Subject: Re: Ali Sajassi's comments on Hybrid VPLS

From: Ali Sajassi <[email-masked]>
Date: Mon, 24 Mar 2003 01:36:24 -0800

Let me give all my comments on the deficiencies of this draft:

1) Need to get the terminologies straight out: the draft talks about an 
Attachment Circuit as demarcation point between provider's CLE and PE as 
well as demarcation point between customer's CE and provider's PE. AC as 
defined in L2VPN framework, refers to demarcation between customer's CE and 
provider's PE and if you go by this, then the service that is provided by 
the PEs is basically just VPWS and nothing more !! and there is no reason 
to mix this up with VPLS service - please refer to L2VPN framework draft.

Now if you add in the CLEs in the mix, then AC becomes the demarcation 
between CEs and CLEs (not between CLEs and PEs) and in that case there are 
other deficiencies as described below ...

2) With CLEs in the mix, then there are two cases: a) a CLE cannot use 
VLANs as virtual interfaces and b) a CLE has a magical ability to use VLANs 
as virtual interfacs. Case (a) is clearly not scalable since one would need 
as many interfaces on a CE/CLE as number of customer sites - so if a 
customer has 100 sites, then you need 100 interfaces on the CLEs for that 
customer alone !!! Case (b) uses VLAN tags not only as service delimiter 
but also as virtual ports in a CLE and the main premise of this draft is 
based on this. This concept is nothing new and was first introduced by 
Kompella in his VPLS draft. But as soon as you introduce such concept, you 
cannot use typical bridges and you need to develop modified bridges for 
such functionality which would defeat the purpose of low-cost CLE. If 
someone wants to develop a modified bridge for using VLAN tags as virtual 
circuits/ports, then he can as easily develop modified bridge using PWs 
(either MPLS or L2TPv3) as VCs and this becomes the good old draft-lasserre.

3) Interworking between disparate Attachment Circuits has already been 
covered by two drafts. draft-shah-ppvpn-arp-mediation talks about 
interworking for IP end points and draft-sajassi-l2vpn-interworking talks 
about more general case of interworking and covers interworking for VPLS as 
well. I didn't see anything new that has not been already covered by these 
two drafts.

4) Furthermore, ARP-mediation is a PtP mechanism and for multi-point 
service, IPLS which is based somewhat on ARP-mdediation was introduced. So 
lets not re-invent the wheel and lets not re-describe IPLS mechanism in 
here again.

5) Discovery deals with the discovery of members of a VPN and there are 
already few proposal on the table (e.g., BGP-based, directory-based such as 
Radius, and MPLS-based). Mapping VLAN-tags to PWs is not related to 
auto-discovery and such mapping in more general sense (ACs to PWs) has 
already been described in details in L2VPN framework.

6) STP : if provider's access network is Ethernet (e.g., .1q or QinQ) and 
these access networks (metro regions) are connected via an MPLS or IP core, 
then my point was that STP is not suitable for putting everything on one 
giant flat network and it would create administrative issues.

Regards,
Ali

At 01:35 AM 3/20/2003 -0500, Cheng-Yin Lee wrote:
>Ali,
>I am trying to understand your comments at PPVPN WG meeting this
>afternoon about Spanning Tree and Hybrid VPLS. Could you elaborate pls?
>
>Thanks,
>Cheng-Yin