Network Working Group F. Jounay (Ed.)
Internet Draft P. Niger
Category: Informational France Telecom Orange
Expires: January 2011
Y. Kamite
L. Martini NTT Communications
Cisco
S. Delord
R. Aggarwal Testra
Juniper Networks
L. Wang
M. Bocci Telenor
M. Vigoureux
Alcatel-Lucent G. Heron
BT
L. Jin
ZTE August 18, 2010
Requirements for Point-to-Multipoint Pseudowire
draft-ietf-pwe3-p2mp-pw-requirements-03.txt
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Abstract
This document presents a set of requirements for providing a Point-
to-Multipoint PWE3 (Pseudowire Emulation Edge to Edge) emulation. The
requirements identified in this document are related to architecture,
signaling and maintenance aspects of a Point-to-Multipoint PW
operation. They are proposed as guidelines for the standardization of
such mechanisms. Among other potential applications Point-to-
Multipoint PWs SHOULD be used to optimize the support of multicast
services (Virtual Private LAN Service and Virtual Private Multicast
Service) as defined in the Layer 2 Virtual Private Network working
group.
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].
Table of Contents
1. Introduction....................................................3
1.1. Problem Statement.............................................3
1.2. Scope of the document.........................................4
2. Definition......................................................4
2.1. Acronyms......................................................4
2.2. Terminology...................................................4
3. P2MP SS-PW Requirements.........................................5
3.1. P2MP SS-PW Reference Model....................................5
3.2. P2MP SS-PW Underlying Layer...................................7
3.3. P2MP SS-PW Construction.......................................8
3.4. P2MP SS-PW Signaling Requirements.............................8
3.4.1. PW Identifier...............................................8
3.4.2. PW type mismatch............................................8
3.4.3. Interface Parameters sub-TLV................................8
3.4.4. Leaf Grafting/Pruning.......................................9
3.5. Failure Detection and Reporting...............................9
3.6. Protection and Restoration....................................9
3.7. Scalability..................................................11
4. P2MP MS-PW Requirements........................................11
4.1. P2MP MS-PW Pseudowire Reference Model........................11
4.2. P2MP SS-PW Underlying Layer..................................12
4.3. P2MP MS-PW Signaling Requirements............................13
4.3.1. Dynamically Instantiated P2MP MS-PW........................13
4.3.2. P2MP MS-PW Setup Mechanisms................................13
4.3.3. PW type mismatch...........................................13
4.3.4. Interface Parameters sub-TLV...............................13
4.3.5. Leaf Grafting/Pruning......................................14
4.3.6. Explicit Routing...........................................14
4.4. Failure Detection and Reporting..............................14
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4.5. Protection and Restoration...................................15
4.6. Scalability..................................................15
5. Manageability considerations...................................15
6. Backward Compatibility.........................................16
7. Security Considerations........................................16
8. IANA Considerations............................................16
9. Acknowledgments................................................16
10. References....................................................17
10.1. Normative References........................................17
10.2. Informative References......................................17
Authors' Addresses............ ...................................18
Copyright and Licence Notice.. ...................................19
1. Introduction
1.1. Problem Statement
As defined in the PWE3 WG charter, a Pseudowire (PW) emulates a
point-to-point bidirectional link over an IP/MPLS network, and
provides a single service which is perceived by its user as an
unshared link or circuit of the chosen service. A Pseudowire is used
to transport non IP traffic (e.g. Ethernet, TDM, ATM, and FR) in an
IP/MPLS-based PSN (Packet Switched Network). PWE3 operates "edge to
edge" to provide the required connectivity between the two endpoints
of the PW.
The P2MP topology mentioned in [VPMS REQ] and required to provide
P2MP L2VPN services can be achieved via a P2MP PW. The use of PW
becomes necessary for some P2MP services requiring specific
encapsulation capabilities. This could be achieved using a set of
point to point PWs, with traffic replication on the PE, but faces
obvious bandwidth limitation issues, as traffic is carried multiple
time on shared links.
This document defines the requirements for the use of a Point-to-
Multipoint PW (P2MP PW). A Point-to-Multipoint (P2MP) Pseudowire (PW)
is a mechanism that emulates the essential attributes of a P2MP
Telecommunications service such as P2MP ATM over PSN. One of the
applicabilities of a P2MP PW is to deliver a non-IP multicast service
that carries multicast frames from a multicast source to one or more
multicast receivers. The required functions of P2MP PWs include
encapsulating service-specific PDUs arriving at an ingress Attachment
Circuit (AC), and carrying them across a tunnel to one or more egress
ACs, managing their timing and order, and any other operations
required to emulate the behavior and characteristics of the service
as faithfully as possible.
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P2MP PWs extend the PWE3 architecture [RFC3985] to offer a P2MP
Telecommunications service.
This document aims at defining the associated requirements related to
the P2MP PW operation (e.g. setup and maintenance, protection,
scalability).
1.2. Scope of the document
The document describes the P2MP PW Reference Model architectures and
outlines specific signaling requirements for the set up and
maintenance of a P2MP PW. The requirements are divided into two
parts, i.e. those applicable in a Single-Segment topology and those
applicable in a Multi-Segment topology. For other aspects of P2MP PW
implementation like packet processing (section 4) and Faithfulness of
Emulated Services (section 7), the document refers to [RFC3916].
Some P2MP PW requirements are derived from the signaling requirements
for P2MP Traffic-Engineered MPLS Label Switched Paths [RFC4461].
2. Definition
2.1. Acronyms
P2P: Point-to-Point
P2MP: Point-to-Multipoint
PW: Pseudowire
SS-PW: Single-Segment Pseudowire
MS-PW: Multi-Segment Pseudowire
2.2. Terminology
This document uses terminology described in [RFC5254], [RFC5659].
It also introduces additional terms needed in the context of P2MP PW.
P2MP PW, (also referred as PW Tree)
Point-to-Multipoint Pseudowire. A PW attached to a source used to
distribute L1/L2 format traffic to a set of one or more receivers (or
leaves). The P2MP PW is unidirectional and optionally bidirectional.
P2MP SS-PW
Point-to-Multipoint Single-Segment Pseudowire. A single segment P2MP
PW set up between the PE attached to the source and the PEs attached
to the receivers. The P2MP SS-PW relies on P2MP LSP as PSN tunnel.
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P2MP MS-PW
Point-to-Multipoint Multi-Segment Pseudowire. A multi-segment P2MP PW
represents an End-to-End PW segmented by means of S-PEs which are in
charge of switching the PW label. Each segment can rely on either
P2P LSP or P2MP LSP as PSN tunnel.
Root PE
P2MP PW Root Provider Edge. Router attached to a Customer Equipment
(traffic source) via an Attachment Circuit (AC). In a MS-PW
architecture the term used is Root T-PE.
Leaf PE
P2MP PW Leaf Provider Edge. Router attached to a set of one or more
Customer Equipments (traffic receivers or leaves). The P2MP PW is
attached to an Attachment Circuit (AC). The Leaf PE is therefore in
charge of replicating the traffic over the CEs based on its Forwarder
function [RFC3985].
Branch S-PE
The Branch S-PE is only defined and required in the context of MS-PW.
The Branch S-PE has one upstream PW (P2P or P2MP) segment and one or
several downstream PW (P2P or P2MP) segments.
P2MP PSN Tunnel
In the P2MP SS-PW topology, The PSN Tunnel is a general term
indicating a virtual P2MP connection between the Root PE and the Leaf
PEs. A P2MP tunnel may potentially carry multiple P2MP PWs inside
(aggregation). This document uses terminology from the document
describing the MPLS multicast architecture [RFC5332] for MPLS PSN.
3. P2MP SS-PW Requirements
3.1. P2MP SS-PW Reference Model
A P2MP SS-PW provides a Point-to-Multipoint connectivity from a Root
PE connected to a traffic source to at least two Leaf PEs connected
to traffic receivers. The PW endpoints connect the PW to its
Attachment Circuit (AC). As for a P2P PW, an AC can be a Frame Relay
DLC, an ATM VP/VC, an Ethernet port, a VLAN, a HDLC link on a
physical interface.
Figure 1 describes the P2MP SS-PW reference model which is derived
from [RFC3985] to support P2MP emulated services.
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|<-----------P2MP SS-PW------------>|
Native | | Native
Service | |<----P2MP PSN tunnel --->| | Service
(AC) V V V V (AC)
| +----+ +-----+ +----+ |
| |PE1 | | P |=========|PE2 |AC2 | +----+
| | | | ......PW1.......>|---------->|CE2 |
| | | | . |=========| | | +----+
| | | | . | +----+ |
| | |=========| . | |
| | | | . | +----+ |
+----+ | AC1 | | | . |=========|PE3 |AC3 | +----+
|CE1 |-------->|........PW1.............PW1.......>|---------->|CE3 |
+----+ | | | | . |=========| | | +----+
| | | | . | +----+ |
| | |=========| . | |
| | | | . | +----+ |
| | | | . |=========|PE4 |AC4 | +----+
| | | | ......PW1.......>|---------->|CE4 |
| | | | |=========| | | +----+
| +----+ +-----+ +----+ |
Figure 1 P2MP SS-PW Reference Model
This architecture applies to the case where a P2MP PSN tunnel extends
between edge nodes of a single PSN domain to transport a
unidirectional P2MP PW with endpoints at these edge nodes.
In this model a single copy of each PW packet is sent over the P2MP
PSN tunnel and is received by all Leaf PEs due to the P2MP nature of
the PSN tunnel. P2MP PW MUST be traffic optimised, only one copy of
P2MP PW packet on one single link. P Router is joining P2MP PSN
tunnel operation but is not participating in the signaling of P2MP
PW. P2MP PW operation is associated with PE1, PE2, PE3 and PE4.
Specifics operations that must be perfomed at the PE on the native
data units are not described here since the required pre-processing
(Forwarder (FWRD) and Native Service Processing (NSP)) defined in the
section 4.2 [RFC3985] are also applicable to P2MP PW.
In nature the P2MP PW is unidirectional, but it may be required for a
Root PE to receive unidirectional P2P traffic from any Leaf PE. For
that purpose the P2MP PW MAY support OPTIONAL bidirectional
connectivity between the Root PE and each Leaf PE
- Downstream: Point-to-Multipoint (Root PE to any Leaf PE)
- Upstream: Point-to-Point (any Leaf PE to Root PE)
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3.2. P2MP SS-PW Underlying Layer
The P2MP SS-PW implies an underlying P2MP PSN tunnel. Figure 2 gives
an example of P2MP SS-PW topology relying on a P2MP LSP. The PW tree
is composed of one Root PE (i1) and several Leaf PEs (e1, e2, e3,
e4).
The P2MP PSN MAY be signaled with P2MP RSVP-TE [RFC4875] or MLDP
[MLDP].
i1
/
/ \
/ \
/ \
/\ \
/ \ \
/ \ \
/ \ / \
e1 e2 e3 e4
Figure 2 Example of P2MP Underlying Layer for P2MP SS-PW
The P2MP PW MAY be supported over multiple P2MP PSN tunnel. These
P2MP PSN tunnels MUST be able to serve more than one P2MP PW.
The P2MP Tunnels MAY also be of different technology (ex. MPLS over
GRE, or P-to-MP MPLS LSP ) or just use different setup protocols.
(ex. MLDP, and P2MP RSVP-TE ).
The P2MP LSP associated to the P2MP PW can be selected either by user
configuration or by dynamically using the multiplexing/demultiplexing
mechanism.
The P2MP PW multiplexing will be based on the overlap rate between
P2MP LSP and P2MP PW. The operator should determine whether the P2MP
PW can accept partially multiplexing with P2MP LSP, and a minimum
congruency rate may be defined. The congruency rate reflects the
amount of overlap in the Leaf PE of P2MP PW that is multiplexed to a
P2MP LSP. If there is a complete overlap, the congruency is perfect
and the rate is 100%. The Root PE can determine whether P2MP PW can
multiplex to a P2MP LSP according to the congruency rate. It is also
possible to extend P2MP LSP to do P2MP PW multiplexing, but this will
reduce the current congruency rate that the P2MP PW is currently
taken. The multiplexing should ensure that the P2MP PW congruency
that is currently taken under P2MP LSP should be larger than minimum
congruency that is configured.
With this procedure a P2MP PW is nested within a P2MP LSP. This
allows multiplexing several PWs over a common P2MP LSP. Prior to the
P2MP PW signaling phase, the Root PE MUST determine which P2MP LSP
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will be used for this P2MP PW. The PSN Tunnel can be an existing PSN
tunnel or the Root PE can create a new P2MP PSN tunnel.
3.3. P2MP SS-PW Construction
As initial step PE nodes have to be configured with P2MP PW
identifier and ACs.
Then discovery mechanism SHOULD allow PE to discover remote PEs
configuration.
Eventually the solution SHOULD allow single-sided operation at the
Root PE for the selection of some AC(s) at the Leaf PE(s) to be
attached to the PW tree so that the Root PE controls the Leaf
attachment.
Note that the Root PE single sided operation is a management
requirement and does not presume any signaling requirement.
The Root PE SHOULD support a method to be informed about the Leaf PE
successfully attached to the PW tree.
3.4. P2MP SS-PW Signaling Requirements
3.4.1. PW Identifier
The P2MP PW MUST be uniquely identified. This unique P2MP PW
identifier MUST be used for all the signaling procedure related to
this PW (PW setup, monitoring).
3.4.2. PW type mismatch
As for P2P PW, the ACs configured at Root PE and Leaf PEs of a P2MP
PW MUST be of the same PW type [RFC4446]. In case of a different
type, the passive PE (Root or Leaf PE, depending on the signaling
process) MUST support mechanisms to reject attempts to establish the
P2MP PW.
3.4.3. Interface Parameters sub-TLV
Some interface parameters [RFC4446] related to the AC capability have
been defined according to the PW type and are signaled during the PW
setup.
When applicable, this mechanism used for the P2P PW setup MUST be
enhanced for P2MP PW setup so as to ascertain that AC at the Leaf PE
is capable to support traffic coming from AC at the Root PE.
In case of mismatch, the passive PE (Ingress or Leaf PE, depending on
the signaling process) MUST support mechanisms to reject attempts to
establish the P2MP SS-PW.
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3.4.4. Leaf Grafting/Pruning
Once the PW tree is setup, the solution MUST allow the addition or
removal of a Leaf PE, or a subset of leaves to/from the existing
tree, without any impact on the PW tree (data and control planes) for
the remaining leaf PEs.
The addition or removal of a Leaf PE MUST also allow to the P2MP PSN
tunnel to be updated accordingly. This MAY cause P2MP PSN tunnel to
add or remove the corresponding Leaf PE.
3.5. Failure Detection and Reporting
Since the underlying layer has an End-to-End P2MP topology between
the Root PE and the Leaf PEs, the failure reporting and processing
procedures are implemented only on the edge nodes.
Failure events MAY cause one or more Leaf PEs to become detached from
the PW tree. These events MUST be reported to the Root PE, using
appropriate out-band or inband OAM messages.
The solution SHOULD allow the Root PE to be informed of Leaf PEs
failure for management purposes.
Based on these failure notifications the solution MUST allow the Root
PE to update the remaining leaves of the PW tree.
- A solution MUST support in-band OAM mechanism to detect failures:
unidirectional point-to-multipoint traffic failure. This SHOULD be
realized by enhancing existing unicast PW methods, such as VCCV for
seamless and familiar operation.
- In case of failure, it SHOULD correctly report which Leaf PEs are
affected. This SHOULD be realized by enhancing existing PW methods,
such as LDP Notification for seamless and familiar operation. The
notification message SHOULD include the type of fault (P2MP PW, AC or
PSN tunnel).
- Respectively a Leaf PE also MAY receive the status of the Root PE's
AC status.
- A solution MUST support OAM message mapping at the Root PE if
failure is detected on the AC. The Leaf PE MUST report accordingly at
the service layer this OAM message on its associated AC.
3.6. Protection and Restoration
It is assumed that if recovery procedures are required the P2MP PSN
tunnel will support standard MPLS-based recovery techniques
(typically based on RSVP-TE). In that case a mechanism SHOULD be
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implemented to avoid race conditions between recovery at the PSN
level and recovery at the PW level.
An alternative protection scheme MAY rely on the PW layer.
Leaf PEs MAY be protected via a P2MP PW redundancy mechanism. In the
example depicted below, a standby P2MP PW is used to protect the
active P2MP. In that protection scheme the AC at the Root PE MUST
serve both P2MP PWs. In this scenario, the condition when to do the
switchover should be implemented, e.g. one or all Leaf failure of
active P2MP PW will course P2MP PW switchover.
CE1
|
active PE1 standby
P2MP PW .../ \....P2MP PW
/ \
P2 P3
/ \ / \
/ \ / \
/ \ / \
PE4 PE5 PE6 PE7
| | | |
| \ / |
\ CE2 /
\ /
-------CE3------
Root PE MAY be protected via a P2MP PW redundancy mechanism. In the
example depicted below, a standby P2MP PW is used to protect the
active P2MP. A single AC at the Leaf PE MUST be used to attach the CE
to the primary and the standby P2MP PW. The Leaf PE MUST support
protection mechanism in order to select the active P2MP PW.
CE1
/ \
| |
active PE1 PE2 standby
P2MP PW1 | | P2MP PW2
| |
P2 P3
/ \/ \
/ /\ \
/ / \ _\
/ / \ \
PE4 PE5
| |
CE2 CE3
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3.7. Scalability
The solution SHOULD scale at least as well as linearly with an
increase in the number of Leaf PEs.
An increase in the number of P2MP PW SHOULD NOT cause the P router to
increase its forwarding table linearly.
The P2MP PW multiplexed/demultiplexed to P2MP PSN Tunnel can improve
the scalability.
4. P2MP MS-PW Requirements
4.1. P2MP MS-PW Pseudowire Reference Model
Figure 3 describes the P2MP MS-PW reference model which is derived
from [RFC5659] to support P2MP emulated services.
|<-----------P2MP MS-PW------------>|
Native | | Native
Service | |<-PSN1-->| |<--PSN2->| | Service
(AC) V V V V V V (AC)
| +----+ +-----+ +----+ |
| |T-PE| |S-PE1|=========|T-PE| | +----+
| | 1 | | ......PW2.....> 2|---------->|CE2 |
| | | | . |=========| | | +----+
| | |=========| . | +----+ |
| | | .....> | |
| | | . | . | +----+ |
| | | . | . |=========|T-PE| | +----+
| | | . | ......PW3.....> 3|---------->|CE3 |
| | | . | |=========| | | +----+
| | | . | | +----+ |
+----+ | | | . +-----+
|CE1 |-------->|.......PW1... +-----+ +----+ |
+----+ | | | . |S-PE2|=========|T-PE| | +----+
| | | . | | ......> 4|---------->|CE4 |
| | | . | | . | | | +----+
| | | . | | . +----+ |
| | | ......>...PW4.. |
| | | | | . +----+ |
| | |=========| | . |T-PE| | +----+
| | | | | ......> 5|---------->|CE5 |
| | | | |=========| | | +----+
| | | | | +----+ |
| +----+ +-----+ |
Figure 3 P2MP MS-PW Reference Model
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Figure 3 extends the P2MP SS-PW architecture of Figure 1 to a multi-
segment configuration. In a P2P MS-PW configuration as described in
[RFC5254] the S-PE is responsible to switch a MS-PW from one input
segment to only one output segment, based on the PW identifier. Here
in a P2MP MS-PW configuration the S-PE is responsible to switch a MS-
PW from one input segment to one or several output segments.
Referring to Figure 3 T-PE1 is the Root T-PE and T-PE2, T-PE3, T-PE4
and T-PE5 are the Leaf T-PEs. In the reference model, the Leaf T-PEs
are assumed to be located in the same PSN (PSN2), but it could be
envisioned that each output PW is located in a different PSN (PSN2,
PSN3, PSN4). The S-PE plays the role of Branch S-PE since S-PE1 and
S-PE are in charge respectively of switching simultaneously the input
P2MP PW1 segment to the output P2P PW2, P2P PW3 and P2MP PW4
segments.
A P2MP MS-PW MAY obviously transit through more than one S-PE along
its path.
As depicted in the Figure 3 a PW segment belonging to a P2MP MS-PW
can also be supported over a P2MP PSN tunnel or a P2P PSN tunnel.
4.2. P2MP SS-PW Underlying Layer
Figure 4 describes an example of P2MP MS-PW topology relying on a
combination of both P2P and P2MP LSPs as PSN tunnels. PW segment over
P2P LSP MAY address inter-provider requirement. The PW tree is
composed of one Root PE (i1) and several Leaf PEs (e1, e2, e3, e4).
The Branch S-PEs are represented as b1, b2, b3, b4, b5. In that case
the traffic replication along the path of the PW tree is performed at
the PW level. For instance the Branch S-PE b5 MUST replicate incoming
packets or data received from b2 and send them to Leaf T-PEs e3 and
e4.
However giving the fact that some PW segments MAY be supported over a
P2MP LSP, the traffic replication along the path of these PW segments
can be performed as well at the underlying LSP level.
Figure 4 describes the case where each segment is supported over a
P2P LSP except for the b1-b3b4 P2MP segment which is conveyed over a
P2MP LSP on this section.
i1
/ \
b1 b2
/ \
/ \
/\ \
/ \ \
b3 b4 b5
/ \ / \
e1 e2 e3 e4
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Figure 4 Example of P2P and P2MP underlying Layer for P2MP MS-PW
The P2MP PSN MAY be signaled with P2MP RSVP-TE [RFC4875] or MLDP
[MLDP].
4.3. P2MP MS-PW Signaling Requirements
4.3.1. Dynamically Instantiated P2MP MS-PW
The PW tree could be statically configured at the T-PEs and each S-PE
crossed. However it is RECOMMENDED that a solution provides the
ability to dynamically setup a MS-PW tree, by allowing the MS-PW
segments to be dynamically discovered.
During the PW tree setup, a Branch S-PE SHOULD be capable to inform
the upstream PEs, including the Root T-PE that a set of Leaf T-PEs
and associated leaves are not reachable.
4.3.2. P2MP MS-PW Setup Mechanisms
The requirements described in this section assume that dynamic setup
of MS-PW segments allows the T-PE and S-PEs to dynamically signal MS-
PW segments and stitch these segments in order to build the MS-PW
tree.
4.3.3. PW type mismatch
As described for P2MP SS-PW, the P2MP MS-PW requires ACs of the same
PW type. Therefore the segments composing the P2MP MS-PW MUST be also
of the same PW type [RFC4446]. The S-PE MAY only support switching
PWs of the same PW type. In case of a different type, the passive PE
(S-PE or T-PE) MUST support mechanisms to reject attempts to
establish the P2MP MS-PW.
4.3.4. Interface Parameters sub-TLV
The section 3.4.3 is also relevant to P2MP MS-PW. When applicable,
the Leaf T-PE or the Root T-PE MUST signal respectively its AC'
interface parameters to the Root T-PE or to the Leaf T-PE so as to
make sure that AC at the Leaf T-PE is capable to support traffic
coming from AC at the Root T-PE. In the P2MP MS-PW case, S-PEs MUST
propagate correctly this information.
In case of mismatch, the passive T-PE (Root or Leaf T-PE, depending
on the signaling process) MUST support mechanisms to reject attempts
to establish the P2MP MS-PW.
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4.3.5. Leaf Grafting/Pruning
Once the PW tree is setup, the solution MUST allow the addition or
removal of a Leaf T-PE, or a subset of leaves to/from the existing
tree, without any impact on the PW tree (data and control planes) for
the remaining Leaf T-PEs.
4.3.6. Explicit Routing
The P2MP MS-PW signaling solution MUST provide a means of
establishing arbitrary P2MP MS-PW, according to pre-computed and
configured S-PE paths as well as dynamically computed S-PE paths on
the Root T-PE.
To support setup of explicitly routed MS-PW tree, the signaling
solution SHOULD support some source-based control that can explicitly
define particular S-PE nodes as Branch S-PEs for the PW tree.
The solution SHOULD let possible Explicit Path Loose Hops. Therefore
the P2MP MS-PW MAY be partially specified with only a subset of
intermediate Branch S-PEs.
4.4. Failure Detection and Reporting
The solution SHOULD rely on specific OAM mechanisms to detect a node
(T-PE and S-PE) or segment failure of a PW tree. The solution SHOULD
also support the ability to inform the Root T-PE of the failure as
well as to indicate the identity of affected Leaf T-PEs.
Based on these failure notifications the solution MUST allow the Root
T-PE to update the remaining Leaf T-PEs of the PW tree.
- A solution MUST support in-band OAM mechanism to detect failures:
unidirectional point-to-multipoint traffic failure. This SHOULD be
realized by enhancing existing unicast PW methods, such as VCCV for
seamless and familiar operation.
- In case of failure, it SHOULD correctly report which Leaf T-PEs and
Branch S-PEs are affected. This SHOULD be realized by enhancing
existing unicast PW methods, such as LDP Notification for seamless
and familiar operation. The notification message SHOULD include the
type of fault (P2MP PW, AC or PSN tunnel).
- Respectively a Leaf T-PE also MAY receive the status of the Root
PE's AC status.
- A solution MUST support OAM message mapping at the Root T-PE if
failure is detected on the AC. The Leaf T-PE MUST report accordingly
at the service layer this OAM message on its associated AC.
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4.5. Protection and Restoration
The solution SHOULD provide mechanisms to recover as fast as possible
following a failure event. The fast protection/recovery is typically
dedicated to P2MP applications sensitive to traffic disruption.
Considering (i) a Root-initiated PW tree setup and (ii) that a local
repair (PSN-tunnel or PW segment-based) is not feasible after a
failure event and that (iii) the PE upstream to the failure receives
by means of OAM mechanisms a message indicating that a subset of Leaf
T-PEs are detached from the PW tree, the solution SHOULD allow the
upstream PE to re-compute the path to those particular Leaf T-PEs. If
the upstream PE failed to compute an alternative path, the procedure
SHOULD be propagated upstream until the Root T-PE is reached.
It is also assumed that recovery procedures can be implemented at the
underlying P2P or P2MP LSP layer, using standard MPLS-based recovery
techniques. These procedures could be used to provide faster recovery
time in case of link or node failure affecting this layer.
A mechanism SHOULD be implemented to avoid race conditions between
recovery at the PSN level and recovery at the PW level.
4.6. Scalability
In definition of solution for P2MP MS-PW a particular attention MUST
be dedicated to scalability.
The solution MUST be designed to scale as well as linearly with an
increase in the number of Leaf T-PEs, Branch S-PEs. The scalability
issues MUST be addressed for the control plane (e.g. addressing of PW
endpoints, number of signaling sessions, etc) and for data plane
(e.g. duplication of PW segments, OAM mechanism, etc).
5. Manageability considerations
The solution SHOULD provide a simple provisioning procedure to build
a P2MP SS-PW or a P2MP MS-PW.
The solution MUST take into consideration the situation where the
Root PE and Leaf PEs are not managed by a single NMS.
In that case it MUST be possible to manage the whole P2MP PW using a
single NMS. Typically the P2MP PW could be managed from the Root PE.
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6. Backward Compatibility
The solution SHOULD be completely backward compatible with
the current PW standards. The solution SHOULD take into account the
capability advertisement and negotiation procedures for the PEs
implementing P2MP PW endpoints.
Implementation of OAM mechanisms also implies the advertisement of PE
capabilities to support specific OAM features. The solution MAY allow
advertising P2MP PW OAM capabilities.
A solution MUST NOT allow PW connection with non-compliant PEs. It
MUST have a mechanism to report an error for non-compliant PEs. In
this case, it SHOULD report which PE (S-PE and T-PEs) are not
compliant.
In some cases, upstream traffic is required from downstream CE to
upstream CE. The P2MPPW solution SHOULD allow a return path (i.e.
from the Leaf to the Root) that provides upstream connection.
In particular, it is expected to be allowed that the same ACs are
shared between downstream and upstream direction. For downstream, a
CE receives from its connected AC traffic originated by the Root PE
transported over a P2MP PW. For upstream, the CE MAY also send over
the same AC traffic destined to the same remote PE.
7. Security Considerations
The security requirements common to PW are raised in Section 10 of
[RFC3916] and common to MS-PW in section 7 of [RFC5254]. P2MP PW (SS
or MS) is a variant of the initial P2P PW definition, and that
statements also apply to P2MP PW.
8. IANA Considerations
This draft does not define any new protocol element, and hence does
not require any IANA action.
9. Acknowledgments
The authors thank the contributors of [RFC4461] since the structure
and content of this document were, for some sections, largely
inspired by [RFC4461].
Many thanks to JL Le Roux and A. Cauvin for the discussions, comments
and support.
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, March 1997.
[RFC3916] McPherson, D.,Pate, P., Xiao, X., "Requirements for
Pseudo-Wire Emulation Edge-to-Edge", September 2004
[RFC3985] Bryant, S., Pate, P. "PWE3 Architecture", March 2005
[RFC4461] Aggarwal, R., Farrel, A., Jork, M., Kamite, Y.,
Kullberg, A., Le Roux, JL., Malis, A., Papadimitriou,
D., Vasseur, JP., Yasukawa, S., "Signaling Requirements
for P2MP TE MPLS LSPs",April 2006
[RFC4875] Aggarwal, R., Papadimitriou, D., Yasukawa, S.,
"Extensions to RSVP-TE for Point-to-Multipoint TE LSPs",
MAY 2007
[RFC4446] Martini, L. "IANA Allocations for Pseudowire Edge to
Edge Emulation (PWE3)", April 2006
[RFC5254] Bitar, N., Bocci, M., and Martini, L., "Requirements for
inter domain Pseudo-Wires", June 2008
[RFC5332] Rosen, E. et al., "MPLS Multicast Encapsulations",
August 2008
[RFC5659] Bocci, M., and Bryant, S.,T., " An Architecture for
Multi-Segment Pseudo Wire Emulation Edge-to-Edge",
October 2009
10.2. Informative References
[MLDP] Minei, I., Wijnands, I., Thomas, B., "Label
Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched
Paths", Internet Draft, draft-ietf-mpls-ldp-p2mp-10,
July 2010
[VPMS REQ] Kamite, Y., Jounay, F. "Framework and Requirements for
Virtual Private Multicast Service (VPMS)", Internet
Draft, draft-ietf-l2vpn-vpms-frmwk-requirements-03,
July 2010
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Author's Addresses
Frederic Jounay
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: frederic.jounay@orange-ftgroup.com
Philippe Niger
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: philippe.niger@orange-ftgroup.com
Yuji Kamite
NTT Communications Corporation
Tokyo Opera City Tower
3-20-2 Nishi Shinjuku, Shinjuku-ku
Tokyo 163-1421
Japan
Email: y.kamite@ntt.com
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
EMail: lmartini@cisco.com
Giles Heron
BT
UK
EMail: giles.heron@gmail.com
Simon Delord
Telstra
242 Exhibition St
Melbourne VIC 3000
Australia
Email: simon.a.delord@team.telstra.com
Lei Wang
Telenor
Snaroyveien 30
Fornebu 1331
Norway
Email: lei.wang@telenor.com
Rahul Aggarwal
Juniper Networks
1194 North Mathilda Ave.
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Sunnyvale, CA 94089
Email: rahul@juniper.net
Martin Vigoureux
Alcatel-Lucent France
Route de Villejust
91620 Nozay
FRANCE
Email: martin.vigoureux@alcatel-lucent.fr
Matthew Bocci
Alcatel-Lucent Telecom Ltd,
Voyager Place
Shoppenhangers Road
Maidenhead
Berks, UK
E-mail: matthew.bocci@alcatel-lucent.co.uk
Lizhong JIN
ZTE Corporation
889, Bibo Road,
Shanghai, 201203, China
Email: lizhong.jin@zte.com.cn
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Jounay et al. Expires January 2011 [Page 19]
