IP address question for all u A+/MCSE geeks

[jimmyhaha]

Which of the following is NOT a valid IP address.

192.168.1.1

172.23.128.227

172.300.264.12

209.247.228.201

The correct answer is the 3rd one....
hmm.. I am puzzled.. Can some one explain it briefly...

btw, if any one can point me to any A+ discussion forum, greatly appreciated..
thanks

 

[Damaged]

172.300.264.12

 

[heat23]

highest number it can be is 255 righT?

 

[AmazonRasta]

Why is the third one, 172.300.264.12, not a REAL IP address?

 

[Damaged]

32 bit number expressed in 4 octets of 8 bits in base 10 for each octet. 8 bits=256, but since we start 0 the highest any given octet could be is 255. 300 is more than that and so is 264.

 

[bigrash]

the highest number that you can use is 256 which is FF in hexadecimal

edit: yup, you're right Damaged

 

[Descartes]

Why isn't the 3rd one valid?

Each octect is composed of 8 bits (hence octet), and 8 bits can hold exactly 256 values (0-255 for unsigned integral values). If you need to figure out the maximum value a certain number of bits can hold, use this formula: 2 ^ num_bits - 1

so, 2 ^ 8 - 1 = 255

 

[BoberFett]

bigrash

Actually, FF is 255.

 

[DaemoN]

Each xxx in xxx.xxx.xxx.xxx represents eight 1's and/or 0's in binary form. an ip address is just a 32bit address in decimal form.
example: 255.255.255.255 = 11111111.11111111.11111111.11111111
Since a 1 is the highest binary number you can't have anything over a .255 in an IP address
Hope this helps.

I won't even get into loop backs and IP classes.. hehe

 

[Tripleshot]

Learn to Subnet .com

 

[phatcow]

172.300.264.12




300 is out of the subnet....

 

[Draco]

That was a tough one!

Is that what they ask you on the A+ test?!

 

[nEoTeChMaN]

Don't listen to them, they are making it hard than it is.

Just memorize this:

Class A: 1.0.0.0 > 126.0.0.0 subnet = 255.0.0.0 (Class A loopback: 127.0.0.1)

Class B: 128.0.0.0 > 191.0.0.0 subnet = 255.255.0.0

Class C: 192.0.0.0 > 223.0.0.0 subnet = 255.255.255.0


See the numbers in bold, it is higher than 255.

172.300.264.12

See the first numbers to the left in bold, it belongs to Class B:

172.300.264.12 (between 128.0.0.0 and 191.0.0.0)


It is very easy as long as you memorize the concepts above. It helped me passed the Network+ a few days ago. It will help with CCNA too.