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Old 11-17-2008, 03:02 PM   #1
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Default Subnet Masks

I have a test in my Intro to Networking class Wednesday, and the instructor hasn't fully taught me about these Subnet Masks, but it is on the test.

In our study guide (its community college), he has these questions written:

- How does subnetting work?
- What is the subnet mask and how does it provide information regarding the associated IP address?
- What is supernetting?
- What is the host address of the following IP addresses (assuming default subnet mask is used) : 125.125.250.45, 120.125.250.75, and 194.194.150.20?
- Is the following subnet mask valid: 255.255.255.16
- How many subnets are possible with the subnet maks below, and how many hosts are available per subnet: 255.255.255.128?
- Same question: 255.255.192.0?
- Given the following IP address and subnet mask, what ist he host and network address of each: 192.168.1.25 using subnet mask of 255.255.255.0?

If you guys can help me out some, that would be wonderful.
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Old 11-17-2008, 03:45 PM   #2
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Default Re: Subnet Masks

I assume this is CCNA? you should have access to watch the tutorials online, they explain it alot better than I can.
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Old 11-17-2008, 03:49 PM   #3
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Default Re: Subnet Masks

http://www.google.co.uk/search?hl=en...G=Search&meta=
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Old 11-17-2008, 04:01 PM   #4
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Default Re: Subnet Masks

Its just an Introduction to Networking class.

I would rather not have links than explanations, I can wiki and google stuff myself thanks.
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Old 11-17-2008, 05:40 PM   #5
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Default Re: Subnet Masks

Quote:
Originally Posted by Antdemo View Post
Snobby response, no?
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Old 11-17-2008, 09:59 PM   #6
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Default Re: Subnet Masks

Quote:
Originally Posted by ~NeonFire~ View Post
Snobby response, no?
+1

Thats absoultely pathetic. He is here asking help. As Members, we are here to help others. Not by posting smart ass replies. He has a good question, And, (Antdemo), if you can't give any USEFUlL information and/or help, then I see no reason why you should even post.

I agree with David, If you have access to tutorials, use them.
Good Luck!
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Old 11-17-2008, 10:36 PM   #7
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Default Re: Subnet Masks

Yeah, I hate when people just direct me to a google/wiki link. It is the same thing as insulting my intelligence, like I don't know how to use a search engine or Wikipedia.

I will look up some tutorials/lessons online, I didn't know if anyone on here had a better way of explaining it or not, thanks fellows.
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Old 11-18-2008, 07:59 AM   #8
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Default Re: Subnet Masks

It basically just means that he doesn't know what he's talking about.


Quote:
- How does subnetting work?
first you must understand what an IP address is, an IP address (eg. 10.0.0.1 is a decimal representation of four 8 bit binary numbers. in the example of 10.0.0.1 the binary is
00001010 . 00000000 . 00000000 . 00000001

a subnet is noted in the same way, (four decimal numbers represent four binary octets).

for example 255.0.0.0 (class A networks subnet)
is
11111111 . 00000000 . 00000000 . 00000000

these two numbers work together to show the address space on a network.
the way this works is that the numbers undergo a AND opperation to determine the complete address space.
(and operation means that result is only true eg 1 & 0=0 1 & 1=1)

00001010 . 00000000 . 00000000 . 00000001
11111111 . 00000000 . 00000000 . 00000000 (bitwise AND opperation)
---------------------------------------------
00001010 . 00000000 . 00000000 . 00000000
10.0.0.0 - 10.255.255.255 is the address space as any address inside of that range gives the same resultant with the bitwise AND opperation

another example

172.16.0.5
with the subnet 255.255.0.0
IP = 10101100 . 00010000 . 00000000 . 00000101
SUB 11111111 . 11111111 . 00000000 . 00000000

result of bitwise and

10101100 . 00010000 . 00000000 . 00000000

another address in the same range
172.16.254.1 (with same subnet)

10101100 . 00010000 . 11111110 . 00000001 (ip)
11111111 . 11111111 . 00000000 . 00000000 (subnet)
10101100 . 00010000 . 00000000 . 00000000 (bitwise and result)

the bitwise and result is in the same, so you know it's in the same subnet.

however, 192.17.0.1 / 255.255.0.0 looks like this
10101100 . 00010001 . 00000000 . 00000001 (ip)
11111111 . 11111111 . 00000000 . 00000000 (subnet)
10101100 . 00010001 . 00000000 . 00000000 (resultant)

here the resultant is different so you know it's not in the same subnet

of course subnets needn't just stay as 255.0.0.0 (class A) 255.255.0.0 (class B) or 255.255.255.0 (Class C).

you can use other subnets to divide ranges
for example 16.8.2.4 with subnet 255.255.255.254
00010000 . 00001000 . 00000010 . 00000100 (IP)
11111111 . 11111111 . 11111111 . 11111110 (subnet)
00010000 . 00001000 . 00000010 . 00000100 (resultant)
it's on the same address as 16.8.2.5
00010000 . 00001000 . 00000010 . 00000101 (IP)
11111111 . 11111111 . 11111111 . 11111110 (subnet)
00010000 . 00001000 . 00000010 . 00000100 (resultant)
but not as 16.8.2.6
00010000 . 00001000 . 00000010 . 00000110 (IP)
11111111 . 11111111 . 11111111 . 11111110 (subnet)
00010000 . 00001000 . 00000010 . 00000110 (resultant)
or 16.8.2.3
00010000 . 00001000 . 00000010 . 00000011 (IP)
11111111 . 11111111 . 11111111 . 11111110 (subnet)
00010000 . 00001000 . 00000010 . 00000010 (resultant)

so you see that the IP subnet 255.255.255.254 allows for just 2 addresses in the network.

Quote:
- What is the subnet mask and how does it provide information regarding the associated IP address?
it's kind of described above, the subnet mask is just a collection of octets that are used in a logical function to show what addresses are in a range.

Quote:
- What is supernetting?
Supernetting is when instead of dividing the host by using host bits to create another network you borrow network bits.

consider a class B network
172.16.0.1 subnet 255.255.0.0
as discussed above you can divide this network easily into multiple ranges
172.16.0.1 subnet 255.255.255.0 divides the 65,000 possibly address ranges into smaller possible chunks.
so with this mask you can have
172.16.0.1
on a seperate network to 172.16.1.1
(with mask 255.255.255.0)

with supernetting you use network bits in the mask rather than host bit to extend the network. using a different mask

172.16.0.1 (255.255.0.0) gives range 172.16.0.1 -> 172.16.255.254 (65,000 addresses)
172.16.0.1 (255.254.0.0) gives range 172.16.0.1 -> 172.17.255.254 (130,000 addresses).

supernetting allows you to conjoin networks that are separate address spaces to what you'd normally subnet with.
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Old 11-18-2008, 09:18 AM   #9
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Default Re: Subnet Masks

Quote:
Originally Posted by Austinn View Post
+1

Thats absoultely pathetic. He is here asking help. As Members, we are here to help others. Not by posting smart ass replies. He has a good question, And, (Antdemo), if you can't give any USEFUlL information and/or help, then I see no reason why you should even post.

I agree with David, If you have access to tutorials, use them.
Good Luck!
sorry but no offence but their are professional free tutorials online instead of waiting for members to reply.

infact I can see only 1 person has helped in 24hours and well, if you google it you'll get 100's of replies.

Sure people can post and help, I'm not saying that but you'll get alot more view of google

Nice root, I +1 you

All I'm doing is giving him thee best advice. ummm
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Old 11-18-2008, 09:20 AM   #10
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Default Re: Subnet Masks

Quote:
Originally Posted by Antdemo View Post
sorry but no offence but their are professional free tutorials online instead of waiting for members to reply.

infact I can see only 1 person has helped in 24hours and well, if you google it you'll get 100's of replies.

Sure people can post and help, I'm not saying that but you'll get alot more view of google

Nice root, I +1 you

All I'm doing is giving him thee best advice. ummm
I'm pretty sure he was well aware that he could search Google and didn't need an explanation of what Google was through a Google search.

I don't think you get "replies" from Google either, but hey - what do I know?
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Old 11-18-2008, 09:23 AM   #11
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Default Re: Subnet Masks

ok, let me just say this.

Ok, I need to know what and How does subnetting work?

O look, I googled it:

http://www.dialogic.com/support/help...SP/courses/ip/

Jeez so much info

Ok maybe I was abit harsh to put google up as what's google but come on, If I want to know how to burn a dvd, I google it as a fast response, now if I couldn't find out on google I simply goto a forums just like this.
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Old 11-18-2008, 09:24 AM   #12
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Default Re: Subnet Masks

Thats one thing that annoys me about this bloody forum, and thats that even though someone has replied with an answer that answers the question;

Root (A fantastic reply),

an argument carries on, taking away the point of the thread, and takes away from the fact that it has been replied to in a positive manner...
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Old 11-18-2008, 09:31 AM   #13
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Default Re: Subnet Masks

root has it more elaborate. I'll just give you a crash course to make things simple, but if you want something well done, root's got a better solution than mine, hands down.

Class range net IDs
Here's a list of common private IP addresses:
Class A= 10.0.0.1 to 10.255.255.254 // SM = 255.0.0.0 default // Bcast= 10.255.255.255 // Ranges from 1-127
Class B= 172.16.0.1 to 172.16.255.254 // SM 255.0.0.0 default // Bcast= 172.16.255.255 // Ranges from 128-191
Class C= 192.168.0.1 to 192.168.0.254 // SM 255.255.255.0 default // Bcast=192.168.0.255 // Ranges from 192-224
Class D= 224-248
Class E=249-255?

Class D and E, I don't know them by heart, but they are experimental, so you don't worry about them, Of course, you can always use them for you home network, just not on the internet.

SUBNET
A subnet basically divides the NetID and the HostID. Take a very common Class C network.

192.168.1.1
255.255.255.0

The long version looks like this:
11000000.10101000.00000001.00000001
11111111.11111111.11111111.00000000

All the 1s hide the network portion, remaining with the .1 at the end for the hosts. You can have 254 hosts in an IP address (255 is the broadcast address. Common in DHCP)


So, the NetID is 192.168.1 and the HostID is .1

On a class B, like 172.16.0.1, and a SM (Subnet Mask) 255.255.0.0, the NetID is 172.16 and the HostID is .0.1, so there's a lot more hosts available. A Class A network, with IP 10.0.0.1 with a SM of 255.0.0.0 gives the most hosts. 10 s the NetID, and the .0.0.1 is the HostID.

Also, you can divide the hostID so that a portion of it may be ussed for subnetting. The best solution to save you the long way and giving you headaches, you can use a subnet calculator. Here's one for you to practice on:
http://www.subnet-calculator.com/

Oh Kage, if you see the argument going on, why not split the thread and remove these nonsense?
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Old 11-18-2008, 09:42 AM   #14
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Quote:
- What is the host address of the following IP addresses (assuming default subnet mask is used) : 125.125.250.45, 120.125.250.75, and 194.194.150.20?
what do you mean by host address?
I'll go with what I assume you mean host address, by saying that I'm assuming that the host address is the first available (or last available) address in the network space.

to answer this question you first need to appreciate network classes, IP ranges are defined as being of 3 classes, (A, B or C) these have address ranges as such.
class A 0.0.0.0 - 127.255.255.255.255 (default mask 255.0.0.0)
class B 128.0.0.0 - 191.255.255.255 (default mask 255.255.0.0)
Class C 192.0.0.0 - 223.255.255.255 (default mask 255.255.255.0)

so...
125.125.250.45, class A (mask 255.0.0.0 / network address x.0.0.0)
first address in range 125.0.0.1 (last address in range 125.255.255.255 -broadcast 125.255.255.255)
120.125.250.75, class A (mask 255.0.0.0 / network address x.0.0.0)
first address in range 120.0.0.1 (last address in range 120.255.255.254 -broadcast 120.255.255.255)
194.194.150.20 class C (mask 255.255.255.0 / network address x.x.x.0)
first address in range 194.194.150.1 (last address in range 194.194.150.254 -broadcast 194.194.150.255)

Quote:
- Is the following subnet mask valid: 255.255.255.16
No.
valid subnets are ones where the binary looks like this
11111111 . 11111111 . 11111111 . 11111111 (255.255.255.255 (/32))
11111111 . 11111111 . 11111111 . 11111000 (255.255.255.248 (/29)
11111111 . 11111111 . 11111111 . 00000000 (255.255.255.0 (/24))
the subnet 255.255.255.16 looks like
11111111 . 11111111 . 11111111 . 00010000 (255.255.255.16)
you can't have a 1 appearing in the middle of 0's cause then when you do the bitwise and operation you get results like this

11000000 . 10101000 . 00000000 . 00000001 (192.168.0.1)
11111111 . 11111111 . 11111111 . 00010000 (255.255.255.16)
11000000 . 10101000 . 00000000 . 00000000 (resultant)

and that's not in the same range as
11000000 . 10101000 . 00000000 . 10010110 (192.168.0.150)
11111111 . 11111111 . 11111111 . 00010000 (255.255.255.16)
11000000 . 10101000 . 00000000 . 00010000 (resultant)

and yet at the same time is in the same network as
11000000 . 10101000 . 00000000 . 11001000 (192.168.0.200)
11111111 . 11111111 . 11111111 . 00010000 (255.255.255.16)
11000000 . 10101000 . 00000000 . 00000000 (resultant)
so your range is what, 192.168.0.1 - 192.168.0.255 BUT excluding certain addresses?

Quote:
- How many subnets are possible with the subnet maks below, and how many hosts are available per subnet: 255.255.255.128?
what's with the vague questions!! that would very much depend on the class of the network!
for example if you took a class A network with that subnet then there are 131072 available subnets with 126 hosts persubnet

a class C networ there are 2 subnets available each 126 hosts per subnet

(i'll assume it's meant to be a class C)

one way to see this is to write out the subnet as binary
11111111.11111111.11111111.10000000
then do a logical NOT opperation, (invert the bits)
00000000.00000000.00000000.01111111
then convert back to decimal.
1111111 = 127
255.255.255.128 = 127 addresses available. then subtract 1 as it's the broadcast address and can't be a host address.

the maximum amount of subnets is the amount of times you can fit this number into the maximum amount of addresses

maximum amount of addresses = 255 (well 254 really cause there is the broadcast)
so you have one network of 127 addresses (including broadcast)
then you can have another network of 127 addresses.
so now you can see there are 254 addresses in the 255 address range used, you can only fit 2 subnets in this range.

255.255.255.128 give 2 subnets, with 126 host in each
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Old 11-18-2008, 10:39 AM   #15
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Default Re: Subnet Masks

Well the arguement can end here, cause I hate it too.

If I had wanted a response from Google, I would have Google'd it Antdemo.

But, I wanted a response from someone that I could maybe ask more questions regarding the subject to. So I got my response, I can now read it, and if I have more questions, I will go on with it.

Thanks for the reply Root, +1.

I am sorry for the vagueness of some of the questions, but you can tell why I was having some problems with them, .

I will read it again some more, to try and understand it better.
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Old 11-18-2008, 10:48 AM   #16
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Default Re: Subnet Masks

Quote:
- Same question: 255.255.192.0?
same again
11111111.11111111.11000000.00000000
invert
00000000.00000000.00111111.11111111 =
11111111111111 (in binary) = 16,383 (in decimal)
take one away for the broadcast
=16282 host addresses available available on each network

in a non sub netted (mask = 255.255.0.0) network there are:
11111111.11111111.00000000.00000000
(invert)
00000000.00000000.11111111.11111111
1111111111111111 (in binary) = 65,535 (in decimal)
16,383 (one subnet)
+16,383 = 32,766 (two subnets)
+16,383 = 49,149 (three subnets)
+16,383 = 65,532 (four subnets)

giving 4 subnets available

Quote:
- Given the following IP address and subnet mask, what ist he host and network address of each: 192.168.1.25 using subnet mask of 255.255.255.0?

basically the subnet mask is indicating the amount of bits that can change.
as you'll have seen above 255.255.255.0 means that nothing in the first three octets can change, any number in the last octet will satisfy the bitwise and operation.

so the 192.168.1.25 / 255.255.255.0
has ranges 192.168.1.0 -> 192.168.1.254 with a broadcast address of 192.168.1.255
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Old 11-18-2008, 12:20 PM   #17
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Default Re: Subnet Masks

Quote:
Originally Posted by BamaFan2989 View Post
Well the arguement can end here, cause I hate it too.

If I had wanted a response from Google, I would have Google'd it Antdemo.

But, I wanted a response from someone that I could maybe ask more questions regarding the subject to. So I got my response, I can now read it, and if I have more questions, I will go on with it.

Thanks for the reply Root, +1.

I am sorry for the vagueness of some of the questions, but you can tell why I was having some problems with them, .

I will read it again some more, to try and understand it better.
Just keep revising it until you think you have it.

give it about an hour maybe and you will have learnt something
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Old 11-18-2008, 03:51 PM   #18
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Quote:
Originally Posted by BamaFan2989 View Post
I am sorry for the vagueness of some of the questions, but you can tell why I was having some problems with them, .

I will read it again some more, to try and understand it better.
some of those questions are really terribly vague! like the one that asks how many subnets you can have with a given mask, that question really does require more detail before you can give an answer...

I think that if there are going to be questions like that then you should be asking in the test for them to clarify the questions.
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