Network Working Group K. Shiomoto, Ed.

Network Working Group K. Shiomoto, Ed.
Request for Comments: 5145 NTT
Category: Informational March 2008

Framework for MPLS-TE to GMPLS Migration

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

The migration from Multiprotocol Label Switching (MPLS) Traffic
Engineering (TE) to Generalized MPLS (GMPLS) is the process of
evolving an MPLS-TE control plane to a GMPLS control plane. An
appropriate migration strategy will be selected based on various
factors including the service provider's network deployment plan,
customer demand, and operational policy.

This document presents several migration models and strategies for
migrating from MPLS-TE to GMPLS. In the course of migration, MPLS-TE
and GMPLS devices, or networks, may coexist that may require
interworking between MPLS-TE and GMPLS protocols. Aspects of the
required interworking are discussed as it will influence the choice
of a migration strategy. This framework document provides a
migration toolkit to aid the operator in selection of an appropriate
strategy.

This framework document also lists a set of solutions that may aid in
interworking, and highlights a set of potential issues.

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Table of Contents

1. Introduction ....................................................3
2. Conventions Used in This Document ...............................3
3. Motivations for Migration .......................................4
4. MPLS to GMPLS Migration Models ..................................5
4.1. Island Model ...............................................5
4.1.1. Balanced Islands ....................................6
4.1.2. Unbalanced Islands ..................................6
4.2. Integrated Model ...........................................7
4.3. Phased Model ...............................................8
5. Migration Strategies and Toolkit ................................8
5.1. Migration Toolkit ..........................................9
5.1.1. Layered Networks ....................................9
5.1.2. Routing Interworking ...............................11
5.1.3. Signaling Interworking .............................12
5.1.4. Path Computation Element ...........................13
6. Manageability Considerations ...................................13
6.1. Control of Function and Policy ............................13
6.2. Information and Data Models ...............................14
6.3. Liveness Detection and Monitoring .........................14
6.4. Verifying Correct Operation ...............................14
6.5. Requirements on Other Protocols and Functional
Components ................................................14
6.6. Impact on Network Operation ...............................15
6.7. Other Considerations ......................................15
7. Security Considerations ........................................15
8. Acknowledgements ...............................................16
9. References .....................................................16
9.1. Normative References ......................................16
9.2. Informative References ....................................17
10. Contributors' Addresses .......................................17

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1. Introduction

Multiprotocol Label Switching Traffic Engineering (MPLS-TE) to
Generalized MPLS (GMPLS) migration is the process of evolving an
MPLS-TE-based control plane to a GMPLS-based control plane. The
network under consideration for migration is, therefore, a
packet-switching network.

There are several motivations for such migration, mainly the desire
to take advantage of new features and functions added to the GMPLS
protocols, which are not present in MPLS-TE for packet networks.
Additionally, before migrating a packet-switching network from
MPLS-TE to GMPLS, one may choose to first migrate a lower-layer
network with no control plane (e.g., controlled by a management
plane) to using a GMPLS control plane. This may lead to the desire
for MPLS-TE/GMPLS (transport network) interworking to provide
enhanced TE support and facilitate the later migration of the
packet-switching network.

Although an appropriate migration strategy will be selected based on
various factors including the service provider's network deployment
plan, customer demand, deployed network equipments, operational
policy, etc., the transition mechanisms used should also provide
consistent operation of newly introduced GMPLS networks, while
minimizing the impact on the operation of existing MPLS-TE networks.

This document describes several migration strategies and the
interworking scenarios that arise during migration. It also examines
the implications for network deployments and for protocol usage. As
the GMPLS signaling and routing protocols are different from the
MPLS-TE control protocols, interworking mechanisms between MPLS-TE
and GMPLS networks, or network elements, may be needed to compensate
for the differences.

Note that MPLS-TE and GMPLS protocols can coexist as "ships in the
night" without any interworking issues.

2. Conventions Used in This Document

This is not a requirements document, nevertheless 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] in order to
clarify the recommendations that are made.

In the rest of this document, the term "GMPLS" includes both packet
switching capable (PSC) and non-PSC. Otherwise, the term "PSC GMPLS"
or "non-PSC GMPLS" is used explicitly.

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In general, the term "MPLS" is used to indicate MPLS traffic
engineering (MPLS-TE) only ([RFC3209], [RFC3630], and [RFC3784]) and
excludes other MPLS protocols, such as the Label Distribution
Protocol (LDP). TE functionalities of MPLS could be migrated to
GMPLS, but non-TE functionalities could not. If non-TE MPLS is
intended, it is indicated explicitly.

The reader is assumed to be familiar with the terminology introduced
in [RFC3945].

3. Motivations for Migration

Motivations for migration will vary for different service providers.
This section is presented to provide background so that the migration
discussions may be seen in context. Sections 4 and 5 provide
examples to illustrate the migration models and processes.

Migration of an MPLS-capable Label Switching Router (LSR) to include
GMPLS capabilities may be performed for one or more reasons,
including, not exhaustively:

o To add all GMPLS PSC features to an existing MPLS network (upgrade
MPLS LSRs).

o To add specific GMPLS PSC features and operate them within an MPLS
network (e.g., [RFC4872] and [RFC4873]).

o To integrate a new GMPLS PSC network with an existing MPLS network
(without upgrading any of the MPLS LSRs).

o To allow existing MPLS LSRs to interoperate with new non-MPLS LSRs
supporting only GMPLS PSC and/or non-PSC features.

o To integrate multiple control networks, e.g., managed by separate
administrative organizations, and which independently utilize MPLS
or GMPLS.

o To build integrated PSC and non-PSC networks. The non-PSC
networks are controlled by GMPLS.

The objective of migration from MPLS to GMPLS is that all LSRs, and
the entire network, support GMPLS protocols. During this process,
various interim situations may exist, giving rise to the interworking
situations described in this document. The interim situations may
exist for considerable periods of time, but the ultimate objective is
not to preserve these situations. For the purposes of this document,
they should be considered as temporary and transitory.

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4. MPLS to GMPLS Migration Models

Three reference migration models are described below. Multiple
migration models may coexist in the same network.

4.1. Island Model

In the island model, "islands" of network nodes operating one
protocol exist within a "sea" of nodes using the other protocol.

For example, consider an island of GMPLS-capable nodes (PSC) that is
introduced into a legacy MPLS network. Such an island might be
composed of newly added GMPLS nodes, or it might arise from the
upgrade of existing nodes that previously operated MPLS protocols.

The opposite is also quite possible. That is, there is a possibility
that an island happens to be MPLS-capable within a GMPLS sea. Such a
situation might arise in the later stages of migration, when all but
a few islands of MPLS-capable nodes have been upgraded to GMPLS.

It is also possible that a lower-layer, manually-provisioned network
(for example, a Time Division Multiplexing (TDM) network) is
constructed under an MPLS PSC network. During the process of
migrating both networks to GMPLS, the lower-layer network might be
migrated first. This would appear as a GMPLS island within an MPLS
sea.

Lastly, it is possible to consider individual nodes as islands. That
is, it would be possible to upgrade or insert an individual
GMPLS-capable node within an MPLS network, and to treat that GMPLS
node as an island.

Over time, collections of MPLS devices are replaced or upgraded to
create new GMPLS islands or to extend existing ones, and distinct
GMPLS islands may be joined together until the whole network is
GMPLS-capable.

From a migration/interworking point of view, we need to examine how
these islands are positioned and how Label Switched Paths (LSPs)
connect between the islands.

Four categories of interworking scenarios are considered: (1)
MPLS-GMPLS-MPLS, (2) GMPLS-MPLS-GMPLS, (3) MPLS-GMPLS, and (4)
GMPLS-MPLS. In case 1, the interworking behavior is examined based
on whether the GMPLS islands are PSC or non-PSC.

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Figure 1 shows an example of the island model for MPLS-GMPLS-MPLS
interworking. The model consists of a transit GMPLS island in an
MPLS sea. The nodes at the boundary of the GMPLS island (G1, G2, G5,
and G6) are referred to as "island border nodes". If the GMPLS
island was non-PSC, all nodes except the island border nodes in the
GMPLS-based transit island (G3 and G4) would be non-PSC devices,
i.e., optical equipment (TDM, Lambda Switch Capable (LSC), and Fiber
Switch Capable (FSC)).

................. .......................... ..................
: MPLS : : GMPLS : : MPLS :
:+---+ +---+ +----+ +---+ +----+ +---+ +---+:
:|R1 |__|R11|___| G1 |_________|G3 |________| G5 |___|R31|__|R3 |:
:+---+ +---+ +----+ +-+-+ +----+ +---+ +---+:
: ________/ : : _______/ | _____ / : : ________/ :
: / : : / | / : : / :
:+---+ +---+ +----+ +-+-+ +----+ +---+ +---+:
:|R2 |__|R21|___| G2 |_________|G4 |________| G6 |___|R41|__|R4 |:
:+---+ +---+ +----+ +---+ +----+ +---+ +---+:
:................: :........................: :................:

|<-------------------------------------------------------->|
e2e LSP

Figure 1: Example of the island model
for MPLS-GMPLS-MPLS interworking

4.1.1. Balanced Islands

In the MPLS-GMPLS-MPLS and GMPLS-MPLS-GMPLS cases, LSPs start and end
using the same protocols. Possible strategies include:

- tunneling the signaling across the island network using LSP nesting
or stitching [RFC5150] (the latter is only for GMPLS-PSC)

- protocol interworking or mapping (both are only for GMPLS-PSC)

4.1.2. Unbalanced Islands

As previously discussed, there are two island interworking models
that support bordering islands. GMPLS(PSC)-MPLS and MPLS-GMPLS(PSC)
island cases are likely to arise where the migration strategy is not
based on a core infrastructure, but has edge nodes (ingress or
egress) located in islands of different capabilities.

In this case, an LSP starts or ends in a GMPLS (PSC) island and
correspondingly ends or starts in an MPLS island. This mode of
operation can only be addressed using protocol interworking or

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mapping. Figure 2 shows the reference model for this migration
scenario. Head-end and tail-end LSRs are in distinct control plane
clouds.

............................ .............................
: MPLS : : GMPLS (PSC) :
:+---+ +---+ +----+ +---+ +---+:
:|R1 |________|R11|_______| G1 |________|G3 |________|G5 |:
:+---+ +---+ +----+ +-+-+ +---+:
: ______/ | _____/ : : ______/ | ______/ :
: / | / : : / | / :
:+---+ +---+ +----+ +-+-+ +---+:
:|R2 |________|R21|_______| G2 |________|G4 |________|G6 |:
:+---+ +---+ +----+ +---+ +---+:
:..........................: :...........................:

|<-------------------------------------------------->|
e2e LSP

Figure 2: GMPLS-MPLS interworking model

It is important to underline that this scenario is also impacted by
the directionality of the LSP, and the direction in which the LSP is
established.

4.2. Integrated Model

The second migration model involves a more integrated migration
strategy. New devices that are capable of operating both MPLS and
GMPLS protocols are introduced into the MPLS network.

In the integrated model, there are two types of nodes present during
migration:

- those that support MPLS only (legacy nodes); and

- those that support MPLS and GMPLS.

In this model, as existing MPLS devices are upgraded to support both
MPLS and GMPLS, the network continues to operate with an MPLS control
plane, but some LSRs are also capable of operating with a GMPLS
control plane. So, LSPs are provisioned using MPLS protocols where
one end point of a service is a legacy MPLS node and/or where the
selected path between end points traverses a legacy node that is not
GMPLS-capable. But where the service can be provided using only
GMPLS-capable nodes [RFC5073], it may be routed accordingly and can
achieve a higher level of functionality by utilizing GMPLS features.

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Once all devices in the network are GMPLS-capable, the MPLS-specific
protocol elements may be turned off, and no new devices need to
support these protocol elements.

In this model, the questions to be addressed concern the coexistence
of the two protocol sets within the network. Actual interworking is
not a concern.

4.3. Phased Model

The phased model introduces GMPLS features and protocol elements into
an MPLS network one by one. For example, some objects or sub-objects
(such as the Explicit Route Object (ERO) label sub-object, [RFC3473])
might be introduced into the signaling used by LSRs that are
otherwise MPLS-capable. This would produce a kind of hybrid LSR.

This approach may appear simpler to implement as one is able to
quickly and easily pick up new key functions without needing to
upgrade the whole protocol implementation. It is most likely to be
used where there is a desire to rapidly implement a particular
function within a network without the necessity to install and test
the full GMPLS function.

Interoperability concerns though are exacerbated by this migration
model, unless all LSRs in the network are updated simultaneously and
there is a clear understanding of which subset of features are to be
included in the hybrid LSRs. Interworking between a hybrid LSR and
an unchanged MPLS LSR would put the hybrid LSR in the role of a GMPLS
LSR, as described in the previous sections, and puts the unchanged
LSR in the role of an MPLS LSR. The potential for different hybrids
within the network will complicate matters considerably. This model
is, therefore, only appropriate for use when the set of new features
to be deployed is well known and limited, and where there is a clear
understanding of and agreement on this set of features by the network
operators of the ISP(s) involved as well as all vendors whose
equipment will be involved in the migration.

5. Migration Strategies and Toolkit

An appropriate migration strategy is selected by a network operator
based on factors including the service provider's network deployment
plan, customer demand, existing network equipment, operational
policy, support from its vendors, etc.

For PSC networks, the migration strategy involves the selection
between the models described in the previous section. The choice
will depend upon the final objective (full GMPLS capability, partial

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upgrade to include specific GMPLS features, or no change to existing
IP/MPLS networks), and upon the immediate objectives (full, phased,
or staged upgrade).

For PSC networks serviced by non-PSC networks, two basic migration
strategies can be considered. In the first strategy, the non-PSC
network is made GMPLS-capable, first, and then the PSC network is
migrated to GMPLS. This might arise when, in order to expand the
network capacity, GMPLS-based non-PSC sub-networks are introduced
into the legacy MPLS-based networks. Subsequently, the legacy
MPLS-based PSC network is migrated to be GMPLS-capable, as described
in the previous paragraph. Finally, the entire network, including
both PSC and non-PSC nodes, may be controlled by GMPLS.

The second strategy is to migrate the PSC network to GMPLS first, and
then enable GMPLS within the non-PSC network. The PSC network is
migrated as described before, and when the entire PSC network is
completely converted to GMPLS, GMPLS-based non-PSC devices and
networks may be introduced without any issues of interworking between
MPLS and GMPLS.

These migration strategies and the migration models described in the
previous section are not necessarily mutually exclusive. Mixtures of
all strategies and models could be applied. The migration models and
strategies selected will give rise to one or more of the interworking
cases described in the following section.

5.1. Migration Toolkit

As described in the previous sections, an essential part of a
migration and deployment strategy is how the MPLS and GMPLS or hybrid
LSRs interwork. This section sets out some of the alternatives for
achieving interworking between MPLS and GMPLS, and it identifies some
of the issues that need to be addressed. This document does not
describe solutions to these issues.

Note that it is possible to consider upgrading the routing and
signaling capabilities of LSRs from MPLS to GMPLS separately.

5.1.1. Layered Networks

In the balanced island model, LSP tunnels [RFC4206] are a solution to
carry the end-to-end LSPs across islands of incompatible nodes.
Network layering is often used to separate domains of different data
plane technology. It can also be used to separate domains of
different control plane technology (such as MPLS and GMPLS
protocols), and the solutions developed for multiple data plane

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technologies can be usefully applied to this situation [RFC3945],
[RFC4206], and [RFC4726]. [MLN-REQ] gives a discussion of the
requirements for multi-layered networks.

The GMPLS architecture [RFC3945] identifies three architectural
models for supporting multi-layer GMPLS networks, and these models
may be applied to the separation of MPLS and GMPLS control plane
islands.

- In the peer model, both MPLS and GMPLS nodes run the same routing
instance, and routing advertisements from within islands of one
level of protocol support are distributed to the whole network.
This is achievable only, as described in Section 5.1.2, either by
direct distribution or by mapping of parameters.

Signaling in the peer model may result in contiguous LSPs, stitched
LSPs [RFC5150] (only for GMPLS PSC), or nested LSPs. If the
network islands are non-PSC, then the techniques of [MLN-REQ] may
be applied, and these techniques may be extrapolated to networks
where all nodes are PSC, but where there is a difference in
signaling protocols.

- The overlay model preserves strict separation of routing
information between network layers. This is suitable for the
balanced island model, and there is no requirement to handle
routing interworking. Even though the overlay model preserves
separation of signaling information between network layers, there
may be some interaction in signaling between network layers.

The overlay model requires the establishment of control plane
connectivity for the higher layer across the lower layer.

- The augmented model allows limited routing exchange from the
lower-layer network to the higher-layer network. Generally
speaking, this assumes that the border nodes provide some form of
filtering, mapping, or aggregation of routing information
advertised from the lower-layer network. This architectural model
can also be used for balanced island model migrations. Signaling
interworking is required as described for the peer model.

- The border peer architecture model is defined in [RFC5146]. This
is a modification of the augmented model where the layer border
routers have visibility into both layers, but no routing
information is otherwise exchanged between routing protocol
instances. This architectural model is particularly suited to the
MPLS-GMPLS-MPLS island model for PSC and non-PSC GMPLS islands.
Signaling interworking is required as described for the peer model.

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5.1.2. Routing Interworking

Migration strategies may necessitate some interworking between MPLS
and GMPLS routing protocols. GMPLS extends the TE information
advertised by the IGPs to include non-PSC information and extended
PSC information. Because the GMPLS information is provided as
additional TLVs that are carried along with the MPLS information,
MPLS LSRs are able to "see" all GMPLS LSRs as though they were MPLS
PSC LSRs. They will also see other GMPLS information, but will
ignore it, flooding it transparently across the MPLS network for use
by other GMPLS LSRs.

- Routing separation is achieved in the overlay and border peer
models. This is convenient since only the border nodes need to be
aware of the different protocol variants, and no mapping is
required. It is suitable to the MPLS-GMPLS-MPLS and
GMPLS-MPLS-GMPLS island migration models.

- Direct distribution involves the flooding of MPLS routing
information into a GMPLS network, and GMPLS routing information
into an MPLS network. The border nodes make no attempt to filter
the information. This mode of operation relies on the fact that
MPLS routers will ignore, but continue to flood, GMPLS routing
information that they do not understand. The presence of
additional GMPLS routing information will not interfere with the
way that MPLS LSRs select routes. Although this is not a problem
in a PSC-only network, it could cause problems in a peer
architecture network that includes non-PSC nodes, as the MPLS nodes
are not capable of determining the switching types of the other
LSRs and will attempt to signal end-to-end LSPs assuming all LSRs
to be PSC. This fact would require island border nodes to take
triggered action to set up tunnels across islands of different
switching capabilities.

GMPLS LSRs might be impacted by the absence of GMPLS-specific
information in advertisements initiated by MPLS LSRs. Specific
procedures might be required to ensure consistent behavior by GMPLS
nodes. If this issue is addressed, then direct distribution can be
used in all migration models (except the overlay and border peer
architectural models where the problem does not arise).

- Protocol mapping converts routing advertisements so that they can
be received in one protocol and transmitted in the other. For
example, a GMPLS routing advertisement could have all of its
GMPLS-specific information removed and could be flooded as an MPLS
advertisement. This mode of interworking would require careful
standardization of the correct behavior especially where an MPLS
advertisement requires default values of GMPLS-specific fields to

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be generated before the advertisement can be flooded further.
There is also considerable risk of confusion in closely meshed
networks where many LSRs have MPLS- and GMPLS-capable interfaces.
This option for routing interworking during migration is NOT
RECOMMENDED for any migration model. Note that converting
GMPLS-specific sub-TLVs to MPLS-specific ones but not stripping the
GMPLS-specific ones is considered a variant of the proposed
solution in the previous bullet (unknown sub-TLVs should be ignored
[RFC3630] but must continue to be flooded).

- Ships in the night refers to a mode of operation where both MPLS
and GMPLS routing protocol variants are operated in the same
network at the same time as separate routing protocol instances.
The two instances are independent and are used to create routing
adjacencies between LSRs of the same type. This mode of operation
may be appropriate to the integrated migration model.

5.1.3. Signaling Interworking

Signaling protocols are used to establish LSPs and are the principal
concern for interworking during migration. Issues of compatibility
arise because of differences in the encodings and codepoints used by
MPLS and GMPLS signaling, but also because of differences in
functionality provided by MPLS and GMPLS.

- Tunneling and stitching [RFC5150] (GMPLS-PSC case) mechanisms
provide the potential to avoid direct protocol interworking during
migration in the island model because protocol elements are
transported transparently across migration islands without being
inspected. However, care may be needed to achieve functional
mapping in these modes of operation since one set of features may
need to be supported across a network designed to support a
different set of features. In general, this is easily achieved for
the MPLS-GMPLS-MPLS model, but may be hard to achieve in the
GMPLS-MPLS-GMPLS model, for example, when end-to-end bidirectional
LSPs are requested, since the MPLS island does not support
bidirectional LSPs.

Note that tunneling and stitching are not available in unbalanced
island models because in these cases, the LSP end points use
different protocols.

- Protocol mapping is the conversion of signaling messages between
MPLS and GMPLS. This mechanism requires careful documentation of
the protocol fields and how they are mapped. This is relatively
straightforward in the MPLS-GMPLS unbalanced island model for LSPs
signaled in the MPLS-GMPLS direction. However, it may be more
complex for LSPs signaled in the opposite direction, and this will

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lead to considerable complications for providing GMPLS services
over the MPLS island and for terminating those services at an
egress LSR that is not GMPLS-capable. Further, in balanced island
models, and in particular where there are multiple small
(individual node) islands, the repeated conversion of signaling
parameters may lead to loss of information (and functionality) or
mis-requests.

- Ships in the night could be used in the integrated migration model
to allow MPLS-capable LSRs to establish LSPs using MPLS signaling
protocols and GMPLS LSRs to establish LSPs using GMPLS signaling
protocols. LSRs that can handle both sets of protocols could work
with both types of LSRs, and no conversion of protocols would be
needed.

5.1.4. Path Computation Element

The Path Computation Element (PCE) [RFC4655] may provide an
additional tool to aid MPLS to GMPLS migration. If a layered network
approach (Section 5.1.1) is used, PCEs may be used to facilitate the
computation of paths for LSPs in the different layers [PCE-INT].

6. Manageability Considerations

Attention should be given during migration planning to how the
network will be managed during and after migration. For example,
will the LSRs of different protocol capabilities be managed
separately or as one management domain? For example, in the Island
Model, it is possible to consider managing islands of one capability
separately from the surrounding sea. In the case of islands that
have different switching capabilities, it is possible that the
islands already have separate management in place before the
migration: the resultant migrated network may seek to merge the
management or to preserve the separation.

6.1. Control of Function and Policy

The most critical control functionality to be applied is at the
moment of changeover between different levels of protocol support.
Such a change may be made without service halt or during a period of
network maintenance.

Where island boundaries exist, it must be possible to manage the
relationships between protocols and to indicate which interfaces
support which protocols on a border LSR. Further, island borders are
a natural place to apply policy, and management should allow
configuration of such policies.

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6.2. Information and Data Models

No special information or data models are required to support
migration, but note that migration in the control plane implies
migration from MPLS management tools to GMPLS management tools.
During migration, therefore, it may be necessary for LSRs and
management applications to support both MPLS and GMPLS management
data.

The GMPLS MIB modules are designed to allow support of the MPLS
protocols, and they are built on the MPLS MIB modules through
extensions and augmentations. This may make it possible to migrate
management applications ahead of the LSRs that they manage.

6.3. Liveness Detection and Monitoring

Migration will not impose additional issues for Operations,
Administration, and Management (OAM) above those that already exist
for inter-domain OAM and for OAM across multiple switching
capabilities.

Note, however, that if a flat PSC MPLS network is migrated using the
island model, and is treated as a layered network using tunnels to
connect across GMPLS islands, then requirements for a multi-layer OAM
technique may be introduced into what was previously defined in the
flat OAM problem-space. The OAM framework of MPLS/GMPLS interworking
will need further consideration.

6.4. Verifying Correct Operation

The concerns for verifying correct operation (and in particular,
correct connectivity) are the same as for liveness detection and
monitoring. Specifically, the process of migration may introduce
tunneling or stitching [RFC5150] into what was previously a flat
network.

6.5. Requirements on Other Protocols and Functional Components

No particular requirements are introduced on other protocols. As it
has been observed, the management components may need to migrate in
step with the control plane components, but this does not impact the
management protocols, just the data that they carry.

It should also be observed that providing signaling and routing
connectivity across a migration island in support of a layered
architecture may require the use of protocol tunnels (such as Generic

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Routing Encapsulation (GRE)) between island border nodes. Such
tunnels may impose additional configuration requirements at the
border nodes.

6.6. Impact on Network Operation

The process of migration is likely to have significant impact on
network operation while migration is in progress. The main objective
of migration planning should be to reduce the impact on network
operation and on the services perceived by the network users.

To this end, planners should consider reducing the number of
migration steps that they perform and minimizing the number of
migration islands that are created.

A network manager may prefer the island model especially when
migration will extend over a significant operational period because
it allows the different network islands to be administered as
separate management domains. This is particularly the case in the
overlay, augmented network and border peer models where the details
of the protocol islands remain hidden from the surrounding LSRs.

6.7. Other Considerations

A migration strategy may also imply moving an MPLS state to a GMPLS
state for an in-service LSP. This may arise once all of the LSRs
along the path of the LSP have been updated to be both MPLS- and
GMPLS-capable. Signaling mechanisms to achieve the replacement of an
MPLS LSP with a GMPLS LSP without disrupting traffic exist through
make-before-break procedures [RFC3209] and [RFC3473], and should be
carefully managed under operator control.

7. Security Considerations

Security and confidentiality is often applied (and attacked) at
administrative boundaries. Some of the models described in this
document introduce such boundaries, for example, between MPLS and
GMPLS islands. These boundaries offer the possibility of applying or
modifying the security as when crossing an IGP area or Autonomous
System (AS) boundary, even though these island boundaries might lie
within an IGP area or AS.

No changes are proposed to the security procedures built into MPLS
and GMPLS signaling and routing. GMPLS signaling and routing inherit
their security mechanisms from MPLS signaling and routing without any
changes. Hence, there will be no additional issues with security in
interworking scenarios. Further, since the MPLS and GMPLS signaling
and routing security is provided on a hop-by-hop basis, and since all

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signaling and routing exchanges described in this document for use
between any pair of LSRs are based on either MPLS or GMPLS, there are
no changes necessary to the security procedures.

8. Acknowledgements

The authors are grateful to Daisaku Shimazaki for discussion during
the initial work on this document. The authors are grateful to Dean
Cheng and Adrian Farrel for their valuable comments.

9. References

9.1. 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.

[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.

[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.

[RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic Engineering (TE)",
RFC 3784, June 2004.

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

[RFC4872] Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou, Ed.,
"RSVP-TE Extensions in Support of End-to-End Generalized
Multi-Protocol Label Switching (GMPLS) Recovery", RFC 4872,
May 2007.

[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
"GMPLS Segment Recovery", RFC 4873, May 2007.

[RFC5073] Vasseur, J., Ed., and J. Le Roux, Ed., "IGP Routing
Protocol Extensions for Discovery of Traffic Engineering
Node Capabilities", RFC 5073, December 2007.

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9.2. Informative References

[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.

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

[RFC4726] Farrel, A., Vasseur, J.-P., and A. Ayyangar, "A Framework
for Inter-Domain Multiprotocol Label Switching Traffic
Engineering", RFC 4726, November 2006.

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

[RFC5146] Kumaki, K., Ed., "Interworking Requirements to Support
Operation of MPLS-TE over GMPLS Networks", RFC 5146, March
2008.

[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.

10. Contributors' Addresses

Dimitri Papadimitriou
Alcatel
Francis Wellensplein 1,
B-2018 Antwerpen, Belgium
Phone: +32 3 240 8491
EMail: [email protected]

Jean-Louis Le Roux
France Telecom
av Pierre Marzin 22300
Lannion, France
Phone: +33 2 96 05 30 20
EMail: [email protected]

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Deborah Brungard
AT&T
Rm. D1-3C22 - 200 S. Laurel Ave.
Middletown, NJ 07748, USA
Phone: +1 732 420 1573
EMail: [email protected]

Zafar Ali
Cisco Systems, Inc.
EMail: [email protected]

Kenji Kumaki
KDDI Corporation
Garden Air Tower
Iidabashi, Chiyoda-ku,
Tokyo 102-8460, JAPAN
Phone: +81-3-6678-3103
EMail: [email protected]

Eiji Oki
NTT
Midori 3-9-11
Musashino, Tokyo 180-8585, Japan
Phone: +81 422 59 3441
EMail: [email protected]

Ichiro Inoue
NTT
Midori 3-9-11
Musashino, Tokyo 180-8585, Japan
Phone: +81 422 59 3441
EMail: [email protected]

Tomohiro Otani
KDDI Laboratories
EMail: [email protected]

Editor's Address

Kohei Shiomoto
NTT
Midori 3-9-11
Musashino, Tokyo 180-8585, Japan
Phone: +81 422 59 4402
EMail: [email protected]

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