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TOPIC: Subnets urgent pliz help

Subnets urgent pliz help 13 years 5 days ago #604

  • rebecca
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:oops: A mask address of 255.255.255.0 is given and you need to have 16subnets.Explain how u would deal with addresses and numerate the IP addresses of the 16 subnets.

please help as soon as possible.
thanks
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Re: Subnets urgent pliz help 13 years 5 days ago #606

  • Chris
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Rebecca,

The answer to your question is simple if you try and break the problem.

1) you need 16 subnets
2) your subnetmask is 255.255.255.0 so I'm guessing your dealing with a Class C network

Now, if we want to answer the above question, by following the rules correctly, then this is the formula that to defines how many bits are required to give us the amount of subnets we need (16):

2^x-2. That is, 2 to the power of X, minus 2.

IF your wondering why the -2, well in theory, we shouldn't use the first or last subnet, but in practice we always do :) Check the subnetting pages for more info on that.

So, after a few calculations, we find that:
2^4=16-2=14 subnets.... not good enough
2^5=32-2=30 subnets. This is the closest we can get to 16 or more subnets.

So, we need to reserve 5 subnet bits in order to produce the 30 subnets. Our new subnet mask will be as follows:

255.255.255.248

We need to translate it into binary in order to show the 5 bits we have reserved for the subnets:

255.255.255.1111 1000
__________
___
Network~~~Subnet~host

Each subnet range, assuming 192.168.0.0 network:

---Network ID----Broadcast ID
1: 192.168.0.0 - 192.168.0.7, valid host range: .1 to .6
2: 192.168.0.8 - 192.168.0.15, valid host range: .9 to .14
3: 192.168.0.16 - 192.168.0.23, valid host range: .17 to .22
4: 192.168.0. 24 - 192.168.0.31, valid host range: .25 to .30
...
...
32: 192.168.0.248 - 192.168.0.255, valid host range: .249 to .254


You must remember that the 1st and last subnets, that is 192.168.0.0 and 192.168.0.248 should not be used.

As noted, this answer is considered correct for a totally theoretical question, e.g if you got this question in your ccna exam, they would expect you to answer it as I showed you.

If on the other hand you just wanted to split your office or home network, then you could use the 2^4=16 subnets and apply them to your network since it would also work.

Both answers will work in practice, but when you look at it from a pure theoretical point, only the 1st answer is considered correct, regardless if the 2nd one would work aswell in a real environment.

I hope I haven't confused you :)

Cheers,
Chris Partsenidis.
Founder & Editor-in-Chief
www.Firewall.cx
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Urgent Subnet Help 13 years 4 days ago #615

  • SixFive7
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Search the Internet for a program called: "Ip subnet calculator" by WildPackets. It is freeware and the most usefull tool I ever used!

Greetz,
SixFive7
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Re: Subnets urgent pliz help 13 years 4 days ago #620

  • Chris
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SixFive,

I've actually got their PDA version and its quite good. A very handy program indeed.

We are planning to introduce a Firewall.cx home made application that will have various network tools, plus an IP subnet calculator!

cheers,
Chris Partsenidis.
Founder & Editor-in-Chief
www.Firewall.cx
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Sunet Calculator 13 years 3 days ago #629

  • SixFive7
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Got the Palm version as well.... Truly a powerfull tool. There is only one thing I don't get: Wat is the CIDR part of the program?

Greetz,
Jori Huisman
SixFive7
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Re: Subnets urgent pliz help 13 years 3 days ago #631

  • Chris
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Oh... the CIDR part .... :)

Take a look at the Supernetting topic under Networking/General and you will learn all about it !

Cheers,
Chris Partsenidis.
Founder & Editor-in-Chief
www.Firewall.cx
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