Network Working Group K. Kumaki, Ed.

Network Working Group K. Kumaki, Ed.
Request for Comments: 5146 KDDI Corporation
Category: Informational March 2008

Interworking Requirements to Support Operation of MPLS-TE
over GMPLS Networks

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Abstract

Operation of a Multiprotocol Label Switching (MPLS) traffic
engineering (TE) network as a client network to a Generalized MPLS
(GMPLS) network has enhanced operational capabilities compared to
those provided by a coexistent protocol model (i.e., operation of
MPLS-TE over an independently managed transport layer).

The GMPLS network may be a packet or a non-packet network, and may
itself be a multi-layer network supporting both packet and non-packet
technologies. An MPLS-TE Label Switched Path (LSP) originates and
terminates on an MPLS Label Switching Router (LSR). The GMPLS
network provides transparent transport for the end-to-end MPLS-TE
LSP.

This document describes a framework and Service Provider requirements
for operating MPLS-TE networks over GMPLS networks.

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Table of Contents

1. Introduction ....................................................3
1.1. Terminology ................................................4
2. Reference Model .................................................4
3. Detailed Requirements ...........................................5
3.1. End-to-End Signaling .......................................5
3.2. Triggered Establishment of GMPLS LSPs ......................5
3.3. Diverse Paths for End-to-End MPLS-TE LSPs ..................6
3.4. Advertisement of MPLS-TE Information via the GMPLS
Network ....................................................6
3.5. Selective Advertisement of MPLS-TE Information via
a Border Node ..............................................6
3.6. Interworking of MPLS-TE and GMPLS Protection ...............7
3.7. Independent Failure Recovery and Reoptimization ............7
3.8. Complexity and Risks .......................................7
3.9. Scalability Considerations .................................7
3.10. Performance Considerations ................................8
3.11. Management Considerations .................................8
4. Security Considerations .........................................8
5. Recommended Solution Architecture ...............................9
5.1. Use of Contiguous, Hierarchical, and Stitched LSPs ........10
5.2. MPLS-TE Control Plane Connectivity ........................10
5.3. Fast Reroute Protection ...................................10
5.4. GMPLS LSP Advertisement ...................................11
5.5. GMPLS Deployment Considerations ...........................11
6. Acknowledgments ................................................11
7. References .....................................................11
7.1. Normative References ......................................11
7.2. Informative References ....................................12
8. Contributors' Addresses ........................................13

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1. Introduction

Multiprotocol Label Switching traffic engineering (MPLS-TE) networks
are often deployed over transport networks such that the transport
networks provide connectivity between the Label Switching Routers
(LSRs) in the MPLS-TE network. Increasingly, these transport
networks are operated using a Generalized Multiprotocol Label
Switching (GMPLS) control plane. Label Switched Paths (LSPs) in the
GMPLS network provide connectivity as virtual data links advertised
as TE links in the MPLS-TE network.

GMPLS protocols were developed as extensions to MPLS-TE protocols.
MPLS-TE is limited to the control of packet switching networks, but
GMPLS can also control technologies at layers one and two.

The GMPLS network may be managed by an operator as a separate network
(as it may have been when it was under management plane control
before the use of GMPLS as a control plane), but optimizations of
management and operation may be achieved by coordinating the use of
the MPLS-TE and GMPLS networks and operating the two networks with a
close client/server relationship.

GMPLS LSP setup may be triggered by the signaling of MPLS-TE LSPs in
the MPLS-TE network so that the GMPLS network is reactive to the
needs of the MPLS-TE network. The triggering process can be under
the control of operator policies without needing direct intervention
by an operator.

The client/server configuration just described can also apply in
migration scenarios for MPLS-TE packet switching networks that are
being migrated to be under GMPLS control. [RFC5145] describes a
migration scenario called the Island Model. In this scenario, groups
of nodes (islands) are migrated from the MPLS-TE protocols to the
GMPLS protocols and operate entirely surrounded by MPLS-TE nodes (the
sea). This scenario can be effectively managed as a client/server
network relationship using the framework described in this document.

In order to correctly manage the dynamic interaction between the MPLS
and GMPLS networks, it is necessary to understand the operational
requirements and the control that the operator can impose. Although
this problem is very similar to the multi-layer networks described in
[MLN-REQ], it must be noted that those networks operate GMPLS
protocols in both the client and server networks, which facilitates
smoother interworking. Where the client network uses MPLS-TE
protocols over the GMPLS server network, there is a need to study the
interworking of the two protocol sets.

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This document examines the protocol requirements for protocol
interworking to operate an MPLS-TE network as a client network over a
GMPLS server network, and provides a framework for such operations.

1.1. Terminology

Although this Informational document is not a protocol specification,
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] for clarity
of exposure of the requirements.

2. Reference Model

The reference model used in this document is shown in Figure 1. It
can easily be seen that the interworking between MPLS-TE and GMPLS
protocols must occur on a node and not on a link. Nodes on the
interface between the MPLS-TE and GMPLS networks must be responsible
for handling both protocol sets and for providing any protocol
interworking that is required. We call these nodes Border Routers.

-------------- ------------------------- --------------
| MPLS Client | | GMPLS Server Network | | MPLS Client |
| Network | | | | Network |
| | | | | |
| ---- --+--+-- ----- ----- --+--+-- ---- |
| | | | | | | | | | | | | |
| |MPLS|_| Border |__|GMPLS|_|GMPLS|__| Border |_|MPLS| |
| |LSR | | Router | | LSR | | LSR | | Router | |LSR | |
| | | | | | | | | | | | | |
| ---- --+--+-- ----- ----- --+--+-- ---- |
| | | | | |
| | | | | |
-------------- ------------------------- --------------

| | GMPLS LSP | |
| |<------------------------->| |
| |
|<--------------------------------------------->|
End-to-End MPLS-TE LSP

Figure 1. Reference model of MPLS-TE/GMPLS interworking

MPLS-TE network connectivity is provided through a GMPLS LSP which is
created between Border Routers. End-to-end connectivity between MPLS
LSRs in the client MPLS-TE networks is provided by an MPLS-TE LSP
that is carried across the MPLS-TE network by the GMPLS LSP using
hierarchical LSP techniques [RFC4206], LSP stitching segments

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[RFC5150], or a contiguous LSP. LSP stitching segments and
contiguous LSPs are only available where the GMPLS network is a
packet switching network.

3. Detailed Requirements

This section describes detailed requirements for MPLS-TE/GMPLS
interworking in support of the reference model shown in Figure 1.

The functional requirements for GMPLS-MPLS interworking described in
this section must be met by any device participating in the
interworking. This may include routers, servers, network management
devices, path computation elements, etc.

3.1. End-to-End Signaling

The solution MUST be able to preserve MPLS signaling information
signaled within the MPLS-TE client network at the start of the MPLS-
TE LSP and deliver it on the other side of the GMPLS server network
for use within the MPLS-TE client network at the end of the MPLS-TE
LSP. This may require protocol mapping (and re-mapping), protocol
tunneling, or the use of remote protocol adjacencies.

3.2. Triggered Establishment of GMPLS LSPs

The solution MUST provide the ability to establish end-to-end MPLS-TE
LSPs over a GMPLS server network. It SHOULD be possible for GMPLS
LSPs across the core network to be set up between Border Routers
triggered by the signaling of MPLS-TE LSPs in the client network, and
in this case, policy controls MUST be made available at the border
routers so that the operator of the GMPLS network can manage how core
network resources are utilized. GMPLS LSPs MAY also be pre-
established as the result of management plane control.

Note that multiple GMPLS LSPs may be set up between a given pair of
Border Routers in support of connectivity in the MPLS client network.
If these LSPs are advertised as TE links in the client network, the
use of link bundling [RFC4201] can reduce any scaling concerns
associated with the advertisements.

The application of the Path Computation Element (PCE) [RFC4655] in
the context of an inter-layer network [PCE-INT] may be considered to
determine an end-to-end LSP with triggered GMPLS segment or tunnel.

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3.3. Diverse Paths for End-to-End MPLS-TE LSPs

The solution SHOULD provide the ability to establish end-to-end
MPLS-TE LSPs having diverse paths for protection of the LSP traffic.
This means that MPLS-TE LSPs SHOULD be kept diverse both within the
client MPLS-TE network and as they cross the server GMPLS network.
This means that there SHOULD be a mechanism to request the provision
of diverse GMPLS LSPs between a pair of Border Routers to provide
protection of the GMPLS span, but also that there SHOULD be a way to
keep GMPLS LSPs between different Border Routers disjoint.

3.4. Advertisement of MPLS-TE Information via the GMPLS Network

The solution SHOULD provide the ability to exchange advertisements of
TE information between MPLS-TE client networks across the GMPLS
server network.

The advertisement of TE information from within an MPLS-TE client
network to all LSRs in the client network enables a head-end LSR to
compute an optimal path for an LSP to a tail-end LSR that is reached
over the GMPLS server network.

Where there is more than one client MPLS-TE network, the TE
information from separate MPLS-TE networks MUST be kept private,
confidential and secure.

3.5. Selective Advertisement of MPLS-TE Information via a Border Node

The solution SHOULD provide the ability to distribute TE reachability
information from the GMPLS server network to MPLS-TE networks
selectively. This information is useful for the LSRs in the MPLS-TE
networks to compute paths that cross the GMPLS server network and to
select the correct Border Routers to provide connectivity.

The solution MUST NOT distribute TE information from within a non-PSC
(Packet Switch Capable) GMPLS server network to any client MPLS-TE
network as that information may cause confusion and selection of
inappropriate paths.

The use of PCE [RFC4655] may provide a solution for non-PSC GMPLS
networks supporting PSC MPLS networks.

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3.6. Interworking of MPLS-TE and GMPLS Protection

If an MPLS-TE LSP is protected using MPLS Fast Reroute (FRR)
[RFC4090], then similar protection MUST be provided over the GMPLS
island. Operator and policy controls SHOULD be made available at the
Border Router to determine how suitable protection is provided in the
GMPLS island.

3.7. Independent Failure Recovery and Reoptimization

The solution SHOULD provide failure recovery and reoptimization in
the GMPLS server network without impacting the MPLS-TE client network
and vice versa. That is, it SHOULD be possible to recover from a
fault within the GMPLS island or to reoptimize the path across the
GMPLS island without requiring signaling activity within the MPLS-TE
client network. Similarly, it SHOULD be possible to perform recovery
or reoptimization within the MPLS-TE client network without requiring
signaling activity within the GMPLS server networks.

If a failure in the GMPLS server network can not be repaired
transparently, some kind of notification of the failure SHOULD be
transmitted to MPLS-TE network.

3.8. Complexity and Risks

The solution SHOULD NOT introduce unnecessary complexity to the
current operating network to such a degree that it would affect the
stability and diminish the benefits of deploying such a solution in
service provider networks.

3.9. Scalability Considerations

The solution MUST scale well with consideration to at least the
following metrics.

- The number of GMPLS-capable nodes (i.e., the size of the GMPLS
server network).

- The number of MPLS-TE-capable nodes (i.e., the size of the MPLS-TE
client network).

- The number of MPLS-TE client networks.

- The number of GMPLS LSPs.

- The number of MPLS-TE LSPs.

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3.10. Performance Considerations

The solution SHOULD be evaluated with regard to the following
criteria.

- Failure and restoration time.

- Impact and scalability of the control plane due to added overheads.

- Impact and scalability of the data/forwarding plane due to added
overheads.

3.11. Management Considerations

Manageability of the deployment of an MPLS-TE client network over
GMPLS server network MUST addresses the following considerations.

- Need for coordination of MIB modules used for control plane
management and monitoring in the client and server networks.

- Need for diagnostic tools that can discover and isolate faults
across the border between the MPLS-TE client and GMPLS server
networks.

4. Security Considerations

Border routers in the model described in this document are present on
administrative domain boundaries. That is, the administrative
boundary does not lie on a link as it might in the inter-Autonomous-
System (inter-AS) case seen in IP networks. Thus, many security
concerns for the inter-domain exchange of control plane messages do
not arise in this model -- the border router participates fully in
both the MPLS and the GMPLS network and must participate in the
security procedures of both networks. Security considerations for
MPLS-TE and GMPLS protocols are discussed in [SECURITY].

However, policy considerations at the border routers are very
important and may be considered to form part of the security of the
networks. In particular, the server network (the GMPLS network) may
wish to protect itself from behavior in the client network (such as
frequent demands to set up and tear down server LSPs) by appropriate
policies implemented at the border routers. It should be observed
that, because the border routers form part of both networks, they are
trusted in both networks, and policies configured (whether locally or
centrally) for use by a border router are expected to be observed.

Nevertheless, authentication and access controls for operators will
be particularly important at border routers. Operators of the client

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MPLS-TE network MUST NOT be allowed to configure the server GMPLS
network (including setting server network policies), and operators of
the server GMPLS network MUST NOT be able configure the client MPLS-
TE network. Obviously, it SHOULD be possible to grant an operator
privileges in both networks. It may also be desirable to give
operators of one network access to (for example) status information
about the other network.

Mechanisms for authenticating operators and providing access controls
are not part of the responsibilities of the GMPLS protocol set, and
will depend on the management plane protocols and techniques
implemented.

5. Recommended Solution Architecture

The recommended solution architecture to meet the requirements set
out in Section 3 is known as the Border Peer Model. This
architecture is a variant of the Augmented Model described in
[RFC3945]. The remainder of this document presents an overview of
this architecture.

In the Augmented Model, routing information from the lower layer
(server) network is filtered at the interface to the higher layer
(client) network and a subset of the information is distributed
within the higher layer network.

In the Border Peer Model, the interface between the client and server
networks is the Border Router. This router has visibility of the
routing information in the server network yet also participates as a
peer in the client network. Thus, the Border Router has full
visibility into both networks. However, the Border Router does not
distribute server routing information into the client network, nor
does it distribute client routing information into the server
network.

The Border Peer Model may also be contrasted with the Overlay Model
[RFC3945]. In this model there is a protocol request/response
interface (the user network interface (UNI)) between the client and
server networks. [RFC4208] shows how this interface may be supported
by GMPLS protocols operated between client edge and server edge
routers while retaining the routing information within the server
network. That is, in the Overlay Model there is no exchange of
routing or reachability information between client and server
networks, and no network element has visibility into both client and
server networks. The Border Peer Model can be viewed as placing the
UNI within the Border Router thus giving the Border Router peer
capabilities in both the client and server network.

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5.1. Use of Contiguous, Hierarchical, and Stitched LSPs

All three LSP types MAY be supported in the Border Peer Model, but
contiguous LSPs are the hardest to support because they require
protocol mapping between the MPLS-TE client network and the GMPLS
server network. Such protocol mapping can be achieved currently
since MPLS-TE signaling protocols are a subset of GMPLS, but this
mechanism is not future-proofed.

Contiguous and stitched LSPs can only be supported where the GMPLS
server network has the same switching type (that is, packet
switching) as the MPLS-TE network. Requirements for independent
failure recovery within the GMPLS island require the use of loose
path reoptimization techniques [RFC4736] and end-to-end make-before-
break [RFC3209], which will not provide rapid recovery.

For these reasons, the use of hierarchical LSPs across the server
network is RECOMMENDED for the Border Peer Model, but see the
discussion of Fast Reroute protection in Section 5.3.

5.2. MPLS-TE Control Plane Connectivity

Control plane connectivity between MPLS-TE LSRs connected by a GMPLS
island in the Border Peer Model MAY be provided by the control
channels of the GMPLS network. If this is done, a tunneling
mechanism (such as GRE [RFC2784]) SHOULD be used to ensure that
MPLS-TE information is not consumed by the GMPLS LSRs. But care is
required to avoid swamping the control plane of the GMPLS network
with MPLS-TE control plane (particularly routing) messages.

In order to ensure scalability, control plane messages for the MPLS-
TE client network MAY be carried between Border Routers in a single
hop MPLS-TE LSP routed through the data plane of the GMPLS server
network.

5.3. Fast Reroute Protection

If the GMPLS network is packet switching, Fast Reroute protection can
be offered on all hops of a contiguous LSP. If the GMPLS network is
packet switching then all hops of a hierarchical GMPLS LSP or GMPLS
stitching segment can be protected using Fast Reroute. If the end-
to-end MPLS-TE LSP requests Fast Reroute protection, the GMPLS packet
switching network SHOULD provide such protection.

However, note that it is not possible to provide FRR node protection
of the upstream Border Router without careful consideration of
available paths, and protection of the downstream Border Router is
not possible where hierarchical LSPs or stitching segments are used.

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Note further that Fast Reroute is not available in non-packet
technologies. However, other protection techniques are supported by
GMPLS for non-packet networks and are likely to provide similar
levels of protection.

The limitations of FRR need careful consideration by the operator and
may lead to the decision to provide end-to-end protection for the
MPLS-TE LSP.

5.4. GMPLS LSP Advertisement

In the Border Peer Model, the LSPs established by the Border Routers
in the GMPLS server network SHOULD be advertised in the MPLS-TE
client network as real or virtual links. In case real links are
advertised into the MPLS-TE client network, the Border Routers in the
MPLS-TE client network MAY establish IGP neighbors. The Border
Routers MAY automatically advertise the GMPLS LSPs when establishing
them.

5.5. GMPLS Deployment Considerations

The Border Peer Model does not require the existing MPLS-TE client
network to be GMPLS aware and does not affect the operation and
management of the existing MPLS-TE client network. Only border
routers need to be upgraded with the GMPLS functionality. In this
fashion, the Border Peer Model renders itself for incremental
deployment of the GMPLS server network, without requiring
reconfiguration of existing areas/ASs, changing operation of IGP and
BGP or software upgrade of the existing MPLS-TE client network.

6. Acknowledgments

The author would like to express thanks to Raymond Zhang, Adrian
Farrel, and Deborah Brungard for their helpful and useful comments
and feedback.

7. References

7.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.

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[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.

[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.

[RFC4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
in MPLS Traffic Engineering (TE)", RFC 4201, October
2005.

[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October
2005.

[RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
"Generalized Multiprotocol Label Switching (GMPLS) User-
Network Interface (UNI): Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Support for the Overlay
Model", RFC 4208, October 2005.

[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008.

7.2. Informative References

[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.

[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.

[RFC4736] Vasseur, JP., Ed., Ikejiri, Y., and R. Zhang,
"Reoptimization of Multiprotocol Label Switching (MPLS)
Traffic Engineering (TE) Loosely Routed Label Switched
Path (LSP)", RFC 4736, November 2006.

[RFC5145] Shiomoto, K., Ed., "Framework for MPLS-TE to GMPLS
Migration", RFC 5145, March 2008.

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[MLN-REQ] Shiomoto, K., Papadimitriou, D., Le Roux, J.L.,
Vigoureux, M., and D. Brungard, "Requirements for GMPLS-
Based Multi-Region and Multi-Layer Networks (MRN/MLN)",
Work in Progress, January 2008.

[PCE-INT] Oki, E., Le Roux , J-L., and A. Farrel, "Framework for
PCE-Based Inter-Layer MPLS and GMPLS Traffic
Engineering," Work in Progress, January 2008.

[SECURITY] Fang, L., "Security Framework for MPLS and GMPLS
Networks", Work in Progress, November 2007.

8. Contributors' Addresses

Tomohiro Otani
KDDI R&D Laboratories, Inc.
2-1-15 Ohara Kamifukuoka
Saitama, 356-8502, Japan

Phone: +81-49-278-7357
EMail: [email protected]

Shuichi Okamoto
NICT JGN II Tsukuba Reserach Center
1-8-1, Otemachi Chiyoda-ku,
Tokyo, 100-0004, Japan

Phone: +81-3-5200-2117
EMail: [email protected]

Kazuhiro Fujihara
NTT Communications Corporation
Tokyo Opera City Tower 3-20-2 Nishi Shinjuku, Shinjuku-ku
Tokyo 163-1421, Japan

EMail: [email protected]

Yuichi Ikejiri
NTT Communications Corporation
Tokyo Opera City Tower 3-20-2 Nishi Shinjuku, Shinjuku-ku
Tokyo 163-1421, Japan

EMail: [email protected]

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Editor's Address

Kenji Kumaki
KDDI Corporation
Garden Air Tower
Iidabashi, Chiyoda-ku,
Tokyo, 102-8460, JAPAN

EMail: [email protected]

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