Re: [Autoconf] Autoconf addressing model

Alexandru Petrescu <alexandru.petrescu@gmail.com> Thu, 05 March 2009 14:19 UTC

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Date: Thu, 05 Mar 2009 15:19:32 +0100
From: Alexandru Petrescu <alexandru.petrescu@gmail.com>
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To: Alexandru Petrescu <alexandru.petrescu@gmail.com>
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Cc: autoconf@ietf.org
Subject: Re: [Autoconf] Autoconf addressing model
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Alexandru Petrescu a écrit :
> Teco Boot a écrit :
>> Hi Alex,
>>
>>
>> |> So the following topology is valid:
>> |>
>> |> +----------+                        +----------+
>> |> |          |fe80::1/64              |          |
>> |> |          +========================+          |
>> |> | router 1 |              fe80::2/64| router 2 |
>> |> |          |fe80::1/64              |          |
>> |> |          +========================+          |
>> |> |          |              fe80::2/64|          |
>> |> +----------+                        +----------+
>> |>
>> |> Agreed on this?
>> |
>> |Agreed.  But why /64?  An address is /128, and the link-local address'
>> |prefix is /10.
>>
>> I used address-prefix format (RFC4291).
>>
>> And RFC2464:
>>
>> 5.  Link-Local Addresses
>>    The IPv6 link-local address [AARCH] for an Ethernet interface is
>>    formed by appending the Interface Identifier, as defined above, to
>>    the prefix FE80::/64.
> 
> Ah!
> 
>> The 54 bits following 1111111011 are zero. There is little difference
>> between FE80::/10 and FE80::/64. On Ethernet, it is the latter.
> 
> Which one should we picture on the AUTOCONF practical addressing scheme? 
>  The /10 or the /64?
> 
> In a picture like that I'd definitely put an address and the prefix like 
> this, in the simplest case:
> 
> ---\
>     \ fe80::1/128   (the address)
>      ---------
>     / 2001:db8::/64 (the prefix of the subnet on which this interface is
> ---/                 attached)

For clarification, I meant this:

  /------\
/        \ fe80::1/128   (the address)
| Router |--------------
\        / 2001:db8::/64 (the prefix of the subnet on which
  \------/                 this interface is attached)

Alex