Re: [atn] [EXTERNAL] Re: Embedding IP information in an IPv6 address (OMNI)

otroan@employees.org Wed, 14 October 2020 17:45 UTC

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Subject: Re: [atn] [EXTERNAL] Re: Embedding IP information in an IPv6 address (OMNI)
From: otroan@employees.org
In-Reply-To: <8c53ec2baafc4b1f827996d822ef67b8@boeing.com>
Date: Wed, 14 Oct 2020 19:45:15 +0200
Cc: =?utf-8?B?56We5piO6YGU5ZOJ?= <jinmei@wide.ad.jp>, Robert Moskowitz <rgm@labs.htt-consult.com>, 6man WG <ipv6@ietf.org>, "atn@ietf.org" <atn@ietf.org>
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To: "Templin (US), Fred L" <Fred.L.Templin@boeing.com>
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Thanks Fred for the explanation.

>>> What in your opinion would be easier - a) update RFC4291 to allow coding of
>>> the link-local address 54 zero bits, or b) update RFC4861 to allow routers to use
>>> site-local addresses instead of link-local?
>>> 
>>> We need a good answer for this - either a) or b). The benefit of what is being
>>> proposed by OMNI is too great to simply say no to both.
>> 
>> It's unclear to me what the benfits are.
>> Would you be able to summarize here, or point to the relevant paragraphs in the OMNI draft? 
> 
> The benefits include:
> 
> + a means for configuring a unique IPv6 link-local address (i.e., the "OMNI LLA")
>  that is known to be unique on the link without requiring SLAAC or MLD/DAD

Benefit is in the eye of the beholder.
Manual configuration is a common cause of duplicate address. Why can't that happen here?
If you the setup here is that you have "some" information pre-configured. Why not also the link-local address?

> + a means for asserting and/or receiving IPv6 GUA prefixes without explicit
>   prefix delegation messaging over the wire

Implied prefix delegation by the implementation knowing that it should find it's prefix at bit position <n:m> in the packet... doesn't seem like following the principle of least astonishment.
Likewise having the routing system glean information from RSs... is that really the level of adaptiveness you need from a routing system?

I'm not sure I get the motivation between these choices?
As opposed to using existing IPv6 mechanisms for the same.

Best regards,
Ole

> 
> So, for example, if a node has been pre-assigned an IPv6 GUA prefix 2001:db8:1:2::/64
> then it can configure the OMNI LLA fe80:2001:db8:1:2:: (but note that this is not RFC4862
> SLAAC; it is a simplified means of setting up an administratively-configured LLA that is
> known to be unique on the link). The node can then assert its IPv6 GUA to the routing
> system by sending an RS with fe80:2001:db8:1:2:: as the source address and with a
> Prefix Length value 'N'.
> 
> In a second example, if a node has no pre-assigned IPv6 GUA then it can send an RS
> message with IPv6 address unspecified. When it gets back an RA, it can determine its
> (delegated) IPv6 GUA prefix by examining the destination address. For example, if
> the RA message has destination address fe80:2001:db8:3:4:: and the message includes
> a Prefix Length 'N' and lifetime value, it can adopt fe80:2001:db8:3:4:: as its own
> OMNI LLA and adopt 2001:db8:1:2::/N as its own IPv6 GUA prefix.
> 
> There are also IPv4-compatible OMNI LLAs of the form fe80::ffff:[v4addr] and
> "Service" OMNI LLAs of the form fe80::[32-bit ID]. All of these address forms
> appear in Section 7 of the document, and their use is discussed throughout:
> 
> https://datatracker.ietf.org/doc/draft-templin-6man-omni-interface/
> 
> Thanks - Fred
> 
>> Best regards,
>> Ole=