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rfc:rfc5089

Network Working Group JL. Le Roux, Ed. Request for Comments: 5089 France Telecom Category: Standards Track JP. Vasseur, Ed.

                                                     Cisco System Inc.
                                                            Y. Ikejiri
                                                    NTT Communications
                                                              R. Zhang
                                                                    BT
                                                          January 2008
                   IS-IS Protocol Extensions for
             Path Computation Element (PCE) Discovery

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 There are various circumstances where it is highly desirable for a
 Path Computation Client (PCC) to be able to dynamically and
 automatically discover a set of Path Computation Elements (PCEs),
 along with information that can be used by the PCC for PCE selection.
 When the PCE is a Label Switching Router (LSR) participating in the
 Interior Gateway Protocol (IGP), or even a server participating
 passively in the IGP, a simple and efficient way to announce PCEs
 consists of using IGP flooding.  For that purpose, this document
 defines extensions to the Intermediate System to Intermediate System
 (IS-IS) routing protocol for the advertisement of PCE Discovery
 information within an IS-IS area or within the entire IS-IS routing
 domain.

Le Roux, et al. Standards Track [Page 1] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

Table of Contents

 1. Introduction ....................................................2
 2. Terminology .....................................................4
 3. Overview ........................................................5
    3.1. PCE Discovery Information ..................................5
    3.2. Flooding Scope .............................................5
 4. The IS-IS PCED Sub-TLV ..........................................5
    4.1. PCE-ADDRESS Sub-TLV ........................................6
    4.2. The PATH-SCOPE Sub-TLV .....................................7
    4.3. PCE-DOMAIN Sub-TLV .........................................9
    4.4. NEIG-PCE-DOMAIN Sub-TLV ...................................10
    4.5. PCE-CAP-FLAGS Sub-TLV .....................................10
 5. Elements of Procedure ..........................................11
 6. Backward Compatibility .........................................12
 7. IANA Considerations ............................................12
 8. Security Considerations ........................................12
 9. Manageability Considerations ...................................13
    9.1. Control of Policy and Functions ...........................13
    9.2. Information and Data Model ................................13
    9.3. Liveness Detection and Monitoring .........................13
    9.4. Verify Correct Operations .................................13
    9.5. Requirements on Other Protocols and Functional
         Components ................................................13
    9.6. Impact on Network Operations ..............................14
 10. Acknowledgments ...............................................14
 11. References ....................................................15
    11.1. Normative References .....................................15
    11.2. Informative References ...................................15

1. Introduction

 [RFC4655] describes the motivations and architecture for a Path
 Computation Element (PCE)-based path computation model for
 Multi-Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
 Traffic Engineered Label Switched Paths (TE LSPs).  The model allows
 for the separation of the PCE from a Path Computation Client (PCC)
 (also referred to as a non co-located PCE) and allows for cooperation
 between PCEs (where one PCE acts as a PCC to make requests of the
 other PCE).  This relies on a communication protocol between a PCC
 and PCE, and also between PCEs.  The requirements for such a
 communication protocol can be found in [RFC4657], and the
 communication protocol is defined in [PCEP].
 The PCE architecture requires that a PCC be aware of the location of
 one or more PCEs in its domain, and, potentially, of PCEs in other
 domains, e.g., in the case of inter-domain TE LSP computation.

Le Roux, et al. Standards Track [Page 2] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 A network may contain a large number of PCEs, each with potentially
 distinct capabilities.  In such a context, it is highly desirable to
 have a mechanism for automatic and dynamic PCE discovery that allows
 PCCs to automatically discover a set of PCEs, along with additional
 information about each PCE that may be used by a PCC to perform PCE
 selection.  Additionally, it is valuable for a PCC to dynamically
 detect new PCEs, failed PCEs, or any modification to the PCE
 information.  Detailed requirements for such a PCE discovery
 mechanism are provided in [RFC4674].
 Note that the PCE selection algorithm applied by a PCC is out of the
 scope of this document.
 When PCCs are LSRs participating in the IGP (OSPF or IS-IS), and PCEs
 are either LSRs or servers also participating in the IGP, an
 effective mechanism for PCE discovery within an IGP routing domain
 consists of utilizing IGP advertisements.
 This document defines extensions to IS-IS [ISO] to allow a PCE in an
 IS-IS routing domain to advertise its location, along with some
 information useful to a PCC for PCE selection, so as to satisfy
 dynamic PCE discovery requirements set forth in [RFC4674].
 Generic capability advertisement mechanisms for IS-IS are defined in
 [RFC4971].  These allow a router to advertise its capabilities within
 an IS-IS area or an entire IS-IS routing domain.  This document
 leverages this generic capability advertisement mechanism to fully
 satisfy the dynamic PCE discovery requirements.
 This document defines a new sub-TLV (named the PCE Discovery (PCED))
 to be carried within the IS-IS Router Capability TLV ([RFC4971]).
 The PCE information advertised is detailed in Section 3.  Protocol
 extensions and procedures are defined in Sections 4 and 5.
 The IS-IS extensions defined in this document allow for PCE discovery
 within an IS-IS routing domain.  Solutions for PCE discovery across
 AS boundaries are beyond the scope of this document, and are for
 further study.
 This document defines a set of sub-TLVs that are nested within each
 other.  When the degree of nesting TLVs is 2 (a TLV is carried within
 another TLV) the TLV carried within a TLV is called a sub-TLV.
 Strictly speaking, when the degree of nesting is 3, a sub-sub-TLV is
 carried within a sub-TLV that is itself carried within a TLV.  For
 the sake of terminology simplicity, a TLV carried within another TLV
 is called a sub-TLV regardless of the degree of nesting.

Le Roux, et al. Standards Track [Page 3] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

2. Terminology

 ABR: IS-IS Area Border Router.
 AS: Autonomous System.
 IGP: Interior Gateway Protocol.  Either of the two routing protocols,
 Open Shortest Path First (OSPF) or Intermediate System to
 Intermediate system (IS-IS).
 Intra-area TE LSP: A TE LSP whose path does not cross an IGP area
 boundary.
 Intra-AS TE LSP: A TE LSP whose path does not cross an AS boundary.
 Inter-area TE LSP: A TE LSP whose path transits two or more IGP
 areas.  That is, a TE LSP that crosses at least one IGP area
 boundary.
 Inter-AS TE LSP: A TE LSP whose path transits two or more ASes or
 sub-ASes (BGP confederations).  That is, a TE LSP that crosses at
 least one AS boundary.
 IS-IS LSP: Link State PDU.
 LSR: Label Switching Router.
 PCC: Path Computation Client.  Any client application requesting a
 path computation to be performed by a Path Computation Element.
 PCE: Path Computation Element.  An entity (component, application, or
 network node) that is capable of computing a network path or route
 based on a network graph and applying computational constraints.
 PCED: PCE Discovery.
 PCE-Domain: In a PCE context, this refers to any collection of
 network elements within a common sphere of address management or path
 computational responsibility (referred to as a "domain" in
 [RFC4655]).  Examples of PCE-Domains include IGP areas and ASes.
 This should be distinguished from an IS-IS routing domain as defined
 by [ISO].
 PCEP: Path Computation Element communication Protocol.
 TE LSP: Traffic Engineered Label Switched Path.
 TLV: Type-Length-Variable data encoding.

Le Roux, et al. Standards Track [Page 4] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

3. Overview

3.1. PCE Discovery Information

 The PCE discovery information is composed of:
  1. The PCE location: an IPv4 and/or IPv6 address that is used to

reach the PCE. It is RECOMMENDED to use an address that is always

    reachable if there is any connectivity to the PCE;
  1. The PCE path computation scope (i.e., intra-layer, inter-area,

inter-AS, or inter-layer);

  1. The set of one or more PCE-Domain(s) into which the PCE has

visibility and for which the PCE can compute paths;

  1. The set of zero, one, or more neighbor PCE-Domain(s) toward which

the PCE can compute paths;

  1. A set of communication capabilities (e.g., support for request

prioritization) and path computation-specific capabilities (e.g.,

    supported constraints).
 PCE discovery information is, by nature, fairly static and does not
 change with PCE activity.  Changes in PCE discovery information may
 occur as a result of PCE configuration updates, PCE
 deployment/activation, PCE deactivation/suppression, or PCE failure.
 Hence, this information is not expected to change frequently.

3.2. Flooding Scope

 The flooding scope for PCE information advertised through IS-IS can
 be a single L1 area, an L1 area and the L2 sub-domain, or the entire
 IS-IS routing domain.

4. The IS-IS PCED Sub-TLV

 The IS-IS PCED sub-TLV contains a non-ordered set of sub-TLVs.
 The format of the IS-IS PCED sub-TLV and its sub-TLVs is identical to
 the TLV format used by the Traffic Engineering Extensions to IS-IS
 [RFC3784].  That is, the TLV is comprised of 1 octet for the type, 1
 octet specifying the TLV length, and a value field.  The Length field
 defines the length of the value portion in octets.

Le Roux, et al. Standards Track [Page 5] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 The IS-IS PCED sub-TLV has the following format:
    TYPE:   5
    LENGTH: Variable
    VALUE:  Set of sub-TLVs
 Five sub-TLVs are defined:
       Sub-TLV type  Length               Name
           1      variable     PCE-ADDRESS sub-TLV
           2         3         PATH-SCOPE sub-TLV
           3      variable     PCE-DOMAIN sub-TLV
           4      variable     NEIG-PCE-DOMAIN sub-TLV
           5      variable     PCE-CAP-FLAGS sub-TLV
 The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within
 the PCED sub-TLV.
 The PCE-DOMAIN and NEIG-PCE-DOMAIN sub-TLVs are optional.  They MAY
 be present in the PCED sub-TLV to facilitate selection of
 inter-domain PCEs.
 The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED
 sub-TLV to facilitate the PCE selection process.
 Any unrecognized sub-TLV MUST be silently ignored.
 The PCED sub-TLV is carried within an IS-IS CAPABILITY TLV defined in
 [RFC4971].
 No additional sub-TLVs will be added to the PCED TLV in the future.
 If a future application requires the advertisement of additional PCE
 information in IS-IS, this will not be carried in the CAPABILITY TLV.
 The following sub-sections describe the sub-TLVs that may be carried
 within the PCED sub-TLV.

4.1. PCE-ADDRESS Sub-TLV

 The PCE-ADDRESS sub-TLV specifies an IP address that can be used to
 reach the PCE.  It is RECOMMENDED to make use of an address that is
 always reachable, provided the PCE is alive and reachable.
 The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the
 PCED sub-TLV.  It MAY appear twice, when the PCE has both an IPv4 and
 IPv6 address.  It MUST NOT appear more than once for the same address
 type.  If it appears more than once for the same address type, only
 the first occurrence is processed and any others MUST be ignored.

Le Roux, et al. Standards Track [Page 6] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 The PCE-ADDRESS sub-TLV has the following format:
    TYPE:   1
    LENGTH: 5 for an IPv4 address or 17 for an IPv6 address.
    VALUE:  This comprises one octet indicating the address-type and 4
            or 16 octets encoding the IPv4 or IPv6 address to be used
            to reach the PCE.
 Address-type:
                1   IPv4
                2   IPv6

4.2. The PATH-SCOPE Sub-TLV

 The PATH-SCOPE sub-TLV indicates the PCE path computation scope,
 which refers to the PCE's ability to compute or take part in the
 computation of paths for intra-area, inter-area, inter-AS, or
 inter-layer TE LSPs.
 The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the
 PCED sub-TLV.  There MUST be exactly one instance of the PATH-SCOPE
 sub-TLV within each PCED sub-TLV.  If it appears more than once only
 the first occurrence is processed and any others MUST be ignored.
 The PATH-SCOPE sub-TLV contains a set of bit flags indicating the
 supported path scopes, and four fields indicating PCE preferences.
 The PATH-SCOPE sub-TLV has the following format:
    TYPE:   2
    LENGTH: 3
    VALUE:  This comprises a 1-octet flags field where each flag
            represents a supported path scope, followed by a 2-octet
            preferences field indicating PCE preferences.
 Here is the structure of the flags field:
    +-+-+-+-+-+-+-+-+
    |0|1|2|3|4|5|Res|
    +-+-+-+-+-+-+-+-+

Le Roux, et al. Standards Track [Page 7] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 Bit      Path Scope
 0      L bit:  Can compute intra-area paths.
 1      R bit:  Can act as PCE for inter-area TE LSP computation.
 2      Rd bit: Can act as a default PCE for inter-area TE LSP
                computation.
 3      S bit:  Can act as PCE for inter-AS TE LSP computation.
 4      Sd bit: Can act as a default PCE for inter-AS TE LSP
                computation.
 5      Y bit:  Can act as PCE for inter-layer TE LSP
                computation.
 6-7   Reserved for future use.
 Here is the structure of the preferences field:
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |PrefL|PrefR|PrefS|PrefY| Res   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 PrefL field: PCE's preference for intra-area TE LSP computation.
 PrefR field: PCE's preference for inter-area TE LSP computation.
 PrefS field: PCE's preference for inter-AS TE LSP computation.
 Pref-Y field: PCE's preference for inter-layer TE LSP computation.
 Res: Reserved for future use.
 The L, R, S, and Y bits are set when the PCE can act as a PCE for
 intra-area, inter-area, inter-AS, or inter-layer TE LSP computation,
 respectively.  These bits are non-exclusive.
 When set, the Rd bit indicates that the PCE can act as a default PCE
 for inter-area TE LSP computation (that is, the PCE can compute a
 path toward any neighbor area).  Similarly, when set, the Sd bit
 indicates that the PCE can act as a default PCE for inter-AS TE LSP
 computation (the PCE can compute a path toward any neighbor AS).
 When the Rd and Sd bit are set, the PCED sub-TLV MUST NOT contain a
 NEIG-PCE-DOMAIN sub-TLV (see Section 4.4).
 When the R bit is clear, the Rd bit SHOULD be clear on transmission
 and MUST be ignored on receipt.  When the S bit is clear, the Sd bit
 SHOULD be clear on transmission and MUST be ignored on receipt.
 The PrefL, PrefR, PrefS and PrefY fields are each three bits long and
 allow the PCE to specify a preference for each computation scope,

Le Roux, et al. Standards Track [Page 8] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 where 7 reflects the highest preference.  Such preferences can be
 used for weighted load balancing of path computation requests.  An
 operator may decide to configure a preference for each computation
 scope at each PCE so as to balance the path computation load among
 them.  The algorithms used by a PCC to balance its path computation
 requests according to such PCE preferences are out of the scope of
 this document and are a matter for local or network-wide policy.  The
 same or different preferences may be used for each scope.  For
 instance, an operator that wants a PCE capable of both inter-area and
 inter-AS computation to be preferred for use for inter-AS
 computations may configure PrefS higher than PrefR.
 When the L, R, S, or Y bits are cleared, the PrefL, PrefR, PrefS, and
 PrefY fields SHOULD respectively be set to 0 on transmission and MUST
 be ignored on receipt.
 Both reserved fields SHOULD be set to zero on transmission and MUST
 be ignored on receipt.

4.3. PCE-DOMAIN Sub-TLV

 The PCE-DOMAIN sub-TLV specifies a PCE-Domain (area and/or AS) where
 the PCE has topology visibility and through which the PCE can compute
 paths.
 The PCE-DOMAIN sub-TLV SHOULD be present when PCE-Domains for which
 the PCE can operate cannot be inferred by other IGP information: for
 instance, when the PCE is inter-domain capable (i.e., when the R bit
 or S bit is set) and the flooding scope is the entire routing domain
 (see Section 5 for a discussion of how the flooding scope is set and
 interpreted).
 A PCED sub-TLV may include multiple PCE-DOMAIN sub-TLVs when the PCE
 has visibility into multiple PCE-Domains.
 The PCE-DOMAIN sub-TLV has the following format:
    TYPE:   3
    LENGTH: Variable
    VALUE:  This is composed of one octet indicating the domain-type
            (area ID or AS Number) and a variable length IS-IS area ID
            or a 32-bit AS number, identifying a PCE-Domain where the
            PCE has visibility and can compute paths.
 Two domain types are defined:
                1   Area ID
                2   AS Number

Le Roux, et al. Standards Track [Page 9] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 The Area ID is the area address as defined in [ISO].
 When the AS number is coded in two octets, the AS Number field MUST
 have its first two octets set to 0.

4.4. NEIG-PCE-DOMAIN Sub-TLV

 The NEIG-PCE-DOMAIN sub-TLV specifies a neighbor PCE-Domain (area or
 AS) toward which a PCE can compute paths.  It means that the PCE can
 take part in the computation of inter-domain TE LSPs with paths that
 transit this neighbor PCE-Domain.
 A PCED sub-TLV may include several NEIG-PCE-DOMAIN sub-TLVs when the
 PCE can compute paths towards several neighbor PCE-Domains.
 The NEIG-PCE-DOMAIN sub-TLV has the same format as the PCE-DOMAIN
 sub-TLV:
    TYPE:   4
    LENGTH: Variable
    VALUE:  This comprises one octet indicating the domain-type (area
            ID or AS Number) and a variable length IS-IS area ID or a
            32-bit AS number, identifying a PCE-Domain toward which
            the PCE can compute paths.
 Two domain types are defined:
                1   Area ID
                2   AS Number
 The Area ID is the area address as defined in [ISO].
 When the AS number is coded in two octets, the AS Number field MUST
 have its first two octets set to 0.
 The NEIG-PCE-DOMAIN sub-TLV MUST be present at least once with
 domain-type set to 1 if the R bit is set and the Rd bit is cleared,
 and MUST be present at least once with domain-type set to 2 if the S
 bit is set and the Sd bit is cleared.

4.5. PCE-CAP-FLAGS Sub-TLV

 The PCE-CAP-FLAGS sub-TLV is an optional sub-TLV used to indicate PCE
 capabilities.  It MAY be present within the PCED sub-TLV.  It MUST
 NOT be present more than once.  If it appears more than once, only
 the first occurrence is processed and any others MUST be ignored.

Le Roux, et al. Standards Track [Page 10] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array
 of units of 32-bit flags numbered from the most significant bit as
 bit zero, where each bit represents one PCE capability.
 The PCE-CAP-FLAGS sub-TLV has the following format:
    TYPE:   5
    LENGTH: Multiple of 4
    VALUE:  This contains an array of units of 32-bit flags numbered
            from the most significant as bit zero, where each bit
            represents one PCE capability.
 The PCE capability registry is managed by IANA; it is common with
 OSPF and defined in [RFC5088].
 Reserved bits SHOULD be set to zero on transmission and MUST be
 ignored on receipt.

5. Elements of Procedure

 The PCED sub-TLV is advertised within an IS-IS Router Capability TLV
 defined in [RFC4971].  As such, elements of procedures are inherited
 from those defined in [RFC4971].
 The flooding scope is controlled by the S flag in the IS-IS Router
 Capability TLV (see [RFC4971]).  When the scope of the PCED sub-TLV
 is area local, it MUST be carried within an IS-IS Router Capability
 TLV having the S bit cleared.  When the scope of the PCED sub-TLV is
 the entire IS-IS routing domain, it MUST be carried within an IS-IS
 Router Capability TLV having the S bit set.  Note that when only the
 L bit of the PATH-SCOPE sub-TLV is set, the flooding scope MUST be
 area local.
 Note that an L1L2 node may include a PCED TLV in a Router Capability
 TLV with the S bit cleared in both in its L1 and L2 LSPs.  This
 allows the flooding scope to be restricted to the L1 area and the L2
 sub-domain.
 When the PCE function is deactivated, the IS-IS speaker advertising
 this PCE MUST originate a new IS-IS LSP that no longer includes the
 corresponding PCED TLV.
 The PCE address (i.e., the address indicated within the PCE-ADDRESS
 sub-TLV) SHOULD be reachable via some prefixes advertised by IS-IS.
 The PCED sub-TLV information regarding a specific PCE is only
 considered current and useable when the router advertising this

Le Roux, et al. Standards Track [Page 11] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 information is itself reachable via IS-IS calculated paths at the
 level of the LSP in which the PCED sub-TLV appears.
 A change in the state of a PCE (activate, deactivate, parameter
 change) MUST result in a corresponding change in the PCED sub-TLV
 information advertised by an IS-IS router (inserted, removed,
 updated) in its LSP.  The way PCEs determine the information they
 advertise, and how that information is made available to IS-IS, is
 out of the scope of this document.  Some information may be
 configured (e.g., address, preferences, scope) and other information
 may be automatically determined by the PCE (e.g., areas of
 visibility).
 A change in information in the PCED sub-TLV MUST NOT trigger any SPF
 computation at a receiving router.

6. Backward Compatibility

 The PCED sub-TLV defined in this document does not introduce any
 interoperability issues.
 An IS-IS router not supporting the PCED sub-TLV will just silently
 ignore the sub-TLV as specified in [RFC4971].

7. IANA Considerations

 IANA has defined a registry for the sub-TLVs carried in the IS-IS
 Router Capability TLV defined in [RFC4971].  IANA has assigned a new
 sub-TLV codepoint for the PCED sub-TLV carried within the Router
 Capability TLV.
 Value      Sub-TLV                   References
 -----     --------                   ----------
   5       PCED sub-TLV              (this document)

8. Security Considerations

 This document defines IS-IS extensions for PCE discovery within an
 administrative domain.  Hence the security of the PCE discovery
 relies on the security of IS-IS.
 Mechanisms defined to ensure authenticity and integrity of IS-IS LSPs
 [RFC3567] and their TLVs, can be used to secure the PCED sub-TLV as
 well.
 IS-IS provides no encryption mechanism for protecting the privacy of
 LSPs and, in particular, the privacy of the PCE discovery
 information.

Le Roux, et al. Standards Track [Page 12] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

9. Manageability Considerations

 Manageability considerations for PCE Discovery are addressed in
 Section 4.10 of [RFC4674].

9.1. Control of Policy and Functions

 Requirements for the configuration of PCE discovery parameters on
 PCCs and PCEs are discussed in Section 4.10.1 of [RFC4674].
 In particular, a PCE implementation SHOULD allow the following
 parameters to be configured on the PCE:
  1. The PCE IPv4/IPv6 address(es) (see Section 4.1).
  1. The PCE Scope, including the inter-domain functions (inter-area,

inter-AS, inter-layer), the preferences, and whether the PCE can

     act as default PCE (see Section 4.2).
  1. The PCE-Domains (see Section 4.3).
  1. The neighbor PCE-Domains (see Section 4.4).
  1. The PCE capabilities (see Section 4.5).

9.2. Information and Data Model

 A MIB module for PCE Discovery is defined in [PCED-MIB].

9.3. Liveness Detection and Monitoring

 This document specifies the use of IS-IS as a PCE Discovery Protocol.
 The requirements specified in [RFC4674] include the ability to
 determine liveness of the PCE Discovery protocol.  Normal operation
 of the IS-IS protocol meets these requirements.

9.4. Verify Correct Operations

 The correlation of information advertised against information
 received can be achieved by comparing the information in the PCED
 sub-TLV received by the PCC with that stored at the PCE using the
 PCED MIB [PCED-MIB].  The number of dropped, corrupt, and rejected
 information elements are available through the PCED MIB.

9.5. Requirements on Other Protocols and Functional Components

 The IS-IS extensions defined in this document do not imply any
 requirements on other protocols.

Le Roux, et al. Standards Track [Page 13] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

9.6. Impact on Network Operations

 Frequent changes in PCE information advertised in the PCED sub-TLV
 may have a significant impact on IS-IS and might destabilize the
 operation of the network by causing the PCCs to swap between PCEs.
 As discussed in Section 4.10.4 of [RFC4674], it MUST be possible to
 apply at least the following controls:
  1. Configurable limit on the rate of announcement of changed

parameters at a PCE.

  1. Control of the impact on PCCs, such as through rate-limiting

the processing of PCED sub-TLVs.

  1. Configurable control of triggers that cause a PCC to swap to

another PCE.

10. Acknowledgments

 We would like to thank Lucy Wong, Adrian Farrel, Les Ginsberg, Mike
 Shand, Lou Berger, David Ward, Ross Callon, and Lisa Dusseault for
 their useful comments and suggestions.

Le Roux, et al. Standards Track [Page 14] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

11. References

11.1. Normative References

 [ISO]        "Intermediate System to Intermediate System Intra-Domain
              Routeing Exchange Protocol for use in Conjunction with
              the Protocol for Providing the Connectionless-mode
              Network Service" ISO/IEC 10589:2002 Second Edition.
 [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3567]    Li, T. and R. Atkinson, "Intermediate System to
              Intermediate System (IS-IS) Cryptographic
              Authentication", RFC 3567, July 2003.
 [RFC3784]    Smit, H. and T. Li, "Intermediate System to Intermediate
              System (IS-IS) Extensions for Traffic Engineering (TE)",
              RFC 3784, June 2004.
 [RFC4971]    Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
              "Intermediate System to Intermediate System (IS-IS)
              Extensions for Advertising Router Information", RFC
              4971, July 2007.
 [RFC5088]    Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and
              R. Zhang, "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5088, January 2008.

11.2. Informative References

 [PCED-MIB]   Stephan, E., "Definitions of Managed Objects for Path
              Computation Element Discovery", Work in Progress, March
              2007.
 [PCEP]       Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path
              Computation Element (PCE) communication Protocol (PCEP)
              ", Work in Progress, November 2007.
 [RFC4655]    Farrel, A., Vasseur, JP., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              August 2006.
 [RFC4657]    Ash, J., Ed., and J. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, September 2006.

Le Roux, et al. Standards Track [Page 15] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

 [RFC4674]    Le Roux, J., Ed., "Requirements for Path Computation
              Element (PCE) Discovery", RFC 4674, October 2006.

Authors' Addresses

 Jean-Louis Le Roux (Editor)
 France Telecom
 2, avenue Pierre-Marzin
 22307 Lannion Cedex
 FRANCE
 EMail: jeanlouis.leroux@orange-ftgroup.com
 Jean-Philippe Vasseur (Editor)
 Cisco Systems, Inc.
 1414 Massachusetts avenue
 Boxborough, MA 01719
 USA
 EMail: jpv@cisco.com
 Yuichi Ikejiri
 NTT Communications Corporation
 1-1-6, Uchisaiwai-cho, Chiyoda-ku
 Tokyo 100-8019
 JAPAN
 EMail: y.ikejiri@ntt.com
 Raymond Zhang
 BT
 2160 E. Grand Ave.
 El Segundo, CA 90025
 USA
 EMail: raymond.zhang@bt.com

Le Roux, et al. Standards Track [Page 16] RFC 5089 IS-IS Protocol Extensions for PCE Discovery January 2008

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Le Roux, et al. Standards Track [Page 17]

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