Internet Engineering Task Force (IETF) Z. Ali, Ed.

Internet Engineering Task Force (IETF) Z. Ali, Ed.
Request for Comments: 8390 Cisco Systems
Updates: 4874 G. Swallow, Ed.
Category: Standards Track SETC
ISSN: 2070-1721 F. Zhang, Ed.
Huawei
D. Beller, Ed.
Nokia
July 2018

RSVP-TE Path Diversity Using Exclude Route

Abstract

RSVP-TE provides support for the communication of exclusion
information during Label Switched Path (LSP) setup. A typical LSP
diversity use case is for protection, where two LSPs should follow
different paths through the network in order to avoid single points
of failure, thus greatly improving service availability. This
document specifies an approach that can be used for network scenarios
where the full path(s) is not necessarily known by use of an abstract
identifier for the path. Three types of abstract identifiers are
specified: client based, Path Computation Element (PCE) based, and
network based. This document specifies two new diversity subobjects
for the RSVP eXclude Route Object (XRO) and the Explicit Exclusion
Route Subobject (EXRS).

For the protection use case, LSPs are typically created at a slow
rate and exist for a long time so that it is reasonable to assume
that a given (reference) path currently existing (with a well-known
identifier) will continue to exist and can be used as a reference
when creating the new diverse path. Re-routing of the existing
(reference) LSP, before the new path is established, is not
considered.

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Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8390.

Copyright Notice

Copyright (c) 2018 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
(https://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.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . 6
1.2. Terms and Abbreviations . . . . . . . . . . . . . . . . . 6
1.3. Client-Initiated Identifier . . . . . . . . . . . . . . . 7
1.4. PCE-Allocated Identifier . . . . . . . . . . . . . . . . 7
1.5. Network-Assigned Identifier . . . . . . . . . . . . . . . 9
2. RSVP-TE Signaling Extensions . . . . . . . . . . . . . . . . 10
2.1. Diversity XRO Subobject . . . . . . . . . . . . . . . . . 10
2.2. Diversity EXRS Subobject . . . . . . . . . . . . . . . . 16
2.3. Processing Rules for the Diversity XRO and EXRS
Subobjects . . . . . . . . . . . . . . . . . . . . . . . 16
3. Security Considerations . . . . . . . . . . . . . . . . . . . 20
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
4.1. New XRO Subobject Types . . . . . . . . . . . . . . . . . 21
4.2. New EXRS Subobject Types . . . . . . . . . . . . . . . . 21
4.3. New RSVP Error Sub-codes . . . . . . . . . . . . . . . . 22
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.1. Normative References . . . . . . . . . . . . . . . . . . 22
5.2. Informative References . . . . . . . . . . . . . . . . . 23
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 24
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26

1. Introduction

Path diversity for multiple connections is a well-known operational
requirement. Diversity constraints ensure that Label Switched Paths
(LSPs) can be established without sharing network resources, thus
greatly reducing the probability of simultaneous connection failures.

The source node can compute diverse paths for LSPs when it has full
knowledge of the network topology and is permitted to signal an
Explicit Route Object (ERO). However, there are scenarios where
different nodes perform path computations, and therefore there is a
need for relevant diversity constraints to be signaled to those
nodes. These include (but are not limited to):

o LSPs with loose hops in the Explicit Route Object, e.g., inter-
domain LSPs; and

o Generalized Multiprotocol Label Switching (GMPLS) User-Network
Interface (UNI), where the core node may perform path computation
[RFC4208].

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[RFC4874] introduced a means of specifying nodes and resources to be
excluded from a route using the eXclude Route Object (XRO) and
Explicit Exclusion Route Subobject (EXRS). It facilitates the
calculation of diverse paths for LSPs based on known properties of
those paths including addresses of links and nodes traversed and
Shared Risk Link Groups (SRLGs) of traversed links. Employing these
mechanisms requires that the source node that initiates signaling
knows the relevant properties of the path(s) from which diversity is
desired. However, there are circumstances under which this may not
be possible or desirable, including (but not limited to):

o Exclusion of a path that does not originate, terminate, or
traverse the source node of the diverse LSP, in which case the
addresses of links and SRLGs of the path from which diversity is
required are unknown to the source node.

o Exclusion of a path that is known to the source node of the
diverse LSP for which the node has incomplete or no path
information, e.g., due to operator policy. In this case, the
source node is aware of the existence of the reference path, but
the information required to construct an XRO object to guarantee
diversity from the reference path is not fully known. Inter-
domain and GMPLS overlay networks can impose such restrictions.

This is illustrated in Figure 1, where the overlay reference model
from [RFC4208] is shown.

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Overlay Overlay
Network +----------------------------------+ Network
+---------+ | | +---------+
| +----+ | | +-----+ +-----+ +-----+ | | +----+ |
| | | | UNI | | | | | | | | UNI | | | |
| -+ EN1+-+-----+--+ CN1 +----+ CN2 +----+ CN3 +---+-----+-+ EN3+- |
| | | | +--+--+ | | | | | | +---+-| | |
| +----+ | | | +--+--+ +--+--+ +--+--+ | | | +----+ |
+---------+ | | | | | | | +---------+
| | | | | | |
+---------+ | | +--+--+ | +--+--+ | | +---------+
| +----+ | | | | | +-------+ +-----+ | +----+ |
| | +-+--+ | | CN4 +---------------+ CN5 | | | | | |
| -+ EN2+-+-----+--+ | | +---+-----+-+ EN4+- |
| | | | UNI | +-----+ +-----+ | UNI | | | |
| +----+ | | | | +----+ |
+---------+ +----------------------------------+ +---------+
Overlay Core Network Overlay
Network Network
Legend: EN - Edge Node
CN - Core Node

Figure 1: Overlay Reference Model [RFC4208]

Figure 1 depicts two types of UNI connectivity: single-homed and
dual-homed ENs (which also applies to higher-order multihomed
connectivity). Single-homed EN devices are connected to a single CN
device via a single UNI link. This single UNI link may constitute a
single point of failure. UNI connection between EN1 and CN1 is an
example of singled-homed UNI connectivity.

Such a single point of failure can be avoided when the EN device is
connected to two different CN devices, as depicted for EN2 in
Figure 1. For the dual-homing case, it is possible to establish two
different UNI connections from the same source EN device to the same
destination EN device. For example, two connections from EN2 to EN3
may use the two UNI links EN2-CN1 and EN2-CN4. To avoid single
points of failure within the provider network, it is necessary to
also ensure path (LSP) diversity within the core network.

In a network providing a set of UNI interfaces between ENs and CNs
such as that shown in Figure 1, the CNs typically perform path
computation. Information sharing across the UNI boundary is
restricted based on the policy rules imposed by the core network.
Typically, the core network topology information as well as LSP path
information is not exposed to the ENs. In the network shown in
Figure 1, consider a use case where an LSP from EN2 to EN4 needs to
be SRLG diverse from an LSP from EN1 to EN3. In this case, EN2 may

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not know SRLG attributes of the EN1-EN3 LSP and hence cannot
construct an XRO to exclude these SRLGs. In this example, EN2 cannot
use the procedures described in [RFC4874]. Similarly, an LSP from
EN2 to EN3 traversing CN1 needs to be diverse from an LSP from EN2 to
EN3 going via CN4. Again, in this case, exclusions based on
[RFC4874] cannot be used.

This document addresses these diversity requirements by introducing
an approach of excluding the path taken by these particular LSP(s).
Each reference LSP or route from which diversity is required is
identified by an abstract "identifier". The type of identifier to
use is highly dependent on the core network operator's networking
deployment scenario; it could be client initiated (provided by the
EN), provided by a PCE, or allocated by the (core) network. This
document defines three different types of identifiers corresponding
to these three cases: a client-initiated identifier, a PCE-allocated
identifier, and an identifier allocated by the CN ingress node
(UNI-N), i.e., a network-assigned identifier.

1.1. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

1.2. Terms and Abbreviations

Diverse LSP: A diverse Label Switched Path (LSP) is an LSP that has
a path that does not have any link or SRLG in common with the path
of a given LSP. Diverse LSPs are meaningful in the context of
protection or restoration.

ERO: Explicit Route Object as defined in [RFC3209].

EXRS: Explicit Exclusion Route Subobject as defined in [RFC4874].

SRLG: Shared Risk Link Group as defined in [RFC4202].

Reference Path: The reference path is the path of an existing LSP to
which the path of a diverse LSP shall be diverse.

XRO: eXclude Route Object as defined in [RFC4874].

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1.3. Client-Initiated Identifier

The following fields MUST be used to represent the client-initiated
identifier: IPv4/IPv6 tunnel sender address, IPv4/IPv6 tunnel
endpoint address, Tunnel ID, and Extended Tunnel ID. Based on local
policy, the client MAY also include the LSP ID to identify a specific
LSP within the tunnel. These fields are defined in Sections 4.6.1.1
and 4.6.2.1 of [RFC3209].

The usage of the client-initiated identifier is illustrated by
Figure 1. Suppose an LSP from EN2 to EN4 needs to be diverse with
respect to an LSP from EN1 to EN3.

The LSP identifier of the EN1-EN3 LSP is LSP-IDENTIFIER1, where LSP-
IDENTIFIER1 is defined by the tuple

(tunnel-id = T1,
LSP ID = L1,
source address = EN1.RID (Route Identifier),
destination address = EN3.RID,
extended tunnel-id = EN1.RID).

Similarly, the LSP identifier of the EN2-EN4 LSP is LSP-IDENTIFIER2,
where LSP-IDENTIFIER2 is defined by the tuple

(tunnel-id = T2,
LSP ID = L2,
source address = EN2.RID,
destination address = EN4.RID,
extended tunnel-id = EN2.RID).

The EN1-EN3 LSP is signaled with an exclusion requirement from LSP-
IDENTIFIER2, and the EN2-EN4 LSP is signaled with an exclusion
requirement from LSP-IDENTIFIER1. In order to maintain diversity
between these two connections within the core network, the core
network SHOULD implement crankback signaling extensions as defined in
[RFC4920]. Note that crankback signaling is known to lead to slower
setup times and suboptimal paths under some circumstances as
described by [RFC4920].

1.4. PCE-Allocated Identifier

In scenarios where a PCE is deployed and used to perform path
computation, typically the ingress node of the core network (e.g.,
node CN1 in Figure 1) could consult a PCE to allocate identifiers,
which are used to signal path diversity constraints. In other
deployment scenarios, a PCE is deployed at a network node(s) or it is

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part of a Network Management System (NMS). In all these cases, the
PCE is consulted and the Path Key, as defined in [RFC5520], can be
used in RSVP signaling as the identifier to ensure diversity.

An example of specifying LSP diversity using a Path Key is shown in
Figure 2, where a simple network with two domains is shown. It is
desired to set up a pair of path-disjoint LSPs from the source in
Domain 1 to the destination in Domain 2, but the domains keep strict
confidentiality about all path and topology information.

The first LSP is signaled by the source with ERO {A, B, loose Dst}
and is set up with the path {Src, A, B, U, V, W, Dst}. However, when
sending the Record Route Object (RRO) out of Domain 2, node U would
normally strip the path and replace it with a loose hop to the
destination. With this limited information, the source is unable to
include enough detail in the ERO of the second LSP to avoid it
taking, for example, the path {Src, C, D, X, V, W, Dst} for path-
disjointness.

--------------------- -----------------------------
| Domain 1 | | Domain 2 |
| | | |
| --- --- | | --- --- --- |
| | A |--| B |--+--+--| U |--| V |---| W | |
| / --- --- | | --- --- --- \ |
| ---/ | | / / \--- |
| |Src| | | / / |Dst| |
| ---\ | | / / /--- |
| \ --- --- | | --- / --- / --- / |
| | C |--| D |--+--+--| X |---| Y |--| Z | |
| --- --- | | --- --- --- |
| | | |
--------------------- -----------------------------

Figure 2: A Simple Multi-domain Network

In order to support LSP diversity, node U consults the PCE and
replaces the path segment {U, V, W} in the RRO with a Path Key
subobject. The PCE function assigns an "identifier" and puts it into
the Path Key field of the Path Key subobject. The PCE ID in the
message indicates that this replacement operation was performed by
node U.

With this additional information, the source node is able to signal
the subsequent LSPs with the ERO set to {C, D, exclude Path Key
(signaled in the EXRS RSVP subobject), loose Dst}. When the
signaling message reaches node X, it can consult the PCE function
associated with node U to expand the Path Key in order to calculate a

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path that is diverse with respect to the first LSP. Alternatively,
the source node could use an ERO of {C, D, loose Dst} and include an
XRO containing the Path Key.

This mechanism can work with all the Path Key resolution mechanisms,
as detailed in Section 3.1 of [RFC5553]. A PCE, co-located or not,
may be used to resolve the Path Key, but the node (i.e., a Label
Switching Router (LSR)) can also use the Path Key information to
index a path segment previously supplied to it by the entity that
originated the Path Key (for example, the LSR that inserted the Path
Key in the RRO or a management system).

1.5. Network-Assigned Identifier

There are scenarios in which the network provides diversity-related
information for a service that allows the client device to include
this information in the signaling message. If the Shared Risk Link
Group (SRLG) identifier information is both available and shareable
(by policy) with the ENs, the procedure defined in [RFC8001] can be
used to collect SRLG identifiers associated with an LSP (LSP1). When
a second LSP (LSP2) needs to be diverse with respect to LSP1, the EN
constructing the RSVP signaling message for setting up LSP2 can
insert the SRLG identifiers associated with LSP1 as diversity
constraints into the XRO using the procedure described in [RFC4874].
However, if the core network SRLG identifiers are either not
available or not shareable with the ENs based on policies enforced by
the core network, existing mechanisms cannot be used.

In this document, a signaling mechanism is defined where information
signaled to the CN via the UNI does not require shared knowledge of
core network SRLG information. For this purpose, the concept of a
Path Affinity Set (PAS) is defined for abstracting SRLG information.
The motive behind the introduction of the PAS is to minimize the
exchange of diversity information between the core network (CNs) and
the client devices (ENs). The PAS contains an abstract SRLG
identifier associated with a given path rather than a detailed SRLG
list. The PAS is a single identifier that can be used to request
diversity and associate diversity. The means by which the processing
node determines the path corresponding to the PAS is beyond the scope
of this document.

A CN on the core network boundary interprets the specific PAS
identifier (e.g., "123") as meaning to exclude the core network SRLG
information (or equivalent) that has been allocated by LSPs
associated with this PAS identifier value. For example, if a path
exists for the LSP with the PAS identifier "123", the CN would use
local knowledge of the core network SRLGs associated with the LSPs
tagged with PAS attribute "123" and use those SRLGs as constraints

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for path computation. If a PAS identifier is used as an exclusion
identifier in the connection request, the CN (UNI-N) in the core
network is assumed to be able to determine the existing core network
SRLG information and calculate a path that meets the determined
diversity constraints.

When a CN satisfies a connection setup for an SRLG-diverse signaled
path, the CN may optionally record the core network SRLG information
for that connection in terms of CN-based parameters and associate
that with the EN addresses in the Path message. Specifically, for
Layer 1 Virtual Private Networks (L1VPNs), Port Information Tables
(PITs) [RFC5251] can be leveraged to translate between client (EN)
addresses and core network addresses.

The means to distribute the PAS information within the core network
is beyond the scope of this document. For example, the PAS and the
associated SRLG information can be distributed within the core
network by an Interior Gateway Protocol (IGP) or by other means such
as configuration. Regardless of means used to distribute the PAS
information, the information is kept inside the core network and is
not shared with the overlay network (see Figure 1).

2. RSVP-TE Signaling Extensions

This section describes the signaling extensions required to address
the aforementioned requirements and use cases.

2.1. Diversity XRO Subobject

New Diversity XRO subobjects are defined below for the IPv4 and IPv6
address families. Most of the fields in the IPv4 and IPv6 Diversity
XRO subobjects are common and are described following the definition
of the two subobjects.

The IPv4 Diversity XRO subobject is defined as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| XRO Type | Length |DI Type|A-Flags|E-Flags| Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Diversity Identifier Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diversity Identifier Value |
// ... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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Similarly, the IPv6 Diversity XRO subobject is defined as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| XRO Type | Length |DI Type|A-Flags|E-Flags| Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Diversity Identifier Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Diversity Identifier Source Address (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Diversity Identifier Source Address (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Diversity Identifier Source Address (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Diversity Identifier Value |
// ... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

L:
The L flag is used in the same way as for the XRO subobjects
defined in [RFC4874], that is:

0 indicates that the diversity constraints MUST be satisfied, and

1 indicates that the diversity constraints SHOULD be satisfied.

XRO Type:
The value is set to 38 for the IPv4 Diversity XRO subobject. The
value is set to 39 for the IPv6 Diversity XRO subobject.

Length:
Per [RFC4874], the Length contains the total length of the
IPv4/IPv6 subobject in bytes, including the XRO Type and Length
fields. The Length is variable, depending on the Diversity
Identifier Value.

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Diversity Identifier Type (DI Type):
Diversity Identifier Type (DI Type) indicates the way the
reference LSP(s) or route(s) with which diversity is required is
identified in the IPv4/IPv6 Diversity subobjects. The following
three DI Type values are defined in this document:

DI Type value Definition
------------- --------------------------------
1 Client-Initiated Identifier
2 PCE-Allocated Identifier
3 Network-Assigned Identifier

Attribute Flags (A-Flags):
The Attribute Flags (A-Flags) are used to communicate desirable
attributes of the LSP being signaled in the IPv4/IPv6 Diversity
subobjects. Each flag acts independently. Any combination of
flags is permitted.

0x01 = Destination node exception
Indicates that the exclusion does not apply to the destination
node of the LSP being signaled.

0x02 = Processing node exception
Indicates that the exclusion does not apply to the node(s)
performing ERO expansion for the LSP being signaled. An
ingress UNI-N node is an example of such a node.

0x04 = Penultimate node exception
Indicates that the penultimate node of the LSP being signaled
MAY be shared with the excluded path even when this violates
the exclusion flags. This flag is useful, for example, when an
EN is not dual homed (like EN4 in Figure 1, where all LSPs have
to go through CN5).

The "Penultimate node exception" flag is typically set when the
destination node is single homed (e.g., EN1 or EN4 in
Figure 2). In such a case, LSP diversity can only be
accomplished inside the core network up to the egress node and
the penultimate hop must be the same for the LSPs.

0x08 = LSP ID to be ignored
This flag is used to indicate tunnel-level exclusion.
Specifically, this flag is used to indicate that if the
diversity identifier contains an LSP ID field, then the LSP ID
is to be ignored, and the exclusion applies to any LSP matching
the rest of the diversity identifier.

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Exclusion Flags (E-Flags):
The Exclusion Flags are used to communicate the desired type(s) of
exclusion requested in the IPv4/IPv6 Diversity subobjects. The
following flags are defined. Any combination of these flags is
permitted. Please note that the exclusion specified by these
flags may be modified by the value of the A-Flags. For example,
the node exclusion flag is ignored for the penultimate node if the
"Penultimate node exception" flag of the A-Flags is set.

0x01 = SRLG exclusion
Indicates that the path of the LSP being signaled is requested
to be SRLG disjoint with respect to the excluded path specified
by the IPv4/IPv6 Diversity XRO subobject.

0x02 = Node exclusion
Indicates that the path of the LSP being signaled is requested
to be "node diverse" from the excluded path specified by the
IPv4/IPv6 Diversity XRO subobject.

0x04 = Link exclusion
Indicates that the path of the LSP being signaled is requested
to be "link diverse" from the path specified by the IPv4/IPv6
Diversity XRO subobject.

0x08 = Reserved
This flag is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt for both IPv4/IPv6 Diversity XRO
subobjects.

Resvd:
This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt for both IPv4/IPv6 Diversity XRO
subobjects.

IPv4/IPv6 Diversity Identifier Source Address:
This field MUST be set to the IPv4/IPv6 address of the node that
assigns the diversity identifier. Depending on the Diversity
Identifier Type, the diversity identifier source may be a client
node, PCE entity, or network node. Specifically:

* When the Diversity Identifier Type is set to the "Client-
Initiated Identifier", the value MUST be set to IPv4/IPv6
tunnel sender address of the reference LSP against which
diversity is desired. The IPv4/IPv6 tunnel sender address is
as defined in [RFC3209].

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* When the Diversity Identifier Type is set to "PCE-Allocated
Identifier", the value MUST be set to the IPv4/IPv6 address of
the node that assigned the Path Key identifier and that can
return an expansion of the Path Key or use the Path Key as
exclusion in a path computation. The Path Key is defined in
[RFC5553]. The PCE ID is carried in the Diversity Identifier
Source Address field of the subobject.

* When the Diversity Identifier Type is set to "Network-Assigned
Identifier", the value MUST be set to the IPv4/IPv6 address of
the node allocating the Path Affinity Set (PAS).

Diversity Identifier Value: Encoding for this field depends on the
Diversity Identifier Type, as defined in the following.

When the Diversity Identifier Type is set to "Client-Initiated
Identifier" in the IPv4 Diversity XRO subobject, the Diversity
Identifier Value MUST be encoded as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Tunnel Endpoint Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The IPv4 Tunnel Endpoint Address, Tunnel ID, Extended Tunnel ID,
and LSP ID are as defined in [RFC3209].

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When the Diversity Identifier Type is set to "Client-Initiated
Identifier" in the IPv6 Diversity XRO subobject, the Diversity
Identifier Value MUST be encoded as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Tunnel Endpoint Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Tunnel Endpoint Address (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Tunnel Endpoint Address (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Tunnel Endpoint Address (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The IPv6 Tunnel Endpoint Address, Tunnel ID, IPv6 Extended Tunnel
ID, and LSP ID are as defined in [RFC3209].

When the Diversity Identifier Type is set to "PCE-Allocated
Identifier" in the IPv4 or IPv6 Diversity XRO subobject, the
Diversity Identifier Value MUST be encoded as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | Path Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Path Key is defined in [RFC5553].

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When the Diversity Identifier Type is set to "Network-Assigned
Identifier" in the IPv4 or IPv6 Diversity XRO subobject, the
Diversity Identifier Value MUST be encoded as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Affinity Set (PAS) Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Path Affinity Set (PAS) Identifier field is a 32-bit value
that is scoped by (i.e., is only meaningful when used in
combination with) the Diversity Identifier Source Address field.
There are no restrictions on how a node selects a PAS identifier
value. Section 1.3 defines the PAS term and provides context on
how values may be selected.

2.2. Diversity EXRS Subobject

[RFC4874] defines the EXRS ERO subobject. An EXRS is used to
identify abstract nodes or resources that must not or should not be
used on the path between two inclusive abstract nodes or resources in
the explicit route. An EXRS contains one or more subobjects of its
own, called EXRS subobjects [RFC4874].

An EXRS MAY include a Diversity subobject as specified in this
document. The same type values 38 and 39 MUST be used.

2.3. Processing Rules for the Diversity XRO and EXRS Subobjects

The procedure defined in [RFC4874] for processing the XRO and EXRS is
not changed by this document. The processing rules for the Diversity
XRO and EXRS subobjects are similar unless the differences are
explicitly described. Similarly, IPv4 and IPv6 Diversity XRO
subobjects and IPv4 and IPv6 Diversity EXRS subobjects follow the
same processing rules.

If the processing node cannot recognize the Diversity XRO/EXRS
subobject, the node is expected to follow the procedure defined in
[RFC4874].

An XRO/EXRS object MAY contain multiple Diversity subobjects of the
same DI Type. For example, in order to exclude multiple Path Keys, a
node MAY include multiple Diversity XRO subobjects, each with a
different Path Key. Similarly, in order to exclude the routes taken
by multiple LSPs, a node MAY include multiple Diversity XRO/EXRS
subobjects, each with a different LSP identifier. Likewise, to
exclude multiple PAS identifiers, a node MAY include multiple

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Diversity XRO/EXRS subobjects, each with a different PAS identifier.
However, all Diversity subobjects in an XRO/EXRS MUST contain the
same Diversity Identifier Type. If a Path message contains an XRO/
EXRS with multiple Diversity subobjects of different DI Types, the
processing node MUST return a PathErr with the error code "Routing
Problem" (24) and error sub-code "XRO/EXRS Too Complex" (68/69).

If the processing node recognizes the Diversity XRO/EXRS subobject
but does not support the DI Type, it MUST return a PathErr with the
error code "Routing Problem" (24) and error sub-code "Unsupported
Diversity Identifier Type" (36).

In the case of DI Type "Client-Initiated Identifier", all nodes along
the path SHOULD process the diversity information signaled in the
XRO/EXRS Diversity subobjects to verify that the signaled diversity
constraint is satisfied. If a diversity violation is detected,
crankback signaling MAY be initiated.

In the case of DI Type "PCE-Allocated Identifier" and "Network-
Assigned Identifier", the nodes in the domain that perform path
computation SHOULD process the diversity information signaled in the
XRO/EXRS Diversity subobjects as follows. In the PCE case, the
ingress node of a domain sends a path computation request for a path
from ingress node to egress node, including diversity constraints to
a PCE. Or, in the PAS case, the ingress node is capable of
calculating the path for the new LSP from ingress node to the egress
node, taking the diversity constraints into account. The calculated
path is then carried in the Explicit Route Object (ERO). Hence, the
transit nodes in a domain and the domain egress node SHOULD NOT
process the signaled diversity information unless path computation is
performed.

While processing the EXRS object, if a loose hop expansion results in
the creation of another loose hop in the outgoing ERO, the processing
node MAY include the EXRS in the newly created loose hop for further
processing by downstream nodes.

The A-Flags affect the processing of the Diversity XRO/EXRS subobject
as follows:

o When the "Processing node exception" flag is set, the exclusion
MUST be ignored for the node processing the XRO or EXRS subobject.

o When the "Destination node exception" flag is set, the exclusion
MUST be ignored for the destination node in processing the XRO
subobject. The destination node exception for the EXRS subobject
applies to the explicit node identified by the ERO subobject that

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identifies the next abstract node. When the "Destination node
exception" flag is set in the EXRS subobject, exclusion MUST be
ignored for said node (i.e., the next abstract node).

o When the "Penultimate node exception" flag is set in the XRO
subobject, the exclusion MUST be ignored for the penultimate node
on the path of the LSP being established.

The penultimate node exception for the EXRS subobject applies to
the node before the explicit node identified by the ERO subobject
that identifies the next abstract node. When the "Penultimate
node exception" flag is set in the EXRS subobject, the exclusion
MUST be ignored for said node (i.e., the node before the next
abstract node).

If the L-flag of the Diversity XRO subobject or Diversity EXRS
subobject is not set, the processing node proceeds as follows.

o If the Diversity Identifier Type is set to "Client-Initiated
Identifier", the processing node MUST ensure that the path
calculated/expanded for the signaled LSP is diverse from the route
taken by the LSP identified in the Diversity Identifier Value
field.

o If the Diversity Identifier Type is set to "PCE-Allocated
Identifier", the processing node MUST ensure that any path
calculated for the signaled LSP is diverse from the route
identified by the Path Key. The processing node MAY use the PCE
identified by the Diversity Identifier Source Address in the
subobject for route computation. The processing node MAY use the
Path Key resolution mechanisms described in [RFC5553].

o If the Diversity Identifier Type is set to "Network-Assigned
Identifier", the processing node MUST ensure that the path
calculated for the signaled LSP is diverse with respect to the
values associated with the PAS Identifier and Diversity Identifier
Source Address fields.

o Regardless of whether the path computation is performed locally or
at a remote node (e.g., PCE), the processing node MUST ensure that
any path calculated for the signaled LSP is diverse from the
requested Exclusion Flags.

o If the excluded path referenced in the XRO subobject is unknown to
the processing node, the processing node SHOULD ignore the
Diversity XRO subobject and SHOULD proceed with the signaling
request. After sending the Resv for the signaled LSP, the

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processing node MUST return a PathErr with the error code "Notify
Error" (25) and error sub-code "Route of XRO LSP identifier
unknown" (14) for the signaled LSP.

o If the processing node fails to find a path that meets the
requested constraint, the processing node MUST return a PathErr
with the error code "Routing Problem" (24) and error sub-code
"Route blocked by Exclude Route" (67).

If the L-flag of the Diversity XRO subobject or Diversity EXRS
subobject is set, the processing node proceeds as follows:

o If the Diversity Identifier Type is set to "Client-Initiated
Identifier", the processing node SHOULD ensure that the path
calculated/expended for the signaled LSP is diverse from the route
taken by the LSP identified in the Diversity Identifier Value
field.

o If the Diversity Identifier Type is set to "PCE-Allocated
Identifier", the processing node SHOULD ensure that the path
calculated for the signaled LSP is diverse from the route
identified by the Path Key.

o If the Diversity Identifier Type is set to "Network-Assigned
Identifier", the processing node SHOULD ensure that the path
calculated for the signaled LSP is diverse with respect to the
values associated with the PAS Identifier and Diversity Identifier
Source Address fields.

o If the processing node fails to find a path that meets the
requested constraint, it SHOULD proceed with signaling using a
suitable path that meets the constraint as far as possible. After
sending the Resv for the signaled LSP, it MUST return a PathErr
message with error code "Notify Error" (25) and error sub-code
"Failed to satisfy Exclude Route" (15) to the source node.

If, subsequent to the initial signaling of a diverse LSP, an excluded
path referenced in the XRO subobject becomes known to the processing
node or a change in the excluded path becomes known to the processing
node, the processing node MUST re-evaluate the exclusion and
diversity constraints requested by the diverse LSP to determine
whether they are still satisfied.

o In the case where the L-flag was not set in the initial setup
message, the exclusion and diversity constraints were satisfied at
the time of the initial setup. If the processing node re-
evaluating the exclusion and diversity constraints for a diverse
LSP detects that the exclusion and diversity constraints are no

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longer met, it MUST send a PathErr message for the diverse LSP
with the error code "Routing Problem" (24) and error sub-code
"Route blocked by Exclude Route" (67). The Path_State_Removed
(PSR) flag [RFC3473] MUST NOT be set. A source node receiving a
PathErr message with this error code and sub-code combination
SHOULD take appropriate actions and move the diverse LSP to a new
path that meets the original constraints.

o In the case where the L-flag was set in the initial setup message,
the exclusion and diversity constraints may or may not be
satisfied at any given time. If the exclusion constraints for a
diverse LSP were satisfied before, and if the processing node re-
evaluating the exclusion and diversity constraints for a diverse
LSP detects that exclusion and diversity constraints are no longer
met, it MUST send a PathErr message for the diverse LSP with the
error code "Notify Error" (25) and error sub-code "Failed to
satisfy Exclude Route" (15). The PSR flag MUST NOT be set. The
source node MAY take no consequent action and keep the LSP along
the path that does not meet the original constraints. Similarly,
if the exclusion constraints for a diverse LSP were not satisfied
before, and if the processing node re-evaluating the exclusion and
diversity constraints for a diverse LSP detects that the exclusion
constraints are met, it MUST send a PathErr message for the
diverse LSP with the error code "Notify Error" (25) and a new
error sub-code "Compliant path exists" (16). The PSR flag MUST
NOT be set. A source node receiving a PathErr message with this
error code and sub-code combination MAY move the diverse LSP to a
new path that meets the original constraints.

3. Security Considerations

This document does not introduce any additional security issues in
addition to those identified in [RFC5920], [RFC2205], [RFC3209],
[RFC3473], [RFC2747], [RFC4874], [RFC5520], and [RFC5553].

The diversity mechanisms defined in this document rely on the new
diversity subobject that is carried in the XRO or EXRS, respectively.
In Section 7 of [RFC4874], it is noted that some administrative
boundaries may remove the XRO due to security concerns on explicit
route information exchange. However, when the diversity subobjects
specified in this document are used, removing at the administrative
boundary an XRO containing these diversity subobjects would result in
the request for diversity being dropped at the boundary, and path
computation would be unlikely to produce the requested diverse path.
As such, diversity subobjects MUST be retained in an XRO crossing an
administrative boundary, even if other subobjects are removed. This

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retention would be based on operator policy. The use of diversity
subobjects is based on mutual agreement. This avoids the need to
share the identity of network resources when supporting diversity.

4. IANA Considerations

IANA has assigned new values defined in this document and summarized
in this section.

4.1. New XRO Subobject Types

In the IANA registry for RSVP parameters, under "Class Names, Class
Numbers, and Class Types", this document defines two new subobjects
for the EXCLUDE_ROUTE object [RFC4874], C-Type 1 (see "Class Types or
C-Types - 232 EXCLUDE_ROUTE" on <https://www.iana.org/assignments/
rsvp-parameters>).

+----------------+-------+
| Description | Value |
+----------------+-------+
| IPv4 Diversity | 38 |
| IPv6 Diversity | 39 |
+----------------+-------+

4.2. New EXRS Subobject Types

The Diversity XRO subobjects are also defined as new EXRS subobjects
(see "Class Types or C-Types - 20 EXPLICIT_ROUTE" on
<https://www.iana.org/assignments/rsvp-parameters>). The same
numeric values have been assigned:

+----------------+-------+
| Description | Value |
+----------------+-------+
| IPv4 Diversity | 38 |
| IPv6 Diversity | 39 |
+----------------+-------+

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4.3. New RSVP Error Sub-codes

In the IANA registry for RSVP parameters, under "Error Codes and
Globally Defined Error Value Sub-Codes", for Error Code "Routing
Problem" (24) (see [RFC3209]), the following sub-codes are defined
(see "Sub-Codes - 24 Routing Problem" on
<https://www.iana.org/assignments/rsvp-parameters>).

+-------+---------------------------------------+-----------+
| Value | Description | Reference |
+-------+---------------------------------------+-----------+
| 36 | Unsupported Diversity Identifier Type | RFC 8390 |
+-------+---------------------------------------+-----------+

For Error Code "Notify Error" (25) (see [RFC3209]), the following
sub-codes are defined (see "Sub-Codes - 25 Notify Error" on
<https://www.iana.org/assignments/rsvp-parameters>).

+-------+-------------------------------------+-----------+
| Value | Description | Reference |
+-------+-------------------------------------+-----------+
| 14 | Route of XRO LSP identifier unknown | RFC 8390 |
| 15 | Failed to satisfy Exclude Route | RFC 8390 |
| 16 | Compliant path exists | RFC 8390 |
+-------+-------------------------------------+-----------+

5. References

5.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
Authentication", RFC 2747, DOI 10.17487/RFC2747, January
2000, <https://www.rfc-editor.org/info/rfc2747>.

[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.

Ali, et al. Standards Track [Page 22]

RFC 8390 RVSP-TE Path Diversity July 2018

[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003,
<https://www.rfc-editor.org/info/rfc3473>.

[RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
<https://www.rfc-editor.org/info/rfc4202>.

[RFC4874] Lee, CY., Farrel, A., and S. De Cnodder, "Exclude Routes -
Extension to Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE)", RFC 4874, DOI 10.17487/RFC4874,
April 2007, <https://www.rfc-editor.org/info/rfc4874>.

[RFC4920] Farrel, A., Ed., Satyanarayana, A., Iwata, A., Fujita, N.,
and G. Ash, "Crankback Signaling Extensions for MPLS and
GMPLS RSVP-TE", RFC 4920, DOI 10.17487/RFC4920, July 2007,
<https://www.rfc-editor.org/info/rfc4920>.

[RFC5553] Farrel, A., Ed., Bradford, R., and JP. Vasseur, "Resource
Reservation Protocol (RSVP) Extensions for Path Key
Support", RFC 5553, DOI 10.17487/RFC5553, May 2009,
<https://www.rfc-editor.org/info/rfc5553>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

5.2. Informative References

[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <https://www.rfc-editor.org/info/rfc2205>.

[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, DOI 10.17487/RFC4208, October 2005,
<https://www.rfc-editor.org/info/rfc4208>.

[RFC5251] Fedyk, D., Ed., Rekhter, Y., Ed., Papadimitriou, D.,
Rabbat, R., and L. Berger, "Layer 1 VPN Basic Mode",
RFC 5251, DOI 10.17487/RFC5251, July 2008,
<https://www.rfc-editor.org/info/rfc5251>.

Ali, et al. Standards Track [Page 23]

RFC 8390 RVSP-TE Path Diversity July 2018

[RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel,
"Preserving Topology Confidentiality in Inter-Domain Path
Computation Using a Path-Key-Based Mechanism", RFC 5520,
DOI 10.17487/RFC5520, April 2009,
<https://www.rfc-editor.org/info/rfc5520>.

[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<https://www.rfc-editor.org/info/rfc5920>.

[RFC8001] Zhang, F., Ed., Gonzalez de Dios, O., Ed., Margaria, C.,
Hartley, M., and Z. Ali, "RSVP-TE Extensions for
Collecting Shared Risk Link Group (SRLG) Information",
RFC 8001, DOI 10.17487/RFC8001, January 2017,
<https://www.rfc-editor.org/info/rfc8001>.

Acknowledgements

The authors would like to thank Xihua Fu for his contributions. The
authors also would like to thank Luyuan Fang and Walid Wakim for
their review and comments.

Contributors

Igor Bryskin
Huawei Technologies
Email: [email protected]

Daniele Ceccarelli
Ericsson
Email: [email protected]

Dhruv Dhody
Huawei Technologies
Email: [email protected]

Don Fedyk
Hewlett-Packard Enterprise
Email: [email protected]

Clarence Filsfils
Cisco Systems, Inc.
Email: [email protected]

Gabriele Maria Galimberti
Cisco Systems
Email: [email protected]

Ali, et al. Standards Track [Page 24]

RFC 8390 RVSP-TE Path Diversity July 2018

Ori Gerstel
SDN Solutions Ltd.
Email: [email protected]

Oscar Gonzalez de Dios
Telefonica I+D
Email: [email protected]

Matt Hartley
Cisco Systems
Email: [email protected]

Kenji Kumaki
KDDI Corporation
Email: [email protected]

Ruediger Kunze
Deutsche Telekom AG
Email: [email protected]

Lieven Levrau
Nokia
Email: [email protected]

Cyril Margaria
Email: [email protected]

Julien Meuric
France Telecom Orange
Email: [email protected]

Yuji Tochio
Fujitsu
Email: [email protected]

Xian Zhang
Huawei Technologies
Email: [email protected]

Ali, et al. Standards Track [Page 25]

RFC 8390 RVSP-TE Path Diversity July 2018

Authors' Addresses

Zafar Ali (editor)
Cisco Systems.

Email: [email protected]

George Swallow (editor)
Southend Technical Center

Email: [email protected]

Fatai Zhang (editor)
Huawei Technologies

Email: [email protected]

Dieter Beller (editor)
Nokia

Email: [email protected]

Ali, et al. Standards Track [Page 26]