Re: Comments on the L2 VPN framework and solutions documents

Mick, Matt,

Mick Seaman wrote:
> From the point of
> view of control connectivity the pseudo-wires have to establish a full mesh
> that is never perceived by layer 2 protocols as being less than complete.
How can this "lower layer emulated LAN" (using full mesh split horizon)
be perceived by IEEE L2 as being _never_ less than complete? 

> STP is running across the service that runs on top of the mechanisms that
> make the service LAN like.

Matt Squire wrote:
> But ensuring the
> emulated and real technologies are transparent to the higher layer, one
> can build arbitrary networks based on traditional bridging models.  I
> hope thats a good thing.
From the architecture point of view, it looks clean to make the lower
layer transparent and to mandate the lower layer should do its job
properly (in this case IEEE 802.1ad assumes PPVPN VPLS always provide a
properly emulated LAN, no configuration loops, connectivity issues,
etc). However, I do not know how loops in the forwarding paths can be
prevented, if a tree is concatenated/spliced with the lower layer
forwarding path (or another tree), unless all common nodes in the
forwarding path (both higher and lower layer) participate in one common
spanning tree or a similar algorithm to prevent forwarding loops.

Thanks
Cheng-Yin