Internet Working Group Y.L., Jiang
Internet Draft Huawei
Intended status: Standards Track July 12, 2010
Expires: January 2011
VPLS PE Model for E-Tree Support
draft-jiang-l2vpn-vpls-pe-etree-01.txt
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Abstract
The feasibility of VPLS as a general E-Tree solution is discussed. A
VPLS Provider Edge(PE) model for the E-Tree support is also proposed.
In this model, a Tree VSI and its PW processing is introduced which
can provide connectivity with dual VLANs for an E-Tree service. MAC
address based Ethernet forwarding engine works in the same way as
before in this architecture. As VLAN mapping may be needed in the
Ethernet PW for better scalability, control signaling needed for the
VLAN mapping is also discussed.
Table of Contents
1. Introduction...................................................2
2. Conventions used in this document..............................4
3. Terminology....................................................4
4. PE Model with E-Tree Support...................................4
4.1. Existing PE Models with E-Tree Support....................4
4.2. A New PE Model with E-Tree Support........................7
5. PW for E-Tree Support..........................................8
5.1. Tagged Mode PW Encapsulation..............................8
5.2. PW Processing.............................................9
5.2.1. PW Processing in the Normal Mode.....................9
5.2.2. PW Processing in the Compatibility Mode.............10
5.2.3. PW Processing in the Optimization Mode..............11
6. LDP Extensions for E-Tree Support.............................11
7. Security Considerations.......................................13
8. IANA Considerations...........................................13
9. References....................................................13
9.1. Normative References.....................................13
9.2. Informative References...................................13
10. Acknowledgments..............................................14
1. Introduction
E-Tree service is defined in Metro Ethernet Forum (MEF) as rooted
multi-point EVC 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. Although VPMS or P2MP multicast is a somewhat simplified
version of this service, in fact there is no exact corresponding
terminology in IETF.
For a generic E-Tree service, connectivity shall be provided for:
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(1) Multicast from a root to all leaves (and maybe all other
roots);
(2) Unicast from a root to any leaf or any other root;
(3) Unicast from a leaf to any root;
(4) Multicast from a leaf to all roots;
Therefore, MAC address based forwarding is needed for a general E-
Tree solution to distinguish between these packets and forward them
in a separate way. VSI in the VPLS can provide the needed
functionality of MAC address based forwarding.
[Etree-frwk] gives the requirements and a framework of a solution for
a E-Tree to filter leaf to leaf traffic in VPLS. [vpls-etree] shows
the details of the solution, where the Ethernet forwarder in the VPLS
is extended to filter the leaf-leaf traffic based on the <ingress
port, egress port, CW L-bit> tuple. This solution needs to change the
forwarding engine of the VSI, and the control word of the Ethernet PW.
Another solution was in discussion wherein root and leaf traffic are
classified and forwarded in two separate PWs. This is similar to the
hub & spoke L3VPN, wherein one PE attached with a root plays the role
of the hub, and all leaf traffic will take the way of this PE to
reach other roots. When a leaf co-sites with another root in a PE
different from the hub, the traffic must also make a detour to the
hub. Split horizon may also need to be extended to avoid loops in it.
This document introduces a dual VLAN 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.
This also means it is possible to deploy a converged E-Tree solution
across both Ethernet and MPLS networks.
As an example, a new VPLS PE model is firstly introduced which
consists of a Tree VSI connected to the S-VLAN bridge with a dual-
VLAN interface. This model also applies to a PE with C-VLAN or B-VLAN
as its provider's encapsulation.
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 the optional VLAN
mapping mechanism are also discussed.
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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.
+-------------------------------+
| 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
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+----------------------------------------+
| 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 an PW in
a single forwarding engine as required in [vpls-etree] is difficult,
sometimes even impossible.
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 model could be further enhanced by the introduction of trunk
VLAN and 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. It was anticipated
IEEE will further standardize this scheme in 802.1Q.
Should this mechanism be implemented in the bridge module, then it is
quite straightforward to infer the following VPLS PE model with E-
Tree support (as shown in Fig. 3). But this model will require two
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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
precise, they are called root and leaf S-VLAN respectively in this
document. In this way, only one VPLS instance and one set of PWs is
needed per E-Tree service. With this model, multiple E-Tree 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
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Both 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.
In fact, this model also applies to a PE with C-VLAN (customer sites
attached with untagged ports), or B-VLAN (with a PBB bridge module in
the PE) as a provider's tag encapsulation. Therefore, the document
will use the VLAN tag as a generalized form in the latter sections.
5. PW for E-Tree Support
T-VSIs from peer PEs in a VPLS are inter-connected with a PW, the
VLANs may be independently provisioned on each PE for better
scalability. That is, the assignment of VLANs in the PE may be local
to simplify the network provisioning.
In order to carry both VLANs (root and leaf VLAN) in a single PW and
map them into the remote peer's local 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 do 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 as described above, the
Ethernet PW should work in the tagged mode (PW type 0x0004) as
described in [RFC4448], and a C-VLAN, S-VLAN, or B-VLAN tag must be
carried in each frame in the PW, either the local or the remote VLAN
tag could be carried depending on the mapping option. In the local
mapping mode, the remote VLANs are carried with no change, while in
the remote mapping mode, the local mapped VLAN are carried instead.
The mapping between the local VLAN and the remote VLAN (local root
VLAN <-> remote root VLAN; local leaf VLAN <-> remote leaf VLAN)
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should be provisioned by management or signaled by a control protocol
such as LDP. The LDP extension for E-Tree support is provided in
Section 6.
5.2. PW Processing
5.2.1. PW Processing in the Normal Mode
In the normal mode, two VPLS PEs both with 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 Compatibility Mode
The new VPLS PE model can work in a traditional VPLS network
seamlessly in the compatibility mode. As shown in Fig. 5, 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
compatibility mode, that is, the egress PW of the T-VSI must
translate frames received over both local root and leaf VLAN into a
single VLAN (local root VLAN if the peer is capable of rewriting the
VLAN, or the remote peer'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 Optimization 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. 6, the
egress PW of the miscellaneous attached PE then work in the
optimization mode, that is, the PE can drop all the frames received
over the local leaf 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. If a
PE receives R=1 from its peer, then it must do VLAN translation
for this peer, otherwise local mapping rule applies.
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 the bit "L" 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.
BGP may also be used to distribute the VLAN mapping TLV.
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.
9.2. Informative References
[vpls-interop] Sajassi, A., et al, "VPLS Interoperability with CE
Bridges", draft-ietf-l2vpn-vpls-bridge-interop-04, November
2008
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[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.
Authors' Addresses
Yuanlong Jiang
Huawei Technologies Co., Ltd.
Bantian industry base, Longgang district
Shenzhen, China
Email: yljiang@huawei.com
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