draft-ietf-pce-path-key-00.txt   draft-ietf-pce-path-key-01.txt 
Networking Working Group Rich Bradford (Ed) Networking Working Group Rich Bradford (Ed)
Internet-Draft JP Vasseur Internet-Draft JP Vasseur
Cisco Systems, Inc. Cisco Systems, Inc.
Adrian Farrel Adrian Farrel
Old Dog Consulting Old Dog Consulting
Proposed Status: Standard Intended Status: Standards Track
Expires: November 1, 2007 Expires: March 12, 2008
May 1, 2007 September 12, 2007
draft-ietf-pce-path-key-00.txt draft-ietf-pce-path-key-01.txt
Preserving Topology Confidentiality in Inter-Domain Path Preserving Topology Confidentiality in Inter-Domain Path
Computation using a key based mechanism Computation Using a Key-Based Mechanism
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
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aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
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Bradford, Vasseur and Farrel 1 Bradford, Vasseur and Farrel 1
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). All rights reserved. Copyright (C) The IETF Trust (2007). All rights reserved.
Abstract Abstract
Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
Label Switched Paths (LSPs) may be computed by Path Computation Traffic Engineering (TE) Label Switched Paths (LSPs) may be
Elements (PCEs). Where the TE LSP crosses multiple domains, such computed by Path Computation Elements (PCEs). Where the TE LSP
as Autonomous Systems (ASs), the path may be computed by multiple crosses multiple domains, such as Autonomous Systems (ASes), the
PCEs that cooperate, with each responsible for computing a segment path may be computed by multiple PCEs that cooperate, with each
of the path. However, in some cases (e.g. when ASs are responsible for computing a segment of the path. However, in some
administered by separate Service Providers), it would break cases (e.g. when ASes are administered by separate Service
confidentiality rules for a PCE to supply a path segment to a PCE Providers), it would break confidentiality rules for a PCE to
in another domain, thus disclosing internal topology information. supply a path segment to a PCE in another domain, thus disclosing
This issue may be circumvented by returning a loose hop and by internal topology information. This issue may be circumvented by
invoking a new path computation from the domain boundary LSR returning a loose hop and by invoking a new path computation from
during TE LSP setup as the LSP enters the second domain, but this the domain boundary LSR during TE LSP setup as the signaling
technique has several issues including the problem of maintaining message enters the second domain, but this technique has several
path diversity. issues including the problem of maintaining path diversity.
This document defines a mechanism to hide the contents of a This document defines a mechanism to hide the contents of a
segment of a path, called the Confidential Path Segment (CPS). The segment of a path, called the Confidential Path Segment (CPS). The
CPS may be replaced by a path-key that can be conveyed in the PCE CPS may be replaced by a path-key that can be conveyed in the PCE
Communication Protocol (PCEP) and signaled within in a Resource Communication Protocol (PCEP) and signaled within in a Resource
Reservation Protocol (RSVP) explicit route object. Reservation Protocol TE (RSVP-TE) explicit route object.
Table of contents Table of contents
1. Terminology..................................................3 1. Terminology..................................................3
2. Introduction.................................................3 2. Introduction.................................................4
3. Path-Key Solution............................................5 3. Path-Key Solution............................................5
3.1. Mode of Operation...........................................5 3.1. Mode of Operation...........................................6
4. PCEP Protocol Extensions.....................................6 4. PCEP Protocol Extensions.....................................7
4.1. PKS sub-object..............................................6 4.1. PATH-KEY Object.............................................7
4.2. PKS bit.....................................................8 4.2. PKS subobject...............................................7
5. PCEP Mode of operation.......................................9 4.3. Path Key Bit...............................................10
6. Security Considerations......................................9 5. PCEP Mode of Operation......................................10
7. Manageability Considerations................................10 6. Security Considerations.....................................11
8. IANA considerations.........................................10 7. Manageability Considerations................................12
9. Intellectual Property Considerations........................11 7.1. Control of Function Through Configuration and Policy.......12
10. References.................................................11 7.2. Information and Data Models................................13
10.1. Normative References.....................................11 7.3. Liveness Detection and Monitoring..........................13
10.2. Informational References.................................12 7.4. Verifying Correct Operation................................14
11. Authors' Addresses:........................................12 7.5. Requirements on Other Protocols and Functional Components..14
7.6. Impact on Network Operation................................14
Bradford, Vasseur, and Farrel 2 Bradford, Vasseur, and Farrel 2
8. IANA Considerations.........................................15
8.1. New Subobjects for the ERO Object..........................15
8.2. New PCEP Object............................................15
8.3. New RP Object Bit Flag.....................................16
9. Intellectual Property Considerations........................16
10. References.................................................17
10.1. Normative References.....................................17
10.2. Informational References.................................17
11. Authors' Addresses:........................................18
Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
RFC-2119 [RFC2119]. RFC-2119 [RFC2119].
1. Terminology 1. Terminology
ASBR: border routers used to connect to another AS of a different AS: Autonomous System.
or the same Service Provider via one or more links inter-
connecting between ASs. ASBR: Autonomous System Border Routers used to connect to another
AS of a different or the same Service Provider via one or more
links inter-connecting between ASes.
CPS: Confidential Path Segment. A segment of a path that contains CPS: Confidential Path Segment. A segment of a path that contains
nodes and links that the AS policy requires to not be disclosed nodes and links that the AS policy requires to not be disclosed
outside the AS. outside the AS.
Inter-AS TE LSP: A TE LSP that crosses an AS boundary. Inter-AS TE LSP: A TE LSP that crosses an AS boundary.
LSR: Label Switching Router. LSR: Label Switching Router.
LSP: Label Switched Path. LSP: Label Switched Path.
PCC: Path Computation Client: any client application requesting a PCC: Path Computation Client: Any client application requesting a
path computation to be performed by a Path Computation Element. path computation to be performed by a Path Computation Element.
PCE: Path Computation Element: an entity (component, application PCE: Path Computation Element: An entity (component, application
or network node) that is capable of computing a network path or or network node) that is capable of computing a network path or
Bradford, Vasseur, and Farrel 3
route based on a network graph and applying computational route based on a network graph and applying computational
constraints. constraints.
TE LSP: Traffic Engineering Label Switched Path TE LSP: Traffic Engineering Label Switched Path
2. Introduction 2. Introduction
Path computation techniques using the Path Computation Element Path computation techniques using the Path Computation Element
(PCE) have been described in [PCE-ARCH] and allow for path (PCE) are described in [RFC4655] and allow for path computation of
computation of inter-domain Multiprotocol Label Switching (MPLS) inter-domain Multiprotocol Label Switching (MPLS) Traffic
traffic engineering (TE) Label Switched Paths (LSPs). Engineering (TE) and Generalized MPLS (GMPLS) Label Switched Paths
(LSPs).
Bradford, Vasseur, and Farrel 3
An important element of inter-domain TE is that TE information is An important element of inter-domain TE is that TE information is
not shared between domains for scalability and confidentiality not shared between domains for scalability and confidentiality
reasons ([RFC4105] and [RFC4216]). Therefore, a single PCE is reasons ([RFC4105] and [RFC4216]). Therefore, a single PCE is
unlikely to be able to compute a full inter-domain path. unlikely to be able to compute a full inter-domain path.
Two path computation scenarios can be used for inter-domain TE Two path computation scenarios can be used for inter-domain TE
LSPs: one using per-domain path computation (defined in [PD-PATH- LSPs: one using per-domain path computation (defined in [PD-PATH-
COMP]), and the other using a PCE-based path computation technique COMP]), and the other using a PCE-based path computation technique
with cooperation between PCEs (as described in [PCE-ARCH]). In with cooperation between PCEs (as described in [RFC4655]). In this
this second case, paths for inter-domain LSPs can be computed by second case, paths for inter-domain LSPs can be computed by
cooperation between PCEs each of which computes a segment of the cooperation between PCEs each of which computes a segment of the
path across one domain. Such a path computation procedure is path across one domain. Such a path computation procedure is
described in [BRPC]. described in [BRPC].
If confidentiality is required between domains (such as would very If confidentiality is required between domains (such as would very
likely be the case between ASs belonging to different Service likely be the case between ASes belonging to different Service
Providers) then cooperating PCEs cannot exchange path segments or Providers) then cooperating PCEs cannot exchange path segments or
else the receiving PCE and the Path Computation Client (PCC) will else the receiving PCE and the Path Computation Client (PCC) will
be able to see the individual hops through another domain thus non be able to see the individual hops through another domain thus
conforming to the confidentiality requirement stated in [RFC4105] breaking the confidentiality requirement stated in [RFC4105] and
and [RFC4216]. We define the part of the path which we wish to [RFC4216]. We define the part of the path which we wish to keep
keep confidential as the Confidential Path Segment (CPS). confidential as the Confidential Path Segment (CPS).
One mechanism for preserving the confidentiality of the CPS is for One mechanism for preserving the confidentiality of the CPS is for
the PCE to return a path containing a loose hop for the segment the PCE to return a path containing a loose hop in place of the
internal to a domain that must be kept confidential. The concept segment that must be kept confidential. The concept of loose and
of loose hops for the route of a TE LSP is described in [RFC3209]. strict hops for the route of a TE LSP is described in [RFC3209].
The Path Computation Element Communication Protocol (PCEP) defined The Path Computation Element Communication Protocol (PCEP) defined
in [PCEP] supports the use of paths with loose hops, and it is a in [PCEP] supports the use of paths with loose hops, and it is a
local policy decision at a PCE whether it returns a full explicit local policy decision at a PCE whether it returns a full explicit
path or uses loose hops. Note that a Path computation Request may path with strict hops or uses loose hops. Note that a Path
request a loose or explicit path as detailed in [PCEP]. computation Request may request an explicit path with strict hops
or may allow loose hops as detailed in [PCEP].
One option may consist of returning loose hop without further Bradford, Vasseur, and Farrel 4
extensions: if loose hops are used, the TE LSPs are signaled as The option of returning a loose hop in place of the CPS can be
achieved without further extensions to PCEP or the signaling
protocol. If loose hops are used, the TE LSPs are signaled as
normal ([RFC3209]), and when a loose hop is encountered in the normal ([RFC3209]), and when a loose hop is encountered in the
explicit route it is resolved by performing a secondary path explicit route it is resolved by performing a secondary path
computation to reach the next loose hop. Given the nature of the computation to reach the resource or set of resources identified
cooperation between PCEs in computing the original path, this by the loose hop. Given the nature of the cooperation between PCEs
secondary computation occurs at a Label Switching Router (LSR) at in computing the original path, this secondary computation occurs
a domain boundary (i.e. an ABR or ASBR) and the path is expanded at or on behalf of a Label Switching Router (LSR) at a domain
as described in [PD-PATH-COMP]. boundary (i.e., an ABR or ASBR) and the path is expanded as
described in [PD-PATH-COMP].
The PCE-based computation model is particularly useful for The PCE-based computation model is particularly useful for
determining mutually disjoint inter-domain paths such as might be determining mutually disjoint inter-domain paths such as might be
required for service protection. A single path computation request required for service protection [INTER-DOM-REC]. A single path
is used. However, if loose hops are returned, the path of each TE computation request is used. However, if loose hops are returned,
the path of each TE LSP must be recomputed at the domain
Bradford, Vasseur, and Farrel 4 boundaries as the TE LSPs are signaled, and since the TE LSP
LSP must be recomputed at the domain boundaries as the TE LSPs are signaling proceeds independently for each TE LSP, disjoint paths
signaled, and since the TE LSP signaling proceeds independently cannot be guaranteed since the LSRs in charge of expanding the
for each TE LSP, disjoint paths cannot be guaranteed since the EROs are not synchronized. Therefore, if the loose hop technique
LSRs in charge of expanding the EROs are not synchronized. is used without further extensions, path segment confidentiality
Therefore, using the loose hop technique without further and path diversity are mutually incompatible requirements.
extensions, path segment confidentiality and path diversity are
mutually incompatible requirements.
This document defines the notion of a Path Key that is a token This document defines the notion of a Path Key that is a token
that replaces a path segment in an explicit route. The Path Key is that replaces a path segment in an explicit route. The Path Key is
encoded as a Path Key Sub-object (PKS) returned in the PCEP Path encoded as a Path Key Subobject (PKS) returned in the PCEP Path
Computation Reply message (PCReq) ([PCEP]). Upon receiving the Computation Reply message (PCRep) ([PCEP]). Upon receiving the
computed path, the PKS sub-object will be carried out in an RSVP- computed path, the PKS will be carried in an RSVP-TE Path message
TE Path message (RSVP-TE [RFC3209]) during signaling. The PKS may (RSVP-TE [RFC3209] and [RSVP-PKS]) during signaling.
also, optionally, be used in recorded routes in RSVP-TE.
3. Path-Key Solution 3. Path-Key Solution
The Path-Key solution may be applied in the PCE-based path The Path-Key solution may be applied in the PCE-based path
computation context as follows. A PCE computes a path segment computation context as follows. A PCE computes a path segment
related to a particular domain and replaces it in the path related to a particular domain and replaces any CPS in the path
reported to the requesting PCC (or another PCE) by one or more reported to the requesting PCC (or another PCE) by one or more
sub-objects referred to as the PKS. The entry and boundary LSR of subobjects referred to as PKSes. The entry boundary LSR of each
each CPS SHOULD be specified as hops in the returned path CPS SHOULD be specified as a hop in the returned path immediately
immediately preceding the PKS, but where two PKSs are supplied in preceding the CPS, but where two PKSes are supplied in sequence
sequence the entry node to the second MAY be encoded within the with no intervening nodes, the entry node to the second CPS MAY be
first. The exit node of a CPS MAY be present as a strict hop part of the first CPS and does not need to be explicitly present
immediately following the PKS, but MAY also be hidden as part of in the returned path. The exit node of a CPS MAY be present as a
the PKS. strict hop immediately following the PKS.
Bradford, Vasseur, and Farrel 5
3.1. Mode of Operation 3.1. Mode of Operation
During path computation, when local policy dictates that During path computation, when local policy dictates that
confidentiality must be preserved for all or part of the path confidentiality must be preserved for all or part of the path
segment being computed or if explicitly requested by the Path segment being computed or if explicitly requested by the Path
Computation Request, the PCE associates a path-key with the Computation Request, the PCE associates a path-key with the
computed path for the CPS, places its own identifier (its PCE-ID computed path for the CPS, places its own identifier (its PCE ID
as defined in [PCE-MONITORING]) along with the path-key in a PKS, as defined in section 4.2. ) along with the path-key in a PKS, and
and inserts the PKS object in the path returned to the requesting inserts the PKS object in the path returned to the requesting PCC
PCC or PCE immediately after the IPv4 sub-object defined in or PCE immediately after the IPv4 subobject defined in [RFC3209]
[RFC3209] sub-object that identifies the LSR that will expand the subobject that identifies the LSR that will expand the PKS into a
PKS into a explicit path hops. This will usually be the LSR that explicit path hops. This will usually be the LSR that is the start
is the start point of the CPS. The PCE that generates a PKS MUST point of the CPS. The PCE that generates a PKS SHOULD store the
computed path segment and the path-key for later retrieval. A
Bradford, Vasseur, and Farrel 5 local policy SHOULD be used to determine for how long to retain
store the computed path segment and the path-key for later such stored information, and whether to discard the information
retrieval. A local policy SHOULD be used to determine for how long after it has been queried using the procedures described below. It
to retain such stored information, and whether to discard the is RECOMMENDED for a PCE to store the PKS for a period of 10
information after it has been queried using the procedures minutes.
described below. It is RECOMMENDED for a PCE to strore the PKS for
a period of 10 minutes.
TBD: Need to define the scope of the PKS and spell out the A path-key value is scoped to the PCE that computed it as
restrictions on Path Key re-use. identified by the PCE-ID carried in the PKS. A PCE MUST NOT re-use
a path-key value to represent a new CPS for at least 30 minutes
after discarding the previous use of the same path-key. A PCE that
is unable to retain information about previously used path-key
values over a restart SHOULD use some other mechanism to guarantee
uniqueness of path-key values such as embedding a timestamp or
version number in the path-key.
A head-end LSR that is a PCC converts the path returned by a PCE A head-end LSR that is a PCC converts the path returned by a PCE
into an explicit route object (ERO) that it includes in the into an explicit route object (ERO) that it includes in the
Resource Reservation Protocol (RSVP) Path message. If the path Resource Reservation Protocol (RSVP) Path message. If the path
returned by the PCE contains PKSs these are included in the ERO. returned by the PCE contains a PKS, this is included in the ERO.
Like any other sub-objects, the PKS is passed transparently from Like any other subobjects, the PKS is passed transparently from
hop to hop, until it becomes the first sub-object in the ERO. This hop to hop, until it becomes the first subobject in the ERO. This
will occur at the start of the CPS which will usually be the will occur at the start of the CPS which will usually be the
domain boundary. The PKS MUST be preceded by an ERO sub-object domain boundary. The PKS MUST be preceded by an ERO subobject that
that identifies the LSR that must expand the PKS, so the PKS will identifies the LSR that must expand the PKS, so the PKS will not
not be encountered in ERO processing until the LSR that can be encountered in ERO processing until the LSR that can process
process it. it.
An LSR that encounters a PKS when trying to identify the next-hop An LSR that encounters a PKS when trying to identify the next-hop
retrieves the PCE-ID from the PKS and sends a Path Computation retrieves the PCE-ID from the PKS and sends a Path Computation
Request (PCReq) message as defined in [PCEP] to the PCE identified Request (PCReq) message as defined in [PCEP] to the PCE identified
by the PCE-ID that contains the path-key object . by the PCE-ID that contains the path-key object .
Bradford, Vasseur, and Farrel 6
Upon receiving the PCReq message, the PCE identifies the computed Upon receiving the PCReq message, the PCE identifies the computed
path segment using the supplied path-key, and returns the path segment using the supplied path-key, and returns the
previously computed path segment in the form of explicit hops previously computed path segment in the form of explicit hops
using an ERO object contained in the Path Computation Reply using an ERO object contained in the Path Computation Reply
(PCReqp) as define in [PCEP] to the requesting node. The (PCReqp) to the requesting node as defined in [PCEP]. The
requesting node inserts the explicit hops into the ERO and requesting node inserts the explicit hops into the ERO and
continues to process the TE LSP setup as per [RFC3209]. continues to process the TE LSP setup as per [RFC3209].
4. PCEP Protocol Extensions 4. PCEP Protocol Extensions
4.1. PKS sub-object 4.1. PATH-KEY Object
When a PCC needs to expand a path-key in order to expand a CPS it
issues a path computation request (PCReq) to the PCE identified in the
PKS in the RSVP-TE ERO that it is processing. The PCC supplies the PKS
to be expanded in a PATH-KEY Object in the PCReq message.
Bradford, Vasseur, and Farrel 6 The PATH-KEY Object is defined as follows.
The PKS object format is identical as in [RSVP-PKS] but redefined
in the context of this document since a PCEP codepoint is
required.
The PKS is a fixed-length sub-object containing a Path-Key and a PATH-KEY Object-Class is to be assigned by IANA (recommended
value=16)
Path Key Object-Type is to be assigned by IANA (recommended value=1)
The PATH-KEY Object MUST contain at least one Path Key Subobject
(see Section 4.2). The first PKS MUST be processed by the PCE.
Subsequent subobjects SHOULD be ignored.
4.2. PKS subobject
The PKS is identical in format to that defined for RSVP-TE
signaling in [RSVP-PKS], but is redefined in the context of this
document since a PCEP codepoint is required.
The PKS is a fixed-length subobject containing a Path-Key and a
PCE-ID. The Path Key is an identifier, or token used to represent PCE-ID. The Path Key is an identifier, or token used to represent
the CPS within the context of the PCE identified by the PCE-ID. the CPS within the context of the PCE identified by the PCE-ID.
The PCE-ID identifies the PCE that can decode the Path Key using a The PCE-ID identifies the PCE that can decode the Path Key using
reachable IPv4 or IPv6 address of the PCE.
Because of the IPv4 and IPv6 variants, two sub-objects are defined Bradford, Vasseur, and Farrel 7
as follows. an identifier that is unique within the domain that the PCE
serves. The PCE-ID has to be mapped to a reachable IPv4 or IPv6
address of the PCE by the first node of the CPS (usually a domain
border router) and a PCE MAY use one of its reachable IP addresses
as its PCE-ID. Alternatively and to provide greater security (see
Section 6), according to domain-local policy, the PCE MAY use some
other identifier that is scoped only within the domain.
PKS IPv4 sub-object To allow IPv4 and IPv6 addresses to be carried, two subobjects are
defined as follows.
PKS Object-Class is to be assigned by IANA (recommended value=16) The Path Key Subobject may be present in the PCEP ERO or the PCEP
PATH-KEY object.
PKS Object-Type is to be assigned by IANA (recommended value=1) PKS with 32-bit PCE ID
The PKS with 32-bit PCE ID Type is to be assigned by IANA
(recommended value 64)
0 1 2 3 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 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| Type | Length | Path Key | |L| Type | Length | Path Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address (4 bytes) | | PCE ID (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L L
The L bit SHOULD NOT be set, so that the sub-object The L bit SHOULD NOT be set, so that the subobject
represents a strict hop in the explicit route. represents a strict hop in the explicit route.
Type Type
TBD Path Key with IPv4 address TBD Path Key with 32-bit PCE ID
Length Length
The Length contains the total length of the subobject in The Length contains the total length of the subobject in
bytes, including the Type and Length fields. The Length is always bytes, including the Type and Length fields. The Length
8. is always 8.
IPv4 address
An IPv4 address of the PCE that can decode this key. The
address used SHOULD be an address of the PCE that is always
Bradford, Vasseur, and Farrel 7 PCE ID
reachable, and MAY be an address that is restricted to the domain
in which the LSR that is called upon to expand the CPS lies.
PKS IPv6 sub-object Bradford, Vasseur, and Farrel 8
A 32-bit identifier of the PCE that can decode this key. The
identifier MUST be unique within the scope of the domain
that the CPS crosses, and MUST be understood by the LSR that
will act as PCC for the expansion of the PKS. The
interpretation of the PCE-ID is subject to domain-local
policy. It MAY be an IPv4 address of the PCE that is always
reachable, and MAY be an address that is restricted to the
domain in which the LSR that is called upon to expand the
CPS lies. Other values that have no meaning outside the
domain (for example, the Router ID) MAY be used to increase
security (see Section 6).
PKS Object-Class is to be assigned by IANA (recommended value=16) PKS with 128-bit PCE ID
PKS Object-Type is to be assigned by IANA (recommended value=2) The PKS with 128-bit PCE ID Type is to be assigned by IANA
(recommended value 65)
0 1 2 3 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 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| Type | Length | Path Key | |L| Type | Length | Path Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address (16 bytes) | | PCE ID (16 bytes) |
| | | |
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L L
As above. As above.
Type Type
TBD Path Key with IPv6 address TBD Path Key with 128-bit PCE ID
Length Length
The Length contains the total length of the subobject in The Length contains the total length of the subobject in
bytes, including the Type and Length fields. The Length is always bytes, including the Type and Length fields. The Length
20. is always 20.
IPv6 address PCE ID
An IPv6 address of the PCE that can decode this key. The Bradford, Vasseur, and Farrel 9
address used SHOULD be an address of the PCE that is always A 128-bit identifier of the PCE that can decode this key.
reachable, but MAY be an address that is restricted to the domain The identifier MUST be unique within the scope of the
in which the LSR that is called upon to expand the CPS lies. domain that the CPS crosses, and MUST be understood by the
LSR that will act as PCC for the expansion of the PKS. The
interpretation of the PCE-ID is subject to domain-local
policy. It MAY be an IPv6 address of the PCE that is
always reachable, but MAY be an address that is restricted
to the domain in which the LSR that is called upon to
expand the CPS lies. Other values that have no meaning
outside the domain (for example, the IPv6 TE Router ID)
MAY be used to increase security (see Section 6).
4.2. PKS bit 4.3. Path Key Bit
[PCEP] specifies the RP object that is used to specify various [PCEP] defines the Request Parameters (RP) object that is used to
characteristics of the path computation request. specify various characteristics of the path computation request.
Bradford, Vasseur, and Farrel 8 In this document we define a new bit named the Path Key bit
In this document we define a new bit named the PKS bit defined as defined as follow:
follow:
PKS (PKS - 1 bit - Value=0x60): when set, the requesting PCC Path Key (P-bit - 1 bit - Value=0x80): When set, the requesting
requires the retrieval of a strict path segment that corresponds PCC requires the retrieval of a strict path segment that
to a PKS carried within the path computation request. The PKS bit corresponds to a PKS carried in a PATH_KEY object in the path
MUST be cleared when the path computation request is not related computation request. The Path Key bit MUST be cleared when the
to a CPS retrieval. path computation request is not related to a CPS retrieval.
5. PCEP Mode of operation 5. PCEP Mode of Operation
The retrieval of the explicit path associated with a PKS by a PCC The retrieval of the explicit path (the CPS) associated with a PKS
is no different than any other path computation request with the by a PCC is no different than any other path computation request
exception that the PCReq message MUST contain a PKS object and the with the exception that the PCReq message MUST contain a PATH_KEY
PKS bit of the RP object MUST the set. object and the Path Key bit of the RP object MUST the set.
If the receiving PCE cannot find any related strict path or the If the receiving PCE does not recognize itself as identified by the
retrieval of such strict path is not allowed by policy, the PCE PCE ID carried in the PKS it MAY forward the PCReq message to
MUST send a PCRep message that contains a NO-PATH object. another PCE according to local policy. If the PCE does not forward
such a PCReq, it MUST respond with a PCRep message containing a NO-
PATH object.
Upon receipt of this negative reply, the requesting LSR MUST fail If the receiving PCE recognizes itself, but cannot find the
the LSP setup and SHOULD use the procedures associated with loose related CPS, or if the retrieval of the CPS is not allowed by
hop expansion failure [RFC3209]. policy, the PCE MUST send a PCRep message that contains a NO-PATH
object.
Bradford, Vasseur, and Farrel 10
Upon receipt of a negative reply, the requesting LSR MUST fail the
LSP setup and SHOULD use the procedures associated with loose hop
expansion failure [RFC3209].
6. Security Considerations 6. Security Considerations
This document proposes tunneling secure topology information This document describes tunneling confidential path information
across an untrusted AS, so the security considerations are many across an untrusted domain (such as an AS). There are many
and apply to PCEP and RSVP-TE. security considerations that apply to PCEP and RSVP-TE.
Issues include: Issues include:
- Security of the CPS (can other network elements probe for - Confidentiality of the CPS (can other network elements probe for
expansion of path-keys, possibly at random?). expansion of path-keys, possibly at random?).
- Authenticity of the path-key (resilience to alteration by - Authenticity of the path-key (resilience to alteration by
intermediaries, resilience to fake expansion of path-keys). intermediaries, resilience to fake expansion of path-keys).
- Resilience from DNS attacks (insertion of spurious path-keys; - Resilience from DNS attacks (insertion of spurious path-keys;
flooding of bogus path-key expansion requests). flooding of bogus path-key expansion requests).
Most of the interactions required by this extension are point to Most of the interactions required by this extension are point to
point, can be authenticated and made secure. These interactions point, can be authenticated and made secure. These interactions
include the: include the:
- PCC->PCE request - PCC->PCE request
Bradford, Vasseur, and Farrel 9
- PCE->PCE request(s) - PCE->PCE request(s)
- PCE->PCE response(s) - PCE->PCE response(s)
- PCE->PCC response - PCE->PCC response
- LSR->LSR request and response (Note that a rogue LSR could - LSR->LSR request and response (Note that a rogue LSR could
modify the ERO and insert or modify Path Keys. This would modify the ERO and insert or modify Path Keys. This would
result in an LSR (which is downstream in the ERO) sending result in an LSR (which is downstream in the ERO) sending
decode requests to a PCE. This is actually a larger problem decode requests to a PCE. This is actually a larger problem
with RSVP. The rogue LSR is an existing issue with RSVP and with RSVP. The rogue LSR is an existing issue with RSVP and
will not be addressed here. will not be addressed here.
- LSR->PCE request. Note that the PCE can check that the LSR - LSR->PCE request. Note that the PCE can check that the LSR
requesting the decode is the LSR at the head of the Path Key. requesting the decode is the LSR at the head of the Path Key.
This largely contains the previous problem to DoS rather than This largely contains the previous problem to DoS rather than
a security issue. A rogue LSR can issue random decode a security issue. A rogue LSR can issue random decode
requests, but these will amount only to DoS. requests, but these will amount only to DoS.
- PCE->LSR response. - PCE->LSR response.
Bradford, Vasseur, and Farrel 11
Thus, the major security issues can be dealt with using standard Thus, the major security issues can be dealt with using standard
techniques for securing and authenticating pt-pt links. In techniques for securing and authenticating point-to-point
addition, it is recommended that the PCE providing a decode communications. In addition, it is recommended that the PCE
response should check that the LSR that issued the decode request providing a decode response should check that the LSR that issued
is the head end of the decoded ERO segment. the decode request is the head end of the decoded ERO segment.
Further protection can be provided by using a PCE ID to identify the
decoding PCE that is only meaningful within the domain that contains
the LSR at the head of the CPS. This may be an IP address that is only
reachable from within the domain, or some not-address value. The former
requires configuration of policy on the PCEs, the latter requires
domain-wide policy.
7. Manageability Considerations 7. Manageability Considerations
To be detailed in a further revision of this document. 7.1. Control of Function Through Configuration and Policy
8. IANA considerations The treatment of a path segment as a CPS, and its substitution in
a PCReq ERO with a PKS, is a function that MUST be under operator
and policy control where a PCE supports the function. The operator
MUST be given the ability to specify which path segments are to be
replaced and under what circumstances. For example, an operator
might set a policy that states that every path segment for the
operator's domain will be replaced by a PKS when the PCReq has
been issued from outside the domain.
IANA assigns value to PCEP parameters. Each PCEP object has an The operation of the PKS extensions require that path-keys are
Object-Class and an Object-Type. retained by the issuing PCE to be available for retrieval by an
LSR (acting as a PCC) at a later date. But it is possible that the
retrieval request will never be made, so good housekeeping
requires that a timer is run to discard unwanted path-keys. A
default value for this timer is suggested in the body of this
document. Implementations SHOULD provide the ability for this
value to be over-ridden through operator configuration or policy.
Two new PCEP objects are defined in this document: the IPv4 PKS After a PKS has been expanded in response to a retrieval request,
and the IPv6 PKS objects. it may be valuable to retain the path-key and CPS for debug
purposes. Such retention SHOULD NOT be the default behavior of an
implementation, but MAY be available in response to operator
request.
Object-Class Name Once a path-key has been discarded, the path-key value SHOULD not
be immediately available for re-use for a new CPS since this might
16 PKS IPv4 Bradford, Vasseur, and Farrel 12
Object-Type lead to accidental misuse. A default timer value is suggested in
1 the body of this document. Implementations SHOULD provide the
ability for this value to be over-ridden through operator
configuration or policy.
Bradford, Vasseur, and Farrel 10 A PCE must set a PCE-ID value in each PKS it creates so that PCCs
16 PKS IPv6 can correctly identify it and send PCReq messages to expand the
Object-Type PKS to a path segment. A PCE implementation SHOULD allow operator
2 or policy control of the value to use as the PCE-ID. If the PCE
allows PCE-ID values that are not routable addresses to be used,
the PCCs MUST be configurable (by the operator or through policy)
to allow them to map from the PCE-ID to a routable address of the
PCE. Such mapping may be algorithmic, procedural (for example,
mapping a PCE-ID equal to the IGP Router ID into a routable
address), or configured through a local or remote mapping table.
7.2. Information and Data Models
A MIB module for PCEP is already defined in [PCEP-MIB]. The
configurable items listed in Section 7.1 MUST be added as readable
objects in the module and SHOULD be added as writable objects.
A new MIB module MUST be created to allow inspection of path-keys.
For a given PCE, this MIB module MUST provide a mapping from path-
key to path segment (that is, a list of hops), and MUST supply
other information including:
- The identity of the PCC that issued the original request that
led to the creation of the path-key.
- The request ID of the original PCReq.
- Whether the path-key has been retrieved yet, and if so, by which
PCC.
- How long until the path segment associated with the path-key
will be discarded.
- How long until the path-key will be available for re-use.
7.3. Liveness Detection and Monitoring
The procedures in this document extend PCEP, but do not introduce
new interactions between network entities. Thus, no new liveness
detection or monitoring is required.
It is possible that a head-end LSR that has be given a path
including PKSs replacing specific CPSs will want to know whether
the path-keys are still valid (or have timed out). However, rather
Bradford, Vasseur, and Farrel 13
than introduce a mechanism to poll the PCE that is responsible for
the PKS, it is considered pragmatic to simply signal the
associated LSP.
7.4. Verifying Correct Operation
The procedures in this document extend PCEP, but do not introduce
new interactions between network entities. Thus, no new tools for
verifying correct operation are required.
A PCE SHOULD maintain counters and logs of the following events
that might indicate incorrect operation (or might indicate
security issues).
- Attempts to expand an unknown path-key.
- Attempts to expand an expired path-key.
- Duplicate attempts to expand the same path-key.
- Expiry of path-key without attempt to expand it.
7.5. Requirements on Other Protocols and Functional Components
The procedures described in this document require that the LSRs
signal PKSs as defined in [RSVP-PKS]. Note that the only changes
to LSRs are at the PCCs. Specifically, changes are only needed at
the head-end LSRs that build RSVP-TE Path messages containing
Path-Key Subobjects in their EROs, and the LSRs that discover such
subobjects as next hops and must expand them. Other LSRs in the
network, even if they are on the path of the LSP, will not be
called upon to process the PKS.
7.6. Impact on Network Operation
As well as the security and confidentiality aspects addressed by
the use of the PKS, there may be some scaling benefits associated
with the procedures described in this document. For example, a
single PKS in an explicit route may substitute for many subobjects
and can reduce the overall message size correspondingly. In some
circumstances, such as when the explicit route contains multiple
subobjects for each hop (including node IDs, TE link IDs,
component link IDs for each direction of a bidirectional LSP, and
label IDs for each direction of a bidirectional LSP) or when the
LSP is a point-to-multipoint LSP, this scaling improvement may be
very significant.
Bradford, Vasseur, and Farrel 14
Note that a PCE will not supply a PKS unless it is knows that the
LSR that will receive the PKS through signaling will be able to
handle it. Furthermore, as noted in Section 7.5, only those LSRs
specifically called upon to expand the PKS will be required to
process the subobjects during signaling. Thus, the only backward
compatibility issues associated with the procedures introduced in
this document arise when a head-end LSR receives a PCRep with an
ERO containing a PKS and does not know how to encode this into
signaling.
Since the PCE that inserted the PKS requires to keep the CPS
confidential, the legacy head-end LSR cannot be protected. It must
either fail the LSP setup, or request a new path computation
avoiding the domain that has supplied it with unknown subobjects.
8. IANA Considerations
IANA assigns value to PCEP parameters in registries defined in
[PCEP]. IANA is requested to make the following additional
assignments.
8.1. New Subobjects for the ERO Object
IANA has previously assigned an Object-Class and Object-Type to
the ERO carried in PCEP messages [PCEP]. IANA also maintains a
list of subobject types valid for inclusion in the ERO.
IANA is requested to assign two new subobject types for inclusion
in the ERO as follows:
7 ERO 1 Explicit route [PCEP]
Subobject Type
64 Path Key with 32-bit PCE ID [This.I-D]
65 Path Key with 128-bit PCE ID [This.I-D]
8.2. New PCEP Object
IANA is requested to assign a new object class in the registry of
PCEP Objects as follows.
Bradford, Vasseur, and Farrel 15
Object Name Object Name Reference
Class Type
16 PATH-KEY 1 Path Key [This.I-D]
Subobjects
This object may carry the following subobjects as defined
for the ERO object.
64 Path Key with 32-bit PCE ID [This.I-D]
65 Path Key with 128-bit PCE ID [This.I-D]
8.3. New RP Object Bit Flag
IANA maintains a registry of bit flags carried in the PCEP RP
object as defined in [PCEP]. IANA is requested to define a new bit
flag as follows:
Bit Hex Name Reference
Number
09 0x0080 Path Key (P-bit) [This.I-D]
9. Intellectual Property Considerations 9. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology to pertain to the implementation or use of the technology
described in this document or the extent to which any license described in this document or the extent to which any license
under such rights might or might not be available; nor does it under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any represent that it has made any independent effort to identify any
such rights. Information on the procedures with respect to rights such rights. Information on the procedures with respect to rights
skipping to change at line 470 skipping to change at line 713
of such proprietary rights by implementers or users of this of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr. at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be required proprietary rights that may cover technology that may be required
to implement this standard. Please address the information to the to implement this standard. Please address the information to the
IETF at ietf-ipr@ietf.org. IETF at ietf-ipr@ietf.org.
Bradford, Vasseur, and Farrel 16
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V. [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC
3209, December 2001. 3209, December 2001.
[PCEP] Vasseur, J.P., Le Roux, J.L., Ayyangar, A., Oki, E., [PCEP] Vasseur, J.P., Le Roux, J.L., Ayyangar, A., Oki, E.,
Bradford, Vasseur, and Farrel 11
Ikejiri, A., Atlas, A., Dolganow, A., "Path Computation Element Ikejiri, A., Atlas, A., Dolganow, A., "Path Computation Element
(PCE) communication Protocol (PCEP)", draft-vasseur-pce-pcep, (PCE) communication Protocol (PCEP)", draft-ietf-pce-pcep,
work in progress. work in progress.
10.2. Informational References
[RSVP-PKS] Bradford, R., Vasseur, J.P., Farrel, A., "RSVP [RSVP-PKS] Bradford, R., Vasseur, J.P., Farrel, A., "RSVP
Extensions for Path Key Support", draft-bradford-ccamp-path-key- Extensions for Path Key Support", draft-bradford-ccamp-path-key-
ero, work in progress. ero, work in progress.
[PCE-MONITORING] Vasseur, J.P, "A set of monitoring tools for Path [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Computation Element based Architecture", draft-vasseur-pce-
monitoring, work in progress.
10.2. Informational References
[PCE-ARCH] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE) Architecture", RFC4655, September 2006. Element (PCE) Architecture", RFC4655, September 2006.
[PD-PATH-COMP] Vasseur, J., et al "A Per-domain path computation [PD-PATH-COMP] Vasseur, J., et al "A Per-domain path computation
method for establishing Inter-domain Traffic Engineering (TE) method for establishing Inter-domain Traffic Engineering (TE)
Label Label
Switched Paths (LSPs)", draft-ietf-ccamp-inter-domain-pd-path- Switched Paths (LSPs)", draft-ietf-ccamp-inter-domain-pd-path-
comp, work in progress. comp, work in progress.
[BRPC] Vasseur, J., et al "A Backward Recursive PCE-based [BRPC] Vasseur, J., et al "A Backward Recursive PCE-based
Computation Computation
skipping to change at line 520 skipping to change at line 758
Engineering Label Switched Path", draft-ietf-pce-brpc, work in Engineering Label Switched Path", draft-ietf-pce-brpc, work in
progress. progress.
[RFC4105] Le Roux, J., Vasseur, JP, Boyle, J., "Requirements [RFC4105] Le Roux, J., Vasseur, JP, Boyle, J., "Requirements
for Support of Inter-Area and Inter-AS MPLS Traffic Engineering", for Support of Inter-Area and Inter-AS MPLS Traffic Engineering",
RFC 4105, June 2005. RFC 4105, June 2005.
[RFC4216] Zhang, R., Vasseur, JP., et. al., "MPLS Inter-AS [RFC4216] Zhang, R., Vasseur, JP., et. al., "MPLS Inter-AS
Traffic Engineering requirements", RFC 4216, November 2005. Traffic Engineering requirements", RFC 4216, November 2005.
Bradford, Vasseur, and Farrel 17
[INTER-DOM-REC] Takeda, T., et al, "Analysis of Inter-domain Label
Switched Path (LSP) Recovery", draft-ietf-ccamp-inter-domain-
recovery-analysis, work in progress.
[PCEP-MIB] Kiran Koushik, A., and Stephan, E., "PCE communication
protocol (PCEP) Management Information Base", draft-kkoushik-pce-
pcep-mib, work in progress.
11. Authors' Addresses: 11. Authors' Addresses:
Rich Bradford (Editor) Rich Bradford (Editor)
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Avenue 1414 Massachusetts Avenue
Boxborough , MA - 01719 Boxborough , MA - 01719
Bradford, Vasseur, and Farrel 12
USA USA
Email: rbradfor@cisco.com EMail: rbradfor@cisco.com
J.-P Vasseur J.-P Vasseur
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Avenue 1414 Massachusetts Avenue
Boxborough , MA - 01719 Boxborough , MA - 01719
USA USA
Email: jpv@cisco.com EMail: jpv@cisco.com
Adrian Farrel Adrian Farrel
Old Dog Consulting Old Dog Consulting
EMail: adrian@olddog.co.uk EMail: adrian@olddog.co.uk
Bradford, Vasseur, and Farrel 18
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Bradford, Vasseur, and Farrel 13
Intellectual Property Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at line 584 skipping to change at line 829
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Bradford, Vasseur, and Farrel 14 Bradford, Vasseur, and Farrel 19
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