Host ranges - confused....

[wellerw]

Hi,

I am studying subnetting and am slightly confused about host ranges.

here goes :

if I use a .224 subnet I get the following subnets:

32
64
96
128
160....

why is it that i cant use .32 as my first range?, I understand the .63 is broadcast, but several books I have read seem to contradict each other.

Some say that I am free to use 32.1 as my first host, where as others say I need to use 33.1

cheers

 

[mainstreetexpress]

Hi
You can use 32.1 as your first host. Tthrow the book away that says you can't, you never know what else is wrong in it !!!

Here is an output using a /19 mask

List of networks
for the 172.16.0.0 network with the subnet mask 255.255.224.0

Network Hosts Address Broadcast
from to
172.16.0.0 172.16.0.1 172.16.31.254 172.16.31.255
172.16.32.0 172.16.32.1 172.16.63.254 172.16.63.255
172.16.64.0 172.16.64.1 172.16.95.254 172.16.95.255
172.16.96.0 172.16.96.1 172.16.127.254 172.16.127.255
172.16.128.0 172.16.128.1 172.16.159.254 172.16.159.255
172.16.160.0 172.16.160.1 172.16.191.254 172.16.191.255
172.16.192.0 172.16.192.1 172.16.223.254 172.16.223.255
172.16.224.0 172.16.224.1 172.16.255.254 172.16.255.255

 

[wellerw]

Thanks, the book I am referring to is the sybex CCNA book, for the old exam.

it says to use the numbers in between, and that the last range before the next subnet is the broadcast address.

 

[wellerw]

hmm, the cisco website also says the same, I'm wondering which way it will be in the ccna tests...

 

[Parcival21]

Well I'm not quite sure what you want to ask.
If you have the following network address:
192.168.0.32 255.255.255.224
You can't use the address 192.168.0.32 because it's the network address of that network. Maybe that is what cisco is referring to.
If you have a 192.168.32.0 255.255.224.0
you cannot use the address 192.168.32.0 but you can use all addresses starting from 192.168.32.1 to 192.168.63.254.
192.168.63.255 will be the broadcast address.
bye, busche

 

[mainstreetexpress]

Aaahh right, sorry about that, I forgot I was perusing the exam section.

I have heard stories that the Cisco exam won't allow subnet 0 i.e 192.168.0.0 cannot be used as a starting network, 192.168.1.0 has to be the starting point!!!!

I would do whatever the books say for the exam then forget it asap, but always remember the correct network ranges (as per above) for real life situations

Good luck

Mark

 

[cryptomap]

The usage of the the first subnet depends on whether ip subnet-zero has been enabled on the router. The RFC permits the user of the first subnet but up until 12.x Cisco IOS did not support it's use.

"There are only 10 types of people in the world - those who understand binary, and those who don't"