Re: Link addressing (was: Re: A Plea for Architectural & Specification Stability with IPv6)

Mark ZZZ Smith <markzzzsmith@yahoo.com.au> Tue, 25 March 2014 08:00 UTC

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Date: Tue, 25 Mar 2014 00:57:16 -0700
From: Mark ZZZ Smith <markzzzsmith@yahoo.com.au>
Subject: Re: Link addressing (was: Re: A Plea for Architectural & Specification Stability with IPv6)
To: Ole Troan <otroan@employees.org>, Glen Turner <gdt@gdt.id.au>
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Cc: RJ Atkinson <rja.lists@gmail.com>, 6man WG <ipv6@ietf.org>
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----- Original Message -----
> From: Ole Troan <otroan@employees.org>
> To: Glen Turner <gdt@gdt.id.au>
> Cc: 6man WG <ipv6@ietf.org>; RJ Atkinson <rja.lists@gmail.com>
> Sent: Monday, 24 March 2014 9:26 PM
> Subject: Link addressing (was: Re: A Plea for Architectural & Specification Stability with IPv6)
> 
>G len,
> 
>>>  that seems like a misunderstanding. manual configuration of addresses 
> has always been part of the IPv6 addressing architecture.
>> 
>>  Hello Ole,
>> 
>>  It's not a statically addressed subnet, it's a EUI-64 autoconf 
> subnet.
> 
> routers (as defined in RFC4861) don't autoconfigure addresses using SLAAC. 
> that's a host function.

Being pedantic, the SLAAC RFC (RFC4862) says that "it is expected that routers will generate link-local addresses using the mechanism described in this document."

The question I've wondered a bit about is what is the common operational or implementation practice when configuring manual addresses on routers.

For people who configure static addresses on router interfaces, do they actively switch SLAAC off for either individual prefixes, or for the whole interface? Switching SLAAC off for the whole interface means that if there is no static LL address, then the interface doesn't comply with the RFC4291 requirement for all IPv6 interfaces to have an LL address, and can't use any functions/protocols that rely on LLs. An interface probably shouldn't be able to be used for IPv6 if there are no LL addresses present.

Alternatively, if SLAAC is left enabled for the LL prefix, then there is likely to now be two LLs on the interface. Static configuration of an LL address would usually indicate preference for its use for all LL traffic over the SLAAC LL address, which may be a problem, because IIRC, RFC6724 doesn't place any preference for static addresses over SLAAC addresses.




> a router may automatically create an EUI-64 based interface-id, but this is 
> based on configuration, not on SLAAC.
> on an IPv6 link there are many ways of creating interface-identifiers. manually 
> configured, EUI-64, random, etc. all of these can co-exist on a link.
> 
>>  Operationally it is extremely useful to select the router's address, 
> overriding autoconf for that address whilst allowing other machines to autoconf 
> as per usual. Autoconfing the router's address escalates a simple 
> "remote hands card replacement" into "engineer to examine 
> configuration and test operation of all IPv6 router features after card 
> replacement" because of the possibility that the interface's address is 
> mentioned in the router's configuration (ACLs, source address for protocols, 
> etc).
> 
> yes, indeed. I configure most of my router interfaces with interface-id 
> <prefix>::1.
> there is obviously nothing prohibiting that in the IPv6 addressing architecture, 
> nor has anything around that changed, or dare I say will ever change.
> 
> cheers,
> 
> Ole
> 
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