



Internet Engineering Task Force (IETF)                        X. Xu, Ed.
Request for Comments: 9013                                 Capitalonline
Category: Standards Track                               B. Decraene, Ed.
ISSN: 2070-1721                                                   Orange
                                                               R. Raszuk
                                                 NTT Network Innovations
                                                            L. Contreras
                                                          Telefonica I+D
                                                                L. Jalil
                                                                 Verizon
                                                              April 2021


              OSPF Advertisement of Tunnel Encapsulations

Abstract

   Networks use tunnels for a variety of reasons.  A large variety of
   tunnel types are defined, and the tunnel encapsulator router needs to
   select a type of tunnel that is supported by the tunnel decapsulator
   router.  This document defines how to advertise, in OSPF Router
   Information Link State Advertisements (LSAs), the list of tunnel
   encapsulations supported by the tunnel decapsulator.

Status of This Memo

   This is an Internet Standards Track document.

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

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9013.

Copyright Notice

   Copyright (c) 2021 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Tunnel Encapsulations TLV
   4.  Tunnel Sub-TLV
   5.  Tunnel Parameter Sub-TLVs
     5.1.  Encapsulation Sub-TLV
     5.2.  Protocol Type Sub-TLV
     5.3.  Tunnel Egress Endpoint Sub-TLV
     5.4.  Color Sub-TLV
     5.5.  Load-Balancing Block Sub-TLV
     5.6.  DS Field Sub-TLV
     5.7.  UDP Destination Port Sub-TLV
   6.  Operation
   7.  IANA Considerations
     7.1.  OSPF Router Information (RI) TLVs Registry
     7.2.  OSPF Tunnel Parameter Sub-TLVs Registry
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   Networks use tunnels for a variety of reasons, such as:

   *  Partial deployment of IPv6 in IPv4 networks or IPv4 in IPv6
      networks, as described in [RFC5565], where IPvx tunnels are used
      between IPvx-enabled routers so as to traverse non-IPvx routers.

   *  Remote Loop-Free Alternate (RLFA) repair tunnels as described in
      [RFC7490], where tunnels are used between the Point of Local
      Repair and the selected PQ node.

   The tunnel encapsulator router needs to select a type of tunnel that
   is supported by the tunnel decapsulator router.  This document
   defines how to advertise, in OSPF Router Information Link State
   Advertisements (LSAs), the list of tunnel encapsulations supported by
   the tunnel decapsulator.  In this document, OSPF refers to both
   OSPFv2 [RFC2328] and OSPFv3 [RFC5340].

2.  Terminology

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

   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.

3.  Tunnel Encapsulations TLV

   Routers advertise their supported tunnel encapsulation type(s) by
   advertising a new TLV of the OSPF Router Information (RI) Opaque LSA
   [RFC7770], referred to as the "Tunnel Encapsulations TLV".  This TLV
   is applicable to both OSPFv2 and OSPFv3.

   The Type code of the Tunnel Encapsulations TLV is 13, the Length
   value is variable, and the Value field contains one or more Tunnel
   Sub-TLVs, as defined in Section 4.  Each Tunnel Sub-TLV indicates a
   particular encapsulation format that the advertising router supports,
   along with the parameters corresponding to the tunnel type.

   The Tunnel Encapsulations TLV MAY appear more than once within a
   given OSPF Router Information (RI) Opaque LSA.  If the Tunnel
   Encapsulations TLV appears more than once in an OSPF Router
   Information LSA, the set of all Tunnel Sub-TLVs from all Tunnel
   Encapsulations TLVs SHOULD be considered.  The scope of the
   advertisement depends on the application, but it is recommended that
   it SHOULD be domain wide.

4.  Tunnel Sub-TLV

   The Tunnel Sub-TLV is structured as shown in Figure 1.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Tunnel Type (2 octets)     |        Length (2 octets)      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |               Tunnel Parameter Sub-TLVs                       |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 1: Tunnel Sub-TLV

   Tunnel Type (2 octets):  Identifies the type of tunneling technology
      signaled.  Tunnel types are shared with the BGP extension
      [RFC9012] and hence are defined in the IANA registry "BGP Tunnel
      Encapsulation Attribute Tunnel Types".  Unknown tunnel types are
      to be ignored upon receipt.

   Length (2 octets):  Unsigned 16-bit integer indicating the total
      number of octets of the Tunnel Parameter Sub-TLVs field.

   Tunnel Parameter Sub-TLVs (variable):  Zero or more Tunnel Parameter
      Sub-TLVs, as defined in Section 5.

   If a Tunnel Sub-TLV is invalid, it MUST be ignored and skipped.
   However, other Tunnel Sub-TLVs MUST be considered.

5.  Tunnel Parameter Sub-TLVs

   A Tunnel Parameter Sub-TLV is structured as shown in Figure 2.

              +---------------------------------------------+
              |   Tunnel Parameter Sub-Type (2 octets)      |
              +---------------------------------------------+
              |   Tunnel Parameter Length (2 octets)        |
              +---------------------------------------------+
              |   Tunnel Parameter Value (variable)         |
              |                                             |
              +---------------------------------------------+

                     Figure 2: Tunnel Parameter Sub-TLV

   Tunnel Parameter Sub-Type (2 octets):  Each sub-type defines a
      parameter of the Tunnel Sub-TLV.  Sub-types are registered in the
      IANA registry "OSPF Tunnel Parameter Sub-TLVs" (see Section 7.2).

   Tunnel Parameter Length (2 octets):  Unsigned 16-bit integer
      indicating the total number of octets of the Tunnel Parameter
      Value field.

   Tunnel Parameter Value (variable):  Encodings of the Value field
      depend on the sub-TLV type.  The following subsections define the
      encoding in detail.

   Any unknown Tunnel Parameter sub-type MUST be ignored and skipped
   upon receipt.  When a reserved value (see Section 7.2) is seen in an
   LSA, it MUST be treated as an invalid Tunnel Parameter Sub-TLV.  When
   a Tunnel Parameter Value has an incorrect syntax or semantics, it
   MUST be treated as an invalid Tunnel Parameter Sub-TLV.  If a Tunnel
   Parameter Sub-TLV is invalid, its Tunnel Sub-TLV MUST be ignored.
   However, other Tunnel Sub-TLVs MUST be considered.

5.1.  Encapsulation Sub-TLV

   This sub-TLV type is 1.  The syntax, semantics, and usage of its
   Value field are defined in Section 3.2 ("Encapsulation Sub-TLVs for
   Particular Tunnel Types") of [RFC9012].

5.2.  Protocol Type Sub-TLV

   This sub-TLV type is 2.  The syntax, semantics, and usage of its
   Value field are defined in Section 3.4.1 ("Protocol Type Sub-TLV") of
   [RFC9012].

5.3.  Tunnel Egress Endpoint Sub-TLV

   The Tunnel Egress Endpoint Sub-TLV specifies the address of the
   egress endpoint of the tunnel -- that is, the address of the router
   that will decapsulate the payload.

   This sub-TLV type is 3.  It MUST be present once and only once in a
   given Tunnel Sub-TLV.  The Value field contains two subfields:

   *  a two-octet Address Family subfield

   *  an Address subfield, whose length depends upon the Address Family


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Address Family           |           Address             ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
       ~                     (variable length)                         ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 3: Tunnel Egress Endpoint Sub-TLV

   The Address Family subfield contains a value from IANA's "Address
   Family Numbers" registry.  In this document, we assume that the
   Address Family is either IPv4 or IPv6; use of other address families
   is outside the scope of this document.

   If the Address Family subfield contains the value for IPv4, the
   Address subfield MUST contain an IPv4 address (a /32 IPv4 prefix).
   In this case, the Length field of the Tunnel Egress Endpoint Sub-TLV
   MUST contain the value 6.

   If the Address Family subfield contains the value for IPv6, the
   address subfield MUST contain an IPv6 address (a /128 IPv6 prefix).
   In this case, the Length field of the Tunnel Egress Endpoint Sub-TLV
   MUST contain the value 18 (0x12).  IPv6 link-local addresses are not
   valid values of the IP address field.

5.4.  Color Sub-TLV

   This sub-TLV type is 4.  It may appear zero or more times in a given
   Tunnel Sub-TLV.  The Value field is a 4-octet opaque unsigned
   integer.

   The color value is user-defined and configured locally on the
   advertising routers.  It may be used by service providers to define
   policies on the tunnel encapsulator routers, for example, to control
   the selection of the tunnel to use.

   This color value can be referenced by BGP routes carrying the Color
   Extended Community [RFC9012].  If the tunnel is used to reach the BGP
   next hop of BGP routes, then attaching a Color Extended Community to
   those routes expresses the willingness of the BGP speaker to use a
   tunnel of the same color.

5.5.  Load-Balancing Block Sub-TLV

   This sub-TLV type is 5.  The syntax, semantics, and usage of its
   Value field are defined in [RFC5640].

5.6.  DS Field Sub-TLV

   This sub-TLV type is 6.  The syntax, semantics, and usage of its
   Value field are defined in Section 3.3.1 ("DS Field") of [RFC9012].

5.7.  UDP Destination Port Sub-TLV

   This sub-TLV type is 7.  The syntax, semantics, and usage of its
   Value field are defined in Section 3.3.2 ("UDP Destination Port") of
   [RFC9012].

6.  Operation

   The advertisement of a Tunnel Encapsulations Sub-TLV indicates that
   the advertising router supports a particular tunnel decapsulation
   along with the parameters to be used for the tunnel.  The decision to
   use that tunnel is driven by the capability of the tunnel
   encapsulator router to support the encapsulation type and the policy
   on the tunnel encapsulator router.  The Color Sub-TLV (see
   Section 5.4) may be used as an input to this policy.  Note that some
   tunnel types may require the execution of an explicit tunnel setup
   protocol before they can be used to transit data.

   A tunnel MUST NOT be used if there is no route toward the IP address
   specified in the Tunnel Egress Endpoint Sub-TLV (see Section 5.3) or
   if the route is not advertised in the same OSPF domain.

7.  IANA Considerations

7.1.  OSPF Router Information (RI) TLVs Registry

   IANA has allocated the following new code point in the "OSPF Router
   Information (RI) TLVs" registry.

               +=======+=======================+===========+
               | Value | TLV Name              | Reference |
               +=======+=======================+===========+
               | 13    | Tunnel Encapsulations | RFC 9013  |
               +-------+-----------------------+-----------+

                      Table 1: Addition to OSPF Router
                       Information (RI) TLVs Registry

7.2.  OSPF Tunnel Parameter Sub-TLVs Registry

   IANA has created a new subregistry called the "OSPF Tunnel Parameter
   Sub-TLVs" registry under the "Open Shortest Path First (OSPF)
   Parameters" registry.  The registration procedures are as follows:

   *  The values in the range 1-34999 are to be allocated using the
      "Standards Action" registration procedure defined in [RFC8126].

   *  The values in the range 35000-65499 are to be allocated using the
      "First Come First Served" registration procedure.

   The initial contents of the registry are as follows:

       +=============+======================+=====================+
       | Value       | TLV Name             | Reference           |
       +=============+======================+=====================+
       | 0           | Reserved             | RFC 9013            |
       +-------------+----------------------+---------------------+
       | 1           | Encapsulation        | RFC 9013 & RFC 9012 |
       +-------------+----------------------+---------------------+
       | 2           | Protocol Type        | RFC 9013 & RFC 9012 |
       +-------------+----------------------+---------------------+
       | 3           | Endpoint             | RFC 9013            |
       +-------------+----------------------+---------------------+
       | 4           | Color                | RFC 9013            |
       +-------------+----------------------+---------------------+
       | 5           | Load-Balancing Block | RFC 9013 & RFC 5640 |
       +-------------+----------------------+---------------------+
       | 6           | DS Field             | RFC 9013 & RFC 9012 |
       +-------------+----------------------+---------------------+
       | 7           | UDP Destination Port | RFC 9013 & RFC 9012 |
       +-------------+----------------------+---------------------+
       | 8-65499     | Unassigned           |                     |
       +-------------+----------------------+---------------------+
       | 65500-65534 | Experimental         | RFC 9013            |
       +-------------+----------------------+---------------------+
       | 65535       | Reserved             | RFC 9013            |
       +-------------+----------------------+---------------------+

         Table 2: Initial Contents of OSPF Tunnel Parameter Sub-
                              TLVs Registry

8.  Security Considerations

   Security considerations applicable to softwires can be found in the
   mesh framework [RFC5565].  In general, security issues of the tunnel
   protocols signaled through this OSPF capability extension are
   inherited.

   If a third party is able to modify any of the information that is
   used to form encapsulation headers, choose a tunnel type, or choose a
   particular tunnel for a particular payload type, user data packets
   may end up getting misrouted, misdelivered, and/or dropped.  However,
   since an OSPF routing domain is usually a well-controlled network
   under a single administrative domain, the possibility of the above
   attack is very low.

   We note that the last paragraph of Section 6 forbids the
   establishment of a tunnel toward arbitrary destinations.  It
   prohibits a destination outside of the OSPF domain.  This prevents a
   third party that has gained access to an OSPF router from being able
   to send the traffic to other destinations, e.g., for inspection
   purposes.

   Security considerations for the base OSPF protocol are covered in
   [RFC2328] and [RFC5340].

9.  References

9.1.  Normative References

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

   [RFC5640]  Filsfils, C., Mohapatra, P., and C. Pignataro, "Load-
              Balancing for Mesh Softwires", RFC 5640,
              DOI 10.17487/RFC5640, August 2009,
              <https://www.rfc-editor.org/info/rfc5640>.

   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [RFC9012]  Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
              "The BGP Tunnel Encapsulation Attribute", RFC 9012,
              DOI 10.17487/RFC9012, April 2021,
              <https://www.rfc-editor.org/info/rfc9012>.

9.2.  Informative References

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC5512]  Mohapatra, P. and E. Rosen, "The BGP Encapsulation
              Subsequent Address Family Identifier (SAFI) and the BGP
              Tunnel Encapsulation Attribute", RFC 5512,
              DOI 10.17487/RFC5512, April 2009,
              <https://www.rfc-editor.org/info/rfc5512>.

   [RFC5565]  Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
              Framework", RFC 5565, DOI 10.17487/RFC5565, June 2009,
              <https://www.rfc-editor.org/info/rfc5565>.

   [RFC7490]  Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
              So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
              RFC 7490, DOI 10.17487/RFC7490, April 2015,
              <https://www.rfc-editor.org/info/rfc7490>.

Acknowledgements

   This document is partially inspired by [RFC5512].

   The authors would like to thank Greg Mirsky, John E. Drake, Carlos
   Pignataro, and Karsten Thomann for their valuable comments on this
   document.  Special thanks should be given to Acee Lindem for his
   multiple detailed reviews of this document and help.  The authors
   would like to thank Pete Resnick, Joe Touch, David Mandelberg,
   Sabrina Tanamal, Tim Wicinski, and Amanda Baber for their Last Call
   reviews.  The authors also thank Spencer Dawkins, Mirja Kühlewind,
   Ben Campbell, Benoit Claise, Alvaro Retana, Adam Roach, and Suresh
   Krishnan for their AD reviews.

Contributors

   Uma Chunduri
   Huawei

   Email: uma.chunduri@gmail.com


Authors' Addresses

   Xiaohu Xu (editor)
   Capitalonline

   Email: xiaohu.xu@capitalonline.net


   Bruno Decraene (editor)
   Orange

   Email: bruno.decraene@orange.com


   Robert Raszuk
   NTT Network Innovations
   940 Stewart Dr
   Sunnyvale, CA 94085
   United States of America

   Email: robert@raszuk.net


   Luis M. Contreras
   Telefonica I+D

   Email: luismiguel.contrerasmurillo@telefonica.com


   Luay Jalil
   Verizon

   Email: luay.jalil@verizon.com
