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

Fernando Gont <> Fri, 19 February 2021 00:10 UTC

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To: "Manfredi (US), Albert E" <>
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From: Fernando Gont <>
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Date: Thu, 18 Feb 2021 20:58:24 -0300
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Subject: Re: [v6ops] [EXTERNAL] Re: Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)
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On 18/2/21 20:39, Manfredi (US), Albert E wrote:
> -----Original Message-----
> From: ipv6 <> On Behalf Of Fernando Gont
>> Well, this is a spec inconsistency. You have one spec (RFC4007) defining
> "scope" and "global scope", and another specs:
>> a) making use of the same terms in an incorrect way, or,
>> b) employing same terms but with a different definition.
>> i.e., either the definition in RFC4007 is incorrect, or the use in
> RFC4193 and implicit use in RFC4291 is incorrect.
> You can also argue, if there are prefix bits sent in the clear, and those prefix bits are used to send the packets to a pre-determined gateway, and that gateway is then used to decrypt all of the remaining address bits, then route packets through a walled garden intranet with global span, then global scope could still apply.

"global span" is defined as "Internet-wide" span. i.e., if an address 
does not unambiguously specify an interface Internet-wide, it's not 
global scope as per RFC4007.

> Just sayin'. These still aren't like RFC 1918.

The only practical differences I see with respect to rfc1918 are:

1) ULAs are not intended to be used with NAT.
However, were RFC1918 strictly specified to be employed along with NAT? 
Besides "not indended" != "won't be".

2) ULAs are intended to have a small probability of collision when a 
subset of ULA-based networks are interconnected.

This is the product of mandating that some bits are generated from a 
PRNG, plus the fact that ULAs have more bits than their RFC1918 counterpart.

If I have missed any other differences, please enlighten me. :-)

Fernando Gont
SI6 Networks
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