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Home > Archive > CCNA > May 2003 > Subnetting 101- Lab 5/14/2003
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Subnetting 101- Lab 5/14/2003
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| anchor40 2003-05-14, 9:11 am |
| Good Morning!
Here's the subnetting practice question for today:
You're implementing a 12 site Frame Relay network in a point-to-point fashion, and the corporate security policy states that all network devices must be configured with a unique IP address. Each remote site has 6 PCs, a printer, a managed Ethernet switch and a router with one Ethernet and one Serial interface. You wish to summarize the networks at the head-end router to reduce the size of your routing table. You've been given 10.165.82.0/24 for this project. Allocate the LAN addressing for the 12 remote sites and the point to point links (HINT: start at the outside and work in).
**NOTE - There are multiple ways to solve this particular problem, but the hint was provided to guide you towards one of them. **
Here's the answer to the 5/12 question:
code:
Given the following IP address and mask, provide the class,
network ID, # subnets, and # of hosts per net:
Address/mask Class Net ID #subs # hosts
================== ===== ================== ======= ========
___.___.___.___/__ _ ___.___.___.___/__ _______ ________
72.53.144.12/20 A 72.53.144.0/20 4094 4094
Net 72. 53.144. 12
Mask 255.255.240. 0
72.0011 0110.1001 0000.0000 0000
255.1111 1111.1111 0000.0000 0000
--| SN |--------- <--subnets
-------------| H | <--hosts
4.192.255.61/8 A 4.0.0.0/8 0 16777214
Net 4.192.255. 61
Mask 255. 0. 0. 0
4.1100 0000.1111 1111.0011 1101
255.0000 0000.0000 0000.0000 0000
--------------------------- <--subnets
---| H | <--hosts
232.214.7.101/23 D N/A N/A N/A
172.17.142.7/20 B 172.17.128.0/20 30 2046
Net 172. 17.142. 7
Mask 255.255.240. 0
172. 17.1001 1110.0000 0111
255.255.1111 0000.0000 0000
--|SN |--------- <--subnets
-------| H | <--hosts
Ok, so I threw a curve ball - Class D's don't have a subnet mask, but rather use the IP address to create the Multicast group ID. 
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| B4yaman3 2003-05-14, 11:26 pm |
| Ip --> 172.17.142.7/20 Mask --> B
Net ID --> 172.17.128.0/20 Sub--> 30 Hosts --> 2046
Is something wrong here.. /20 gives me 12 bits remaining which yields 2^12 = 4096.
Also can you say how you got the network ID?
You explanation will be greatly appreciated! | |
| anchor40 2003-05-15, 9:29 am |
| quote:
Is something wrong here.. /20 gives me 12 bits remaining which yields 2^12 = 4096.
Also can you say how you got the network ID?
Nope, you're absolutely right. I was using my trusy Windoze calculator in scientific mode and accidentally hit 2^11 instead of 2^12.
On the Net ID, I inadvertenly added a bit in the 16's place (the decimal equivalent of what was shown is actually 158, not 142), but 128 is the correct network ID.
Double whammy for me today! 
Here's the corrected answer for that one:
code:
172.17.142.7/20 B 172.17.128.0/20 30 4094
Net 172. 17.142. 7
Mask 255.255.240. 0
172. 17.1000 1110.0000 0111
255.255.1111 0000.0000 0000
--|SN |--------- <--subnets
-------| H | <--hosts
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| isn't this class B --> 172.17.142.7/20 ? /20 will give you 4 subnet bits remaining in a class B. Why will I get (2^12=4096) subnets if i only have 4 bits remaining to do subnet ? this should be
(2^4=16) subnets . hmmmm just wondering ?
please correct me if im wrong ..
thanks | |
| anchor40 2003-05-15, 12:47 pm |
| Is this Monday? It sure feels like it...
It is class B, and there are 4096 HOSTS (2^12) and 16 subnets (2^4).
When I did the math the first time, and accidentally used 2^11 for hosts (original note from B4Yaman3), and 2^5 for subnets (your note).
Needless to say, I corrected the value for the hosts, but not the nets.
Thanks to all of you for not only reading and catching my mistakes, but asking me when you have questions. Ever read something so many times, you start to see what you expect to be there, and not what's really there?  | |
| B4yaman3 2003-05-15, 1:42 pm |
| Anchor40 that's for all your explanations.By the time I am ready for the ccna exam i will close my eyes when I see a subnetting question because you taught me. | |
| anchor40 2003-05-15, 4:51 pm |
| It was my pleasure! 
Keep us posted on your progress!
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