Internet Working Group Y.L. Jiang
Internet Draft Huawei
Intended status: Standards Track March 1, 2010
Expires: September 2010
VPLS PE Model with E-Tree Support
draft-jiang-l2vpn-vpls-pe-etree-00.txt
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Abstract
A scalable VPLS Provider Edge (PE) model with E-Tree support is
proposed in this document. In this model, a Tree VSI is introduced
which can provide connectivity for both root VLAN and leaf VLAN for
the E-Tree service. MAC address based Ethernet forwarding engine
works in the same way as before. As VLAN mapping is needed in the
Ethernet PW to keep the VLAN domains in different PEs of the same
VPLS instance independent, the PW processing needed for this kind of
VLAN mapping is also discussed.
Table of Contents
1. Introduction...................................................2
2. Conventions used in this document..............................3
3. Terminology....................................................3
4. PE Model with E-Tree Support...................................3
4.1. Existing PE Models with E-Tree Support....................3
4.2. A New PE Model with E-Tree Support........................6
5. PW for E-Tree Support..........................................7
5.1. Tagged Mode PW Encapsulation..............................7
5.2. PW Processing.............................................7
5.2.1. PW Processing in the Normal Mode.....................8
5.2.2. PW Processing in the Compatible Mode.................9
5.2.3. PW Processing in the Optimized Mode.................10
6. LDP Extensions for E-Tree Support.............................10
7. Security Considerations.......................................12
8. IANA Considerations...........................................12
9. References....................................................12
9.1. Normative References.....................................12
9.2. Informative References...................................13
10. Acknowledgments..............................................13
1. Introduction
E-Tree service is defined in Metro Ethernet Forum (MEF) as multi-root
to multi-leaf service, where traffic from a root can reach any root
or leaf, and traffic from a leaf can reach any root, but never reach
a leaf.
[Etree-frwk] gives the requirements and a framework of a solution for
the E-Tree in VPLS. [vpls-etree] shows the details of the solution,
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where the Ethernet forwarder in the VPLS is extended to filter the
leaf-leaf traffic based on the 3-tuple <ingress port, egress port, CW
L-bit>. This solution needs to change the forwarding engine of the
VSI, and the control word of the Ethernet PW.
This document introduces another solution for E-Tree support in VPLS,
which is more compatible with the traditional Ethernet and PW
technology, and VPLS scalability and simplicity is also well kept.
Firstly, a new VPLS PE model is introduced which consists of a Tree
VSI connected to the S-VLAN Bridge with a dual-VLAN interface.
This document then discusses the PW encapsulation and PW processing
such as VLAN mapping options for transporting E-Tree services in a
VPLS.
Finally the LDP extensions needed to support this mechanism are also
discussed.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Terminology
Most of the terminology used here is from [IEEE802.1Q], [IEEE802.1ad],
[RFC4664] and [RFC4762]. Terminology specific to this document is
introduced as needed in later sections.
4. PE Model with E-Tree Support
4.1. Existing PE Models with E-Tree Support
According to [RFC4664], there are at least three models for a VPLS PE,
including:
o A single bridge module, a single VSI;
o A single bridge module, multiple VSIs;
o Multiple bridge modules, each attaches to a VSI.
The second PE model as depicted in Fig. 1 and Fig. 2 is the most
suitable one for VPLS [vpls-interop], where the S-VLAN bridge module
is connected to multiple VSIs each with a single VLAN interface.
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+-------------------------------+
| 802.1ad Bridge Module Model |
| |
+---+ | +------+ +-----------+ |
|CE |---------|C-VLAN|------| | |
+---+ | |bridge|------| | |
| +------+ | | |
| o | S-VLAN | |
| o | | |
| o | Bridge | |
+---+ | +------+ | | |
|CE |---------|C-VLAN|------| | |
+---+ | |bridge|------| | |
| +------+ +-----------+ |
+-------------------------------+
Figure 1 The Model of 802.1ad Bridge Module
+----------------------------------------+
| VPLS-capable PE model |
| +---------------+ +------+ |
| | | |VSI-1 |------------
| | |==========| |------------ PWs
| | Bridge ------------ |------------
| | | S-VLAN-1 +------+ |
| | Module | o |
| | | o |
| | (802.1ad | o |
| | bridge) | o |
| | | o |
| | | S-VLAN-n +------+ |
| | ------------VSI-n |-------------
| | |==========| |------------- PWs
| | | ^ | |-------------
| +---------------+ | +------+ |
| | |
+-------------------------|--------------+
LAN emulation Interface
Figure 2 VPLS-capable PE Model
In the above model, Ethernet service from the CEs will cross multiple
stages of bridge modules (i.e., C-VLAN and S-VLAN bridge) to access
the egress PWs. Therefore, the association of an AC port and a PW in
a single forwarding engine as required in [vpls-etree] is difficult,
sometimes even impossible.
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Asymmetric VLAN is firstly introduced in IEEE 802.1Q, where traffics
from the root and the leaves are assigned with different VLANs, so
that the switch can filter on each leaf port all the traffic from the
VLANs associated with the leaves.
This mechanism could be further enhanced by the introduction of a
trunk VLAN and a branch VLAN. All the traffics from the trunk VLAN
are received both on the roots and the leaves, while traffics from
the branch VLAN are received on the roots and dropped on the leaves.
It was demonstrated in [ETree-802.1Q] that E-Tree on Ethernet itself
could be well provisioned with this mechanism.
Should this mechanism be deployed in Ethernet access domain, and if
the above VPLS PE model is to be maintained, then it is quite
straightforward to infer the following VPLS PE model (as shown in Fig.
3) with E-Tree support. But this model will require two VSIs per PE
and two sets of full meshed PWs per E-Tree service, which is poorly
scalable in a large MPLS/VPLS network.
+----------------------------------------+
| VPLS-capable PE model |
| +---------------+ +------+ |
| | | |VSI-1 |------------
| | |==========| |------------ PWs
| | Bridge ------------ |------------
| | | Trunk +------+ |
| | Module | S-VLAN o |
| | | o |
| | (802.1ad | o |
| | bridge) | o |
| | | Branch o |
| | | S-VLAN +------+ |
| | ------------VSI-2 |-------------
| | |==========| |------------- PWs
| | | ^ | |-------------
| +---------------+ | +------+ |
| | |
+-------------------------|--------------+
LAN emulation Interface
Figure 3 VPLS PE Model with E-Tree Support
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4.2. A New PE Model with E-Tree Support
To provide for E-Tree support in a more scalable way, a new VPLS PE
model is proposed as depicted in Fig. 4, where the S-VLAN Bridge
module is connected to the Tree VSI (T-VSI, a VSI with E-Tree support)
with a dual-VLAN interface. That is, both the trunk S-VLAN and the
branch S-VLAN are connected to the Tree VSI (T-VSI). To be more
specific, they are called root and leaf S-VLAN respectively in this
document. In this way, only one VPLS instance (one VSI per PE) and
one set of PWs is needed per E-Tree service. With this model,
multiple E-Trees can also be provided by the same T-VSI if needed,
and further increase the scalability of VPLS.
+----------------------------------------+
| VPLS-capable PE model |
| +---------------+ +------+ |
| | |==========|TVSI-1|------------
| | ------------ |------------ PWs
| | Bridge ------------ |------------
| | | Root & +------+ |
| | Module | Leaf VLAN o |
| | | o |
| | (802.1ad | o |
| | bridge) | o |
| | | o |
| | | S-VLAN-n +------+ |
| | ------------VSI-n |-------------
| | |==========| |------------- PWs
| | | ^ | |-------------
| +---------------+ | +------+ |
| | |
+-------------------------|--------------+
LAN emulation Interface
Figure 4 E-Tree VPLS-capable PE Model
These two VLANs should share the same FIB and work in shared VLAN
learning. The traffic from the root UNIs are firstly tagged with root
C-VLAN by the C-VLAN bridge module, and then tagged with root S-VLAN
by the S-VLAN bridge module, thus can only be transported on the root
S-VLAN. Similarly, the traffic from the leaves can only be
transported on the leaf S-VLAN.
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5. PW for E-Tree Support
T-VSIs from peer PEs in a VPLS are inter-connected with a PW, the S-
VLANs should be independently provisioned on each PE. That is, the
assignment of S-VLANs in the PE should be local to simplify the
network provisioning.
In order to carry both S-VLANs (root and leaf S-VLAN) in a single PW
and map them into the remote peer's local S-VLANs, cares must be
taken on both the PEs associated with the PW.
Two options of VLAN mapping are possible for a PW:
o local mapping, VLAN mapping is usually done when a frame exits the
PW. That is, the egress PE is responsible for mapping VLANs into
its local VLANs.
o remote mapping, VLAN mapping is done when a frame enters the PW.
That is, the remote PE is responsible for mapping VLANs into the
local PE's VLANs.
Normally, each PE does its own local mapping. But when a PE is not
capable of VLAN mapping, then remote mapping must be done on its peer.
5.1. Tagged Mode PW Encapsulation
For a VPLS instance to support E-Tree, the Ethernet PW should work in
the tagged mode (PW type 0x0004) as described in [RFC4448], and an S-
VLAN tag must be carried in each frame in the PW, either the local or
the remote S-VLAN tag could be carried depending on the mapping
option. In the local mapping mode, the remote S-VLANs are carried
with no change, while in the remote mapping mode, the local mapped S-
VLAN are carried instead.
The mapping between the local S-VLAN and the remote S-VLAN (local
root S-VLAN <-> remote root S-VLAN; local leaf S-VLAN <-> remote leaf
S-VLAN) should be provisioned by management or signaled by a control
protocol such as LDP. The LDP extensions for E-Tree support are
provided in Section 6.
5.2. PW Processing
Three modes of PW processing are provided for E-Tree in different
scenarios.
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5.2.1. PW Processing in the Normal Mode
In the normal mode, two VPLS PE each with a T-VSI in it are inter-
connected and both sides are miscellaneously attached with roots and
leaves, as shown in the scenario of Fig. 5. At the PE where a frame
exits the PW, if a frame with the remote leaf VLAN is received, then it
is mapped to the local leaf VLAN, otherwise, if a frame with the remote
root VLAN is received, then it is mapped to the local root VLAN.
+--------------------------------+
| VPLS PE with T-VSI |
| |
+----+ | +------+ +-------+ +-----+ | PW
|Root|------|C-VLAN|---|S-VLAN |---|T-VSI|----------
+----+ | | BRG | | BRG | | |----------
+----+ | | |---| |---| |----------
|Leaf|------| | | | | |---------+
+----+ | +------+ +-------| +-----+ | |
| | |
+--------------------------------+ |
|
+--------------------------------+ |
| VPLS PE with T-VSI | |
| | |
+----+ | +------+ +-------+ +-----+ | PW |
|Root|------|C-VLAN|---|S-VLAN |---|T-VSI|---------+
+----+ | | BRG | | BRG | | |----------
+----+ | | |---| |---| |----------
|Leaf|------| | | | | |----------
+----+ | +------+ +-------| +-----+ |
| |
+--------------------------------+
Figure 5 T-VSI Interconnected in the Normal Mode
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5.2.2. PW Processing in the Compatible Mode
The new VPLS PE model can work in a traditional VPLS network
seamlessly in the compatibility mode. As shown in Fig. 6, the VPLS PE
with T-VSI can access both root and leaf node, while the VPLS PE with
VSI can only access the root node.
+--------------------------------+
| VPLS PE with T-VSI |
| |
+----+ | +------+ +-------+ +-----+ | PW
|Root|------|C-VLAN|---|S-VLAN |---|T-VSI|----------
+----+ | | BRG | | BRG | | |----------
+----+ | | |---| |---| |----------
|Leaf|------| | | | | |---------+
+----+ | +------+ +-------| +-----+ | |
| | |
+--------------------------------+ |
|
+--------------------------------+ |
| VPLS PE with VSI | |
| | |
+----+ | +------+ +-------+ +-----+ | PW |
|Root|------|C-VLAN|---|S-VLAN |---|VSI |---------+
+----+ | | BRG | | BRG | | |----------
+----+ | | |---| | | |----------
|Root|------| | | | | |----------
+----+ | +------+ +-------| +-----+ |
| |
+--------------------------------+
Figure 6 T-VSI interconnected with Traditional VSI
In this case, the PE with a T-VSI in it must work in the compatible
mode, that is, the egress PW of the T-VSI must translate frames
received over both local root and leaf S-VLAN into a single S-VLAN
(local root VLAN if the peer is capable of rewriting the S-VLAN, or
the remote peer's S-VLAN otherwise), while the ingress PW only
translates the frames received over the PW into the local root VLAN.
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5.2.3. PW Processing in the Optimized Mode
When two VPLS PE with T-VSI are inter-connected and one side is
attached with pure leaves, as shown in the scenario of Fig. 7, the
egress PW of the miscellaneous attached PE then work in the optimized
mode, that is, the PE can drop all the frames received over the local
leaf S-VLAN rather than transport them over the PW and be discarded
on the remote PE. Thus bandwidth efficiency of the VPLS can be
improved.
+--------------------------------+
| VPLS PE with T-VSI |
| |
+----+ | +------+ +-------+ +-----+ | PW
|Root|------|C-VLAN|---|S-VLAN |---|T-VSI|----------
+----+ | | BRG | | BRG | | |----------
+----+ | | |---| |---| |----------
|Leaf|------| | | | | |---------+
+----+ | +------+ +-------| +-----+ | |
| | |
+--------------------------------+ |
|
+--------------------------------+ |
| VPLS PE with T-VSI | |
| | |
+----+ | +------+ +-------+ +-----+ | PW |
|Leaf|------|C-VLAN|---|S-VLAN |---|T-VSI|---------+
+----+ | | BRG | | BRG | | |----------
+----+ | | |---| |---| |----------
|Leaf|------| | | | | |----------
+----+ | +------+ +-------| +-----+ |
| |
+--------------------------------+
Figure 7 T-VSI interconnected with 1-side of pure Leaves
6. LDP Extensions for E-Tree Support
To dynamically provision the E-Tree service using the signaling
procedures specified in [RFC4447], an E-Tree specific interface
parameter sub-TLV is proposed as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| E-Tree | Length=8 | Reserved |P|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Root VLAN ID | Leaf VLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 E-Tree Sub-TLV
Where:
o E-Tree is the sub-TLV identifier to be assigned by IANA.
o Length is the length of the sub TLV in octets.
o Reserved bits MUST be set to zero on transmit and be ignored on
receive.
o P is a Pure Leaf bit, it is set to 1 to indicate that the PE is
attached with all leaves, and set to 0 otherwise.
o R is a request bit of Remote VLAN Translation. If a PE is capable
of translating VLANs, then set R to 0, otherwise set R to 1.
o Root VLAN ID is the value of the local root VLAN.
o Leaf VLAN ID is the value of the local leaf VLAN.
When the VPLS supporting an E-Tree service is setting up the PW, the
PW endpoints negotiate the E-Tree support using the above E-Tree sub-
TLV. Note PW type of 0x0004 should be used during the PW negotiation.
A PE that wishes to support E-Tree service includes in its PW label
mapping message an E-Tree Sub-TLV, with its local root VLAN and leaf
VLAN carried in the Root VLAN ID and Leaf VLAN ID field respectively.
A PE that has E-Tree capability and willing to support it MUST
include an E-Tree Sub-TLV with its own local root VLAN and leaf VLAN.
A PE that is incapable of translating VLANs MUST set the R bit to 1.
And a PE is attached with pure leaves SHOULD set the P bit to 1.
If a PE has sent an E-Tree Sub-TLV and has received an E-Tree Sub-TLV,
then it must work as described in Section 5.2.1. If a PE receives R=1
from its peer, then it must do VLAN translation for this peer,
otherwise local mapping rule applies. If the bit P is set, then it
should work as described in Section 5.2.3.
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If a PE has sent an E-Tree Sub-TLV and does not receive an E-Tree
Sub-TLV, then it must work in the mode of compatibility as described
in Section 5.2.2.
7. Security Considerations
To be added in the next version.
8. IANA Considerations
IANA is requested to allocate a value for E-Tree in the Pseudowire
Interface Parameters Sub-TLV type registry.
Parameter ID Length Description
========================================
TBD 8 E-Tree
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4447] Martini, L., et al, "Pseudowire Setup and Maintenance Using
Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC4448] Martini, L., et al, "Encapsulation Methods for Transport of
Ethernet over MPLS Networks", RFC 4448, April 2006.
[RFC4664] Andersson, L., and Rosen, E., "Framework for Layer 2
Virtual Private Networks (L2VPNs)", RFC 4664, September
2006.
[RFC4762] Lasserre, M. and Kompella, V., "Virtual Private LAN
Services using LDP", RFC 4762, January 2007.
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9.2. Informative References
[vpls-interop] Sajassi, A., et al, "VPLS Interoperability with CE
Bridges", draft-ietf-l2vpn-vpls-bridge-interop-04, November
2008
[ETree-frwk] Key, R., et al, "A Framework for E-Tree Service over
MPLS Network", draft-key-l2vpn-etree-frwk-01, January 2010
[vpls-etree] Delord, S., et al, "Extension to VPLS for E-Tree",
draft-key-l2vpn-vpls-etree-02, January 2010
[ETree-802.1Q] Haddock, S., E-Tree Support in 802.1Q, January 2010,
http://www.ieee802.org/1/files/public/docs2010/new-haddock-
E-TREE-support-0110-v01.pdf
10. Acknowledgments
The author would like to thank Adrian Farrel for his valuable
comments.
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Authors' Addresses
Yuanlong Jiang
Huawei Technologies Co., Ltd.
Bantian industry base, Longgang district
Shenzhen, China
Email: yljiang@huawei.com
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