Re: [DNA] L2 link and L3 link

[Bernard Aboba <aboba@internaut.com>]

> Let me be more precise. A host will detect the distinct difference between AP1 and AP2.
> It will receive a different BSS ID and observe it has attached to a different link-layer
> medium (AP).
>
> Roughly saying, it will notice Current Link/ Current AP Down and New Link/ New AP Up

The host can also detect a difference between Ethernet Switch 1 and
Ethernet Switch 2, since it will receive packets from a different switch
MAC address.  For example, the source address for 802.1X packets will be
different, as could the contents of the EAP-Request/Identity packet (e.g.
the nas-id field will be different).

> What I mean is that they are at the different BSS, which requires new association.

The notion of "association" is not unique to 802.11.  This is required for
any layer 2 protocol that allows multiple networks to be resident on the
same media.  This is because, unlike classic IEEE 802 media,
receipt of packets is not sufficient to conclude that the sender wishes to
"join" the network.  An explicit association step is required.

PPP over Ethernet supports the notion of association, as will IEEE
802.1af.

> But we'd better make it clear that, in 802.11,
> 1) link and AP are different.
> 2) An 'AP change' should not be automatically termed as a 'link change'

I agree that there is a difference between 'link' and 'point of
attachment'.  While the 'point of attachment' may change, this does not
imply that the 'link' changes.

> We may define a new term corresponding to AP, for example L2 link :-).

I'd suggest that we continue to use the term 'link' to refer to L3
links.  Otherwise, when VLANs are implemented, we will find ourselves
drowning in confusion.