question about private address 192.168.0.0/16

: I am just a little confused....

The private addresses are:
Class A 10.0.0.0/8............. 10.0.0.0 - 10.255.255.255
Class B 172.16.0.0/12.........172.16.0.0 - 172.31.255.255
Class C 192.168.0.0/16.......192.168.0.0 - 192.168.255.255

I thought 192.168.0.0 should be a classs C address, so why wouldn't be 192.168.0.0/24

or am I not understanding something correctly ?

Really startin to panic, going to write the CCNA cert tomorrow !

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Comments

kjpou1

ziggy wrote:

: I am just a little confused....

The private addresses are:
Class A 10.0.0.0/8............. 10.0.0.0 - 10.255.255.255
Class B 172.16.0.0/12.........172.16.0.0 - 172.31.255.255
Class C 192.168.0.0/16.......192.168.0.0 - 192.168.255.255

I thought 192.168.0.0 should be a classs C address, so why wouldn't be 192.168.0.0/24

or am I not understanding something correctly ?

The subnet mask is the key to the question. Class C is the range you specify above with /16 but with the /24 subnet mask:

Class C 192.168.0.0/24.......192.168.0.0 - 192.168.0.255.

Yes it would be a class C address but the /24 does not cover the full range of private class C addresses.

I believe I have seen this question before somewhere but it did not come up on the exams.

Good luck with the exam.

Regards

Kenneth

gojericho0

ziggy wrote:

The private addresses are:
Class A 10.0.0.0/8............. 10.0.0.0 - 10.255.255.255
Class B 172.16.0.0/12.........172.16.0.0 - 172.31.255.255
Class C 192.168.0.0/16.......192.168.0.0 - 192.168.255.255

I thought 192.168.0.0 should be a classs C address, so why wouldn't be 192.168.0.0/24

Normally class B and C by default are x.x.y.y/16 and x.x.x.y/24 as you mentioned.

Default class B and C private IP address have been supernetted (instead of subnetted) So bits were borrowed from the network portion of the address so that more hosts would be available

Hope this helps...Good Luck Tommorow!!!

kjpou1

gojericho0 wrote:

Normally class B and C by default are x.x.y.y/16 and x.x.x.y/24 as you mentioned.

Yes I agree that we normally think of class B and C as /16 and /24 but he has mentioned the RFC 1597 private address ranges from section 3.

http://www.faqs.org/rfcs/rfc1597.html

The /12 subnet mask is the reason for the range 172.16.0.0 - 172.31.255.255.

It would also depend on the question that is asked as well which is not specified.

Anyway that was the basis for the answer I gave.

Regards

Kenneth

ziggy

Thanks,

I don't know what I was thinking.....forgot all about CIDR and supernetting. Thanks to all for clearing it up for me. Been studying way to hard, brain is all filled up and stuff is starting to leak out :P

Drakonblayde

RFC1597 really isn't the one you'll see referred to as well. RFC1918 is the updated private ip address space, and most references you'll see will be to that instead.

kjpou1

Drakonblayde wrote:

RFC1597 really isn't the one you'll see referred to as well. RFC1918 is the updated private ip address space, and most references you'll see will be to that instead.

Yes thanks for that. The 1597 was the first that popped in my head.

I still refer to the telnet 5250 rfc as 1205 and it has the enhancements in 2877 but can not for the life of me remember the 2877. The ones I have read first stick.

Regards

Kenneth