Re: [Autoconf] Autoconf addressing model

Alexandru Petrescu <alexandru.petrescu@gmail.com> Thu, 05 March 2009 14:15 UTC

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Date: Thu, 05 Mar 2009 15:15:47 +0100
From: Alexandru Petrescu <alexandru.petrescu@gmail.com>
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To: Teco Boot <teco@inf-net.nl>
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Subject: Re: [Autoconf] Autoconf addressing model
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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)


> |> I repeated the test with the link local addresses. Here also, I
> |> experienced no problems. This is because there are two links with
> |> exactly the same address pairs (an advantage to use same LL addresses
> |> on all interfaces).
> |
> |Demonstrating the advantage of loopback0 vs eth0 would have implied that
> |you start OSPFv3 on eth0 instead of loopback0 and that it would have
> |crashed.
> 
> My routing protocols do not crash. I told you before.

Sorry, I don't remember. So then they could work without loopback0 
interface, only over the Ethernet interface, right? (they wouldn't crash 
when the interface goes down and then up).

> |But even then, I'm sure there may exist OSPFv3 implementation which
> |would not crash when running over eth0 and ifconfig down eth0.
> |
> |In this sense, if the loopback0 interface is a solution to crashing
> |OSPFv3-over-eth0, then it is an implementation solution. Some
> |implementations do, others don't.
> 
> You totally missed the point.

Your point seemed to motivate the use of loopback0 interface.  And so, 
because presumably the physical interfaces are not enough.  Am I 
catching your point?

Alex