7 May
2022
7 May
'22
10:38 p.m.
On May 7, 2022, at 9:14 AM, ron minnich <rminnich(a)gmail.com> wrote:
I first learned in the 80s that 127.1 meant 127.0.0.1. I always
assumed zero padding was defined in a standard *somewhere*, but am
finding out maybe not. I talked to the IP OG, and he tells me that
padding was not in any standard. [side note: it's weird and wonderful
to still have so many people "present at the creation" of computing as
we know it still around, and to find they are so willing to answer
naive questions!]
Padding is a standard in ip6, possibly because the addresses are so
long. :: is your friend.
IP4 padding came up recently: the ip command interprets 10.2 as
10.2.0.0, whereas most things (golang libraries, ping, ...) interpret
it as 10.0.0.2. The latter interpretation accords with what I learned
40y ago.
But, I find myself wondering: where was the first use of the IP4 zero
padding convention?
From RFC791:
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.
So n.m format == network-number.local-address. The converse question is
who came up with the a.b.c.d format where each of a,b,c,d is in 0..255?