RE: Comments on the L2 VPN framework and solutions documents

May be an example will clear up some confusion... :-)

Lets suppose there is PE-x which is connected to island A
and island B. There is PE-y that is connected to island A
and island C. and there is PE-z that is connected to
island B and island C.

Based on what I understand from Mick's explanation is that
there is 

1. (using your terminology) network-facing (i.e. PW
   based) emulated Vlan ports (one for each island) and 
   1 emulated LAN port (for P-STP, 1 instance MSTP) 
   in each PE. 
2. There is P-STP BPDUs generation/propagation on emulated
   LAN port to determine its forwarding state.
3. The state of the emulated LAN port also determines the
   state of each emulated VLAN port in a PE.

Please let me know if above understanding is correct.

Now further suppose,

1. there is 10GB backdoor connection between island A
  (behind PE-x and PE-y).
2. Emulated LAN port in PE-x blocks thus causing emulated
   VLAN port blocking for island A and island B.

How does the traffic from island B behind PE-z reaches to
island B behind PE-x?
   
Now let me guess to what you and/or Mick are saying,

1. 802.1ad does not participate in P-STP. It simply
   takes a received P-BPDU from island facing port
   and forwards it out to respective emulated 
   VLAN port (something like what you are suggesting 
   in your response but not the impression I got from 
   Mick's explanation)
or

1a. 802.1ad does not participate in P-STP. It drops
   any P-BPDU received from its island facing port.

or

2. 802.1ad does participate in P-STP but only on
   island/access facing ports. P-BPDU received from
   island facing ports is processed for that port
   state and forwarded to respective emulated VLAN port.
   
or 

3. 802.1ad participates in P-STP on emulated LAN port
   to determine the states of all emulated VLAN ports
   (my impression from Mick's explanation)

or 

4. Each PW is treated as separate emulated port (I
   don't think anybody is saying this, including me. 
   This is what old bridges used to do for WAN  
   ports but does not make sense for VPLS model at all)


I think option 1 or 1a makes sense but
has implications of how STP is built and where the 
root gets selected (possibility of having traffic
passing through cloud twice).

/himanshu


-----Original Message-----
From: Ali Sajassi [mailto:[email protected]]
Sent: Thursday, May 08, 2003 7:03 PM
To: Himanshu Shah; [email protected]; Norman Finn; Muneyoshi Suzuki;
Tony Jeffree; Les Bell; Paul Congdon; Neil Jarvis
Cc: [email protected]; [email protected]
Subject: RE: Comments on the L2 VPN framework and solutions documents




At 05:46 PM 5/8/2003 -0400, Himanshu Shah wrote:
>I understand this approach. Its a simple approach.
>And if you want to run M-STP (1 instance) across PWs
>you may want to use this approach.
>
>However, the VPLS drafts in IETF explicitly
>talks about not having to run the P-STP across PWs.
>Dual-homing/external loop in Provider's network
>is handled without using P-STP.
>
>There seems to be some disconnect in understanding
>between these two groups that needs to be worked
>out.

I don't think there is a disconnect. When you talk about P-STP, you need to 
consider both intra-island and inter-island. P-STP is NOT used for 
inter-island - for that we use full-mesh with split horizon. However, for 
intra-island where you can have an arbitrary topology of bridges within an 
access domain, then P-STP is the only viable solution (refer to section 
11.2 of draft-lasserre-vkompella). Also keep in mind that P-STP is 
suggested for Ethernet access domain and not MPLS access domain.

-Ali


>/himanshu
>