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I’ve noticed that Linux and *BSD systems allow user to skip octets when using dot-decimal notation.

Here are some examples:

$ ping 10.1
PING 10.1 (10.0.0.1) 56(84) bytes of data.

$ ping 10.15.1
PING 10.15.1 (10.15.0.1) 56(84) bytes of data.

Note that this isn’t limited to the ping command.

I’ve found document defining textual representations of IPv4, but it doesn’t seem to cover that feature: Textual Representation of IPv4 and IPv6 Addresses.

Is there any other document defining this behavior? Is there a specific name for this behavior?

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Barnaba
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    it's possible that this isn't part of the standard, but instead a short cut in the specific applications. it could be widespread and a de facto standard, but maybe not official? – mfsiega Apr 13 '12 at 00:47
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    I found http://www.linuxsa.org.au/pipermail/linuxsa/2007-September/088131.html moderately insightful. It links to http://tools.ietf.org/html/draft-main-ipaddr-text-rep-02 for the "full saga". – tripleee Jul 23 '13 at 10:41

2 Answers2

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See inet_aton() man page. The last part is the numerical value representing the contents of the remaining bits in the address, i.e., a 24-bit y in x.y, and a 16-bit z in x.y.z.

ib.
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Stefan Lindblad
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-1

Abbreviated prefixes.

https://www.rfc-editor.org/rfc/rfc3779

prefix - a bit string that consists of some number of initial bits of an address, written as an address followed by a "/", and the number of initial bits. 10.5.0.0/16 and 2001:0:200:3:0:0:0:0/64 (or 2001:0:200:3::/64) are examples of prefixes. A prefix is often abbreviated by omitting the less-significant zero fields, but there should be enough fields to contain the indicated number of initial bits. 10.5/16 and 2001:0:200:3/64 are examples of abbreviated prefixes.

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Yves Dorfsman
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