| anchor40 2003-05-05, 9:43 am |
| Good Morning!
First, let me thank everyone who voted in the poll last week. Of the 31 responses, 27 were "Yes" and 4 were "I'm interested, but focused on something else." To you 4, join in at any time! 
Ground Rules - As with any "class" there are usually some ground rules:
* First, I will post a practice question "every" day (if I miss one, it means I have a life - for a moment).
* Second, starting tomorrow, there will be a question AND the answer to the previous question.
* Third, PLEASE do not reply and post your answer to the current question. You will take away the value of these questions from everyone else. Please wait for the next day, and then post away!!
* Fourth, feel free to ask questions and/or give me feedback (public or private). There will be some basic practice questions, as well as some "real" world practicals. Some might say real TWISTED world, but you be the judge. 
Okay, enough of that, on with lesson one.
An IP address has two components, the network portion and the host portion, right? Early IP networks had default network bits assigned depending on the Class of Address that the number belonged, Class A, B, C, D, or E. Class D is used for multicast groups and Class E is for experimental use only.
The "class" of the address is determined by converting the IP Address to its binary format, and examining the left-most bits - Class A=0, Class B=10, Class C=110, Class D=1110, and Class E=11110.
The subnet mask identifies the line between the network and host addresses. For Class A, the default mask is 255.0.0.0, for Class B, 255.255.0.0, and for Class C, 255.255.255.0. You can see, as the class moves up a level, another octet of the address gets used for network bits. Beware - routing protocols that do not support Variable Length Subnet Masks (VLSM) rely on the default masks.
"Subnetting" uses VLSM to borrow bits from the host address component to make more networks with fewer hosts per network. "Supernetting" borrows network bits to increase the amount of hosts on a network.
VLSM introduced another way to annotate the subnet masks, by using a slash and the number of bits the masks uses. For example, 1.2.3.4/24 means that 24 bits are used as a mask for this address, 1.2.3.0 is the network ID and 4 is the host id. 16 bits were borrowed from the host portion of the Class A address (second and third octets) leaving the 4th octet for host addresses.
Given the following IP address and mask, provide the class, network ID, # subnets, and # of hosts per net:
Address/mask Class Net ID #subs # hosts
================== ===== ================== ======= ========
___.___.___.___/__ _ ___.___.___.___/__ _______ ________
201.17.24.27/28
6.122.3.92/24
135.256.17.1/20
126.0.0.1/16
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