Hi everybody.

Just have few questions about Subnetting. Iam Using the shortcut method(magic no method) described in the Cisco press ICND book. However Iam stuck and cannot figure out how to solve this problem. Here goes...


1) Given the IP address 140.1.1.1 and the mask 255.255.255.248, what are the assignable
IP addresses in this subnet?

I cant make out which octet in the subnet mask is the so called "interesting" octet. The IP address given is a class B address, so is the interesting octet the 3rd octet? but the book at times says that the interesting octet is the octet with non 0's or 1's( as in other than 0 or 255)?

Another example to make myself clear---

2) IP 167.88.99.66 and the mask 255.255.255.192 or

even

3) 10.5.118.3 and the mask 255.255.255.0

In the last example even though there is no so called "difficult" octets, which octet do we use to find the "magic no". Although in the example the resultting magic no will be same i.e 1, but the end result would certainly be different.

Can someone pls help me, if iam not clear pls let me know.

Thanks

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