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Date: Wed, 27 Sep 2023 16:35:27 -0600
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Subject: Re: Cygwin/Win32 utility function to convert "raw" IPv6 address
 string into *.ipv6-literal.net string ?
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From: Brian Inglis via Cygwin <cygwin AT cygwin DOT com>
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On 2023-09-27 11:02, Lavrentiev, Anton (NIH/NLM/NCBI) [C] via Cygwin wrote:
>> Does Cygwin (or Win32) have a function to convert "raw" ASCII IPv6 addresses into *.ipv6-
>> literal.net per

Not hard to change ":" to "-" and append .ipv6-literal.net - in bash:

	${addrv6//:/-}.ipv6-literal.net

	$ getent ahosts -- --1.ipv6-literal.net
	::1             STREAM ::1
	::1             DGRAM  ::1

> If Windows API is documented to have such a function, you should be able find
> it in the w32api package in Cygwin.
> As for the "literal" representation, the only "standard" and documented IPv6 
> DNS notation is in the .ip6.arpa domain (the analog for IPv4's 
> "in-addr.arpa").
> Microsoft seems to have uniquely "enhanced" that convention to use a more
> compact notation... > Even though it says it resolves internally without DNS on Windows, this
> convention is not likely portable (and will cause an actual DNS hit on other
> platforms that do not specially recognize ".ipv6-literal.net" -- unlike the
> treatment of ".ip6.arpa").
> And a likely result of that is going to be "NXDOMAIN" (domain does not
> exist).
Just have to unstuff any "::" to enough ":0000...:" to make 8 groups, fill to 4 
hex digits each, strip the ":"s then reverse the (hex) digits or vice versa, add 
"."s after each, and add ip6.arpa e.g.

::1 ->
0000:0000:0000:0000:0000:0000:0000:0001 -> 
1000:0000:0000:0000:0000:0000:0000:0000 ->
10000000000000000000000000000000 ->
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa

$ host -t ptr \
	1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa domain 
name pointer localhost.

but there may be few PTR records set up or recognized for IP V6 addresses.

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry


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