Subject: Add I-BEB to VPLS interop to draft-ietf-l2vpn-vpls-bridge-interop

From: Maarten Vissers <[email-masked]>
Date: Sun, 05 Oct 2008 20:02:07 +0200

Ali, Dinesh,

draft-ietf-l2vpn-vpls-bridge-interop includes a paragraph in section 5.3 MAC
Address Learning that refers to 802.1ah. It mentions a u-PE capable of
encapsulating customers' MAC addresses. With 802.1ah now being approved, I
propose that the draft-ietf-l2vpn-vpls-bridge-interop should describe this
interoperability in more detail.

The simple case is when the u-PE is an 802.1ah I-BEB and this I-BEB connects
to the n-PE via an I-Tagged LAN as illustrated in the figure below.

      u-PE
    ---------              --------
  --|       |              |      |
  --| I-BEB |--------------|      |
  --|       | I-Tagged LAN | VPLS |-----
    ---------              |      |-----
                           | n-PE |----- HVPLS network
      u-PE                 |      |-----
    ---------              |      |-----
  --|       |              |      |-----
  --|  PEB  |--------------|      | 
  --|       | S-Tagged LAN |      |
    ---------              --------

In this configuration it is possible to support the following 802.1ah
defined customer services:
1) port-based service
2) S-tagged service, one-to-one
3) S-tagged service, bundling or all-to-one bundling.

Each customer service is mapped into one Backbone Service Instance (BSI) and
the set of BSI signals created in the I-BEB is multiplexed into the I-Tagged
LAN. Each BSI frame is extended with an I-Tag during this multiplexing. In
addition BSI OAM frames (i.e. Ethernet OAM frames) are added to each BSI;
the B-SA value is present twice in the I-Tagged BSI OAM frame (in B-SA and
in C-SA fields) and the B-DA value is present in the C-DA field and a copy
of this B-DA or a translated version of it is present in the B-DA field.
Those services result in the following frames on the I-Tagged LAN:

                  1-to-1         bundling
 port-based      S-Tagged        S-Tagged
  service         service         service         BSI OAM
   frame:          frame:          frame:          frame:

    B-DA            B-DA            B-DA            B-DA
    B-SA            B-SA            B-SA            B-SA
    I-TPID          I-TPID          I-TPID          I-TPID
    I-PCP           I-PCP           I-PCP           I-PCP
    I-DEI           I-DEI           I-DEI           I-DEI
    UCA=0           UCA=0           UCA=1           UCA=1
    RES1/2          RES1/2          RES1/2          RES1/2
    I-SID           I-SID           I-SID           I-SID
    C-DA            C-DA            C-DA            C-DA=B-DA
    C-SA            C-SA            C-SA            C-SA=B-SA
    C-TAG (opt)     C-Tag (opt)     S-Tag           TYPE:89-02
    MSDU            MSDU            C-Tag (opt)     OAM PDU
                                    MSDU

The I-Tagged LAN interface port on the n-PE must terminate the I-Tagged LAN
and treat each individual BSI signal as a VPLS instance. For this purpose,
the VPLS-capable n-PE model includes a I-Tagged LAN interface port with a
BSI (de)multiplexer function. This BSI demultiplexer function demultiplexes
the BSI signals from the I-Taggged LAN, extracts the I-Tag on the basis of
the BSI demultiplexer specification in clause 6.18.1/802.1ah and translates
the BSI Group address within a B-DA into a broadcast address. The BSI
multiplexer function muiltiplexes the BSI signals received from the VLAN
Bridge function into the I-Tagged LAN and inserts the I-Tag on the basis of
the BSI multiplexer specification in clause 6.18.2/802.1ah.

The "B-DA[BSI Group address] to B-DA[broadcast address]" translation in the
BSI demultiplexer function is possible while the HVPLS network uses
point-to-point MPLS tunnels which forward the VPLS frames independent of the
value in the B-DA field (i.e. there is no need to restrict the flooding
scope of broadcast/multicast frames). This translation is necessary while
the HVPLS network is not capable to translate such BSI Group address in the
DA field every time the PW label value identifying the VPLS frame is
swapped.
    
        +------------------------------------------------+ 
        |                 VPLS-capable n-PE model        | 
        |           +---------------+          +------+  |   
        |           |               |          |VPLS-1|------------ 
        |+------+   |     VLAN      |==========|Fwdr  |------------ PWs 
  I-LAN ||      |---|     Bridge    ------------      |------------ 
    -----|  BSI | o |               |   VLAN-1 +------+  | 
        ||(d)mux| o |               |             o      | 
        ||      |---|               |             o      | 
        |+------+   |               |             o      | 
        |           |               |             o      | 
        |+------+   |               |             o      | 
  S-LAN ||      |---|               |   VLAN-n +------+  | 
    -----|S-VLAN| o |               ------------VPLS-n|------------- 
        ||(d)mux| o |               |==========| Fwdr |------------- PWs 
        ||      |---|               |     ^    |      |------------- 
        |+------+   +---------------+     |    +------+  | 
        |                                 |              | 
        +---------------------------------|--------------+ 
                               LAN emulation Interface 
    
           Figure - VPLS-capable n-PE Model with S-Tagged LAN and I-Tagged
LAN interfaces

At the output ports of the BSI demultiplexer function we will find the
following frames:

                  1-to-1         bundling
 port-based      S-Tagged        S-Tagged
  service         service         service         BSI OAM
   frame:          frame:          frame:          frame:

    B-DA            B-DA            B-DA            B-DA
    B-SA            B-SA            B-SA            B-SA
    TYPE:89-10      TYPE:89-10      TYPE:89-10      TYPE:89-02
    C-DA            C-DA            C-DA            OAM PDU
    C-SA            C-SA            C-SA            
    C-TAG (opt)     C-Tag (opt)     S-Tag           
    MSDU            MSDU            C-Tag (opt)     
                                    MSDU

The I-Tag specific fields are replaced in the BSI demultiplexer by a TYPE
field with value 89-10 for non-BSI OAM frames (89-10 is defined in clause
6.18/802.1ah as "802.1Q Encapsulated Addresses" EtherType). For BSI OAM
frames the B-DA* to I-SID fields are removed from the frame. After these
frames have passed the VLAN Bridge function and the VPLS Fwdr function,
those frames will be extended with the Control Word and the PW label stack
entry in order to transport those frames over the MPLS tunnels:

                  1-to-1         bundling
 port-based      S-Tagged        S-Tagged
  service         service         service         BSI OAM
   frame:          frame:          frame:          frame:

    PW              PW              PW              PW
    CW              CW              CW              CW
    B-DA            B-DA            B-DA            B-DA
    B-SA            B-SA            B-SA            B-SA
    TYPE:89-10      TYPE:89-10      TYPE:89-10      TYPE:89-02
    C-DA            C-DA            C-DA            OAM PDU
    C-SA            C-SA            C-SA            
    C-TAG (opt)     C-Tag (opt)     S-Tag           
    MSDU            MSDU            C-Tag (opt)     
                                    MSDU

Regards,
Maarten