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IETF RFC 7796
Last modified on Wednesday, March 16th, 2016
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1;2c.
Internet Engineering Task Force (IETF) Y. Jiang, Ed.
Request for Comments: 7796 L. Yong
Category: Standards Track Huawei
ISSN: 2070-1721 M. Paul
Deutsche Telekom
March 2016
Ethernet-Tree (E-Tree) Support in Virtual Private LAN Service (VPLS)
 Abstract
This document specifies a generic Virtual Private LAN Service (VPLS)
solution, which uses VLANs to indicate root or leaf traffic to
support Ethernet-Tree (E-Tree) services. A VPLS Provider Edge (PE)
model is illustrated as an example for the solution. In the
solution, E-Tree VPLS PEs are interconnected by Pseudowires (PWs),
which carry the VLAN indicating the E-Tree attribute. The MAC
address-based Ethernet forwarding engine and the PW work in the same
way as specified in RFC 4762 and RFC 4448, respectively. A signaling
mechanism is described to support E-Tree capability and VLAN mapping
negotiation.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 7796.
Jiang, et al. Standards Track PAGE 1 
RFC 7796 E-Tree Support in VPLS March 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. PE Model with E-Tree Support . . . . . . . . . . . . . . . . 5
4.1. Existing PE Models . . . . . . . . . . . . . . . . . . . 5
4.2. A New PE Model with E-Tree Support . . . . . . . . . . . 8
5. PW for E-Tree Support . . . . . . . . . . . . . . . . . . . . 9
5.1. PW Encapsulation . . . . . . . . . . . . . . . . . . . . 9
5.2. VLAN Mapping . . . . . . . . . . . . . . . . . . . . . . 10
5.3. PW Processing . . . . . . . . . . . . . . . . . . . . . . 11
5.3.1. PW Processing in the VLAN Mapping Mode . . . . . . . 11
5.3.2. PW Processing in the Compatible Mode . . . . . . . . 12
5.3.3. PW Processing in the Optimized Mode . . . . . . . . . 13
6. Signaling for E-Tree Support . . . . . . . . . . . . . . . . 14
6.1. LDP Extensions for E-Tree Support . . . . . . . . . . . . 14
6.2. BGP Extensions for E-Tree Support . . . . . . . . . . . . 17
7. OAM Considerations . . . . . . . . . . . . . . . . . . . . . 19
8. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Other PE Models for E-Tree . . . . . . . . . . . . . 23
A.1. A PE Model with a VSI and No Bridge . . . . . . . . . . . 23
A.2. A PE Model with External E-Tree Interface . . . . . . . . 24
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 25
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
Jiang, et al. Standards Track PAGE 2
RFC 7796 E-Tree Support in VPLS March 2016
1. Introduction
The Ethernet-Tree (E-Tree) service is defined in the Metro Ethernet
Forum (MEF) Technical Specification MEF 6.2 [MEF6.2] as a Rooted-
Multipoint Ethernet Virtual Connection (EVC) service. An MEF 6.2
E-Tree solution must meet the following design requirements: the
Ethernet frames from a root may be received by any other root or
leaf, and the frames from a leaf may be received by any root, but
must not be received by a leaf. Further, an E-Tree service may
include multiple roots and multiple leaves. Although Virtual Private
Multicast Service (VPMS) [VPMS] and Point-to-Multipoint (P2MP)
multicast are somewhat simplified versions of this service, in fact,
they are both multicast services and are different from an E-Tree
service that may include both unicast and multicast traffic.
[RFC 7152] gives the requirements for providing E-Tree solutions in
the VPLS and the need to filter leaf-to-leaf traffic. [RFC 7387]
further describes a Multiprotocol Label Switching (MPLS) framework
for providing E-Tree. Though there were proposals for using the
Pseudowire (PW) control word or PWs to indicate the root/leaf
attribute of an E-Tree frame, both methods are limited in that they
are only applicable to "VPLS only" networks.
A VPLS PE usually consists of a bridge module itself (see [RFC 4664]
and [RFC 6246]); and moreover, E-Tree services may cross both Ethernet
and VPLS domains. Therefore, it is necessary to develop an E-Tree
solution both for "VPLS only" scenarios and for interworking between
Ethernet and VPLS.
IEEE 802.1 has incorporated the generic E-Tree solution into 802.1Q
[IEEE-802.1Q-2014], which is an improvement on the traditional
asymmetric VLAN mechanism. In the asymmetric VLAN mechanism as
described in Section B.1.3 of IEEE 802.1Q [IEEE-802.1Q-2003], a VLAN
ID is used to indicate the traffic from a server, and multiple VLAN
IDs are used to indicate the traffic from the clients (one VLAN ID
per client). In the new IEEE 802.1Q solution, only two VLANs are
used to indicate root/leaf attributes of a frame: one VLAN ID is used
to indicate the frames originated from the roots and another VLAN ID
is used to indicate the frames originated from the leaves. At a leaf
port, the bridge can then filter out all the frames from other leaf
ports based on the VLAN ID. It is better to reuse the same mechanism
in VPLS than to develop a new mechanism. A new mechanism would
introduce more complexity to interwork with the new IEEE 802.1Q
solution.
This document specifies how the Ethernet VLAN solution can be used to
support generic E-Tree services in VPLS. The solution specified here
is fully compatible with the IEEE bridge architecture and with IETF
Jiang, et al. Standards Track PAGE 3
RFC 7796 E-Tree Support in VPLS March 2016
Pseudowire Emulation Edge-to-Edge (PWE3) technology, thus it will not
change the FIB (such as installing E-Tree attributes in the FIB) or
need any specially tailored implementation. Furthermore, VPLS
scalability and simplicity are also maintained. With this mechanism,
it is also convenient to deploy a converged E-Tree service across
both Ethernet and MPLS networks.
A typical VPLS PE model is introduced as an example; the model is
then extended in which a Tree VSI is connected to a 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
VPLS.
Finally, this document describes the signaling extensions and
processing procedures for E-Tree support in VPLS.
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 [RFC 2119].
3. Terminology
AC: Attachment Circuit
B-VLAN: Backbone VLAN
C-VLAN: Customer VLAN
E-Tree: Ethernet Tree, a Rooted-Multipoint EVC service as defined in
[MEF6.2]
EVC: Ethernet Virtual Connection, as defined in [MEF4]
FIB: Forwarding Information Base, also known as "forwarding table"
I-SID: Backbone Service Instance Identifier, as defined in IEEE
802.1ah [IEEE-802.1Q-2014]
Leaf AC: An AC attached with a leaf
Leaf VLAN: A VLAN Identifier (ID) used to indicate all the frames
that are originated at a leaf AC. It may be a C-VLAN, an S-VLAN,
or a B-VLAN
Jiang, et al. Standards Track PAGE 4
RFC 7796 E-Tree Support in VPLS March 2016
OAM: Operations, Administration, and Maintenance
PBB: Provider Backbone Bridge
PE: Provider Edge
PW: Pseudowire
Root AC: An AC attached with a root
Root VLAN: A VLAN ID used to indicate all the frames that are
originated at a root AC. It may be a C-VLAN, an S-VLAN, or a
B-VLAN
S-VLAN: Service VLAN
T-VSI: Tree VSI, a VSI with E-Tree support
VLAN: Virtual Local Area Network
VPLS: Virtual Private LAN Service
VSI: Virtual Switching Instance as defined in [RFC 4664], also known
as "VPLS Forwarder" in [RFC 7041]
4. PE Model with E-Tree Support
The problem scenario of E-Tree as shown in Figure 1 of [RFC 7152] is a
simplification of the L2VPN architecture. Several common VPLS PE
architectures are discussed in more detail in [RFC 4664] and
[RFC 6246].
Below, an E-Tree solution in VPLS is demonstrated with the help of a
typical VPLS PE model. Its use in other PE models is discussed in
Appendix A.
4.1. Existing PE Models
According to [RFC 4664], there are at least three models possible 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.
Jiang, et al. Standards Track PAGE 5
RFC 7796 E-Tree Support in VPLS March 2016
The second PE model is commonly used. A typical example is further
depicted in Figure 1 and Figure 2 (both figures are extracted from
[RFC 6246]), where an S-VLAN bridge module is connected to multiple
VSIs each with a single VLAN virtual interface.
+-------------------------------+
| 802.1ad Bridge Module Model |
| |
+---+ AC | +------+ +-----------+ |
|CE |---------|C-VLAN|------| | |
+---+ | |bridge|------| | |
| +------+ | | |
| o | S-VLAN | |
| o | | | ---> to VSI
| o | Bridge | |
+---+ AC | +------+ | | |
|CE |---------|C-VLAN|------| | |
+---+ | |bridge|------| | |
| +------+ +-----------+ |
+-------------------------------+
Figure 1: A 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: A VPLS-Capable PE Model
Jiang, et al. Standards Track PAGE 6
RFC 7796 E-Tree Support in VPLS March 2016
In this PE model, Ethernet frames from Customer Edges (CEs) will
cross multiple stages of bridge modules (i.e., C-VLAN and S-VLAN
bridge), and a VSI in a PE before being sent on the PW to a remote
PE. Therefore, the association between an AC port and a PW on a VSI
is difficult.
This model could be further enhanced: when Ethernet frames arrive at
an ingress PE, a root VLAN or a leaf VLAN tag is added. At an egress
PE, the frames with the root VLAN tag are transmitted both to the
roots and the leaves, while the frames with the leaf VLAN tag are
transmitted to the roots but dropped for the leaves (these VLAN tags
are removed before the frames are transmitted over the ACs). It was
demonstrated in [IEEE-802.1Q-2014] that the E-Tree service in
Ethernet networks can be well supported with this mechanism.
Assuming this mechanism is implemented in the bridge module, it is
quite straightforward to infer a VPLS PE model with two VSIs to
support the E-Tree (as shown in Figure 3). But this model will
require two VSIs per PE and two sets of PWs per E-Tree service, which
is poorly scalable in a large MPLS/VPLS network; in addition, both of
these VSIs have to share their learned MAC addresses.
+----------------------------------------+
| VPLS-Capable PE Model |
| +---------------+ +------+ |
| | | |VSI-1 |------------
| | |==========| |------------ PWs
| | Bridge ------------ |------------
| | | Root +------+ |
| | Module | S-VLAN |
| | | |
| | (802.1ad | |
| | bridge) | |
| | | Leaf |
| | | S-VLAN +------+ |
| | ------------VSI-2 |-------------
| | |==========| |------------- PWs
| | | ^ | |-------------
| +---------------+ | +------+ |
| | |
+-------------------------|--------------+
LAN Emulation Interface
Figure 3: A VPLS PE Model for E-Tree with 2VSIs
Jiang, et al. Standards Track PAGE 7
RFC 7796 E-Tree Support in VPLS March 2016
4.2. A New PE Model with E-Tree Support
In order to support the E-Tree in a more scalable way, a new VPLS PE
model with a single Tree VSI (T-VSI, a VSI with E-Tree support) is
specified. As depicted in Figure 4, the bridge module is connected
to the T-VSI with a dual-VLAN virtual interface, i.e., both the root
VLAN and the leaf VLAN are connected to the same T-VSI, and they
share the same FIB and work in shared VLAN learning. In this way,
only one VPLS instance and one set of PWs is needed per E-Tree
service, and the scalability of VPLS is improved.
+----------------------------------------+
| VPLS-Capable PE Model |
| +---------------+ +------+ |
| | |==========|TVSI-1|------------
+---+ AC | | ------------ |------------ PWs
|CE |--------| Bridge ------------ |------------
+---+ | | | Root & +------+ |
| | Module | Leaf VLAN o |
| | | o |
| | | o |
| | | o |
| | | o |
+---+ AC | | | VLAN-n +------+ |
|CE |--------| ------------VSI-n |-------------
+---+ | | |==========| |------------- PWs
| | | ^ | |-------------
| +---------------+ | +------+ |
| | |
+-------------------------|--------------+
LAN Emulation Interface
Figure 4: A VPLS PE Model for E-Tree with a Single T-VSI
For an untagged AC port (frames over this port are untagged) or a
VLAN unaware port (VLAN tags in the frames are ignored), where the
bridge module is a C-VLAN bridge, the Ethernet frames received from
the root ACs MUST be tagged with a root C-VLAN. When the bridge
module is an 802.1ad bridge [IEEE-802.1Q-2014], the Ethernet frames
received from the root ACs MUST be tagged with a root S-VLAN. Note,
this can be done by adding a root C-VLAN first in a C-VLAN bridge,
but this is out of the scope of this document.
For a C-VLAN tagged port, the Ethernet frames received from the root
ACs MUST be tagged with a root S-VLAN.
Jiang, et al. Standards Track PAGE 8
RFC 7796 E-Tree Support in VPLS March 2016
For an S-VLAN tagged port, the S-VLAN tag in the Ethernet frames
received from the root ACs SHOULD be translated to the root S-VLAN in
the VPLS network domain.
Alternatively, for an S-VLAN tagged port, the PBB VPLS PE model
(where an IEEE 802.1ah bridge module is embedded in the PE) as
described in [RFC 7041] MAY be used. A root B-VLAN or a leaf B-VLAN
MAY be added. The E-Tree attribute may also be indicated with two
I-SID tags in the bridge module, and the frames are then encapsulated
and transported transparently over a single B-VLAN. Thus, the PBB
VPLS works in the same way as described in [RFC 7041] and will not be
discussed further in this document. When many S-VLANs are
multiplexed in a single AC, PBB VPLS has the advantages of both VLAN
scalability and MAC address scalability.
In a similar way, the traffic from the leaf ACs is tagged and
transported on the leaf C-VLAN, S-VLAN, or B-VLAN.
In all cases, the outermost VLAN in the resulting Ethernet header is
used to indicate the E-Tree attribute of an Ethernet frame; this
document uses VLAN to refer to this outermost VLAN for simplicity in
the latter sections.
5. PW for E-Tree Support
5.1. PW Encapsulation
To support an E-Tree service, T-VSIs in a VPLS MUST be interconnected
with a bidirectional Ethernet PW. The Ethernet PW SHOULD work in the
tagged mode (PW type 0x0004) as described in [RFC 4448], in which case
a VLAN tag MUST be carried in each frame in the PW to indicate the
frame originated from either root or leaf (the VLAN tag indicating
the frame originated from either root or leaf can be translated by a
bridge module in the PE or added by an outside Ethernet edge device,
even by a customer device). In the tagged PW mode, two service-
delimiting VLANs MUST be allocated in the VPLS domain for an E-Tree.
PW processing for the tagged PW will be described in Section 5.3 of
this document.
A raw mode PW (PW type 0x0005 in [RFC 4448]) MAY also be used to carry
an E-Tree service for a PW in Compatible mode as shown in
Section 5.3.2. As defined in [RFC 4448], for a raw mode PW, an
Ethernet frame's 802.1Q VLAN tag is not meaningful to the PEs and it
passes transparently through them.
Jiang, et al. Standards Track PAGE 9
RFC 7796 E-Tree Support in VPLS March 2016
5.2. VLAN Mapping
There are two ways of manipulating VLANs for an E-Tree in VPLS:
o Global VLAN based, that is, provisioning two global VLANs (Root
VLAN and Leaf VLAN) across the VPLS network, thus no VLAN mapping
is needed at all, or the VLAN mapping is done completely in the
Ethernet domains.
o Local VLAN based, that is, provisioning two local VLANs for each
PE (that participates in the E-Tree) in the VPLS network
independently.
The first method requires no VLAN mapping in the PW, but two unique
service-delimiting VLANs must be allocated across the VPLS domain.
The second method is more scalable in the use of VLANs, but needs a
VLAN mapping mechanism in the PW similar to what is already described
in Section 4.3 of [RFC 4448].
Global or local VLANs can be manually configured or provisioned by an
Operational Support System. Alternatively, some automatic VLAN
allocation algorithm may be provided in the management plane, but it
is out of scope of this document.
For both methods, VLAN mapping parameters from a remote PE can be
provisioned or determined by a signaling protocol as described in
Section 6 when a PW is being established.
Jiang, et al. Standards Track PAGE 10
RFC 7796 E-Tree Support in VPLS March 2016
5.3. PW Processing
5.3.1. PW Processing in the VLAN Mapping Mode
In the VLAN mapping mode, two VPLS PEs with E-Tree capability are
inter-connected with a PW (for example, the scenario of Figure 5
depicts the interconnection of two PEs attached with both root and
leaf nodes).
+----------------------------+
| VPLS PE with T-VSI |
| |
+----+ | +------+ Root VLAN +-----+ | PW
|Root|------| VLAN |-----------|T-VSI|----------
+----+ | | BRG | Leaf VLAN | |----------
+----+ | | |-----------| |----------
|Leaf|------| | | |-----+
+----+ | +------+ +-----+ | |
| | |
+----------------------------+ |
|
+----------------------------+ |
| VPLS PE with T-VSI | |
| | |
+----+ | +------+ Root VLAN +-----+ | | PW
|Root|------| VLAN |-----------|T-VSI|-----+
+----+ | | BRG | Leaf VLAN | |----------
+----+ | | |-----------| |----------
|Leaf|------| | | |----------
+----+ | +------+ +-----+ |
| | BRG: Bridge Module
+----------------------------+
Figure 5: T-VSI Interconnected in the Normal Mode
If a PE is in the VLAN mapping mode for a PW, then in the data plane,
the PE MUST map the VLAN in each frame as follows:
o Upon transmitting frames on the PW, map from the local VLAN to the
remote VLAN (i.e., the local leaf VLAN in a frame is translated to
the remote leaf VLAN; the local root VLAN in a frame is translated
to the remote root VLAN).
o Upon receiving frames on the PW, map from the remote VLAN to the
local VLAN, and the frames are further forwarded or dropped in the
egress bridge module using the filtering mechanism as described in
[IEEE-802.1Q-2014].
Jiang, et al. Standards Track PAGE 11
RFC 7796 E-Tree Support in VPLS March 2016
The signaling for VLANs used by E-Tree is specified in Section 6.
5.3.2. 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 Figure 6, the VPLS
PE with T-VSI can be attached with root and/or leaf nodes, while the
VPLS PE with a traditional VSI can only be attached with root nodes.
A raw PW SHOULD be used to connect them.
+------------------------+
| VPLS PE with T-VSI |
| |
+----+ | +------+ +-----+ | PW
|Root|------| VLAN |-------|T-VSI|----------
+----+ | | BRG | | |----------
+----+ | | |-------| |----------
|Leaf|------| | | |---------+
+----+ | +------+ +-----+ | |
| | |
+------------------------+ |
|
+------------------------+ |
| VPLS PE with VSI | |
| | |
+----+ | +------+ +-----+ | PW |
|Root|------| VLAN |-------|VSI |---------+
+----+ | | BRG | | |----------
+----+ | | | | |----------
|Root|------| | | |----------
+----+ | +------+ +-----+ |
| |
+------------------------+
Figure 6: T-VSI Interconnected with Traditional VSI
If a PE is in the Compatible mode for a PW, then in the data plane,
the PE MUST process the frame as follows:
o Upon transmitting frames on the PW, remove the root or leaf VLAN
in the frames.
o Upon receiving frames on the PW, add a VLAN tag with a value of
the local root VLAN to the frames.
Jiang, et al. Standards Track PAGE 12
RFC 7796 E-Tree Support in VPLS March 2016
5.3.3. PW Processing in the Optimized Mode
When two PEs (both with E-Tree capability) are inter-connected with a
PW and one of them (e.g., PE2) is attached with only leaf nodes, as
shown in the scenario of Figure 7, its peer PE (e.g., PE1) should
then work in the Optimized mode for this PW. In this case, PE1
should not send the frames originated from the local leaf VLAN to
PE2, i.e., these frames are dropped rather than transported over the
PW. The bandwidth efficiency of the VPLS can thus be improved. The
signaling for the PE attached with only leaf nodes is specified in
Section 6.
+------------------------+
|VPLS PE with T-VSI (PE1)|
| |
+----+ | +------+ +-----+ | PW
|Root|------| VLAN |-------|T-VSI|----------
+----+ | | BRG | | |----------
+----+ | | |-------| |----------
|Leaf|------| | | |---------+
+----+ | +------+ +-----+ | |
| | |
+------------------------+ |
|
+------------------------+ |
|VPLS PE with T-VSI (PE2)| |
| | |
+----+ | +------+ +-----+ | PW |
|Leaf|------| VLAN |-------|T-VSI|---------+
+----+ | | BRG | | |----------
+----+ | | |-------| |----------
|Leaf|------| | | |----------
+----+ | +------+ +-----+ |
| |
+------------------------+
Figure 7: T-VSI Interconnected with PE Attached with Only Leaf Nodes
If a PE is in the Optimized Mode for a PW, upon transmit, the PE
SHOULD drop a frame if its VLAN ID matches the local leaf VLAN ID.
Jiang, et al. Standards Track PAGE 13
RFC 7796 E-Tree Support in VPLS March 2016
6. Signaling for E-Tree Support
6.1. LDP Extensions for E-Tree Support
In addition to the signaling procedures as specified in Section 5.3.3
of [RFC 4447], this document specifies a new interface parameter sub-
TLV to provision an E-Tree service and negotiate the VLAN mapping
function, as follows:
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(0x1A) | Length=8 | Reserved |P|V|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ | Root VLAN ID | MBZ | Leaf VLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: E-Tree Sub-TLV
Where:
o E-Tree is the sub-TLV identifier (0x1A) as 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 leaf-only bit, it is set to 1 to indicate that the PE is
attached with only leaf nodes, and set to 0 otherwise.
o V is a bit indicating the sender's VLAN mapping capability. A PE
capable of VLAN mapping MUST set this bit, and clear it otherwise.
o Must Be Zero (MBZ), 4 bits MUST be set to zero on transmit and be
ignored on receive.
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 setting up a PW for the E-Tree based VPLS, two peer PEs
negotiate the E-Tree support using the above E-Tree sub-TLV. Note
that the PW type of 0x0004 SHOULD be used during the PW negotiation.
A PE that wishes to support an E-Tree service MUST include an E-Tree
sub-TLV in its PW Label Mapping message and include its local root
VLAN ID and leaf VLAN ID in the TLV. A PE that has the VLAN mapping
Jiang, et al. Standards Track PAGE 14
RFC 7796 E-Tree Support in VPLS March 2016
capability MUST set the V bit to 1, and a PE attached with only leaf
nodes SHOULD set the P bit to 1.
A PE that receives a PW Label Mapping message with an E-Tree sub-TLV
from its peer PE, after saving the VLAN information for the PW, MUST
process it as follows:
1) For this PW, set VLAN-Mapping-Mode, Compatible-Mode, and
Optimized-Mode to FALSE.
2) If either the root VLAN ID in the message is not equal to the
local root VLAN ID, or the leaf VLAN ID in the message is not
equal to the local leaf VLAN ID {
If the bit V is cleared {
If the PE is capable of VLAN mapping, it MUST set
VLAN-Mapping-Mode to TRUE;
Else {
A Label Release message with the error code "E-
Tree VLAN mapping not supported" is sent to the
peer PE and exit the process;
}
}
If the bit V is set, and the PE is capable of VLAN mapping,
the PE with the minimum IP address MUST set
VLAN-Mapping-Mode to TRUE;
}
3) If the P bit is set
{
If the PE is a leaf-only node itself, a Label Release
message with a status code "Leaf-to-Leaf PW released" is
sent to the peer PE and exits the process;
Else the PE SHOULD set the Optimized-Mode to TRUE.
}
Jiang, et al. Standards Track PAGE 15
RFC 7796 E-Tree Support in VPLS March 2016
A PE SHOULD send a Label Mapping message with an E-Tree sub-TLV as
per Section 5.3.3 of [RFC 4447]. A PE MUST send a Label Mapping
message with an updated E-Tree sub-TLV to all other PEs over
corresponding LDP sessions when its role changes from leaf-only to
not leaf-only (i.e., when a root node is added to a PE attached with
only leaf nodes).
If a PE has sent a Label Mapping message with an E-Tree sub-TLV but
does not receive any E-Tree sub-TLV in its peer's PW Label Mapping
message, the PE SHOULD then establish a raw PW with this peer as in
traditional VPLS and set Compatible-Mode to TRUE for this PW.
Data plane processing for this PW is as follows:
o If Optimized-Mode is TRUE, then data plane processing as described
in Section 5.3.3 applies.
o If VLAN-Mapping-Mode is TRUE, then data plane processing as
described in Section 5.3.1 applies.
o If Compatible-Mode is TRUE, then data plane processing as
described in Section 5.3.2 applies.
o PW processing as described in [RFC 4448] proceeds as usual for all
cases.
When VPLS is set up using the Pseudowire ID (PWid) Forwarding
Equivalence Class (FEC) Element (see Appendix A of [RFC 4762]), its
E-Tree signaling is similar to the above process. Dynamic
re-configuration of E-Tree should be avoided for this case. However,
when re-configuration of E-Tree is forced on a PE for some reason
(e.g., a configuration error), the PE may close the LDP sessions with
its peer PEs for this VPLS instance and re-install its PW labels, so
that its peer PEs can send out the LDP Label Mapping messages again.
Jiang, et al. Standards Track PAGE 16
RFC 7796 E-Tree Support in VPLS March 2016
6.2. BGP Extensions for E-Tree Support
A new E-Tree extended community (0x800b) has been allocated by IANA
for E-Tree signaling in BGP VPLS:
+------------------------------------+
| Extended community type (2 octets) |
+------------------------------------+
| MBZ | Root VLAN (12 bits) |
+------------------------------------+
| MBZ | Leaf VLAN (12 bits) |
+------------------------------------+
| Reserved |P|V|
+------------------------------------+
Figure 9: E-Tree Extended Community
Where:
o Must Be Zero (MBZ), 4 bits MUST be set to zero on transmit and be
ignored on receive.
o Root VLAN ID is the value of the local root VLAN.
o Leaf VLAN ID is the value of the local leaf VLAN.
o Reserved, 14 bits MUST be set to zero on transmit and be ignored
on receive.
o P is a leaf-only bit, it is set to 1 to indicate that the PE is
attached with only leaf nodes, and set to 0 otherwise.
o V is a bit indicating the sender's VLAN mapping capability. A PE
capable of VLAN mapping MUST set this bit, and clear it otherwise.
The PEs attached with both leaf and root nodes MUST support BGP
E-Tree signaling as described in this document, and SHOULD support
VLAN mapping in their data planes. The traditional PE attached with
only root nodes may also participate in an E-Tree service. If some
PEs don't support VLAN mapping, global VLANs as per Section 5.2 MUST
be provisioned for an E-Tree service.
In BGP VPLS signaling, besides attaching a Layer2 Info Extended
Community as detailed in [RFC 4761], an E-Tree Extended Community MUST
be further attached if a PE wishes to participate in an E-Tree
service. The PE MUST include its local root VLAN ID and leaf VLAN ID
Jiang, et al. Standards Track PAGE 17
RFC 7796 E-Tree Support in VPLS March 2016
in the E-Tree Extended Community. A PE attached with only leaf nodes
of an E-Tree SHOULD set the P bit in the E-Tree Extended Community to
1.
A PE that receives a BGP UPDATE message with an E-Tree Extended
Community from its peer PE, after saving the VLAN information for the
PW, MUST process it as follows (after processing procedures as
specified in Section 3.2 of [RFC 4761]):
1) For this PW, set VLAN-Mapping-Mode, Compatible-Mode, and
Optimized-Mode to FALSE.
2) If either the root VLAN ID in the E-Tree Extended Community is
not equal to the local root VLAN ID, or the leaf VLAN ID in the
E-Tree Extended Community is not equal to the local leaf VLAN ID {
If the bit V is cleared {
If the PE is capable of VLAN mapping, it MUST set VLAN-
Mapping-Mode to TRUE;
Else {
Log with a message "E-Tree VLAN mapping not
supported" and exit the process;
}
}
If the bit V is set, and the PE is capable of VLAN mapping,
the PE with the minimum IP address MUST set VLAN-Mapping-Mode
to TRUE;
}
3) If the P bit is set {
If the PE is a leaf-only PE itself, forbids any traffic on the
PW;
Else the PE SHOULD set the Optimized-Mode to TRUE.
}
A PE that does not recognize this attribute SHALL ignore it silently.
If a PE has sent an E-Tree Extended Community but does not receive
any E-Tree Extended Community from its peer, the PE SHOULD then
Jiang, et al. Standards Track PAGE 18
RFC 7796 E-Tree Support in VPLS March 2016
establish a raw PW with this peer as in traditional VPLS and set
Compatible-Mode to TRUE for this PW.
The data plane in the VPLS is the same as described in Section 4.2 of
[RFC 4761], and data plane processing for a PW is the same as
described at the end of Section 6.1 in this document.
7. OAM Considerations
The VPLS OAM requirements and framework as specified in [RFC 6136] are
applicable to E-Tree, as both Ethernet OAM frames and data traffic
are transported over the same PW.
Ethernet OAM for E-Tree including both service OAM and segment OAM
frames SHALL undergo the same VLAN mapping as the data traffic; and
root VLAN SHOULD be applied to segment OAM frames so that they are
not filtered.
8. Applicability
The solution specified in this document is applicable to both LDP
VPLS [RFC 4762] and BGP VPLS [RFC 4761].
This solution is applicable to both "VPLS Only" networks and VPLS
with Ethernet aggregation networks.
This solution is also applicable to PBB VPLS networks.
9. IANA Considerations
IANA allocated the following value for E-Tree in the "Pseudowire
Interface Parameters Sub-TLV type Registry".
Parameter ID Length Description
=======================================
0x1A 8 E-Tree
IANA allocated the two following new LDP status codes in the "Status
Code Name Space" registry.
Range/Value E Description
------------- ----- ----------------------
0x20000003 1 E-Tree VLAN mapping not supported
0x20000004 0 Leaf-to-Leaf PW released
Jiang, et al. Standards Track PAGE 19
RFC 7796 E-Tree Support in VPLS March 2016
IANA allocated the following value for E-tree in the "Generic
Transitive Experimental Use Extended Community Sub-Types" registry
within the BGP Extended Community registry.
Type Value Sub-Type Value Name
========== ============== ============
0x80 0x0b E-Tree Info
10. Security Considerations
This solution requires implementations to prevent leaf-to-leaf
communication in the data plane of VPLS when its PEs are
interconnected with PWs. If all PEs enforce that, then network
attacks from one leaf to another leaf are avoided, and security can
be enhanced for customers with this solution. However, if a PE is
compromised or inappropriately configured, a leaf node may be taken
as a root node and may receive traffic from other leaf nodes
inappropriately. Authenticity and integrity measures for LDP need to
be considered as in RFC 5036 [RFC 5036]. Security considerations as
described in [RFC 4448], [RFC 4761], and [RFC 4762] also apply.
11. References
11.1. Normative References
[IEEE-802.1Q-2014]
IEEE, "Bridges and Bridged Networks", IEEE 802.1Q,
DOI 10.1109/ieeestd.2014.6991462, November 2014.
[MEF6.2] Metro Ethernet Forum 6.2, "EVC Ethernet Services
Definitions Phase 3", August 2014.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<http://www.rfc-editor.org/info/RFC 2119>.
[RFC 4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
G. Heron, "Pseudowire Setup and Maintenance Using the
Label Distribution Protocol (LDP)", RFC 4447,
DOI 10.17487/RFC 4447, April 2006,
<http://www.rfc-editor.org/info/RFC 4447>.
[RFC 4448] Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, DOI 10.17487/RFC 4448, April 2006,
<http://www.rfc-editor.org/info/RFC 4448>.
Jiang, et al. Standards Track PAGE 20
RFC 7796 E-Tree Support in VPLS March 2016
[RFC 4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and
Signaling", RFC 4761, DOI 10.17487/RFC 4761, January 2007,
<http://www.rfc-editor.org/info/RFC 4761>.
[RFC 4762] Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, DOI 10.17487/RFC 4762, January 2007,
<http://www.rfc-editor.org/info/RFC 4762>.
[RFC 5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC 5036,
October 2007, <http://www.rfc-editor.org/info/RFC 5036>.
11.2. Informative References
[IEEE-802.1Q-2003]
IEEE, "Virtual Bridged Local Area Networks", IEEE 802.1,
DOI 10.1109/IEEESTD.2003.94280, May 2003.
[MEF4] Metro Ethernet Forum 4, "Metro Ethernet Network
Architecture Framework - Part 1: Generic Framework", May
2004.
[RFC 3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC 3985, March 2005,
<http://www.rfc-editor.org/info/RFC 3985>.
[RFC 4664] Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
2 Virtual Private Networks (L2VPNs)", RFC 4664,
DOI 10.17487/RFC 4664, September 2006,
<http://www.rfc-editor.org/info/RFC 4664>.
[RFC 6136] Sajassi, A., Ed. and D. Mohan, Ed., "Layer 2 Virtual
Private Network (L2VPN) Operations, Administration, and
Maintenance (OAM) Requirements and Framework", RFC 6136,
DOI 10.17487/RFC 6136, March 2011,
<http://www.rfc-editor.org/info/RFC 6136>.
[RFC 6246] Sajassi, A., Ed., Brockners, F., Mohan, D., Ed., and Y.
Serbest, "Virtual Private LAN Service (VPLS)
Interoperability with Customer Edge (CE) Bridges",
RFC 6246, DOI 10.17487/RFC 6246, June 2011,
<http://www.rfc-editor.org/info/RFC 6246>.
Jiang, et al. Standards Track PAGE 21
RFC 7796 E-Tree Support in VPLS March 2016
[RFC 7041] Balus, F., Ed., Sajassi, A., Ed., and N. Bitar, Ed.,
"Extensions to the Virtual Private LAN Service (VPLS)
Provider Edge (PE) Model for Provider Backbone Bridging",
RFC 7041, DOI 10.17487/RFC 7041, November 2013,
<http://www.rfc-editor.org/info/RFC 7041>.
[RFC 7152] Key, R., Ed., DeLord, S., Jounay, F., Huang, L., Liu, Z.,
and M. Paul, "Requirements for Metro Ethernet Forum (MEF)
Ethernet-Tree (E-Tree) Support in Layer 2 Virtual Private
Network (L2VPN)", RFC 7152, DOI 10.17487/RFC 7152, March
2014, <http://www.rfc-editor.org/info/RFC 7152>.
[RFC 7387] Key, R., Ed., Yong, L., Ed., Delord, S., Jounay, F., and
L. Jin, "A Framework for Ethernet Tree (E-Tree) Service
over a Multiprotocol Label Switching (MPLS) Network",
RFC 7387, DOI 10.17487/RFC 7387, October 2014,
<http://www.rfc-editor.org/info/RFC 7387>.
[VPMS] Kamite, Y., JOUNAY, F., Niven-Jenkins, B., Brungard, D.,
and L. Jin, "Framework and Requirements for Virtual
Private Multicast Service (VPMS)", Work in Progress,
draft-ietf-l2vpn-vpms-frmwk-requirements-05, October 2012.
Jiang, et al. Standards Track PAGE 22
RFC 7796 E-Tree Support in VPLS March 2016
Appendix A. Other PE Models for E-Tree
A.1. A PE Model with a VSI and No Bridge
If there is no bridge module in a PE, the PE may consist of Native
Service Processors (NSPs) as shown in Figure 10 (adapted from
Figure 5 of [RFC 3985]) where any transformation operation for VLANs
(e.g., VLAN insertion/removal or VLAN mapping) may be applied. Thus,
a root VLAN or leaf VLAN can be added by the NSP depending on the
User Network Interface (UNI) type (root/leaf) associated with the AC
over which the packet arrives.
Further, when a packet with a leaf VLAN exits a forwarder and arrives
at the NSP, the NSP must drop the packet if the egress AC is
associated with a leaf UNI.
Tagged PW and VLAN mapping work in the same way as in the typical PE
model.
+----------------------------------------+
| PE Device |
Multiple+----------------------------------------+
AC | | | Single | PW Instance
<------>o NSP # + PW Instance X<---------->
| | | |
|------| VSI |----------------------|
| | | Single | PW Instance
<------>o NSP #Forwarder + PW Instance X<---------->
| | | |
|------| |----------------------|
| | | Single | PW Instance
<------>o NSP # + PW Instance X<---------->
| | | |
+----------------------------------------+
Figure 10: A PE Model with a VSI and No Bridge Module
This PE model may be used by a Multi-Tenant Unit switch (MTU-s) in a
Hierarchical VPLS (H-VPLS) network or a Network-facing PE (N-PE) in
an H-VPLS network with non-bridging edge devices, wherein a spoke PW
can be treated as an AC in this model.
Jiang, et al. Standards Track PAGE 23
RFC 7796 E-Tree Support in VPLS March 2016
A.2. A PE Model with External E-Tree Interface
+----------------------------------------+
| PE Device |
Root +----------------------------------------+
VLAN | | Single | PW Instance
<------>o + PW Instance X<---------->
| | |
| VSI |----------------------|
| | Single | PW Instance
| Forwarder + PW Instance X<---------->
| | |
Leaf | |----------------------|
VLAN | | Single | PW Instance
<------>o + PW Instance X<---------->
| | |
+----------------------------------------+
Figure 11: A PE Model with External E-Tree Interface
A more simplified PE model is depicted in A.2, where Root/Leaf VLANs
are directly or indirectly connected over a single PW to the same VSI
forwarder in a PE, any transformation of E-Tree VLANs, e.g., VLAN
insertion/removal or VLAN mapping, can be performed by some outer
equipment, and the PE may further translate these VLANs into its own
local VLANs. This PE model may be used by an N-PE in an H-VPLS
network with bridging-capable devices, or scenarios such as providing
E-Tree Network-to-Network interfaces.
Jiang, et al. Standards Track PAGE 24
RFC 7796 E-Tree Support in VPLS March 2016
Acknowledgements
The authors would like to thank Stewart Bryant, Lizhong Jin, Deborah
Brungard, Russ Housley, Stephen Farrell, Sheng Jiang, Alvaro Retana,
and Ben Campbell for their detailed reviews and suggestions, and
Adrian Farrel, Susan Hares, Shane Amante, and Andrew Malis for their
valuable advice. In addition, the authors would like to thank Ben
Mack-crane, Edwin Mallette, Donald Fedyk, Dave Allan, Giles Heron,
Raymond Key, Josh Rogers, Sam Cao, and Daniel Cohn for their valuable
comments and discussions.
Contributors
The following people made significant contributions to this document:
Frederic Jounay
Salt Mobile SA
Rue du Caudray 4
1020 Renens
Switzerland
Email: frederic.jounay@salt.ch
Florin Balus
Alcatel-Lucent
701 East Middlefield Road
Mountain View, CA 94043
United States
Email: florin.balus@alcatel-lucent.com
Wim Henderickx
Alcatel-Lucent
Copernicuslaan 50
2018 Antwerp
Belgium
Email: wim.henderickx@alcatel-lucent.com
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134
United States
Email: sajassi@cisco.com
Jiang, et al. Standards Track PAGE 25
RFC 7796 E-Tree Support in VPLS March 2016
Authors' Addresses
Yuanlong Jiang (editor)
Huawei
Bantian, Longgang district
Shenzhen 518129
China
Email: jiangyuanlong@huawei.com
Lucy Yong
Huawei
207 Estrella Xing
Georgetown, TX 78628
United States
Email: lucyyong@huawei.com
Manuel Paul
Deutsche Telekom
Winterfeldtstrasse 21
Berlin 10781
Germany
Email: manuel.paul@telekom.de
Jiang, et al. Standards Track PAGE 26
RFC TOTAL SIZE: 52584 bytes
PUBLICATION DATE: Wednesday, March 16th, 2016
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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