That is an allowed form according to the
inet_aton(3) function docs:
inet_aton() converts the Internet host address cp from the IPv4 num‐
bers-and-dots notation into binary form (in network byte order) and
stores it in the structure that inp points to. inet_aton() returns
nonzero if the address is valid, zero if not. The address supplied in
cp can have one of the following forms:
a.b.c.d Each of the four numeric parts specifies a byte of the
address; the bytes are assigned in left-to-right order to
produce the binary address.
a.b.c Parts a and b specify the first two bytes of the binary
address. Part c is interpreted as a 16-bit value that
defines the rightmost two bytes of the binary address. This
notation is suitable for specifying (outmoded) Class B net‐
a.b Part a specifies the first byte of the binary address. Part
b is interpreted as a 24-bit value that defines the rightmost
three bytes of the binary address. This notation is suitable
for specifying (outmoded) Class C network addresses.
a The value a is interpreted as a 32-bit value that is stored
directly into the binary address without any byte rearrange‐
$ perl -MSocket=inet_aton,inet_ntoa -E 'say inet_ntoa(inet_aton("10.0.15"))'
$ perl -MSocket=inet_aton,inet_ntoa -E 'say inet_ntoa(inet_aton("10.15"))'
However these days it would likely be better to instead use the
inet_ntop calls for IPv6 support. The "Class B" stuff became legacy back in 1994 or so now that we have CIDR and
Hey you can also give it a big old integer (but please don't)
$ perl -MSocket=inet_aton,inet_ntoa -E 'say inet_ntoa(inet_aton("2130706433"))'
$ getent hosts 2130706433
$ ssh 2130706433
The authenticity of host '2130706433 (127.0.0.1)' can't be established.
(This may not be portable to other unix; in particular OpenBSD cannot resolve 2130706433...)