Network Working Group F. Jounay (Ed.)
Internet Draft France Telecom Orange
Category: Informational
Expires: January 2012 Y. Kamite
NTT Communications
G. Heron
Cisco
M. Bocci
Alcatel-Lucent
July 08, 2011
Requirements and Framework for Point-to-Multipoint Pseudowire
draft-ietf-pwe3-p2mp-pw-requirements-04.txt
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute working
documents as Internet-Drafts. The list of current Internet-Drafts is
at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 08, 2012.
Abstract
This document presents a set of requirements and a framework for
providing a Point-to-Multipoint Pseudowire (PW). The requirements
identified in this document are related to architecture, signaling
and maintenance aspects of 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 layer 2 services (Virtual
Private LAN Service and Virtual Private Multicast Service) as defined
in the Layer 2 Virtual Private Network Working Group.
Jounay et al. Expires January 2011 [Page 1]
Internet Draft P2MP PW Requirements July 2011
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 [RFC2119].
Table of Contents
1. Introduction....................................................3
1.1. Problem Statement.............................................3
1.2. Scope of the document.........................................3
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.............................9
3.4.1. PW Identifier...............................................9
3.4.2. PW type mismatch............................................9
3.4.3. Interface Parameters sub-TLV................................9
3.4.4. Leaf Grafting/Pruning.......................................9
3.5. Failure Detection and Reporting...............................9
3.6. Protection and Restoration...................................10
3.7. Scalability..................................................11
4. P2MP MS-PW Requirements........................................12
4.1. P2MP MS-PW Pseudowire Reference Model........................12
4.2. P2MP SS-PW Underlying Layer..................................13
4.3. P2MP MS-PW Signaling Requirements............................14
4.3.1. Dynamically Instantiated P2MP MS-PW........................14
4.3.2. P2MP MS-PW Setup Mechanisms................................14
4.3.3. PW type mismatch...........................................14
4.3.4. Interface Parameters sub-TLV...............................15
4.3.5. Leaf Grafting/Pruning......................................15
4.3.6. Explicit Routing...........................................15
4.4. Failure Detection and Reporting..............................15
4.5. Protection and Restoration...................................16
4.6. Scalability..................................................16
5. Manageability considerations...................................16
6. Backward Compatibility.........................................17
7. Security Considerations........................................17
8. IANA Considerations............................................17
9. Acknowledgments................................................17
10. References....................................................18
10.1. Normative References........................................18
10.2. Informative References......................................18
Authors' Addresses................................................19
Copyright and Licence Notice......................................20
Jounay et al. Expires January 2012 [Page 2]
Internet Draft P2MP PW Requirements July 2011
1. Introduction
1.1. Problem Statement
As defined in the pseudowire architecture [RFC3985], a Pseudowire
(PW) is a mechanism that emulates the essential attributes of a
telecommunications service (such as a T1 leased line or Frame Relay)
over an IP or MPLS PSN. It 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 layer 1 or layer 2 traffic
(e.g. Ethernet, TDM, ATM, and FR) over a layer 3 PSN. PWE3 operates
"edge to edge" to provide the required connectivity between the two
endpoints of the PW.
The Point-to-Multipoint (P2MP) topology described in [VPMS REQ] and
required to provide P2MP L2VPN services can be achieved using one or
more P2MP PWs. The use of PW encapsulation enables P2MP services
transporting layer 1 or layer 2 data. This could be achieved using a
set of point to point PWs, with traffic replication on the PE, but at
the cost of bandwidth efficiency, as duplicate traffic would be
carried multiple times on shared links.
This document defines the requirements for a Point-to-Multipoint PW
(P2MP PW). A P2MP PW is a mechanism that emulates the essential
attributes of a P2MP Telecommunications service such as a P2MP ATM VC
over a PSN. 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.
P2MP PWs therefore extend the PWE3 architecture [RFC3985] to offer a
P2MP Telecommunications service.
This document also defines the associated requirements related to the
P2MP PW operation (e.g. setup and maintenance, protection and
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 PW architecture and
those applicable in a Multi-Segment PW architectre. For other aspects
of P2MP PW implementation, such as packet processing (section 4) and
Faithfulness of Emulated Services (section 7), the document refers to
[RFC3916].
Jounay et al. Expires January 2012 [Page 3]
Internet Draft P2MP PW Requirements July 2011
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] and [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 CE used to
distribute Layer 1 or Layer 2 traffic to a set of one or more
receiver CEs. 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 CE and the PEs
attached to the receiver CEs. The P2MP SS-PW uses P2MP LSPs as PSN
tunnels.
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 perform
PW label switching. Each segment can use either a P2P LSP or a P2MP
LSP as its PSN tunnel.
Root PE
P2MP PW Root Provider Edge. The PE attached to the traffic source CE
for the P2MP PW via an Attachment Circuit (AC). In a MS-PW
architecture the term used is Root T-PE.
Leaf PE
Jounay et al. Expires January 2012 [Page 4]
Internet Draft P2MP PW Requirements July 2011
P2MP PW Leaf Provider Edge. A PE attached to a set of one or more
traffic receiver CEs, via ACs. The Leaf PE replicates traffic to 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-
PWs. The Branch S-PE has one upstream PW segment, which may be P2P or
P2MP, and one or more downstream PW segments, which may also be P2P
or P2MP.
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 Point-to-Multipoint connectivity from a Root PE
connected to a traffic source CE to one or more Leaf PEs connected to
traffic receiver CEs.
Figure 1 describes the P2MP SS-PW reference model which is derived
from [RFC3985] to support P2MP emulated services.
Jounay et al. Expires January 2012 [Page 5]
Internet Draft P2MP PW Requirements July 2011
|<-----------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 PW on
the P2MP PSN tunnel and is received by all Leaf PEs due to the P2MP
nature of the PSN tunnel. The P2MP PW MUST be traffic optimised i.e.
only one copy of a P2MP PW packet is sent on any single link. P
Routers participate in P2MP PSN tunnel operation but not in the
signaling of P2MP PWs.
The Reference Model outlines the basic pieces of a P2MP SS-PW.
However, several levels of replication MAY be used when designing a
P2MP SS-PW
- Ingress PE replication: traffic is replicated to a set of P2P or
P2MP PSN transport tunnels or to local receiver CEs
- P router replication: traffic replicated by means of P2MP PSN
tunnel (P2MP LSP)
- Egress PE replication: traffic replicated to local receiver CEs
Specific operations that must be performed 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
section 4.2 of [RFC3985] are also applicable to P2MP PW.
Jounay et al. Expires January 2012 [Page 6]
Internet Draft P2MP PW Requirements July 2011
P2MP PWs are generally unidirectional, but a Root PE MAY need to
receive unidirectional P2P traffic from any Leaf PE. For that purpose
the P2MP PW can 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 or Multipoint-to-Point (any Leaf PE to
Root PE).
Depending on the service using the P2MP PW, the Root PE may benefit
from information sent by e.g. a Leaf PE using P2P connectivity at
the expense of the amount of state and configuration overhead for
the P2P return path. However, in most situations a Mutipoint-to-
point (MP2P) connectivity is expected to be sufficient. Hence it
MUST be possible for the operator to configure the attributes (P2P
or MP2P) of the return path.
3.2. P2MP SS-PW Underlying Layer
If Ingress PE replication is used, a P2MP PW MAY be supported over
multiple P2MP PSN tunnels, or OPTIONALLY P2P PSN tunnels, or a mix of
both. These PSN tunnels MUST be able to serve more than one P2MP PW.
The P2MP SS-PW underlying layer MAY be P2P, but this will be at the
expense of bandwidth consumption.
Typically 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 mechanisms for establishing the PSN tunnel are outside the scope
of this document, as long as they enable the essential attributes of
the service to be emulated.
i1
/
/ \
/ \
/ \
/\ \
/ \ \
/ \ \
/ \ / \
e1 e2 e3 e4
Figure 2 Example of P2MP Underlying Layer for P2MP SS-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 ).
Jounay et al. Expires January 2012 [Page 7]
Internet Draft P2MP PW Requirements July 2011
The P2MP LSP associated to the P2MP PW can be selected either by user
configuration or by dynamically using a multiplexing/demultiplexing
mechanism.
The P2MP PW multiplexing will be based on the overlap rate between
P2MP LSP and P2MP PW. As an example an existing P2MP LSP may attach
more leaves than the ones defined as Leaf PEs for a given P2MP PW. It
may be interesting to reuse it to minimize new configuration, but
using this P2MP LSP would imply non-Leaf PEs receive unwanted
traffic, not destined to Leaf PE at the service layer. The operator
should determine whether the P2MP PW can accept partially
multiplexing with P2MP LSP, and a minimum congruency rate may be
defined. The Root PE can determine whether P2MP PW can multiplex to a
P2MP LSP according to the congruency rate. The congruency rate should
take into account several items, here are some of them
- the amount of overlap between the number of Leaf PEs of P2MP PW and
existing egress P routers of a P2MP LSP. If there is a complete
overlap, the congruency is perfect and the rate is 100%.
- at the expense of the additional traffic (e.g. other VPNs)
supported over the P2MP LSP.
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
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
The following requirements apply to the establishment of P2MP SS-PWs:
- PE nodes MUST be configurable with the P2MP PW identifiers and
ACs.
- A discovery mechanism SHOULD allow the Root PE to discover the
Leaf PEs, or vice versa.
- Solutions 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.
The Root PE SHOULD support a method to be informed about whether a
Leaf PE has successfully attached to the PW tree.
Jounay et al. Expires January 2012 [Page 8]
Internet Draft P2MP PW Requirements July 2011
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 signaling procedures related to this
PW (PW setup, monitoring, etc).
3.4.2. PW type mismatch
The Root PE and Leaf PEs of a P2MP PW MUST be configured with the
same PW type as defined in [RFC4446] for P2P PW. In case of a
different type, a PE MUST abort 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.
Where applicable, a solution is REQUIRED to ascertain whether the AC
at the Leaf PE is capable of supporting traffic coming from the AC at
the Root PE.
In case of a mismatch, the passive PE (Root or Leaf PE, depending on
the signaling process) MUST support mechanisms to reject attempts to
establish the P2MP SS-PW.
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 the P2MP PSN
tunnel to be updated accordingly. This MAY cause the 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-of-band or inband OAM messages.
Jounay et al. Expires January 2012 [Page 9]
Internet Draft P2MP PW Requirements July 2011
It MUST be possible for the operator to choose the out-of-band or
inband OAM tools or both to monitor the Leaf PE status.
The solution SHOULD allow the Root PE to be informed of Leaf PEs
failure for management purposes.
Based on these failure notifications, solutions 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 defined in [RFC5085] and [RFC6073].
- 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 Status Notification. The notification message SHOULD
include the type of fault (P2MP PW, AC or PSN tunnel).
- A Leaf PE MAY be notified of the status of the Root PE's AC.
- A solution MUST support OAM message mapping [OAM MSG MAP] at the
Root PE and Leaf PE if a failure is detected on the source CE 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
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.
Jounay et al. Expires January 2012 [Page 10]
Internet Draft P2MP PW Requirements July 2011
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 mechanisms in order to select the active P2MP PW.
CE1
/ \
| |
active PE1 PE2 standby
P2MP PW1 | | P2MP PW2
| |
P2 P3
/ \/ \
/ /\ \
/ / \ _\
/ / \ \
PE4 PE5
| |
CE2 CE3
3.7. Scalability
The solution SHOULD scale at least linearly with the number of Leaf
PEs.
Increasing the number of P2MP PWs between a Root PE and a given set
of Leaf PEs SHOULD NOT cause the P router to increase the number of
entries in its forwarding table by the same or greater proportion.
Multiplexing P2MP PWs to P2MP PSN Tunnels achieves this.
Jounay et al. Expires January 2012 [Page 11]
Internet Draft P2MP PW Requirements July 2011
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
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
[RFC5659] the S-PE is responsible for switching a MS-PW from one
ingress segment to only one egress segment, based on the PW
identifier. Here in a P2MP MS-PW configuration the S-PE is
responsible for switching a MS-PW from one ingress segment to one or
more egress 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 egress PW is located in a different PSN (PSN2,
PSN3, PSN4). S-PEs play the role of Branch S-PEs since S-PE1 and S-
Jounay et al. Expires January 2012 [Page 12]
Internet Draft P2MP PW Requirements July 2011
PE2 are in charge respectively of switching the ingress P2MP PW1
segment to the egress P2P PW2, P2P PW3 and P2MP PW4 segments.
A P2MP MS-PW MAY transit through more than one S-PE along its path.
As depicted in Figure 3 a PW segment belonging to a P2MP MS-PW can be
supported over a P2MP PSN tunnel or a P2P PSN tunnel.
The Reference Model outlines the basic pieces of a P2MP MS-PW,
however several levels of replication MAY be used when designing a
P2MP MS-PW
- Ingress T-PE replication: traffic replicated to a set of P2P or
P2MP PSN tunnels or to local receiver CEs
- P router replication: traffic replicated by means of P2MP PSN
tunnel (P2MP LSP)
- S-PE replication: traffic replicated to a set of P2P or P2MP PSN
tunnels
- Egress T-PE replication : traffic replicated to local receiver CEs
As described in section 3.1, P2MP MS-PWs are generally
unidirectional, but a Root T-PE MAY need to receive unidirectional
P2P traffic from any Leaf PE. For that purpose the P2MP MS-PW MAY
support bidirectional connectivity between the Root T-PE and each
Leaf T-PE.
4.2. P2MP SS-PW Underlying Layer
Due to Ingress PE or S-PE replication, the P2MP PW segment MAY be
supported over multiple concatenated P2MP PSN tunnels and optionally
P2P PSN tunnels or a mix of both.
Figure 4 describes an example of a P2MP MS-PW architecture relying on
a combination of both P2P and P2MP LSPs as PSN tunnels. PW segments
over P2P LSPs MAY be used to address inter-provider requirements, for
example. 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 this 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 since some PW segments MAY be supported over a P2MP LSP, the
traffic replication along the path of these PW segments can be
performed 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 segment.
Jounay et al. Expires January 2012 [Page 13]
Internet Draft P2MP PW Requirements July 2011
i1
/ \
b1 b2
/ \
/ \
/\ \
/ \ \
b3 b4 b5
/ \ / \
e1 e2 e3 e4
Figure 4 Example of P2P and P2MP underlying Layer for P2MP MS-PW
The mechanisms for establishing the PSN tunnel are outside the scope
of this document, as long as they enable the essential attributes of
the service to be emulated.
4.3. P2MP MS-PW Signaling Requirements
4.3.1. Dynamically Instantiated P2MP MS-PW
The PW tree could be statically configured at each T-PE and S-PE
along its path. 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 at S-PE.
During the PW tree setup, a Branch S-PE SHOULD be capable of
informing 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-PEs 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]. When P2MP MS-PW is statically
configured, the S-PE MUST support switching PWs of the same PW type
Jounay et al. Expires January 2012 [Page 14]
Internet Draft P2MP PW Requirements July 2011
as outined in [RFC5659]. When MS-PW is dynamically configured by
signaling, in case of a different type a PE MUST abort attempts to
establish the P2MP MS-PW.
4.3.4. Interface Parameters sub-TLV
Section 3.4.3 is also relevant to P2MP MS-PW. When applicable, the
Leaf T-PE or the Root T-PE MUST signal its AC interface parameters to
the Root T-PE or the Leaf T-PEs to make sure the AC at each Leaf T-PE
is capable of supporting traffic coming from the AC at the Root T-PE.
In the P2MP MS-PW case, S-PEs MUST propagate this information.
In case of a 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.
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 P2MP MS-PWs according to pre-computed and configured S-
PE paths as well as dynamically computing S-PE paths at the Root T-
PE.
To support the setup of an explicitly routed MS-PW tree, the
signaling solution SHOULD support th ability for a Root PE to
explicitly define particular S-PE nodes as Branch S-PEs for the PW
tree.
The solution SHOULD enable 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.
Jounay et al. Expires January 2012 [Page 15]
Internet Draft P2MP PW Requirements July 2011
- 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 a failure, it SHOULD report which Leaf T-PEs and Branch
S-PEs are affected. This SHOULD be realized by enhancing existing
unicast PW methods, such as LDP Status Notification. The notification
message SHOULD include the type of fault (P2MP PW, AC or PSN tunnel).
- A Leaf T-PE MAY be notified of the status of the Root PE's AC.
- A solution MUST support OAM message mapping [OAM MSG MAP] at the
Root T-PE and Leaf T-PE if a failure is detected on the source CE AC.
4.5. Protection and Restoration
The solution SHOULD provide mechanisms to recover the emulated
service as fast as possible following a failure event.
In the case of Root-initiated PW tree setup, where a local repair
(PSN-tunnel or PW segment-based) is not feasible after a failure
event, and where the PE upstream to a failure is notified that a
subset of Leaf T-PEs have become detached from the PW tree, solutions
SHOULD allow the upstream PE to re-compute the path to those
particular Leaf T-PEs. If the upstream PE fails to compute an
alternative path, this procedure SHOULD be propagated upstream until
the Root T-PE is reached.
Note that recovery procedures can be implemented at the underlying
P2P or P2MP LSP layer, using standard MPLS-based recovery techniques.
A mechanism SHOULD be provided to avoid race conditions between
recovery at the PSN level and recovery at the PW level.
4.6. Scalability
Solutions for P2MP MS-PW MUST take into account scalability
considerations.
Solutions MUST scale linearly, or better, with an increase in the
number of Leaf T-PEs and Branch S-PEs. Scalability issues MUST be
addressed for the control plane (e.g. addressing of PW endpoints,
number of signaling sessions, etc) and the data plane (e.g.
duplication of PW segments, OAM mechanism, etc).
5. Manageability considerations
Jounay et al. Expires January 2012 [Page 16]
Internet Draft P2MP PW Requirements July 2011
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.
6. Backward Compatibility
Solutions SHOULD be backward compatible with current PW standards.
Solutions SHOULD utilize existing capability advertisement and
negotiation procedures for the PEs implementing P2MP PW endpoints.
The 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 a P2PW to be established to PEs that do not
support P2MP PW functionality. It MUST have a mechanism to report an
error for incompatble PEs. In this case, it SHOULD report which PEs
(S-PE and T-PEs) are not compatible.
In some cases, upstream traffic is required from downstream CEs to
upstream CEs. The P2MP PW solution SHOULD allow a return path (i.e.
from the Leaf to the Root) that provides upstream connectivity.
In particular, the same ACs may be shared between downstream and
upstream directions. For downstream, a CE receives traffic originated
by the Root PE over its AC. For upstream, the CE MAY also send
traffic destined to the same Root PE over the same AC.
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 those
sections also apply to P2MP PW.
8.
IANA Considerations
This draft does not define any new protocol elements, and hence does
not require any IANA action.
9. Acknowledgments
Jounay et al. Expires January 2012 [Page 17]
Internet Draft P2MP PW Requirements July 2011
The authors thank the authors 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.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, March 1997.
[RFC5332] Rosen, E. et al., "MPLS Multicast Encapsulations",
August 2008
[RFC4446] Martini, L. "IANA Allocations for Pseudowire Edge to
Edge Emulation (PWE3)", April 2006
[RFC5085] Nadeau, T., Pignataro, C. "Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", December 2007
[RFC6073] Martini, L. et al. "Segmented Pseudowire", January 2011
10.2. Informative References
[RFC3985] Bryant, S., Pate, P. "PWE3 Architecture", March 2005
[RFC3916] McPherson, D.,Pate, P., Xiao, X., "Requirements for
Pseudo-Wire Emulation Edge-to-Edge", September 2004
[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
[RFC5254] Bitar, N., Bocci, M., and Martini, L., "Requirements for
inter domain Pseudo-Wires", June 2008
[RFC5659] Bocci, M., and Bryant, S.,T., " An Architecture for
Multi-Segment Pseudo Wire Emulation Edge-to-Edge",
October 2009
[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
Jounay et al. Expires January 2012 [Page 18]
Internet Draft P2MP PW Requirements July 2011
[OAM MSG MAP] Aissaoui, M., et al. "Pseudowire OAM Message Mapping",
Internet Draft, draft-ietf-pwe3-oam-msg-map-16, April
2011
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
Cisco Systems, Inc.
9 New Square
Bedfont Lakes
Feltham
Middlesex
TW14 8HA
United Kingdom
EMail: giheron@cisco.com
Lei Wang
Telenor
Snaroyveien 30
Fornebu 1331
Norway
Email: lei.wang@telenor.com
Jounay et al. Expires January 2012 [Page 19]
Internet Draft P2MP PW Requirements July 2011
Rahul Aggarwal
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
Email: rahul@juniper.net
Simon Delord
Alcatel-Lucent
Email:
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
Copyright (c) 2011 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.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
Jounay et al. Expires January 2012 [Page 20]
Internet Draft P2MP PW Requirements July 2011
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Jounay et al. Expires January 2012 [Page 21]