all zeroes/all ones used in host IP's...

From: Mike A. Harris (mharris@meteng.on.ca)
Date: Fri Jan 28 2000 - 12:44:51 EST

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    On another mailing list I'm on there is a small discussion about
    using "0's" in IP addresses. Nobody could categorically say
    wether or not they are allowed or not including myself, so I
    hunted down RFC 1123, and found the relevant section.

    Here it is:

                IP addresses are not permitted to have the value 0 or -1 for
                any of the <Host-number>, <Network-number>, or <Subnet-
                number> fields (except in the special cases listed above).
                This implies that each of these fields will be at least two
                bits long.

    Now I interpreted that as meaning that none of the octets in an
    IP address could be 0 or "-1" in either the network/subnet or
    host portions of a valid host IP. The definition of "-1" is "all
    ones" in the host or network/subnet portion.

    I interpret the above as meaning that it is not legal to have a
    network like this:

    192.168.0.0/24 or 23.0.0.0/24

    with hosts 192.168.0.1 through 192.168.0.254 or with hosts
    23.0.0.1 through 23.0.0.254.

    The first zero makes it illegal no? Could someone in the know
    please clarify this as it has been bugging me for some time and
    nobody else seems to be able to say with 100% certainty what the
    proper rule is. Also, would a network like:

    142.255.255.0/24 be illegal?

    Someone has suggested that my interpretation is wrong, and if
    that is indeed so, I'd like to know the proper interpretation and
    share it with everyone.

    I looked through some of the kernel source and couldn't find any
    special handling of such addresses.

    Thanks very much in advance.
    Take care!
    TTYL 

    --
Mike A. Harris                                     Linux advocate     
Computer Consultant                                  GNU advocate  
Capslock Consulting                          Open Source advocate

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