subnet 0 problem

Unanswered Question
Sep 26th, 2007

The network administrator needs to address seven LANs. RIP version 1 is the only routing protocol in use on

the network and subnet 0 is not being used. What is the maximum number of usable IP addresses that can be

supported on each LAN if the organization is using one class C address block?

A. 6

B. 8

C. 14

D. 16

E. 30

F. 32

What's the correct answer?

I have this problem too.
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keesjan.schilstra Wed, 09/26/2007 - 05:45

Hi,

I might have a solotion for others in finding more time during the exam.

Subnetting should cost you 10 sec a question there are some 10 questions about subnetting so that would not cost you more then 2 minutes. Subnetting in 10 seconds?

Yes its simple.

Write down the bitnumbers of the last 2 octets and the sequence of 128 64 etc.

_17,18,19,20,21,22,23,24

_25,26,27,28,29,30,31,32

128,64,32,16,_8,_4,_2,_1

for example give me the subnet and broadcastadress of 172.168.61.1/22

it's simple look at the table 22 is step 4

Divide 61 by step 4 and multiply the WHOLE NUMBER 15 by step 4 the subnet is 60 next subnet is 60 plus step 4 = 64 so broadcastadress is 63.255 (B-class)

61/4=15*4=60 next subnet 64 so subnet is 63.255

or 172.168.61.1/19 look at the table. 19 is step 32

61/32=1*32 subnet= 32 next subnet is 32+32=64 so broadcast is 63.255

or 192.161.15.1 /28

15/16=0 0*16=0 so subnet is 0 next subnet is 16 broadcast is 15 (C- class)

Succes

keesjan.schilstra Wed, 09/26/2007 - 06:06

hi.

you have 256 ip adresses in a C class subnet 0 upto 255

if subnet 0 not used then you have to divide 256 by 8 subnets (7 including the 0 subnet)

8/256\is 32 ip adresses but you need a subnet and broadcast adress so 32-2 =30 usable ip adresses on each lan.

succes

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