CIDR - networking

[Joseph]

The class should never be determined by the mask but by the range in which
the ip address falls.
The standard masks are class a 255.0.0.0 class b 255.255.0.0 and class c
255.255.255.0 these are also known as classful.
A classless mask such as 255.255.192.0 can be used with an ip that is in the
class a or b but not with class c.
Classless is useful when subnetting host bit into subnets. 

For class a ip with a mask of 255.255.192.0
The first 8 bits 255 are the network bits
The next 10 bits 255.192 is the subnet bits
And the 14 last bits would be the host bits.


For class b ip with a mask of 255.255.192.0
The first 16 bits 255.255 are the network bits
The next 2 bits 192 is the subnet bits
And the 14 would be the host bits.

Class c can't use 255.255.192.0 because class c has to have at least a
standard mask of 255.255.255.0
You could use a classless mask of 255.255.255.192 to subnet the last octet.

If not done properly there could be overlapping.

That's my 2 cents or bits
Joseph
  

-----Original Message-----
From: owner-tlug-lxSQFCZeNF4 at public.gmane.org [mailto:owner-tlug-lxSQFCZeNF4 at public.gmane.org] On Behalf Of Kihara
Muriithi
Sent: Sunday, January 08, 2006 11:38 PM
To: tlug-lxSQFCZeNF4 at public.gmane.org
Subject: Re: [TLUG]: CIDR - networking

> Then again, given the scarcity of non-CIDR systems these days, why are 
> you so concerned with it?  In the 12 years I've been working with IP, 
> I've never seen anything but CIDR.  Address classes have been obsolete 
> for years.
  That sentence has homed at the problem. Its that I can't tell how a class
address look like. My understanding was that, if you see a netmask like
255.0.0.0 or 255.255.0.0 on what they were calling A and B respectively,
then that is class system. That is how my box is currently set up. ie
192.168.1.3  255.255.255.0
  I thought CIRD carry a mask like 255.128.0.0? ie no clean 255 to 0
transition. How would I identify a non-CIDR if I see one? I am very sorry
for my ignorance by the way

William

On 1/8/06, James Knott <james.knott-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org> wrote:
> Kihara Muriithi wrote:
> > Hi
> >  Thanks for the response. I suspected most modern host will work 
> > with CIRD, but haven't seen it used widely. Since it has been over 
> > 10 years since CIRD came to existance, this should not be the case 
> > and I wondered whether there was a technical reason behind it and 
> > hence the email  Now Knott, since you have experience with this set 
> > up, have you came across a problem that you can attribute to CIRD 
> > misconfiguration? What were the symptoms, just in case I ever happen 
> > to come across that issue? Allen mentioned an instance where CIRD 
> > can not be used and this may lead to a situation where classed and 
> > classless system network.
> >  One last thing, am I correct to assume one identify whether a host 
> > is configured with class or classless system by using "ifconfig" and 
> > "route" commands and then looking at the netmask?
>
> As I understand it, if you have a subnet mask where you can specify 
> how many bit to use, you have CIRD.  As I don't ever recall working 
> with a non CIDR system, I can't speak to any problems caused by it.  
> Bear in mind, that any CIDR system can be configured to behave like a 
> non CIDR system.
>

>
>
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