Re: Re: Re: Re: Re: Re: gethostbyname("1.1.1") returns 1.1.0.1 ????

RFC0791

Addresses are fixed length of four octets (32 bits). An address begins with a network number, followed by local address (called the "rest" field). There are three formats or classes of internet addresses: in class a, the high order bit is zero, the next 7 bits are the network, and the last 24 bits are the local address; in class b, the high order two bits are one-zero, the next 14 bits are the network and the last 16 bits are the local address; in class c, the high order three bits are one-one-zero, the next 21 bits are the network and the last 8 bits are the local address.

    Address Formats:

      High Order Bits   Format                           Class
      ---------------   -------------------------------  -----
            0            7 bits of net, 24 bits of host    a
            10          14 bits of net, 16 bits of host    b
            110         21 bits of net,  8 bits of host    c
            111         escape to extended addressing mode

      A value of zero in the network field means this network.  This is
      only used in certain ICMP messages.  The extended addressing mode
      is undefined.  Both of these features are reserved for future use.

once you have grokked this your question will be answered.

Comment on Re: Re: Re: Re: Re: Re: gethostbyname("1.1.1") returns 1.1.0.1 ????

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Re: Re: Re: Re: Re: Re: Re: gethostbyname("1.1.1") returns 1.1.0.1 ???? by MarkM (Curate) on Mar 12, 2003 at 06:22 UTC
I do not consider this to be an answer. Class A, Class B, and Class C addresses are methods of assigning network numbers. They have nothing to do with the format of the 'dotted decimal' form. The above describes an allocation scheme, it does not describe a syntax for dotted decimal notation. The words "dotted decimal notation" appear nowhere in the text. To prove this to yourself, consider the wording of a Class C address: "21 bits of net, 8 bits of host". If this section was not speaking about an allocation scheme, and it was talking about the suggested decimal notation syntax, would it not be an indication that "a.b" should mean a=21bits, and b=8bits? Of course not. This section defines how the 32 bit address space is logically classified into different sized network partitions. Now, I can believe that the BSD people assumed that they could extend the traditional 'quad dotted decimal' form, and 'enhance' inet_aton/inet_addr to allow nodes within a Class A allocation to be addressed using a single integer, however, nowhere have I found an official syntax (BNF or otherwise) that defines this method of accepting/parsing dotted decimal ip addresses as a requirement, or even a suggestion. Also, as I stated before, the email specifications seem to require that ip addresses are strictly checked, and that ip addresses used in email headers must be in quad form with values of 0-255 for each decimal integer. The inet_aton/inet_addr implementation in GLIBC further extends 'decimal integer' form to allow base 8 and base 16 integers. I have not found a reference that defines this implementation as standard or portable either.	[reply]

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Re: Re: Re: Re: Re: Re: Re: gethostbyname("1.1.1") returns 1.1.0.1 ????
by MarkM (Curate) on Mar 12, 2003 at 06:22 UTC

I do not consider this to be an answer. Class A, Class B, and Class C addresses are methods of assigning network numbers. They have nothing to do with the format of the 'dotted decimal' form. The above describes an allocation scheme, it does not describe a syntax for dotted decimal notation. The words "dotted decimal notation" appear nowhere in the text.

To prove this to yourself, consider the wording of a Class C address: "21 bits of net, 8 bits of host". If this section was not speaking about an allocation scheme, and it was talking about the suggested decimal notation syntax, would it not be an indication that "a.b" should mean a=21bits, and b=8bits? Of course not. This section defines how the 32 bit address space is logically classified into different sized network partitions.

Now, I can believe that the BSD people assumed that they could extend the traditional 'quad dotted decimal' form, and 'enhance' inet_aton/inet_addr to allow nodes within a Class A allocation to be addressed using a single integer, however, nowhere have I found an official syntax (BNF or otherwise) that defines this method of accepting/parsing dotted decimal ip addresses as a requirement, or even a suggestion. Also, as I stated before, the email specifications seem to require that ip addresses are strictly checked, and that ip addresses used in email headers must be in quad form with values of 0-255 for each decimal integer.

The inet_aton/inet_addr implementation in GLIBC further extends 'decimal integer' form to allow base 8 and base 16 integers. I have not found a reference that defines this implementation as standard or portable either.

[reply]