Re: [DNA] Definition of "Link Up" and "Link Down" events?

[Brett Pentland <brett.pentland@eng.monash.edu.au>]

Bernard Aboba wrote:
> Using Alper's definition as a starting point, here a proposed definition
> of "Link Down" and "Link Up".  What do people think?
> 
> Link Down
>      An event provided by the link layer that signifies that the link is
>      no longer capable of communicating IP packets.
> 
> Link Up
>      An event provided by the link layer that signifies that the link
>      has become capable of communicating IP packets.

Works for me.  My only concern would be about what would happen if an L2
technology comes along that can move its attachment point without any
intermediate period of disconnection, perhaps through some out-of-band
pre-establishmment of the new connection (and it would be good if such a
technology did!).

Perhaps it would just be a matter of using these definitions, but
ensuring that a transition like above causes a matched pair of Link Down
/ Link Up events to be generated.

As an aside: for draft-pentland-dna-solution-00 we only really
considered Link Up, because that is the point at which the network
layer on that interface is able to take some action (sending an RS, in
this case, to find out what the Link Up means).  Link Down is probably
useful for coordinating between multiple interfaces, as are some of
the events that might be able to be triggered by the intermediate
connectivity situations that you described, but that is outside the
scope of what we tried to achieve in the proposal.

Brett.