Failed the 70-291 649 score : Help on subnet

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Hi everyone.

Can somebody help me with this problem?

Given the IP address 192.168.1.10 and a gateway 192.168.0.1, what subnet mask should I use to support 6 maximum subnet?

Help pls.

 

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wouldn't it be /27 or 255.255.255.224, right? You would be starting with 192.168.1.0 /24 and you need 6 subnets so:

2^n = 6
2^2=4 so that's not enough
2^3= 8 so that's enough and that means you are borrowing 3 bits which gives you a /27 or 255.255.255.224

 

Not quite Gosh, your theories right but your an octet down given the IP's from kmmanio.

You'd need a 255.255.224.0 mask or 192.168.0.0/19

IP: 192.168.1.10
Gateway: 192.168.0.1

Giving 6 subnets with 8190 hosts each.

192.168.0.1 - 192.168.31.254
192.168.32.1 - 192.168.64.254
192.168.64.1 - 192.168.96.254

...etc

For Kmmanio:

As Gosh said, to figure out how many bits to borrow you need to do the 2^n calculation that he did.

You then know that you need to borrow 3 bits from the host part and use them in the network part, this covers the "6 subnets" part of the question.

You know you have a gateway of 192.168.0.1 and an IP of 192.168.1.10, which means your first subnet has to include both these values. This means that you can't use a traditional C class (or /24 in CIDR) as you would only be using the range of 192.168.0.0 -> 192.168.0.255, so you need to start from the basis of a B class (or /16 in CIDR) mask which is 255.255.0.0 or 11111111.11111111.00000000.00000000 in binary.

Currently the split is
NetworkHost or 11111111.11111111.00000000.00000000 for the mask

From the first calculation you did you know you need to use 3 host bits to give you your 6 subnets, so this would then give us 11111111.11111111.11100000.00000000 in binary, or 255.255.224.0 as a mask, or /19 in CIDR.

So you end up with 192.168.0.0/19, or 192.168.0.0 with a subnet mask of 255.255.224.0 with ranges list further up.

Hope that explains it a bit more.

 

Crap! I didn't even look closely enough at the gateway to notice the 3rd octet was different! I have such a bad habit of not reading the question closely enough on practice tests and now that I'm in school I do the same thing on quizzes and homework. When I sit an exam I have to force myself to read a question two or three times so I don't make silly mistakes like this.

 

Same here, I read and answer once, then rinse and repeat double reading everything, used to get loads wrong due to trying to be too quick, hell still get stuff wrong but at leasts its wrong for a good reason these days!

 

thanks guys. I am really having bad times with that of subnetting. I'll take the second shot this Oct. 5, I hope I'll be ready for the so called beast. I'll keep you noted. Thanks a lot.

 

guys, my problem is I still don't know how to figure out how to get the needed subnet given just the IP address if required by the question on how many subnet to be use. can you give me some reference site for me to read and review this topic?

Thanks.

 

Are you able to get your hands on CBT nuggets? the guy explains the subnetting pretty well.

 

Posted this in a different thread, it's a comprehensive explanation: http://www.akadia.com/services/ip_routing_on_subnets.html

 

http://www.certforums.co.uk/forums/showthread.php?t=39172 this thread is pretty good