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Help needed in LAB!
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| overkast 2003-03-19, 10:03 pm |
| Hi crew,
I'm stumped on this question from one of my lab books. I know how to subnet no worries but what do they mean by having no more than 230 hosts on any segment?
NNNNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH
How many host bits do I borrow?
ie. 2^10-2=1022 this /4(4segments)= 256??
More than 230 hosts?? hmmm
so do I borrow 9 bits?
ie. 2^9-2=510
Any help would be greatly appreciated.
Thanks for your time.
I have attached an image to explain the topography!
Overkast
Sorry - I didn't realise the image would be resized.
The Notes section says:
1. Given the network number 167.45.0.0
there is only to be a maximum of 230 hosts
on any segment then devise an ip addressing
scheme for the accompanying diagram.
2. Prevent hosts, in the lower range of the last octet of the ip addess space, from telnetting into the adelaide router while allowing the upper addresses of the last octet from gaining access to the same router.
Presuming we are the Perth Router. | |
| mcsefarmboy 2003-03-20, 7:30 am |
| Based on what I can tell in your question it looks like they are looking for a subnet mask of 255.255.255.128 because that would allow you to have 510 subnets and 126 nodes per subnet. The reason I say that is because if the subnet mask was 255.255.255.0 then that would leave you with 254 nodes per subnet, which would be over the 'maximum.' That is the only logical answer I can conclude from this sample question.
Would others agree?
MCSEFARMBOY | |
| Townsend 2003-03-20, 7:53 am |
| If there is the possibility of having a mawimum of 230 hosts woulldn't it be necessary to borrow 8 bits. This would give you 254 usable subnets and 254 usable hosts. Which allows for the maximum of 230 given in this problem. | |
| edmonds_robert 2003-03-20, 8:26 am |
| I agree with Townsend. When they say a maximum of 230 hosts on a subnet, they mean there won't be any more computers than that. They don't mean don't allow more than that with your subnet mask. The correct answer here is 255.255.255.0. | |
| mcsefarmboy 2003-03-20, 8:30 am |
| But when it says maximum I take that as meaning that you can't have more then 230 hosts. Consequently, borrowing only 8 bits would go over 230 host maximum. | |
| mcsefarmboy 2003-03-20, 9:03 am |
| But when it says maximum I take that as meaning that you can't have more then 230 hosts. Consequently, borrowing only 8 bits would go over 230 host maximum. | |
| clarkv 2003-03-20, 10:30 am |
| I agree with Townsend. You cannot choose a subnet mask that will give a maximum of 230 hosts - it just doesn't work like that. Using 7 bits for hosts will give you a max of 126 (2^7 - 2). Using 8 bits for hosts will give you a max of 254 (2^8 - 2). They didn't mention a minimum, which would make more sense, but the bottom line is you cannot get 230 hosts from 7 host bits.
With a subnet of 167.45.0.0, this being a class B address, you will end up with a subnet mask of 255.255.255.0 - just what edmonds_robert said. | |
| edmonds_robert 2003-03-20, 12:09 pm |
| I see where mcsefarmboy is coming from, but when it says that on the test, trust me, it means that it is the maximum number of hosts on the subnet, and that you should create a subnet mask to accomodate ALL of them. In this case, that means a /24 network. This all goes back the most sound testing advice, "Don't read anything into it." | |
| b_baruah 2003-03-21, 6:26 am |
| no more then 230 hosts per subnet.
so 2^n - 2 > = 230
i.e. n = 8
8 bits are required for hosts.
mask is 255.255.255.0
in that way you can have
subnets starting from 167.45.1.0 to
167.45.254.0. | |
| overkast 2003-03-24, 5:10 am |
| Hey crew thanks for all your replies. Very much appreciated.
I'm about to log off the net here in OZ and was wondering if anyone if they had the chance could show me their working out for this LAB - a big request I know(but some may have a spare minute whilst at work or something). I will be working on the router commands tonite and just wanted to double check that I had the access lists and commands correct before I try the lab on the routers tomorrow - just to make sure I am on the right track.
Thanks for your time people!
Overkast | |
| overkast 2003-03-25, 5:09 am |
| Hey guys,
I'm now really struggling with this lab question and won't be seeing anyone else that can help me with it until later in the week. Could anyone help me with this LAB?
Thanks guys - sorry to bug ya,
Overkast | |
| darronb 2003-03-25, 10:44 am |
| The only combinations that you can have which fits closest to your questions is:
Class B Address
Sub net of 255.255.255.0
Network address of 167.45.0.0
Each subnet can have 254 hosts. (you have 24 spare, you lucky thing)
And a maximum of 254 subnets avalable.
giving you a maxamum of 64516 hosts.
As stated before if the subnet 255.255.255.128 is used then you only have the capability of having 126 hosts.
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| overkast 2003-03-27, 12:36 am |
| Hi People,
Just wondering if someone could set this right for me. I've tried to find out details on using an ACL to deny the lower part of the ip address!! So I'm presuming they mean the lower part of the IP address of the perth E0 Network - 167.45.1.0 (see image)
How do I do this LAB? :-(
Thanks again crew,
Overkast | |
| edmonds_robert 2003-03-27, 8:06 am |
| Your access-list should look something like this:
access-list 1 permit 167.45.1.1 0.0.0.127
line vty 0 4
access-class 1 in | |
| overkast 2003-03-27, 10:37 pm |
| Edmond_Robert - could you please clarify how this would stop people from telnetting into the Adelaide router? Wouldn't that stop people from telnetting the Perth router (167.45.1.1)? Sorry to ask more questions.
I'm struggling to get a grip on ACL's!
Also the question I think is confusing - it says to "while allowing the upper addresses from gaining access to the same router"
So I'm presuming we are denying this range!
Access-list 2 deny 167.45.1.1 0.0.0.128
Does that make sense or is there no point in setting this deny access-list because of the Implicit deny on the router!
Thats why I am confused - or does the question really mean to "permit" this range!
Sorry about all the questions - but thanks alot for the help!
Cheers,
Overkast | |
| edmonds_robert 2003-03-28, 7:04 am |
| Actually, I'm having trouble reading the lab, so I just kind of guessed at what to put. But basically, an access list similar to that one should be placed on the appropriate router, either permitting or denying the range you want. The access-class command is similar to the access-group command, except it is used on your vty lines instead of physical interfaces. |
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