Zefram <[email protected]> wrote:
> Peter Vince wrote:
>> Class E addresses?
>
> IPv4 address space is for some purposes divided into five classes:
> class A is 0.0.0.0/1, class B is 128.0.0.0/2, class C is 192.0.0.0/3,
> class D is 224.0.0.0/4, and class E is 240.0.0.0/4. Classes A, B, and
> C form the unicast address space, originally with subnet sizes linked
> to the classes but now with no real class distinction. Class D is the
> multicast address space. Class E, apart from the limited-broadcast
> address 255.255.255.255, remains reserved for future use.
Richard Stevens used to work for the National Observatory (U.S.) back in the
dawn time and the original edition of his TCP/IP Illustrated books used our
class B network for examples. It used to be a way to describe the size (or at
least scope) of an organization whether they were class B or C. (Very few
class A.) E.g., a large university might be class B, a university department
class C.
Probably no risk attached, but we should perhaps exclude 255.255.255.255 from
the encoding. For my current encoding, PHK's CRC keeps the final octet out of
harm's way:
255.255.255.47 -> OK 2142 8 127 -1 (1, 1)
As shown, the first three 255s would require a negative leap second at the end
of July 2142 with a specific prior offset. It might be a bit pedantic to worry
about this explicitly ;-) Other encodings might be more likely but we can
choose a CRC/SHA that avoids it.
Rob
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