RE: VLSM

Unanswered Question
Mar 17th, 2008
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Hello,

Please help, this has already been posted but i am having problems seeing your replies.


I have two main sites:

Glasgow: 300 staff

Birmingham: 300 staff


Five regional sites:

Aberdeen: 20 staff

Newcastle: 40 staff

Liverpool: 20 staff

Bristol: 20 staff

London: 30 staff


Branch sites:

each region also has a number (up to 5)of smaller branch sites smaller sites with 10 staff.


All addressing must allow for 30% growth over 3 years.


The company leases a range of class C networks of public IP addresses from its main ISP, which have been assigned as required as the network has grown.


what I am trying to do is find a suitable network address that will support this addressing scheme using VLSM.


Sorry if this sounds confusing, but I am confused myself as I dont think this can be done either but according to my lecturer it has been done in the past.


Regards


Scott


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d.metheny Wed, 05/07/2008 - 12:42
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Sounds like you need to use private IP addresses, and NAT, on your network. If you have only a single Class C available, you cannot possibly split it up into this many IP's.


There really isn't enough information here to determine exactly where you MUST use the leased Class C IP's.

Hi there


This question was posted a while back and the question and the responses it received can be found at this link http://forums.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Career%20Certifications&topic=Training&topicID=.ee702b3&fromOutline=&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.2cbfee24


As I stated in my response to the previous post , designing a VLSM addressing scheme for the above is totally possible and is not too difficult. However some of the first pieces of information that will be needed are

(a) Exactly how many Class C networks your company has leased from your ISP


(b) What are the network numbers of these networks


(c) Is this a contiguous block of Class C networks or are they discontiguous network ranges?


You stated in your post above that "The company leases a range of class C networks of public IP addresses from its main ISP". By the use of the words "range of Public IP addresses" I take this to mean that the company leased more than a single Class C network. Also that these are NOT RFC-1918 private IP addersses in the 192.168.0.0/16 range (see the word "Public"), so NAT will not be required in this situation. Anyway the question is about designing a VLSM scheme, not configuring NAT on a router.


Then you just work out the following


Glasgow: 300 staff + 30% = 400 staff. Use a /23 subnet which yeilds 510 usable IP addresses


Birmingham: 300 staff + 30% = 400 staff. Use a /23 subnet which yeilds 510 usable IP addresses


Five regional sites:


Aberdeen: 20 staff + 30% = 27 staff. Use a /27 subnet which yeilds 30 usable IP addresses


Newcastle: 40 staff + 30% = 53/54 staff. Use a /26 subnet which yeilds 62 usable IP addresses


Liverpool: 20 staff + 30% = 27 staff. Use a /27 subnet which yeilds 30 usable IP addresses


Bristol: 20 staff + 30% = 27 staff. Use a /27 subnet which yeilds 30 usable IP addresses


London: 30 staff + 30% = 40 staff. Use a /26 subnet which yeilds 62 usable IP addresses


"Branch sites:

each region also has a number (up to 5)of smaller branch sites smaller sites with 10 staff. "


Each Branch Site currently has 10 staff + 30% = 13/14 staff. Use a /28 subnet for each Branch Site, which will yeild 14 usable IP addresses for each /28 subnet.


After that, it's just working out the range of each subnet and for this you need the answers to questions a, b & c above.


HTH


Best Regards,


Michael

ipmask2007 Fri, 06/06/2008 - 14:14
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Hi Scott!

I'm not sure if I can post such a message here.

But if u r in Scotland and studying for CCNP would u like to do some labs together? I'm in Glasgow preparing for the BCMSN exam, and don't know anyone else who is studying for CCNP now.

Cheers,

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