Practice Exam Question

[Frank]

What is a valid and assignable IP address would be used for the network 192.0.2.0/23? I just do not see why 192.0.2.255 is the valid and assignable IP address, because i thought 192.0.2.255 would be the network range broadcast address. Am I right? Below are my examples. then the answers.

192.0.2.0 ~ 192.0.2.255
192.0.3.0 ~ 192.0.3.255

A. 192.0.3.255
B. 192.0.2.0
C. 192.0.4.0
D. 192.0.2.255

[Sey]

i thought 192.0.2.255 would be the network range broadcast address

Well this would be true if you had 192.0.2.0/24. But the network given is 192.0.2.0/23, which means that

1) network address is 192.0.2.0
2) broadcast address is 192.0.3.255
3) the valid range of assignable addresses is 192.0.2.1 - 192.0.3.254

So 192.0.2.255 is a valid address. Likewise, 192.0.3.0 is a valid address, too.

Here is a detailed explanation:

192.0.2.0 is 11000000 00000000 00000010 00000000 in binary
the mask is /23 = 255.255.254.0 = 11111111 11111111 11111110 00000000

Let's line this up
11000000 00000000 0000001|0 00000000 - network address
11111111 11111111 1111111|0 00000000 - subnet mask

Now we can get broadcast address by filling the right part of network address with 1s:

11000000 00000000 0000001|1 11111111 - broadcast address = 192.0.3.255

[Keith Barker]

Valid range for subnet 192.0.2.0/23 will be 192.0.2.1-192.0.3.254

Third and 4th octets of first host in subnet:
0000 001|0 . 0000 0001

last valid host on the subnet would be 192.0.3.254/23
0000 001|1 . 1111 1110

Everything between 192.0.2.1 and 192.0.3.254 (inclusive) would be valid hosts for this subnet.


Best wishes,
Keith

[eiryck]

Let me share with you my simple idea about this - What is a valid and assignable IP address would be used for the network 192.0.2.0/23? I just do not see why 192.0.2.255 is the valid and assignable IP address, because i thought 192.0.2.255 would be the network range broadcast address. - By taking and computing how many hosts could be made out of /23 subnet, it is about 512 hosts. With the first and and the last as the network and broadcast addressess, with all hosts within this 2 addressess as valid and assignable host addresses and 192.0.2.255 is one and among this valid and assignable hosts... got my point??? 192.0.2.255 ip address would only be a broadcast address if your subnet mask is /24.

[sbjones]

Correct.

/23 provides 7 bits for subnets.
7 bits allows 128 subnets
128 subnets means the subnets increment by 2

192.0.0.0
192.0.2.0
192.0.4.0
192.0.6.0
192.0.8.0 and so on to
192.0.254.0

You should see that 192.0.2.255 is just another host on the 192.0.2.0 subnet

192.0.3.anything are also hosts on the 192.0.2.0 subnet
192.0.3.255 is the last address before the next subnet (and is therefore the broadcast for the 192.0.2.0 subnet)

The next subnet is 192.0.4.0
If the mask was /24 the subnets would increment by 1

192.0.0.0
192.0.1.0
192.0.2.0
192.0.3.0
192.0.4.0 and so on

In this case (/24)

192.0.2.255 would be broadcast for the 192.0.2.0 subnet

and (/24)

192.0.3.255 would be broadcast for the 192.0.3.0 subnet

[Sal]

I ahve attached a poster on IPv4 subnetting , you can also view this video for Keith Barker on youtube link:

http://www.youtube.com/watch?v=ZTJIkjgyuZE
https://learningnetwork.cisco.com/servl ... etting.pdf


best wishes

[Frank]

Thanks Sey. I like how I can post something that has been rolling around in my head and get the correct answer formso many different techs and engineers. Thank you all.

[Frank]

Thanks, I need that Doc.