wdiff rfc8476.original rfc8476.txt


OSPF Working Group
Internet Engineering Task Force (IETF)                       J. Tantsura
Internet-Draft
Request for Comments: 8476                                  Apstra, Inc.
Intended status:
Category: Standards Track                                    U. Chunduri
Expires: April 20, 2019
ISSN: 2070-1721                                      Huawei Technologies
                                                               S. Aldrin
                                                            Google, Inc Inc.
                                                               P. Psenak
                                                           Cisco Systems
                                                        October 17,
                                                           December 2018

              Signaling MSD (Maximum Maximum SID Depth) using Depth (MSD) Using OSPF
                 draft-ietf-ospf-segment-routing-msd-25

Abstract

   This document defines a way for an Open Shortest Path First (OSPF)
   Router
   router to advertise multiple types of supported Maximum SID(Segment
   Identifier) SID Depths
   (MSDs) at node and/or link granularity.  Such advertisements allow
   entities (e.g., centralized controllers) to determine whether a
   particular SID Segment Identifier (SID) stack can be supported in a given
   network.  This document defines only one type of MSD, refers to the Signaling MSD as defined
   in RFC 8491, but it defines an encoding that can support other MSD
   types.  Here  Here, the term OSPF "OSPF" means both OSPFv2 and OSPFv3.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list  It represents the consensus of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid the IETF community.  It has
   received public review and has been approved for a maximum 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 six months this document, any errata,
   and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 20, 2019.
   https://www.rfc-editor.org/info/rfc8476.

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
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   described in the Simplified BSD License.

Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2 ....................................................2
      1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . .   3 ................................................3
      1.2. Requirements Language . . . . . . . . . . . . . . . . . .   4 ......................................4
   2. Node MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4 ..........................................4
   3. Link MSD sub-TLV  . . . . . . . . . . . . . . . . . . . . . .   5 Sub-TLV ................................................5
   4. Procedures for Defining and Using Node and Link MSD
      Advertisements  . . . . . . . . . . . . . . . . . . . . . . .   6 ..................................................6
   5. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7 .............................................7
   6. Security Considerations . . . . . . . . . . . . . . . . . . .   8 .........................................7
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1. ......................................................8
      7.1. Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2. .......................................8
      7.2. Informative References  . . . . . . . . . . . . . . . . .   9 .....................................9
   Acknowledgements ..................................................10
   Contributors ......................................................10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11 ................................................10

1.  Introduction

   When Segment Routing (SR) paths are computed by a centralized
   controller, it is critical that the controller learns learn the Maximum SID
   (Segment Identifier)
   Depth (MSD) that can be imposed at each node/
   link node/link on a given SR path to ensure path.
   This ensures that the Segment Identifier (SID) stack depth of a
   computed path doesn't exceed the number of SIDs the node is capable
   of imposing.

   [I-D.ietf-pce-segment-routing]

   [PCEP-EXT] defines how to signal MSD in the Path Computation Element communication
   Communication Protocol (PCEP).  However, if PCEP is not supported/configured supported/
   configured on the head-end of an SR tunnel or a Binding-SID anchor node
   node, and the controller does not participate in IGP routing, it has
   no way to learn of learning the MSD of nodes and links.  BGP-LS (Distribution
   of Link-State and TE Information using Border Gateway
   Protocol) Using BGP) [RFC7752] defines a way
   to expose topology and associated attributes and capabilities of the
   nodes in that topology to a centralized controller.  MSD signaling by
   BGP-LS has been defined in
   [I-D.ietf-idr-bgp-ls-segment-routing-msd]. [MSD-BGP].  Typically, BGP-LS is
   configured on a small number of nodes that do not necessarily act as
   head-ends.  In order for BGP-LS to signal MSD for all the nodes and
   links in the network for which MSD is relevant, MSD capabilities
   SHOULD be advertised by every OSPF router in the network.

   Other types of MSD MSDs are known to be useful.  For example,
   [I-D.ietf-ospf-mpls-elc] [ELC-ISIS]
   defines Entropy Readable Label Depth Capability
   (RLDC) that (ERLD), which is used by a
   head-end to insert an Entropy Label (EL) at a depth that could where it can be
   read by transit nodes.

   This document defines an extension to OSPF used to advertise one or
   more types of MSD MSDs at node and/or link granularity.  In the future future,
   it is expected, expected that new MSD-types MSD-Types will be defined to signal
   additional
   capabilities capabilities, e.g., entropy labels, ELs, SIDs that can be imposed through
   recirculation, or SIDs associated with another dataplane e.g., data plane such
   as IPv6.

   MSD advertisements MAY be useful even if Segment Routing SR itself is not enabled.
   For example, in a non-SR MPLS network, MSD defines the maximum label
   depth.

1.1.  Terminology

   This memo makes use of the terms defined in [RFC7770] [RFC7770].

   BGP-LS:  Distribution of Link-State and TE Information using Border
   Gateway Protocol Using BGP

   OSPF:    Open Shortest Path First

   MSD:     Maximum SID Depth - the number of SIDs supported by a node
            or a link on a node

   SID:     Segment Identifier as defined in [RFC8402]

   Label Imposition:  Imposition is the act of modifying and/or adding
            labels to the outgoing label stack associated with a packet.
            This includes:

   o

            *  replacing the label at the top of the label stack with a
               new label

   o

            *  pushing one or more new labels onto the label stack
   The number of labels imposed is then the sum of the number of labels
   which
   that are replaced and the number of labels which that are pushed.  See
   [RFC3031] for further details.

   PCC: Path Computation Client

   PCE: Path Computation Element

   PCEP:    Path Computation Element Communication Protocol

   SR:      Segment Routing

   SID: Segment Identifier

   LSA:     Link state advertisement State Advertisement

   RI: OSPF      Router Information LSA

1.2.  Requirements Language

   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.

2.  Node MSD Advertisement

   The node Node MSD TLV within the body of the OSPF RI Opaque LSA [RFC7770]
   is defined to carry the provisioned SID depth of the router
   originating the RI LSA.  Node MSD is the smallest MSD supported by
   the node on the set of interfaces configured for use by the
   advertising IGP instance.  MSD values may be learned via a hardware
   API or may be provisioned.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Type                       |  Length                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    MSD-Type   |  MSD-Value    |  MSD-Type...  |  MSD-Value... |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 1: Node MSD TLV

   Type: 12

   Length: variable (multiple of 2 octets) and octets); represents the total length
   of the value field in octets.

   Value: consists of one or more pairs of a 1 octet MSD-type 1-octet MSD-Type and 1
   octet
   1-octet MSD-Value.

   MSD-Type: one of the values defined in the IGP MSD-Types "IGP MSD-Types" registry
   defined in [I-D.ietf-isis-segment-routing-msd]. [RFC8491].

   MSD-Value: a number in the range of 0-255.  For all MSD-Types, 0
   represents the lack of the ability to impose an MSD stack of any depth;
   any other value represents that of the node.  This value MUST
   represent the lowest value supported by any link configured for use
   by the advertising OSPF instance.

   This TLV is optional and is applicable to both OSPFv2 and to OSPFv3 and is optional. OSPFv3.
   The scope of the advertisement is specific to the deployment.

   When multiple Node MSD TLVs are received from a given router, the
   receiver MUST use the first occurrence of the TLV in the Router
   Information (RI) LSA.  If the Node MSD TLV appears in multiple Router
   Information RI
   LSAs that have different flooding scopes, the Node MSD TLV in the Router Information RI
   LSA with the area-scoped flooding scope MUST be used.  If the Node
   MSD TLV appears in multiple Router
   Information RI LSAs that have the same flooding
   scope, the Node MSD TLV in the Router Information (RI) RI LSA with the numerically smallest
   Instance ID MUST be used and other instances of the Node MSD TLV MUST
   be ignored.  The RI LSA can be advertised at any of the defined
   opaque flooding scopes (link, area, or Autonomous System (AS)).  For
   the purpose of Node MSD TLV advertisement, area-scoped flooding is
   RECOMMENDED.

3.  Link MSD sub-TLV Sub-TLV

   The link Link MSD sub-TLV is defined to carry the MSD of the interface
   associated with the link.  MSD values may be learned via a hardware
   API or may be provisioned.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Type                       |  Length                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    MSD-Type   |  MSD-Value    |  MSD-Type...  |  MSD-Value... |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 2: Link MSD Sub-TLV
   Type:

      For OSPFv2, the Link level link-level MSD-Value is advertised as an optional
   Sub-TLV
      sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], [RFC7684]
      and has a type of 6.

      For OSPFv3, the Link level link-level MSD-Value is advertised as an optional
   Sub-TLV
      sub-TLV of the E-Router-LSA TLV as defined in [RFC8362], [RFC8362] and has a
      type of 9.

   Length: variable and variable; same as defined in Section 2.

   Value: consists of one or more pairs of a 1 octet MSD-type 1-octet MSD-Type and 1
   octet
   1-octet MSD-Value.

   MSD-Type: one of the values defined in the MSD-Types "IGP MSD-Types" registry
   defined in [I-D.ietf-isis-segment-routing-msd]. [RFC8491].

   The MSD-Value field contains the Link MSD of the router originating
   the corresponding LSA as specified for OSPFv2 and OSPFv3.  The Link
   MSD is a number in the range of 0-255.  For all MSD-Types, 0
   represents the lack of the ability to impose an MSD stack of any depth;
   any other value represents that of the particular link when used as
   an outgoing interface.

   If this sub-TLV is advertised multiple times in the same OSPFv2
   Extended Link Opaque LSA/E-Router-LSA, only the first instance of the
   TLV MUST be used by receiving OSPF routers.  This situation SHOULD be
   logged as an error.

   If this sub-TLV is advertised multiple times for the same link in
   different OSPF Extended Link Opaque LSAs/E-Router-LSAs LSAs / E-Router-LSAs originated
   by the same OSPF router, the OSPFv2 Extended Link TLV sub-TLV in the OSPFv2 Extended Link
   Opaque LSA with the smallest Opaque ID or in the OSPFv3 E-Router-LSA
   with the smallest Link State ID MUST be used by receiving OSPF
   routers.  This situation MAY SHOULD be logged as a warning. an error.

4.  Procedures for Defining and Using Node and Link MSD Advertisements

   When Link MSD is present for a given MSD-type, MSD-Type, the value of the Link
   MSD MUST take precedence over the Node MSD.  When a Link MSD-type MSD-Type is
   not signaled but the Node MSD-type MSD-Type is, then the Node MSD-type MSD-Type value
   MUST be considered as the MSD value for that link.

   In order to increase flooding efficiency, it is RECOMMENDED that
   routers with homogenous link Link MSD values advertise just the Node MSD
   value.

   The meaning of the absence of both Node and Link MSD advertisements
   for a given MSD-type MSD-Type is specific to the MSD-type.  Generally MSD-Type.  Generally, it can
   only be inferred that the advertising node does not support
   advertisement of that MSD-type. MSD-Type.  However, in some cases the lack of
   advertisement might imply that the functionality associated with the
   MSD-type
   MSD-Type is not supported.  The  Per [RFC8491], the correct interpretation
   MUST be specified when an MSD-type MSD-Type is defined in
   [I-D.ietf-isis-segment-routing-msd]. defined.

5.  IANA Considerations

   This specification updates several existing OSPF registries.

   IANA has allocated TLV type 12 from the OSPF "OSPF Router Information (RI)
   TLVs Registry
   TLVs" registry as defined by [RFC7770].

      Value     Description                      Reference
      -----     ---------------                  -------------
      12        Node MSD                         This document

                           Figure 3: RI Node MSD

   IANA has allocated sub-TLV type 6 from the OSPFv2 "OSPFv2 Extended Link TLV
   Sub-TLVs
   Sub-TLVs" registry.

      Value     Description                      Reference
      -----     ---------------                  -------------
      6         OSPFv2 Link MSD                  This document

                         Figure 4: OSPFv2 Link MSD

   IANA has allocated sub-TLV type 9 from the OSPFv3 "OSPFv3 Extended-LSA Sub-
   TLV
   Sub-TLVs" registry.

      Value     Description                      Reference
      -----     ---------------                  -------------
      9         OSPFv3 Link MSD                  This document

                         Figure 5: OSPFv3 Link MSD

6.  Security Considerations

   Security concerns for OSPF are addressed in [RFC7474], [RFC4552] [RFC4552], and
   [RFC7166].  Further security analysis for the OSPF protocol is done
   in [RFC6863].  Security considerations, considerations as specified by [RFC7770],
   [RFC7684]
   [RFC7684], and [RFC8362] are applicable to this document.

   Implementations MUST assure ensure that malformed TLV TLVs and Sub-TLV sub-TLVs defined
   in this document are detected and do not provide a vulnerability for
   attackers to crash the OSPF router or routing process.  Reception of
   malformed TLV TLVs or Sub-TLV sub-TLVs SHOULD be counted and/or logged for
   further analysis.  Logging of malformed TLVs and Sub-TLVs sub-TLVs SHOULD be rate-
   limited
   rate-limited to prevent a Denial of Service Denial-of-Service (DoS) attack (distributed
   or otherwise) from overloading the OSPF control plane.

   Advertisement of an incorrect MSD value may have negative
   consequences.  If the value is smaller than supported, path
   computation may fail to compute a viable path.  If the value is
   larger than supported, an attempt to instantiate a path that can't be
   supported by the head-end (the node performing the SID imposition)
   may occur.

   The presence of this information also may also inform an attacker of how
   to induce any of the aforementioned conditions.

   There's no Denial of Service DoS risk specific to this extension, and it is not
   vulnerable to replay attacks.

7.  Contributors

   The following people contributed to this document:

   Les Ginsberg

   Email: ginsberg@cisco.com

8.  Acknowledgments

   The authors would like to thank Acee Lindem, Ketan Talaulikar, Tal
   Mizrahi, Stephane Litkowski and Bruno Decraene for their reviews and
   valuable comments.

9.  References

9.1.

7.1.  Normative References

   [I-D.ietf-isis-segment-routing-msd]
              Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling MSD (Maximum SID Depth) using IS-IS", draft-
              ietf-isis-segment-routing-msd-19 (work in progress),
              October 2018.

   [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>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684,
              November 2015, <https://www.rfc-editor.org/info/rfc7684>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [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>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362,
              April 2018, <https://www.rfc-editor.org/info/rfc8362>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

9.2.  Informative References
   [I-D.ietf-idr-bgp-ls-segment-routing-msd]

   [RFC8491]  Tantsura, J., Chunduri, U., Mirsky, G., Aldrin, S., and S. Sivabalan, L. Ginsberg,
              "Signaling MSD (Maximum Maximum SID Depth) using Border Gateway
              Protocol Link-State", draft-ietf-idr-bgp-ls-segment-
              routing-msd-02 (work in progress), August 2018.

   [I-D.ietf-ospf-mpls-elc] Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,
              <https://www.rfc-editor.org/info/rfc8491>.

7.2.  Informative References

   [ELC-ISIS] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "Signaling Entropy Label Capability and Entropy
              Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
              mpls-elc-07 (work Work in progress), Progress,
              draft-ietf-ospf-mpls-elc-07, September 2018.

   [I-D.ietf-pce-segment-routing]

   [MSD-BGP]  Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
              "Signaling MSD (Maximum SID Depth) using Border Gateway
              Protocol Link-State", Work in Progress, draft-ietf-idr-
              bgp-ls-segment-routing-msd-02, August 2018.

   [PCEP-EXT] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "PCEP Extensions for Segment Routing",
              draft-ietf-pce-segment-routing-12 (work
              Work in progress), June Progress, draft-ietf-pce-segment-routing-14,
              October 2018.

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

   [RFC6863]  Hartman, S. and D. Zhang, "Analysis of OSPF Security
              According to the Keying and Authentication for Routing
              Protocols (KARP) Design Guide", RFC 6863,
              DOI 10.17487/RFC6863, March 2013,
              <https://www.rfc-editor.org/info/rfc6863>.

   [RFC7166]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
              Authentication Trailer for OSPFv3", RFC 7166,
              DOI 10.17487/RFC7166, March 2014,
              <https://www.rfc-editor.org/info/rfc7166>.

   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
              <https://www.rfc-editor.org/info/rfc7474>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

Acknowledgements

   The authors would like to thank Acee Lindem, Ketan Talaulikar, Tal
   Mizrahi, Stephane Litkowski, and Bruno Decraene for their reviews and
   valuable comments.

Contributors

   The following person contributed to this document:

   Les Ginsberg

   Email: ginsberg@cisco.com

Authors' Addresses

   Jeff Tantsura
   Apstra, Inc.
   Email: jefftant.ietf@gmail.com

   Uma Chunduri
   Huawei Technologies
   Email: uma.chunduri@huawei.com

   Sam Aldrin
   Google, Inc Inc.
   Email: aldrin.ietf@gmail.com

   Peter Psenak
   Cisco Systems
   Email: ppsenak@cisco.com