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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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