CCNA - Subnetting practice

Author

Subnetting practice

soccer4net

2003-07-03, 3:25 pm

Hi all,

In anchor's abscence I figured I give you some subnetting material to chew on. Rather than come up with some real challenging CIDR type questions I figured I'd use some more basic multiple choice CCNA type questions from certyourself, and work on speed.

So Click on the link below and do the first five questions - you can skip ahead and take the whole test but that's cheating

. Then post your choices back here and how you got them. In a few days I'll give you my solutions. Again the idea is speed here, you don't have much time on the CCNA so when you get multiple choice subnetting questions want to eliminate answers as quickly as possible and maximize your time.

http://www.certyourself.com/exams/c...hp?excode=ccna7

If you don't understand any of the questions, post your problem and I'll try to answer them along with the rest of the solutions.

Jax_Jaguars

2003-07-03, 7:57 pm

I have done the whole 15 questions, seems interesting and easy hope to get similar rating questions for 640-607 exams. THANKS

soccer4net

2003-07-05, 9:15 am

Youre welcome Jax

I found them easy too but once again the idea is knowing how to eliminate answers without converting the entire address to binary and back again, also this is geared towards those still confused on basic subnetting not people who are comfortable with it.

soccer4net

2003-07-09, 12:58 pm

Alright here we are. Click on the above link to follow along with the answers. If you have any questions fire away, if this was helpful let me know, if you want harder ones let me know. Cheers.

Q1. Answer=B

We can eliminate half the choices right off the bat which are ridiculous in one way or another(eg a. is a class A subnetted mask and the question says we're using a class B network ID). Now we need 8 subnets with at 2500 hosts each. Also were just looking at the third octect, forget about the rest of the mask, we just need to worry about 8 bits. Generally, unless the question says to optimize for subnets or hosts, there is only one mask that will fulfill the requirment. So we want to tackle the problem from the easiest end which is of course subnets(8 vs 2500) Let's try using 3 bits (2>nb-2=s) 8-2=6 not enough, try 4, 16-2=14, that works. You should memorize all the mask values(i.e. 128=1 192=11 224=111) but if you only memorize one do 240=11110000 this divides an octect in half, which makes it easy to figure out a mask value up or down from here. It so happens that this is the mask were looking for, 240=4 bits. We cut our time in half by taking the easiest route to the answer.

Q3(q2 is sorta braindead if you hadn't noticed) Answer=D

Note: We only care about the third octect forget about the rest of them. ANd again its extremely helpful to know all the masks to answer questions quickly. 128,192,224,240,248,252,254,25
5. Now we can easily remember 240=4 bits borrowed, 128=1 255=8 we know 224 is one before 240 in sequence so its 3 bits borrowed. The final bit value is always the subnet increment(third bit here, which equals 32 in decimal) First subnet is 32 next is 64(32 +32) all the numbers are 64 or higher except d, so we have our answer.

Q4 Answer= ACE

If you tried to convert every address here you'd be killing your self(not to mention your time) All you need to look at for class id is the first two bits A=01(>128) B=10(128-191) C=11(192> ) ACE are the only addresses that match the pattern. Now if they wanted to be tricky they might put some invalid addresses in there(we're looking for valid hosts only) So we just need to make sure that that the netowork or host portion aren't all one's or zeroes. We've got class B so that means first two octects is network second two, hosts. Again don't convert just make sure they aren't all ones or zeroes. No problems there, see aren't shortcuts fun??

Q5 Answer=C

Take this one octect at a time. COnvert 191=10111111, eliminate all but c,d and f. Now you'll notice all the addresses have the same last octect, so don't worry about that. Fs third octect is the same as the last one(11) were looking for 10 there so drop it. Between c and d there's only the second octect to differentiate. Don't bother converting this either, one more little trick odd numbers always have the 8th bit turned on (1) in this case were looking for an even number in the second octect D has the eighth bit turned on! Drop that and were left with C. To conclude, with multiple choice subnet questions, look for ways to eliminate answers, with converting everything back and forth between decimal and binary. Don't get me wrong, you need to be sharp at converting, but don't bother doing it when you don't have to.

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