I pulled excerpts from the discussion page, to verify my own results. It seems that you have to use the whole Class C space to make the subnets even if you don`t need all the hosts. The hint is don`t worry about wasted addressing space, it`s a game for fast subnet calculations and it gets very addicting.
It`s a race against time to subnet the networks for the buildings in Area 51 before the aliens attack!
The moderator writes:
A common mistake new players make is failing to set the correct subnet mask. Even if all of the subnets have a green arrow, you still must enter the correct subnet mask in order for the game to advance. For example, if the instructions ask you to designate 2 subnets, the mask must be set to 255.255.255.128
Also, remember to click the "Set" button after each entry.
Level 1 by C Byington
Janet Area
2 Areas = 255.255.255.128
1st room
Network 192.168.1.0
Broadcast 192.168.1.127
Router 192.168.1.1
2nd Room
Network 192.168.1.128
Broadcast 192.168.1.255
Router 192.168.1.129
J Vaagen has some tips:
Memorize the subnet masks and the associated number of networks.
Then work at the 8x multiplications all the way to 248.
A tip to use in the 224 mask;
network 192.168.0.0
last ip (gateway + 30 = 31)
gateway 192.168.0.1
a lot of the scenarios use 224 as the mask..
David the Instructor:
The following table shows you possible subnet masks and why they are a certain value. Remember we borrow from the left and move to the right for more subnets.
bit 8 7 6 5 4 3 2 1
---------------------------------------------
weight 128 64 32 16 8 4 2 1
128 1 = 2 subnets
192 1 1 = 4 subnets
224 1 1 1 = 8 subnets
240 1 1 1 1 = 16 subnets
248 1 1 1 1 1 = 32 subnets
252 1 1 1 1 1 1 = 64 subnets
More hints about valid hosts and usable subnets, by Zose:
The formula 2^(number of bits) - 2 only applies to "host" bits. When determining the number of hosts in a network you use this formula. The "-2" comes from subtracting the Network Host (first IP address) and the Broadcast Host (last IP address).
When determining the correct number of subnets you do not subtract 2 normally. The only time you would subtract 2 to find the number of usable subnets is if the "ip subnet zero" command was in use (meaning the 1st subnet is not usable), and if the router is using a classful (IGRP, RIPv1) routing protocol. Usually this is not the case as both IGRP and RIPv1 are older protocols and are not commonly used any more. Instead classless protocols such as RIPv2, EIGRP, and OSPF are used.
Emmanuel has finished the game!
Okay. I've just finished the game with 32445 points. I understand your frustration cause the text is not so explicit. In this case, it means that for each of the initial subnets (8 subnets for a maximum of 16) you have to consider that this subnet could be extended in the future. So 16 subnets for the mask is the right answer (255.255.255.240) but you must leave one reserved subnet between two of these 8 initial subnets. For example suppose the network number is 192.168.1.0. With a /28 mask, the first subnet is 192.168.1.0 (With a broadcast of 192.168.1.15), the second is 192.168.1.32 (192.168.1.16 reserved for the first subnet and broadcast = 192.168.1.47), the third is 192.1.168.64 (With a broadcast of 192.168.1.79) ... Etc.
An answer with contiguous subnet numbers is wrong cause for a subnet to be extended in the future, the future reserved part must be contiguous with the initial part in order to get the possibility to migrate easier from or to the 255.255.255.224 mask (In this case we really have no more than 8 subnets but each subnet is equivalent of 2 initial subnets).
I've noticed you might have to solve this kind of problem in level 4 and 5 too with more text or no text. For the Aliens rooms there's no text and you have 8 rooms with devices. You have to imagine that aliens population will grow like the science fiction films
and therefore in this case other rooms or subnets would be necessary... I guess it's this concept of creating more subnets than showed on the screen which is the same problem for us, Jesse, David, James, Joel, Joseph and others : green everywhere except that the great "Finished" doesn't appear. I take this example of the aliens cause they are impredictible... Once you have been lucky to consider the same number of devices per room, next time you might have one alien room with 16 devices whereas 4 for another : Welcome VLSM ! Different situation and i understand why there is no text about what to do !
Applying these rules to solve your problem, i am sure you will successful in finishing the game. For me, the most difficult is the 32 subnets challenge in level 5 cause it needs to save time with the previous problems in typing correctly as fast as possible : in this question, you have to enter 32x3 numbers plus the subnet mask !
