I'm confused with this subnet address

Sa'ad

Find the broadcast address of the following IP address.

192.168.82.90/20

If this is a class c address why isn't all of the 3rd octet being used in this case. This is confusing.

I didn't even try asnwering this, but their answer was 192.168.95.255

doesn't make sense to me at all. Anyone who shed some light this is appreciated. Thanks.

Silver Bullet

This is how I would calculate that.

192.168.82.90/20

11000000 10101000 01010010 01011010 = 192.168.82.90 = IP Address

11111111 11111111 11110000 00000000 = 255.255.240.0 = Subnet Mask

Given that there are 12 free bits, you change the last 12 bits to 0 to calculate the Network Address and change the last 12 bits to 1 to calculate the Broadcast Address. Which should look like this.

11000000 10101000 01010000 00000000 = 192.168.80.0 = network address


11000000 10101000 01011111 11111111 = 192.168.95.255 = broadcast address

I believe that this is right and someone that is more familiar with this may be able to give you a more detailed explanation.

Damishi

your subnet for the 192.168.82.90/20

breaking it down:
Subnet: 192.168.80.0
Broadcast: 192.168.95.255

SV

Saad,

Go through the link:
http://www.techexams.net/forums/viewtopic.php?t=11417

This will give you an idea of supernetting.

Anyway lets take 192.168.82.90/20
For the time being ignore about classes. If you look at the third octet, it is 11110000.(ie dec value of xxx.xxx.240.xxx). Thus the maximum number hosts (not valid hosts) = 16.
That is 0, 16, 32,......"80", "96"

Address range = xxx.xxx.80.0 to xxx.xxx.95.255
192.168.80.0 = network ID
192.168.95.255 = Broadcast ID

Sa'ad

I knew how to answer the question, but what I didn't understand is that I thought when it comes to class c subnetting you can only subnet in the last or 4th octet. What is confusing me isn't figuring out the answer, rather the way the ip address it self is made up. Because all this time I have been reading that class c ip addresses use /24 in other words all the first 3 octets and if that isn't enough it can go on to borrow more from the 4th octet.

e.g.

n = network
h = host

class a = n.h.h.h
class b = n.n.h.h
class c = n.n.n.h

so if class c is to use all of the 3rd octet b4 subnetting is needed why is this ip address subnetted b4 all of the class c default ip address is used.

Maybe you guys aren't getting my point. But at least thank you all for trying to help me, I apprecate it. Thnx a bunch. I'll go back to my books and find out what I'm missing.

EdTheLad

Read the post on supernetting.
http://www.techexams.net/forums/viewtopic.php?t=11417

pizzafart

The /20 designator makes it neither a class a, b, or c network. Seeing as your address is in the 192.168.x.x numbering range, you could say that it's 16 supernetted class c networks. Or, you could say that it's simply a network with a /20 subnet mask, allowing a total of 4094 hosts (4096 - 2 to account for the network number and the broadcast address).

Many newer network schemes don't bother with the class designations. Some related terms are CIDR, VLSM, supernetting, and route summarization.