Which of the following addresses do not share the same subnet number?


IP = 151.100.225.1; Mask = 255.255.192.0
IP = 151.100.193.100; Mask =255.255.192.0
IP = 151.100.156.1; Mask = 255.255.192.0
IP = 151.100.255.210; Mask = 255.255.192.0

Why is the answer:

IP = 151.100.156.1; Mask = 255.255.192.0

Report this post to a moderator

Well a mask of 255.255.192.0 will basically split your class B subnet in half - i.e, the first half will consist of 151.100.0.0 - 151.100.191.255, the second half will be 151.100.192.0 - 151.100.255.255.

So the first two and the last one all fall into the same subnet range when that mask is used and 151.100.156.1 will be in another subnet.

Make sense??

Report this post to a moderator

Sort of..

Why are the subnets not incremented by 64 though?

Report this post to a moderator

Actually the subnets do increment by 64, and all but the third address is in the 151.100.192.0 network. Valid hosts 151.100.192.1 through 151.100.255.254. Feel free to correct me, just doing this from my head and I'm not a net admin.

Report this post to a moderator

Ok I got it..

So the thrid address would actually be in the 151.100.128.0 net right?

Report this post to a moderator

Class B : 150.100.0.0 network with the subnet mask 255.255.192.0

1st Ip

Network : 150.100.0.0
Host : 150.100.0.1 to 150.100.63.254
Brdcast : 150.100.63.255


2nd Ip

Network : 150.100.64.0
Host : 150.100.64.1 to 150.100.127.254
Brdcast : 150.100.127.255

3rd Ip

Network : 150.100.128.0
Host : 150.100.128.1 to 150.100.191.254
Brdcast : 150.100.191.255


4th Ip

Network : 150.100.192.0
Host : 150.100.192.1 to 150.100.255.254
Brdcast : 150.100.255.255

As you can see the :
IP = 151.100.225.1; Mask = 255.255.192.0
IP = 151.100.193.100; Mask =255.255.192.0
IP = 151.100.255.210; Mask = 255.255.192.0

all belongs to the 4th Ip table

And the :

IP = 151.100.156.1; Mask = 255.255.192.0

is the only one that belongs to the 3rd Ip table

Hope this helps ~~~

Report this post to a moderator

I am trying to understand your reply about the 4 subnets.

I was wondering if there should only be 2 valid subnets. 192 is 2 bits of subnetting and 2 * 2 = 4 -2 results in 2 subnets.

Then only the middle two subnets would be valid to use.

Is this correct?

Larry

Report this post to a moderator

quote:

---

Originally posted by lollivie
I am trying to understand your reply about the 4 subnets.

I was wondering if there should only be 2 valid subnets. 192 is 2 bits of subnetting and 2 * 2 = 4 -2 results in 2 subnets.

Then only the middle two subnets would be valid to use.

Is this correct?

Larry

---

__________________
The Computer is a creation of man. Man is a creation of God! -
Joe from Brooklyn

Report this post to a moderator

Forget the Microsoft teaching and join the real world! asteheske posted the correct answer

Yankee

Report this post to a moderator

If a network address is subnetted, the first subnet obtained after subnetting the network address is called subnet zero . And the last subnet obtained is called the all-ones subnet


Problems with Subnet Zero and the All-Ones Subnet:

IT was strongly recommended that subnet zero and the all-ones subnet not be used for addressing. According to rfc 950 , "It is useful to preserve and extend the interpretation of these special (network and broadcast) addresses in subnetted networks. This means the values of all zeros and all ones in the subnet field should not be assigned to actual (physical) subnets." This is the reason why network engineers required to calculate the number of subnets obtained by borrowing three bits would calculate 23-2 (6) and not 23 (8). The "-2" takes into account that subnet zero and the all-ones subnet are not used traditionally.


Using Subnet Zero and the All-Ones Subnet:


It should be noted that even though it was discouraged, the entire address space including subnet zero and the all-ones subnet has always been usable. The use of the all-ones subnet was explicitly allowed and the use of subnet zero is explicitly allowed since Cisco IOS version 12.0. Even prior to Cisco IOS version 12.0, subnet zero could be used by entering the ip subnet-zero global configuration command.



Using Subnet Zero and the All-Ones Subnet:


It should be noted that even though it was discouraged, the entire address space including subnet zero and the all-ones subnet has always been usable. The use of the all-ones subnet was explicitly allowed and the use of subnet zero is explicitly allowed since Cisco IOS version 12.0. Even prior to Cisco IOS version 12.0, subnet zero could be used by entering the ip subnet-zero global configuration command.

On the issue of using subnet zero and the all-ones subnet, rfc 1878 states, "This practice (of excluding all-zeros and all-ones subnets) is obsolete! Modern software will be able to utilize all definable networks." Today, the use of subnet zero and the all-ones subnet is generally accepted and most vendors support their use, though, on certain networks, particularly the ones using legacy software, the use of subnet zero and the all-ones subnet can lead to problems.


These are the explaination frm cisco with regards to subnetting you can read more
here

And to add that, the question asked by justindu:

quote:

---

Which of the following addresses do not share the same subnet number?

---

I created the subnet table to give a clearer picture of how they get the answer.

I hope this will clear the misundertanding and help you with the subnetting (ie: Cisco Style)

Cheers~~

Report this post to a moderator