Subject: Re: AYIYA link local address

From: Jeroen Massar <[email-masked]>
Date: Tue, 01 Feb 2005 16:11:21 +0100

On Mon, 2005-01-31 at 21:54 +0000, Colm MacCarthaigh wrote:
> On Mon, Jan 31, 2005 at 07:14:22PM +0100, Jeroen Massar wrote:
> > Correct, but what if you don't know the IPv4 address? Which I don't know
> > in my case. The global IPv6 address is unique and won't change/is
> > stable, which is mentioned in 2373 to be one of the things one should
> > use.
> 
> In order to construct a stable tunnel, there has to be *some* kind of
> stable endpoint identifier ;) In the case of ayiya, this seems to be a
> complex combination of source address and the optional "identity" field,
> which varies between 0 and 256 bytes in size :/

Indeed between 0 and 256. In general though the identity will match the
IPv6 address of the tunnel endpoint when doing 6-in-*, which is why I
picked the IPv6 address.

> > > for example. This kind of approach seems much more inline with the idea
> > > behind link-local addresses (at least to me anyway). For 6-over-6
> > > ayiya, I'd just use ::1, ::2 and so on, but that's me.
> > 
> > That indeed works, but then one has fe80::1, say a hundred times on the
> > same machine, which is for debugging purposes also not very handy.
> 
> Maybe in the case of ayiya best practise would be to advise such
> operators to use identities that can double up as interface identifiers
> (a 32-bit integer will happily suffice) ?

Indeed, this is what I am doing now in the AICCU code and in the
serverside stuff by using the IPv6 address. Unique bit is cleared so it
should be according to the RFC.

RFC2373 mentions btw:
8<-------------------------
   The link-unique interface identifier should be generated in a manner
   that it does not change after a reboot of a node or if interfaces are
   added or deleted from the node.
-------------------------->8

Many tunneling implementations, proto-41 tunnels on Linux/BSD etc use
the IPv4 address of the local side as the Interface Identifier, which
does change when the source address changes. Is this to be considered
correct or can this be seen that one gets a new 'link' between the two
endpoints?

Greets,
 Jeroen

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