Mail from ILUG-BOM list (Non-Digest Mode)
On Thu, 22 Jun 2000, Philip S Tellis wrote:
> Mail from ILUG-BOM list (Non-Digest Mode)
>
> Sometime Today, Rajen Parekh assembled some asciibets to say:
>
> > BTW, what is Netmask? And what do the nos. 255.0.0.0 [or something like
> > that] means.
>
> You have IP addresses: 202.54.1.18, 192.168.0.1, 127.0.0.1, 89.1.1.200
> etc
>
> It is actually a 32 bit integer split into 4 8 bit integers so that it
> becomes easier for humans to handle.
>
> These IP addresses come in different classes depending on how big a
> network they can service.
>
> If you have a really large network (a few million computers) then you'd
> want what is known as a class A network address.
>
> Class A networks have the most significant bit as zero. So basically, the
> first number in your IP address dotted format will range from 0 to 127.
> 0 of course is reserved, so you can't use that.
>
> 1.0.0.0 to 127.0.0.0 Are your class A networks - each of which can
> address 16777214 machines (note, 2^24 - 2 because 0 and 255 are not
> allowed).
All this is quite technical. Still I am trying to understand it. Can you
tell me what you mean by most significant bit?
> 127.0.0.1 is your loopback address, so is also eliminated.
>
> Now, you have class B addresses, that have msb 1 and next bit 0. So this
> creates a range from 128.0.0.0 to 191.0.0.0. This isn't your network
> address though. Your network address is 128.x.0.0 to 191.x.0.0 where x is
> any integer from 0 to 255.
Same question here and also below, what is the meaning of most significant
bit? And how is related to assign IP addresses?
> Similarly, Class C addresses start with 110 (in binary) and range from:
> 192.0.0.0 to 224.0.0.0 (not entirely sure about this), with network
> addresses 192.x.y.0 to 224.x.y.0
>
> There's also Class D, and many more subclasses that aren't important right
> now.
>
> Now the big question is, how do you figure out what part of an IP address
> is the network address, and which part is the actual machine number.
>
> That's where the netmask comes in.
>
> For a class A network, the mask is 255.0.0.0. If you perform a bitwise
> ANDing of this with an Class A IP address (eg: 10.0.0.18) you will get the
> network address: 10.0.0.0
> If you NAND it with the network address, you get the number of hosts that
> can be addressed by that network: 0.255.255.255 = 16777216.
Sorry Philip, but what is ANDing and what is NANDing? I think due to my
non-engineering background, I will be asking you such [silly?]
questions. Since this is a Linux ML and not a networking learning ML, I
think other users may not like it. If so, if you don't mind then I could
communicate in this matter to you directly.
> Now, if you have a really small network (<100 machines) you want a really
> restrictive netmask: 255.255.255.127 maybe
> and with a network address like 240.120.15.0, you would be able to address
> 240.120.15.0 NAND 255.255.255.127 = 128 machines.
>
> Your network address and subnet mask together tell machines which network
> they belong to, what broadcast address they should use etc. It also tells
> them which other machines belong to their network - which makes it easy
> for you to have to different logical networks on the same cable.
>
> Hope this explains it.
>
> Philip
>
>
Rajen.
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