Subnetting practice problems 1

[Cluebird]

Practice your subnetting skills with the following:

1. You have a router with 9 interfaces that need IP addresses. You are assigned 195.33.44.0. Construct a complete addressing plan for your router. Use FLSM only.

2. You have two hosts that are unable to connect with each other. On one host you see the ip address 192.168.100.33 255.255.255.240. On the other host you see 192.168.100.28 255.255.255.240. What is the problem?

3. Your administrator tells you to address a host with the following address: 172.16.2.255 255.255.252.0. Will this work? Why or why not?

4. What mask will give me 18 hosts with max number of networks if I start out with 192.168.255.0?

5. What class is the following mask: 255.255.255.0?
A. Class C
B. Class B
C. Class G
D. Not enough information to decide

6. Your server administrator wants to use the 172.168.200.127 255.255.255.128 address on his Exchange server. What is your response?
A. No problem
B. Won't work because that is a local broadcast
C. Won't work because that is a network address
D. Won't work because that is a directed broadcast
E. None of the above

Enjoy

 

[maczen]

Burt,
Good point.. But still that would require aggregating/supernetting and I said subnetting but I do see your point and supernetting honestly did not occur to me... Now who's the Tappity Tap Tap Dancer?? LoL

B Haines
CCNA R&S, ETA FOI

 

[Cluebird]

Bobby,

Big problem with what you just did. You were assigned a Class C and you made changes in the third octet. Not allowed because you are now dealing with someone else's addresses. You can't get more than 254 hosts with any Class C. Likewise, you can't get more than 65534 with a Class B.

The answer for the question you posed in the problem is "it can't be done."

When we get into the world of supernets/CIDR blocks and combine several contiguous Class C's together, then we can get more that 254 hosts on a network. That is beyond what is expected for CCENT. However, ICND/CCNA composite...fair game.

 

[Cluebird]

Will clarify further. Even though we are using private IP addresses for the subnet examples, for the exams you are not to change bits you were not assigned in the first place. Despite the fact that you can legitimately argue that the supernet is valid and all you have to do is implement NAT/PAT so you don't tick off the other administrator you miss the point that Cisco is trying to test. For the Cisco exams, you are your worst enemy. You won't believe the mindgames you'll play with yourself as you try to talk yourself into bogus answers because the correct answer "just doesn't look right"! Keep the basics but within those basics watch for the landmines. Know Class C subnetting COLD...I mean backwards and forwards and inside out and outside in. Know how to work around the dot with the second or third octet. You're more likely to see Class B than Class A subnetting. Most of the time Cisco takes the lazy way out with subnetting for their courses by applying /24 to everything. However, if you understand the binary patterns, the decimal shortcuts work well. If you don't understand the binary patterns, the decimal shortcuts will be confusing and lead down the rosy path to failure.

For test takers I always say RTFQ TWICE...all the way to the end. Then answer it mentally. Then look for your answer in the choices given. Most of the time you can narrow your selections to 2 possible choices of 4 selections. However, always look for the MOST CORRECT CHOICE. You make have two correct answers but one is technically more accurate than the other. Yes, they do test punctuation, especially with IOS commands. After all, there is a big difference between:

Router(config)#hostname MyRouter

and
Router(config)>hostname My Router

isn't there?

 

[bobbyforhire]

I'm starting to think that i'm spending to much time with subnetting. I mean i had it at first but then by talking and trying to do all of these questions it has messed up my original "formula". If you look at my first post of the other forum you can see that i felt as if i had no issue with it...But then came the questions. So i'm kinda happy that I am taking these questions but as BB(Burt) stated i just need to keep it simple. The questions i'm asking are just off the top of the nog, first thing that comes into my head.

1) How to get the answer with Hosts needed.
2) How to get teh answer with Networks needed.
3) How to know the limits of the subnets
4) How to do simple math


I am going to do the most simple of problems.

192.168.1.0 needs 20 hosts per network
20 = 5 Bits
255.255.255.0 becomes

11111111.11111111.11111111.11100000

ip: 192.168.1.X
Subnet: 255.255.255.224 /27

192.168.1.0 - 192.168.1.31 (29 aval hosts)
192.168.1.32 - 192.168.1.63
192.168.1.64 - 192.168.1.95
192.168.1.96 - 192.168.1.127
.....



What is the Network and Broadcast for 192.168.1.66

Network: 192.168.1.64
Broadcast: 192.168.1.95

 

[Cluebird]

You did that one correctly. You have the knowledge and you seem to understand the process, you just tend to rush and make simple errors that will hurt you on an exam. The questions I had you work through are more typical of the way Cisco will test you. Very seldom will they say: Subnet a Class C for at least 10 hosts while getting the most number of subnets. They will try to put the subnetting in a context you might see in a production environment. Such as:

You're a network administrator who is assigned the 195.34.43.0 address space. You have several small networks supporting no more than 10 users with no expected changes in the future. From your assigned address space create as many networks as possible that will accomodate your users. From that address space assign the first usable address to your router fastethernet interfaces. Starting with the first two subnets, what are the two adddresses you'll use on the router?

This is merely a subnetting problem but there is a lot of extra information you need to sort through to get a solution. If you've ever worked with users, you'll understand that they often get very verbose in explaining problems with their PCs and you'll have to sort through that unnecessary information to get the job done. Results matter.

 

[maczen]

Bobby,
You are approaching this correctly. It takes practice to actually grasp subnetting. Identify the areas that you don't quite understand.. Like I did yesterday and LEARN them.. So good job!

1) How to get the answer with Hosts needed.
~You answered this yourself (2n-2).. so..
Need 20 hosts in class C.. x.x.x.NNNnnnnn (30 hosts)
2) How to get teh answer with Networks needed.
~The same way.. (2n-2) Class C.. so..
Need 20 subnets/networks in class C.. x.x.x.XXXXXnnn (30 Networks)
3) How to know the limits of the subnets
~The limits or range can be calculated in many ways..but..
Shortcut = total amount of node addresses.. IE
x.x.x.NNNnnnnn = 32 so..
x.x.x.0 - 31
x.x.x.32 - 63
OR the other example..
x.x.x.NNNNNnnn = 8 so..
x.x.x.0 - 7
x.x.x.8 - 15
etc...

4) How to do simple math
You can always try the shortcut methods listed above but I personally prefer to write out the binary (Especially where VLSM is concerned).. You will see that VLSM is the exact same thing that you are doing now.. same process with the exception that you continue further...

I prefer to do the binary ONLY and not the shortcuts so that I have ONE WAY and only one way of obtaining my info and thus do not (usually) confuse myself... I have developed the binary subnetting to the point of pattern recognition like you are doing. I believe that the reason that you are growing confused is because you are trying different approaches. Just pick one and develop that.. I personally like this way...
-Quoted from Bobby-
"192.168.1.0 needs 20 hosts per network
20 = 5 Bits
255.255.255.0 becomes

11111111.11111111.11111111.11100000

ip: 192.168.1.X
Subnet: 255.255.255.224 /27

192.168.1.0 - 192.168.1.31 (29 aval hosts)
192.168.1.32 - 192.168.1.63
192.168.1.64 - 192.168.1.95
192.168.1.96 - 192.168.1.127"




B Haines
CCNA R&S, ETA FOI

 

[reddevil2]

I have read these posts and comments with much enjoyment and interest, and would like to say if, I could have found this forum earlier in my study, and worked through some of the questions set by cluebird, whether my answers were wrong or right. I feel it would not have taken the two previous attempts at the CCENT and the third attempt that will follow shortly.
As the explinations on FSLM I found very enlightening, although I still get slightly confused with VSLM as well. I just wish I could have one of you for my instructor, rather than struggling through on a distance learning course at home.
I do like the EIEIO, and the AD Infinitum addages to the certifications.
One thing I need to clear up is I have no computer background as such, only what I have picked up in life as I meander thhrough, so with no experience commercial or otherwise will the CCENT help me secure a junior position in IT? Th eCompTIA Network+ failed to help when I put it on my CV, even the Diploma in PC Repair and Upgrading seemed to fire blankly into space, OR AM I TO BE AN OVERQUALIFIED CORPSE WHO COULDN'T LAND A FISH LET ALONE AN IT JOB????

 

[reddevil2]

I have read these posts and comments with much enjoyment and interest, and would like to say if, I could have found this forum earlier in my study, and worked through some of the questions set by cluebird, whether my answers were wrong or right. I feel it would not have taken the two previous attempts at the CCENT and the third attempt that will follow shortly.
As the explinations on FSLM I found very enlightening, although I still get slightly confused with VSLM as well. I just wish I could have one of you for my instructor, rather than struggling through on a distance learning course at home.
I do like the EIEIO, and the AD Infinitum addages to the certifications.
One thing I need to clear up is I have no computer background as such, only what I have picked up in life as I meander thhrough, so with no experience commercial or otherwise will the CCENT help me secure a junior position in IT? Th eCompTIA Network+ failed to help when I put it on my CV, even the Diploma in PC Repair and Upgrading seemed to fire blankly into space, OR AM I TO BE AN OVERQUALIFIED CORPSE WHO COULDN'T LAND A FISH LET ALONE AN IT JOB????

 

[reddevil2]

What is the WRATGAS certification and the BFD??????

 

[Cluebird]

Who Really and Truly Gives a S**t.
Big F***ing Deal.

 

[reddevil2]

TO CLUEBIRD
I have two books by Wendell Odom CISCO INTROand the CISCO ICND, I have CISCO FLASH CARDS and EXAM PRACTICE PACK by Eric Rivard and Jim Doherty, also I have CISCO PRESS BOOKS Networking for home and Small Businesses Allan Reid and Jim Lorenz, with Working at a Small to Medium Business or ISP by again Jim Lorenz and Allan Reid, Introducing Routing and Switching in the Enterprise by Cheryl Schmidt, Jim Lorenz and Allan Reid. The EXAMPREP CCENT 640-822 by Jeremy Cioara, David Minutella and Heather Stevenson, and Scott Bennett's 31 days before your CCENT Certification. So I think I am well armed with literature.
As to the lab, on a restricted budget, trying to support three kids, wife and pay the mortgage, the Cisco routers and switches seem to be well out of my league. So unfortunately I don't have a lab, and the lab at firewall.cx has been undergoing maintenance so I haven't been able to use that one. Though I found on the old course the live lab provided by CISCO to be very beneficial, unfortunately when they changed the course they seem to have deleted that part of it. So any advice as to get HANDS ON practice would be appreciated.

 

[maczen]

Answered you here:

http://www.tek-tips.com/viewthread.cfm?qid=1496691&page=1

B Haines
CCNA R&S, ETA FOI