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Re: IP address fee??

  • From: Ted Fischer
  • Date: Fri Sep 06 12:35:46 2002

At 10:00 AM 9/6/02 -0400, Joe Abley postulated:

On Thu, Sep 05, 2002 at 01:13:27PM -0500, Stephen Sprunk wrote:
> Because "Cee" is easier to pronounce than "slash twenty-four".  Ease of use
> trumps open standards yet again :)

Nobody was talking. "/24" is easier to type than "class C". No
trumps!  Everybody loses!

How many people learn about networks from certification courses or
in school, anyway? It was always my impression that people learnt
mainly by listening to other people.

If networking on the front lines is an informal oral tradition more
than it is a taught science, then perhaps it's natural for obsolete
terminology to continue to be "taught" long after it stopped having
any relevance.


   The class of an address is determined by the bit-pattern of the first octet of the address. will always be a Class A address. will always be a Class B address, and will always be Class C address.  I'm not aware of any RFC that rescinded the definition of the Class of an address.

   Masks, when associated with an address, enable one to determine  (a), what network I'm on (if I'm an IP host) or (b) how many addresses exist within a given range of addresses (if I'm a routing table).

   Subnetting (robbing mask host bits (0's) to make network bits (1's) allowed one to more effectively use the decreasing amounts of networks that required less than the default number of addresses (65,536 in the case of a Class B) by more effeciently using the space one had been allocated.  With subnetting, I can take one Classful network and make many (sub)networks from it.  There was no way prior to 1993, however, to effectively represent the range of addresses in more than one Classful network.

   CIDR, simply stated, says that one can use any address with any mask, regardless of the original class of the address, to represent a range of addresses (i.e. rob network bits to make host bits).  It allows the properties of IP to be more effectively used for IP host addressing (only need a /23 to support 400 IP hosts (a very effecient  78% use of the allocated space), as well as (one of the original, primary reasons for CIDR) aggregate ("Supernet") "X" traditional Class C's into one routing statement (who today would advertise delivery to the range of 4,096 addresses from, for example, through with 16 individual traditional Class C statements?).

   Since NANOG is "the front line", then perhaps that is where the oral tradition should be teaching the history of IP addressing, from Classful addressing (default masks) to Subnetting (other than default) to Supernetting (ranges of addresses regardless of original - or legacy if you will - class (Classless)).

   The prefix, of course, does not refer to the class of the address, but the number of contiguous ones in the mask.  As far as pronounciation goes, I prefer "slash 24" to "two fifty five dot two fifty five dot two fifty five dot zero" :)


Ted Fischer

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