[c-nsp] Building E-Trees

[Pshem Kowalczyk]

Hi,

We have a setup that currently uses a local bridge domain on asr9k, one
local physical interface and a number of P2P PWE3 that terminate on PWHE on
other asr9ks. The setup is used for broadband termination. The P2P PWE3 go
to BNGs.
The main reason for using a bridge domain with multiple PWE3 so we can
load-balance the subscribers among larger number of BNGs but also to
provide more graceful fail-over to what can be achieved  with a backup
PWE3.

Currently the bridge domain learns MAC addresses, but as the number of
subscriber grows that's likely to become a limiting factor.  In reality we
need something like an e-tree where the BNGs are the leafs and the physical
interface is the root but with limited MAC address learning. In fact what
all we need is one MAC address per BNG plus a 'default route' that points
to the physical interface.  Is there a way to define something like that?

kind regards
Pshem