Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)

Fernando Gont <fgont@si6networks.com> Sat, 13 February 2021 20:33 UTC

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To: Brian E Carpenter <brian.e.carpenter@gmail.com>, Ted Lemon <mellon@fugue.com>
Cc: v6ops@ietf.org, Fernando Gont <fernando@gont.com.ar>
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From: Fernando Gont <fgont@si6networks.com>
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Date: Sat, 13 Feb 2021 17:33:00 -0300
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Subject: Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)
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Hi, Brian,

On 13/2/21 17:18, Brian E Carpenter wrote:
[....]
>> ---- cut here ----
>> 5.1.  Address Attributes in Programming Languages
>>
>>      Python's ipaddress library [Python-ipaddr] defines 'IPv6Address'
>>      objects that have a number of attributes, including:
>>
>>      o  'True' if the address is allocated for private networks.
>>
>>      o  'True' if the address is allocated for public networks.
>>
>>      For ULAs, the is_private attribute is 'True', while the is_global
>>      attribute is 'False'.  This contradicts the definition of ULAs as
>>      having "global scope" [RFC4291] [RFC4193], but is in line with the
>>      specification update performed by this document (see Section 6).
>> ---- cut here ----
>>
>> (this one is documented in our draft, but credit goes to Brian for
>> spotting it).
> 
> The fact is that I spotted it due to an issue with running code.
> Just for fun, here is the test for ULAness according to the Python
> ipaddress module's semantics:
> 
> def is_ula(a):
>      """Test for ULA"""
>      return (a.is_private and not a.is_link_local
>               and not a.is_loopback
>               and not a.is_unspecified)

IIRC, I don't remember seeing a "is_ula" attribute. -- will recheck.



>> Are the is_private and is_global attributes employed by such library
>> correct? Do they match our specs? Do they match the obvious
>> interpretation of such attributes?  Should they be changed? Why, or why not?
> 
> A bit off topic, but I think the .is_private attribute is a very poor
> choice, because it might be misunderstood as implying privacy properties.

I believe the name attribute is borrowed from the IPv4 world (i.e., 
RFC1918).

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
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