RE: Comments on the L2 VPN framework and solutions documents

At 08:29 AM 5/9/2003 -0400, Himanshu Shah wrote:
>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.

PE-x, y, and z should be considered as part of their corresponding islands. 
Also if there is a single PE in each island, then there is no need to run 
STP over the big emulated LAN ports between the PEs because if that big 
emulated LAN ports fails, then there is no other PE to connect the island 
into the backbone. However, STP is run within an island to take care of 
loop within among different Etherent nodes in that island. Now if you have 
more than one PE in an island, then you run STP between the emulated LAN 
port of different PE within that island so if one fails, you can connect to 
the core through another PE.

-Ali


>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
> >