Regular Expression for IPv6 addresses
marka at isc.org
Sun Feb 7 00:43:15 UTC 2010
In message <6eb799ab1002061452s51f9cf61p303d36130291301 at mail.gmail.com>, James
> On Fri, Feb 5, 2010 at 12:15 AM, <sthaug at nethelp.no> wrote:
> >> > And now for the trick question. =A0Is ::ffff:077.077.077.077 a legal
> >> > mapped address and if it, does it match 077.077.077.077?
> Wasn't there an internet draft on that subject, recently?
> 077.077.077.077 is equivalent to 184.108.40.206 if valid at all
> RFC 4038 is very clear that the text representation of a mapped IPv4
> address is Base 10. http://tools.ietf.org/html/rfc4038#section-5.1
But 077.077.077.077 is octal dotted quad. Decimal dotted quad does
*not* have leading zeros. The point of allowing for dotted quad
is to allow for easy mapping between IPv4 representation and IPv6
with encoded IPv4 representations. Accepting a octal representation
as decimal is a bad thing and leads to none obvious failures.
% ping 077.077.077.077
PING 077.077.077.077 (220.127.116.11): 56 data bytes
--- 077.077.077.077 ping statistics ---
4 packets transmitted, 0 packets received, 100% packet loss
"ping ::ffff:077.077.077.077" would not get to same box if my ping
accepted that as a address literal which luckily it doesn't.
> This is a bit like asking if "::ffff:10.1.2" is a valid IP
> address though.
Except it clearly isn't as there are not 4 components.
> And is it the same as the ip address "10.1.2" ?
> (Which of course expands to 10.1.0.2, on common implementations of
> inet_pton, inet_aton, and getaddrinfo) Or ::ffff:0xA010002
inet_pton() did not accept 10.1.2 when it was originally written.
This was a *deliberate* decision. Some vendors have changed it to
accept it but they are wrong. I can say that because I was involved
in making that decision.
> I would say these are perfectly valid _shorthands_ and
> abbreviations for entering an IP address, which may be provided by
> some systems, but that they are non-canonical text representations
> for displaying publishing or sharing IP addresses.
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: marka at isc.org
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