Questions

# ip/subnets

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### ip/subnets

Given an IP address of 192.168.1.42 255.255.255.248, what is the subnet address?
A. 192.168.1.8/29
B. 192.168.1.32/27
C. 192.168.1.40/29
D. 192.168.1.16/28
E. 192.168.1.48/29

and if anyone can explain how they got the answer i will appreciate that..thanks

### is that

school work?

no its not, what is the difference anyway?

considering that your first question was and you outright admitted it was homework, one can only assume that it is. It matters because if we do it FOR you, you will not learn anything from it. Once again, Google is your friend as are your textbooks.

again i know the answer but the book seems to disagree. so i was just checking to see maybe i was wrong

.248 mask uses 5 bits (1111 1000).
.42 IP in binary is (0010 1010)

The base subnet therefore is the lowest binary value that can be written without changing the output of an AND operation of the subnet mask and IP ...
1111 1000 AND
0010 1010 equals
0010 1000 - which is .40

/24 is standard class C mask.

As an aside: the broadcast address would be the HIGHEST binary value without changing the output of an AND operation of the subnet mask and IP ...

0010 1000 - Base subnet
0010 1111 - (.47) Last three 1's is the highest value without changing the AND operation .. as in .. making it .48 would result in 0011 0000 which changes the outcome of the AND operation against the subnet mask)
usable addresses: .47 - .40 = 7 .. less 2 = 5 usable addresses in that range
(take away 2 because the base subnet and broadcast address can't be used as end device IPs)

Hope that makes sense.
I'm admittedly quite rusty on my IP theory so if I've got anything wrong, please excuse me .. 9and others please feel free to correct me.

Thanks for the answer, i understand how binary numbers work and all that but i still dont get why you are or where you are getting the 42 from? thanks

i still dont get why you are or where you are getting the 42 from This sounds like a Douglas Adams quip. :)

The .42 was just a valid IP in the range determined by your subnet mask. As stated above by [jedi] 29 bits are network and 3 are host. Your host range is .41 through .46 and .42 is a valid host IP. EG

11000000.10101000.00000001.00101010 192.168.1.42
11111111.11111111.11111111.11111000 255.255.255.248 or 29+3
11000000.10101000.00000001.00101000 192.168.1.40 (after AND op)

Make more sense?

ADDENDUM: You get six host IP's in this example. 3 bits = 8 possible combinations or the range 0-7. 8-2=6 = 41,42,43,44,45 & 46 that can be assigned to host devices.

So even though the block size is 8 since 248 you dont use that information? i am sorry but still dont see why the host range is 41 thru 46, where are you getting that from? Thanks

I see i think i got it! Thanks alot!

thne how come it doesnt work in real application?

### Homework

Is funny how after someone says we don't do homework for others that someone still carries on to do the homework for them. We end up with CCNA's in the field that can't do anything I am looking to fire two just like this got a paper cert but not bright enough to use it really takes away from the clout the old CCNA certs had.

I agree that one shouldn't do the homework, but explaining how subnets work is different from just giving an answer. Somewhere along the line somebody has to say this is the right way to do it and here is why. Otherwise you are making unresonable demands (similar to the Foxconn iPhone5 assembly SNAFU ongoing.)

Not really unreasonable to expect someone to learn. Most books are great resources for CCNA and it would be different if the guest came in and said I am trying to understand how subnets work not just posting a question from their homework. Training a generation who expects to be able to get the answer to anything for free off the internet and they make for lousy employees.

Am I to understand that from the statement

Training a generation who expects to be able to get the answer to anything for free off the internet and they make for lousy employees.

You believe that internet research == lousy employee?

You know something its not fair of you to accuse me of using internet to do my homework. its not homework my friend and i do know subnetting but abviously not good enough, i am not trying to get easy answers but for someone who can explain to meso i would learn it once and for all. an not all book s have good explanations., so before you star firing people and accusing someone not being bright enough ask a question why someone is asking for help. You dont know anything about me so to make an assesment that i am not that bright is very arrogant and rude on your part, plus you sound very pissed off.

and as far as this example Which two commands will display the current ip address and basic layer 1 and layer 2 status of an interface?(choose two)
*router#show version
*router#show ip interface
*router#show protocols
*router#show controllers
*router#show running config
i was just trying to confirm that i was right, because in packet tracer the answer is different then what the book says. the book gives the answer as show protocols and show controllers but in packet tracer show contorollers doesnt give IP address so i was just wondering why the book has it like that

Not sure what your issue with this is. I was an IT instructor for many years and have had to explain subnetting principles to many. Textbooks give one explanation and for some that just does not gel. The oringinal question was not just "Waht is the answer" but also "can you explain how you got it". That indicates someone who is having trouble grasping the basic ANDing concept behind subnetting. I have had to work with people who tried to learn before but were always told "Look it up" and found they were usually lacking in skills. I saw the answer by Charles and it was concise and very well explained.
As for the Internet, I have 20 years experience in IT and still use the Internet for research. I for one think it is an invaluable tool. If you know everthing already, then hooray for you . You should be a CCIE then. For the rest of us, going to sites like this and asking questions is part of increasing our knowledge base.

Thanks jglover, i know the basic of subnetting but just wasnt sure as to how they got the answer. i also posted another question as i said using packettracer or GNS3 i get a different answer but the book dissagrees so i would like to know if i am right or the book made a missprint

Chances are that your textbook is most likely correct

You are correct.... Years ago I was asked by my supervisor to help him hire someone. We decided to NOT allow anyone to get hired just because of the certification. We based all of our decisions on experience and answers to "common sense". Most if not all of the people that had a certification or two, and had little or no experience, did not make it.
I might be opening a can of worms here, but we found out, as did many other people in the industry, that people that paid schools to obtain a certificate, were only "thought" enough to pass the certification test. Result: Schools got their money, Students got their "certificate", we got applicants with a nice peace of paper, but no usable knowledge.

fyi greatnewproducts3 i have been in IT for 12yrs doing programminf but decided to switch, so when you say its just a cert its not do not put everyone in 1 category, Also it depends on a school, just beacuse someone went to svhool doesnt mean they dont know anything. Remember everyone was in this position one time or another, no one was born a cisco geneous

### Packet Tracer

There are errors in a few Packet Tracer exercises.

### OK, in response to the last question about how it works in real life -

I gather you understand the subnet size and number of hosts id decided by the bit position you mark the subnet at ie 000/xxxxx as against 00000/xxx etc. Well once you do that, what's actually available is shy two host numbers as the very first and last are stolen by the network for administration purposes like broadcasting etc. this happens in ALL networks and sub-networks, the more sub-nets the more admin hosts numbers that are used up.

Thus a subnet of 0000/xxxx is technically 16 hosts from .000 to .015 in decimal usage, but .000 and .015 are lost to administration and you get hosts .001 to .014 for actual usage.

Now mark the earlier answers with a thumbs up to show they answered the question for you.