在我的网络中,我有一个 IP 地址为 10.0.0.15 的服务器。偶然间,我发现命令:ping 10.0.15
结果是
64 bytes from 10.0.0.15: icmp_seq=1 ttl=64 time=9.09 ms
...所以正确的服务器响应 ping。即使我尝试:ping 10.15
我也会得到类似的结果。此外,远程登录到部分地址也可以按预期工作。但是,SSH 失败。为什么发送到部分地址的数据包会到达正确的服务器?
答案1
根据inet_aton(3)
函数文档,这是允许的形式:
DESCRIPTION
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‐
work addresses.
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‐
ment.
例如
$ perl -MSocket=inet_aton,inet_ntoa -E 'say inet_ntoa(inet_aton("10.0.15"))'
10.0.0.15
$ perl -MSocket=inet_aton,inet_ntoa -E 'say inet_ntoa(inet_aton("10.15"))'
10.0.0.15
$
然而,现在最好改用getaddrinfo
或inet_ntop
要求 IPv6 支持。 “B 类”东西早在 1994 年左右就成为遗产,现在我们有了 CIDR 并且/24
......
嘿,你也可以给它一个大的旧整数(但请不要)
$ perl -MSocket=inet_aton,inet_ntoa -E 'say inet_ntoa(inet_aton("2130706433"))'
127.0.0.1
$ getent hosts 2130706433
127.0.0.1 2130706433
$ ssh 2130706433
The authenticity of host '2130706433 (127.0.0.1)' can't be established.
...
(这可能无法移植到其他 unix;特别是 OpenBSD 无法解析 2130706433...)