Re: Info aggregation

Alex> Some more questions here: when taken to a large scale
Alex> (not necessarily just one VPLS)

Alex> o what VPLS info from other AS'es do PEs need to know? 

Vach has been pushing a hierarchical model, in which, for each VPLS, each AS
has a "gateway" that only needs to  know how to reach a gateway in the other
ASes, and  within an AS,  each PE only  needs to know  how to reach  its own
gateway. 

I've been  pushing a somewhat different model  in which each PE  has to know
how to reach its gateway (to a  particular AS), and has to know how many PEs
supporting that  same VPLS there  are in  the other AS.   A PE sets  up that
number of pseudowires  to the gateway, which splices  them together with pws
that go to  the next AS.  (The splicing can  be done in such a  way as to be
transparent to  the forwarding  plane, though some  have suggested  that the
gateway  might  need  to  be  an  OAM  boundary,  even  if  that  sacrifices
scalability.) 

Both  models provide  a good  summarization of  information, I  think.  They
differ  in regard  to the  amount and  kind of  state needed  in the  PEs as
opposed to the gateway.  The hierarchical  model helps with the scale of the
individual PEs, but  requires MAC lookup in the  gateways, and also requires
of course that a hierarchy be provisioned. 

(I hope I've not done Vach's model too much of an injustice.)

Alex>  o given the edge-to-edge nature of PWs, is it feasible
Alex>    to summarize signalling information among AS'es at all? 

Both models bound the number  of signaling inter-AS connections, so that the
number of  these connections does not grow  as the number of  PEs grows. The
hierarchical model limits some of the signaling information to the hierarchy
boundaries.

Alex>  o if not, how do we scope distribution of signalling info
Alex>    so amount of info per participating node has reasonable
Alex>    growth characteristics? 

I think it is impossible to make L2 scale as well as L3, because of the flat
and non-aggregatable  address space,  and because of  the need  to multicast
packets with  unknown DAs.  However, whereas  we want our L3  networks to be
able to grow  without bound, I don't think the  same requirement exists with
respect to L2 networks.

Alex>  o is it feasible to summarize VPLS membership information
Alex>    among AS'es? 

Yes, to a certain extent, as explained above.