Network Working Group H. Cho
Internet Draft J. Ryoo
Intended status: Standards Track ETRI
Expiration Date: April 28, 2012 D. King
Old Dog Consulting
October 28, 2011
Stitching Dynamically and Statically Provisioned Segments
To Construct End-To-End Multi-Segment Pseudowires
draft-cho-pwe3-mpls-tp-mixed-ms-pw-setup-01.txt
Abstract
The MPLS Transport Profile (MPLS-TP) transport paths can be
statically provisioned via a Network Management System (NMS) or
dynamically provisioned via a control plane. The transport paths
provided by MPLS-TP are used as a server layer for pseudowires
carrying client signals other than IP or MPLS. It may be necessary
to support MPLS-TP pseudowires, to extend across multiple domains.
This document outlines the requirements and solution for
coordinating MPLS-TP transport paths and a multi-segment PWs that
will traverse multiple domains, where some domains are statically
provisioned, and other domains that are dynamically provisioned.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge
(PWE3) architectures to support the capabilities and functionalities
of a packet transport network as defined by the ITU-T.
Status of this Memo
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Table of Contents
1. Introduction ...........................................3
1.1 Statically Provisioned PWs across MPLS-TP ..........4
1.2 Dynamically Provisioned PWs across MPLS-TP .........4
1.3 Multi-Segment Pseudowire (MS-PW) ...................4
1.4 Multi-segment Pseudowire Path Selection ............4
2. Terminology ............................................5
2.1 Requirements Language...............................5
3. Reference Model ........................................5
4. Problem Statement ......................................7
4.1 Requirements .......................................8
5. Procedures .............................................8
6. Protocol Extensions ....................................8
7. Security Considerations ................................9
8. Operations and Maintenance (OAM) .......................9
9. IANA Considerations ....................................9
10. References .............................................9
10.1 Normative References ..............................9
10.2.Informative References ...........................10
11. Authors' Addresses ....................................10
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1. Introduction
The MPLS Transport Profile (MPLS-TP) is being defined in a joint
effort between the International Telecommunications Union (ITU) and
the IETF. The requirements for MPLS-TP are defined in the
requirements document [RFC5654]. A general framework for MPLS-TP
has been defined in [RFC5921].
An MPLS-TP network can be operated via static provisioning of
transport paths, or the elective use of GMPLS control plane to
support dynamic provisioning of transport paths. The MPLS-TP
LSP control plane is based on GMPLS. The framework for MPLS-TP
dynamic provisioning and is described in [MPLS-TP-CP].
The LSPs provided by MPLS-TP are used as a server layer for
Pseudowires (PWs). The PWs are essential Communication Service
Providers (CSP) as they are used to carry client signals other than
IP or MPLS.
It may be necessary to extend the reach of an MPLS-TP transport path,
and PWs, across multiple domains. A domain can be defined as a
separate administrative, geographic, or switching environment within
the CSP network. Additionally a domain can also be categorized as a
separate AS or IGP area.
The MPLS-TP transport path would consist of two or more contiguous
MPLS-TP and PW segments, each segment would traverse a single domain.
The segments are concatenated so that they behave and function as a
single MPLS-TP transport and PW path.
For these multi-segment transport and PW paths the intermediate
segments, or domains, may be statically or dynamically provisioned.
There may be a requirement to automatically set up transport path
that will traverse multiple domains that are managed both statically
and dynamically. There must therefore be some coordination between
domains that are managed statically and dynamically to ensure the
end-to-end MPLS-TP transport path and PW are successfully setup.
This document outlines the requirements and solution for
coordinating MPLS-TP transport paths and PWs and that will traverse
multiple domains, where some domains are statically provisioned, and
other domains are dynamically provisioned.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunications Union Telecommunications
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and PWE3 architectures to support the
capabilities and functions of a packet transport network as defined
by the ITU-T.
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1.1 Statically Provisioned PWs across MPLS-TP
A PW is a mechanism that carries a native service over an emulated
service from one PE to one or more other PEs over a PSN. [RFC3985],
defines the signaling and encapsulation techniques for establishing
Single-segment PW (SS-PWs) between a pair of terminating PEs.
1.2 Dynamically Provisioned PWs across MPLS-TP
[MS-PW-DYN] describes the procedure and extensions to dynamically
place the segments of the Multi-segment Pseudowire (MS-PW) among a
set of PE routers. The dynamic PW capability is based on the
existing PW control plane [RFC4447], and the PW architecture
[RFC3985].
1.3 Multi-Segment Pseudowire (MS-PW)
A set of two or more contiguous PW segments that behave and function
as a single point-to-point PW, can be considered a MS-PW. The
architecture for MS-PWs across multi-domain environments is described
in [RFC5659].
The switching points (S-PEs), in addition to the terminating (T-PEs),
are manually provisioned for each segment. They are configured
to direct the MPLS packets from one PW into the other. There is no
control protocol involved in this case.
Dynamic end-to-end signaling of MS-PWs is achieved by using
information present in S-PEs to support the determination of the next
PW signaling hop. This selection information is disseminated via
inter-domain routing protocols (e.g. BGP).
[RFC6073] describes a procedure for connecting multiple pseudowires
together where each domain is dynamically provisioned. This procedure
requires each S-PE to be manually configured with the information
required to terminate and initiate the Single-segment Pseudowire
(SS-PW) part of the Multi-segment Pseudowire (MS-PW).
The issue exists when an end-to-end PW is requested across domains
that are comprised of both statically and dynamically configured.
1.4 Multi-segment Pseudowire Path Selection
An important feature of the establishment of a multi-domain multi-
segment pseudowires is the determination of the path of the
pseudowire. That is, the selection of the LSP tunnels and PW
switching points that the end-to-end PW will traverse.
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Selecting this path can be an off-line management task using
information gathered from a number of sources or pre-known by the
management tools. Alternatively, the path can be selected dynamically
using policy-based tools that operate on information gathered from
the network in a manner similar to existing MPLS traffic engineering
mechanisms, and using routing protocols.
However, in multi-domain environments there may be issues of
confidentiality of network topology information. For example, one
service provider may not wish to fully reveal the extent to which it
supports cross-domain LSP tunnels, or where its internal PW stitching
points are. These issues significantly complicate the mechanisms
available for selecting end-to-end multi-segment pseudowire paths.
The Path Computation Element (PCE) [RFC4655] was developed to
facilitate inter-domain path computation. The PCE uses topology
and resource availability information to compute paths inside a
domain. To support inter-domain path computation, PCEs responsible
for different coordinate with each other to calculate end-to-end
multi-domain paths.
Cooperating PCEs could be used to compute end-to-end MPLS-TP
transport paths and the stitching points of PW segments. This
document concentrates on the issues of signalling and not path
determination. The method and procedure of how this may be
achieved is not in scope of this document.
2. Terminology
MS-PW Multi-segment Pseudowire
PW Pseudowire
S-PE Pseudowire Switching Provider Edge
SS-PW Single-segment Pseudowire
T-PE Pseudowire Terminating Provider Edge
Additional definitions and terminology can be found in [RFC5921] and
[ROSETTA].
2.1 Requirements Language
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].
3. Reference Model
The control plane reference model is based on the general MPLS-TP
reference model as defined in the MPLS-TP framework [RFC5921]. Per
the MPLS-TP framework [RFC5921], where relevant the MPLS-TP control
plane is based on GMPLS with RSVP-TE for LSP signaling and targeted
LDP for PW signaling [RFC6073].
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PSN1 PSN2 PSN3 PSN4
+--------+ +--------+ +--------+ +--------+
| | | | | | | |
| | | | | | | |
+-+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +-+
|A|...|B|====|C|==|D|===|E|===|F|==|G|====|H|...|I|
+-+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +-+
| | | | | | | | | | | |
| | | | | | | | | | | |
+--------+ +--------+ +--------+ +--------+
| |<PW>| |<--PW-->| |<--PW-->| |<PW>| |
| |
|<-----Multi-Segment Pseudowire------>|
Figure 1: ABRs Acting as Pseudowire Switching Provider Edges
PSN1 PSN2 PSN3
+-------+ +---------+ +----------+
| | | | | |
| | | | | |
+-+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +-+
|A|....|B|==|C|==|D|==|E|==|F|==|G|=====|H|....|I|
+-+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +-+
| || | | | | || |
| || | | | | || |
+-------+ +---------+ +----------+
||<PW>|<PW>|<--PW--->|<PW>|<--PW->||
| |
|<----Multi-Segment Pseudowire---->|
Figure 2: ASBRs Acting as Pseudowire Switching Provider Edges
A: Customer Edge
B: Pseudowire Terminating Provider Edge
C: Pseudowire Switching Provider Edge
D: Provider Router
E: Pseudowire Switching Provider Edge
F: Provider Router
G: Pseudowire Switching Provider Edge
H: Pseudowire Terminating Provider Edge
I: Customer Edge
In the reference models described above any of the domains (PSNs) may
support static or dynamic PW establishment, for instance:
PSN1: Static Provisioning
PSN2: Dynamic Provisioning
PSN3: Static Provisioning
PSN4: Dynamic Provisioning
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4. Problem Statement
The requirements and mechanisms for the establishment of MS-PWs are
given in [RFC6073]. This includes all of the signaling extensions to
describe PW capabilities, the S-PEs and T-PEs to be navigated (i.e.,
the PW path), and the identities of the ACs that the PW connects.
However, when some of the segments are statically provisioned, there
is a requirement to carry this PW information across the statically
provisioned domains to make the information available in subsequent
dynamically provisioned domains.
For example, consider that in Figure 3, domains 1 and 2 are
dynamically provisioned, domain 3 is statically provisioned and
domain 4 is dynamically provisioned:
Dyn Dyn Static Dyn
+--------+ +--------+ +--------+ +--------+
| | | | | | | |
| | | | | | | |
+-+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +-+
|A|...|B|====|C|==|D|===|E|===|F|==|G|====|H|...|I|
+-+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +-+
| | | | | | | | | | | |
| | | | | | | | | | | |
+--------+ +--------+ +--------+ +--------+
| |<PW>| |<--PW-->| |<--PW-->| |<PW>| |
| |
|<-----Multi-Segment Pseudowire------>|
Figure 3: Dynamic and Static Domain Topology
The normal techniques of [RFC6073] can be used to request an
end-to-end MS-PW from B to H, and this can be signaled from B to E.
Furthermore, S-PE E can select a statically pre-provisioned PW
segment from E to G to use as the next segment in the MS-PW. Node E
can set up the necessary switching mechanisms for this connectivity.
However, [RFC6073] does not describe how node G is informed about the
end-to-end MS-PW or how G is triggered to resume dynamic signalling
toward T-PE H. It is not just a simple trigger that is required,
because all of the PW configuration parameters signaled by T-PE B
must be conveyed in the signaling from G to H.
This simple scenario can be further complicated by the existence of
multiple domains (static or dynamic in any sequence) along the path.
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4.1 Requirements
The requirements for setting up end-to-end PWs across MPLS-TP
transport paths, across statically and dynamically provisioned
domains, are document in [RFC5659], specific attention should be
given to:
o End-to-end PW setup across the MPLS-TP LSP: the destination and BW
requirements MUST be met.
o Traffic engineering and QoS consistency: the PW traffic engineering
and QoS requirements MUST be met.
o Resiliency: when requested, the maintaining of mechanisms to
protect a MS-PW when an element on the existing path of a MS-PW
fails SHOULD be maintained.
PW resiliency is provided using end-to-end protection techniques.
That is, two path-diverse PWs are established to serve as working
and protected PWs.
In a MS-PW environment, these two PWs must be kept path diverse
across the whole of their paths. Where the path of the PWs is
pre-planned, this can be archived within the scope of the management
tool, and where both PWs are fully dynamic they can be established
sequentially with the second PW having the awareness of the route
of the first PW.
However, where there is a mix of static and dynamic segments, care
will be required to ensure that the end-to-end working and
protection MS-PWs follow diverse paths.
5. Procedures
The following section describe the procedures to satisfy the
problem and requirements specified in the previous section.
6. Protocol Extensions
Where possible existing control protocol and procedures will be
reused. However, to meet the setup and control of PWs over MPLS-TP
transport paths, that traverse statically and dynamically
provisioned domains, a set of new extensions of the existing control
plane mechanisms are required.
This section will clarify the areas where PW control plane extensions
are required.
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7. Security Considerations
The MPLS-TP data plane does not provide any specific security
mechanisms. MS-PW connections that wish to secure data carried over
MPLS-TP transport entities are REQUIRED to apply their own
security mechanisms.
Where control plane protocols are used to dynamically install
label switching operations necessary to establish MPLS-TP transport
paths, those protocols are equipped with security features that
network operators may use to securely create the transport paths.
The use of static configuration exposes the CSP to another set of
security risks, compared to dynamic configuration. If an MPLS-TP
transport path is misconfigured in a statically configured network,
it may result traffic looping and lack of end-to-end connectivity.
Further details of MPLS and MPLS-TP security can be found in
[RFC5921] and [RFC5920]. The PWE3 security considerations are
described in [RFC3985].
8. Operations and Maintenance (OAM)
To be discussed in future revisions of this document.
9. IANA Considerations
To be discussed in future revisions of this document.
10. References
10.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4447] "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", Martini L.,et al, RFC 4447,
June 2005.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, September 2009.
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10.2 Informative References
[RFC3985] Bryant, S. and P. Pate, "Pseudowire Emulation Edge-
to-Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-
Segment Pseudo Wire Emulation Edge-to-Edge", RFC 5659,
October 2009.
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
Berger, "A Framework for MPLS in Transport Networks",
RFC 5921, July 2010.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.
[MS-PW-DYN] Martini, L., Bocci, M., Bitar, N., Shah, H., Aissaoui,
M., and F. Balus, et al. "Dynamic Placement of Multi
Segment Pseudo Wires",
draft-ietf-pwe3-dynamic-ms-pw-14 (work in progress),
July 2011.
[MPLS-TP-CP] Andersson, L., Berger, L., Fang, L., Bitar, N.,
Takacs, A., Vigoureux, M., and E. Bellagamba,
"MPLS-TP Control Plane Framework",
draft-abfb-mpls-tp-control-plane-framework-02
(work inprogress), January 2011.
[ROSETTA] Van Helvoort, H., Ed., Andersson, L., and N. Sprecher, "A
Thesaurus for the Terminology used in Multiprotocol Label
Switching Transport Profile (MPLS-TP) drafts/RFCs and
ITU-T's Transport Network Recommendations", draft-ietf-
mpls-tp-rosetta-stone, Work in Progress.
11. Authors' Addresses
Hyunwoo Cho
ETRI
161 Gajeong, Yuseong, Daejeon, 305-700, South Korea.
Email: tenace@etri.re.kr
Jeong-dong Ryoo
ETRI
161 Gajeong, Yuseong, Daejeon, 305-700, South Korea.
Email: ryoo@etri.re.kr
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Daniel King
Old Dog Consulting
UK
Email: daniel@olddog.co.uk
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