8800GTX W/ HR-03 Plus 120MM ~ Asus DVD-RW LiteScribe ~ LG DVD-RW ~ Corsair Voyager 2GB ReadyBoost Drive ~ Vantec Nexus Fan Controller ~ ThermalTake Armor 25CM fan ~ Personal Finance Blog: Dent Your Debt

Sep 28, 2004, 06:35 PM	#10
GutterPunk I = Greatest Dood Join Date: Nov 2003 Location: Nebraska Posts: 5,945 Rep Power: 54	ooops lol.... 4 bytes or 32 bits... i didnt really get them confused just messed up lol thx for pointing that out __________________ Rock On \m/ Thank you Mousey for the Sig! --------------- Intel Core2Duo E6660 (3.4GHZ) ~ Tuniq Tower 120 ~ Enermax Galaxy 1000W ~ Corsair Dominator @ 1090MHZ 5-5-5-15 (OCZ XTC Modded Cooler)~ EVGA 8800GTX W/ HR-03 Plus 120MM ~ Asus DVD-RW LiteScribe ~ LG DVD-RW ~ Corsair Voyager 2GB ReadyBoost Drive ~ Vantec Nexus Fan Controller ~ ThermalTake Armor 25CM fan ~ Personal Finance Blog: Dent Your Debt

Sep 28, 2004, 09:16 PM	#11
BWX Spinal Tapped Join Date: Nov 2002 Location: USNY Posts: 19,566 Rep Power: 90 System Specs	Wow, nice guide/ info. ...will have to paste it into a text doc and study it, lots of info there. __________________ One Big Ass Mistake America

Sep 28, 2004, 09:32 PM	#12
kbleft DriverHeaven Junior Member Join Date: Jun 2002 Posts: 88 Rep Power: 0	Also, the conversion between binary and decimal is not explained correctly at all. When discussing conversion from binary to decimal, the article has a table on the first page where the values of the binary digits are converted to decimal numbers 0 through 7 and then those numbers are squared. For example, the first line of the table states 17^2=128. This explanation is totally wrong. Each binary digit represents a power of two. The digits correspond to the following powers of two from left to right: 7 6 5 4 3 2 1 0. Thus, on the lefthand side, the digit represents a possible increment of 2^7 or 128. Likewise, the second digit from the left represents a possible increment of 2^6 or 64, and so on. The digit on the right represents a possible increment of 2^0 or 1. The values of binary digits can be either 0 or 1. Accordingly, for the first digit on the lefthand side, a value of 1 represents an increment of 128, while a value of 0 represents no increment of 128. Thus, the proper expression for the decimal value of the Jth digit is either (02^J) or (12^J). It is never, ever, 17^2.

Sep 28, 2004, 11:00 PM	#14
Falstaff Old Codger Join Date: Sep 2002 Location: USAFA Posts: 18,137 Rep Power: 131	I know it sounds cheezy but I used the calculator in windows accessories to do the conversions. __________________ The tallest blade of grass is the first to be cut by the scythe.

Sep 29, 2004, 03:18 AM	#16
Falstaff Old Codger Join Date: Sep 2002 Location: USAFA Posts: 18,137 Rep Power: 131	You put so much work into that Greg, and you ignored your women, tsk tsk.... more for me, woo hoo __________________ The tallest blade of grass is the first to be cut by the scythe.

Sep 29, 2004, 11:19 AM	#17
GutterPunk I = Greatest Dood Join Date: Nov 2003 Location: Nebraska Posts: 5,945 Rep Power: 54	I proof read it so many times cant believe i didnt catch those __________________ Rock On \m/ Thank you Mousey for the Sig! --------------- Intel Core2Duo E6660 (3.4GHZ) ~ Tuniq Tower 120 ~ Enermax Galaxy 1000W ~ Corsair Dominator @ 1090MHZ 5-5-5-15 (OCZ XTC Modded Cooler)~ EVGA 8800GTX W/ HR-03 Plus 120MM ~ Asus DVD-RW LiteScribe ~ LG DVD-RW ~ Corsair Voyager 2GB ReadyBoost Drive ~ Vantec Nexus Fan Controller ~ ThermalTake Armor 25CM fan ~ Personal Finance Blog: Dent Your Debt

Sep 29, 2004, 11:42 AM	#18
tek DriverHeaven Senior Member Join Date: May 2003 Location: Boston, US Posts: 2,103 Rep Power: 0	I'm currently in a Cisco class, and we learned about all this stuff (binary to decimal, etc) in Module 1 (chapter 1). Pretty simple stuff... just use the Windows Calculator... lol __________________ [COLOR=White][/COLOR]

Sep 29, 2004, 01:32 PM	#19
GutterPunk I = Greatest Dood Join Date: Nov 2003 Location: Nebraska Posts: 5,945 Rep Power: 54	the conversions are easy the stupid address space assigning sucks... it took me awhile to get the hang of it, but once you understand it, your golden __________________ Rock On \m/ Thank you Mousey for the Sig! --------------- Intel Core2Duo E6660 (3.4GHZ) ~ Tuniq Tower 120 ~ Enermax Galaxy 1000W ~ Corsair Dominator @ 1090MHZ 5-5-5-15 (OCZ XTC Modded Cooler)~ EVGA 8800GTX W/ HR-03 Plus 120MM ~ Asus DVD-RW LiteScribe ~ LG DVD-RW ~ Corsair Voyager 2GB ReadyBoost Drive ~ Vantec Nexus Fan Controller ~ ThermalTake Armor 25CM fan ~ Personal Finance Blog: Dent Your Debt

Sep 29, 2004, 02:12 PM	#20
Chaos Number Nine Join Date: May 2002 Location: Nova Scotia Posts: 5,176 Rep Power: 94 System Specs	excellent guide GutterPunk, takes me back to TCP/IP classes of my MCSE training (shudders) __________________

Sep 30, 2004, 01:50 AM	#21
Falstaff Old Codger Join Date: Sep 2002 Location: USAFA Posts: 18,137 Rep Power: 131	now you got time for women greg....lol __________________ The tallest blade of grass is the first to be cut by the scythe.

Sep 30, 2004, 12:01 PM	#22
GutterPunk I = Greatest Dood Join Date: Nov 2003 Location: Nebraska Posts: 5,945 Rep Power: 54	Lol, I always have time for a good woman __________________ Rock On \m/ Thank you Mousey for the Sig! --------------- Intel Core2Duo E6660 (3.4GHZ) ~ Tuniq Tower 120 ~ Enermax Galaxy 1000W ~ Corsair Dominator @ 1090MHZ 5-5-5-15 (OCZ XTC Modded Cooler)~ EVGA 8800GTX W/ HR-03 Plus 120MM ~ Asus DVD-RW LiteScribe ~ LG DVD-RW ~ Corsair Voyager 2GB ReadyBoost Drive ~ Vantec Nexus Fan Controller ~ ThermalTake Armor 25CM fan ~ Personal Finance Blog: Dent Your Debt

Sep 30, 2004, 07:58 PM	#23
SiikMiike DriverHeaven Junior Member Join Date: Oct 2004 Location: California Posts: 60 Rep Power: 0	=Ã¦ do you guys really read all this?

Aug 27, 2006, 02:56 PM	#25
mtsaint DriverHeaven Addict Join Date: Aug 2006 Posts: 257 Rep Power: 0	wow...im going to eat some cheetoes now