PROBLEM IN SUBNETs CLASSFULL AND CLASSLESS!!!!!!!

[Anand Solgama]

SUBNET PROBLEM

In classfull we can use 10.0.0.0/8 as class A so we can start subnettting from /8/9...upto/32 so in short we have to start from /8 ..upto /8 all r NETWORK....

But in classless 10.0.0.0 we can use from /1 right or /25 or any mask

Questions::

1-why no need to start from /8 on class A

/16 on class B etc ...why ??

2-why we can use NETWORK bits upto /9 /10/15 etc ....????

3-how to know I have been ask on 10.0.0.0/8 from classA(classfull) or classless so how to calculate???

I have good picture example attached with this message...

In that I used 172.16.1.1/16 so in classfull 172.16.0.0/16 start host from /17 right??? so UPTO /16 ALL ARE NETWORK AFTER THAT SUBNET AND HOSTlike in my picture

but in classless picture calculator start from /20 as well and UPTO /20 ALL ARE NETWORK AND AFTER THAT HOST AND SUBNET??why???

[Jon Marshall]

Anand

1) because it is classless so 10.0.0.0/1 is a perfectly valid range ie. that address covers all the class A networks

2) don't understand the question - please clarify

3)  10.0.0.0/8 is the classful address ie. a class A network uses 255.0.0.0 as the network mask

In that I used 172.16.1.1/16 so in classfull 172.16.0.0/16 start host from /17 right???

the above doesn't make a lot of sense. if you have 172.16.0.0/16 the first host address is 172.16.0.1 and the last host address is 172.16.255.254.  

I'm not sure what your document is meant to be showing as the second window is empty.

Perhaps you could try and be more precise in exactly what you want to know ?

Jon

[Joseph W. Doherty]

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Posting

Perhaps you're a bit confused about classful vs. classless addressing.

For both, we need some method to distinguish between the network portion of the address and the host portion of the address.

With classless, whenever we "send" a network IP address, we included a network mask.  This allows the "recipient" to know what portion of the address is to be used for the network number and which portion contains a host number.  This also allows us to have no predefined network/host boundaries.  So we can have 10.0.0.1/24 or 196.168.1.1/8; pretty much anything we want except for the IP addresses set aside for multicast and experimental.

With classfull addresses (when both bandwidth and router memory were very expensive, i.e. we don't want to send or store the mask), we determine what the network and host portions of the IP address are by some rules.  If the first bit of the IP address is zero, it's a class A (/8).  If the first bit of the address is a one, but the second bit is a zero, it's a class B (/16).  If both the first bit and second bits are ones, it's a class C (/24).  (BTW, there are also performance advantages to looking at just the first or first two bits on very early computers.)

Classfull is a neat "trick", but having just 3 predefined network masks is often rather inconvenient.  So, often the "natural" class networks were subdivided (i.e. subnetted).  Doing so, though, comes with a bunch of dos and don'ts, because network masks are not provided with the IP address.

[Guru Mysoruu]

Hi Anand,

IPv4 Ip address is 32 bit Binary address and which contains four octets.

so each octet is represented by eight bits

		8 bit	7 Bit	6 Bit	5 Bit	4 Bit	3 Bit	2 Bit	1 Bit
		128	64	32	16	8	4	2	1
Class A	0-127	0	1	1	1	1	1	1	1
Class B	128-191	1	0	1	1	1	1	1	1
Class C	192-224	1	1	0	1	1	1	1	1

In Classfull,Class A network i.e 8 bit value 128 will never become one.In any other bit it may be 0 or one.at most it can have a value of 127.thats how classfull network defined.

Class A Network 10.0.0.0 can be represented has

10= (128*0)+(64*0)+(32*0)+(16*0)+(8*1)+(4*0)+(2*1)+(1*0)

   =8+2=10

0=(128*0)+(64*0)+(32*0)+(16*0)+(8*0)+(4*0)+(2*0)+(1*0)

  =0

0=(128*0)+(64*0)+(32*0)+(16*0)+(8*0)+(4*0)+(2*0)+(1*0)

=0

0=(128*0)+(64*0)+(32*0)+(16*0)+(8*0)+(4*0)+(2*0)+(1*0)

  =0

For class A Subnet mask

255= (128*1)+(64*1)+(32*1)+(16*1)+(8*1)+(4*1)+(2*1)+(1*1)

   =128+64+32+16+8+4+2+1

   =255

0=(128*0)+(64*0)+(32*0)+(16*0)+(8*0)+(4*0)+(2*0)+(1*0)

  =0

0=(128*0)+(64*0)+(32*0)+(16*0)+(8*0)+(4*0)+(2*0)+(1*0)

=0

0=(128*0)+(64*0)+(32*0)+(16*0)+(8*0)+(4*0)+(2*0)+(1*0)

  =0

For class A-It will start from 0-126,subnet will be 255.0.0.0 i.e /8

For Class B it will start from 128-192,subnet will 255.255.0.0.i.e /16

For Class C,it will start from 192-224,subnet will be 255.255.255.0 i.e /24

These are classfull networks.

In Classless network,as per our requirement changes will be done to subnet mask

In your Classfulll screen diagram,you have assigined 20 bits for network and 12 bit for host and for 16 subnets.i.e /20 network

In your classless,you have assigned 24 bit for network and 8 bit for host i.e /24 network

Regards,

Guru