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Versions: (draft-ietf-ospf-transport-instance) 00

LSR Workgroup                                                  A. Lindem
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                   Y. Qu
Expires: March 14, 2021                                        Futurewei
                                                                  A. Roy
                                                            Arrcus, Inc.
                                                            S. Mirtorabi
                                                           Cisco Systems
                                                      September 10, 2020


                   OSPF Transport Instance Extensions
               draft-acee-lsr-ospf-transport-instance-00

Abstract

   OSPFv2 and OSPFv3 include a reliable flooding mechanism to
   disseminate routing topology and Traffic Engineering (TE) information
   within a routing domain.  Given the effectiveness of these
   mechanisms, it is convenient to envision using the same mechanism for
   dissemination of other types of information within the domain.
   However, burdening OSPF with this additional information will impact
   intra-domain routing convergence and possibly jeopardize the
   stability of the OSPF routing domain.  This document presents
   mechanism to relegate this ancillary information to a separate OSPF
   instance and minimize the impact.

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents 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 March 14, 2021.








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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Possible Use Cases  . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  MEC Service Discovery . . . . . . . . . . . . . . . . . .   3
     3.2.  Application Data Dissemination  . . . . . . . . . . . . .   4
   4.  OSPF Transport Instance . . . . . . . . . . . . . . . . . . .   4
     4.1.  OSPFv2 Transport Instance Packet Differentiation  . . . .   4
     4.2.  OSPFv3 Transport Instance Packet Differentiation  . . . .   5
     4.3.  Instance Relationship to Normal OSPF Instances  . . . . .   5
       4.3.1.  Ships in the Night Relationship to Normal OSPF
               Instances . . . . . . . . . . . . . . . . . . . . . .   5
       4.3.2.  Tighter Coupling with Normal OSPF Instances . . . . .   5
     4.4.  Network Prioritization  . . . . . . . . . . . . . . . . .   5
     4.5.  OSPF Transport Instance Omission of Routing Calculation .   6
     4.6.  Non-routing Instance Separation . . . . . . . . . . . . .   6
     4.7.  Non-Routing Sparse Topologies . . . . . . . . . . . . . .   7
       4.7.1.  Remote OSPF Neighbor  . . . . . . . . . . . . . . . .   7
   5.  OSPF Transport Instance Information Encoding  . . . . . . . .   8
     5.1.  OSPFv2 Transport Instance Information Encoding  . . . . .   8
     5.2.  OSPFv3 Transport Instance Information Encoding  . . . . .   8
   6.  Manageability Considerations  . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10






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1.  Introduction

   OSPFv2 [RFC2328] and OSPFv3 [RFC5340] include a reliable flooding
   mechanism to disseminate routing topology and Traffic Engineering
   (TE) information within a routing domain.  Given the effectiveness of
   these mechanisms, it is convenient to envision using the same
   mechanism for dissemination of other types of information within the
   domain.  However, burdening OSPF with this additional information
   will impact intra-domain routing convergence and possibly jeopardize
   the stability of the OSPF routing domain.  This document presents
   mechanism to relegate this ancillary information to a separate OSPF
   instance and minimize the impact.

   This OSPF protocol extension provides functionality similar to
   "Advertising Generic Information in IS-IS" [RFC6823].  Additionally,
   OSPF is extended to support sparse non-routing overlay topologies
   Section 4.7.

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.

3.  Possible Use Cases

3.1.  MEC Service Discovery

   Multi-Access Edge Computing (MEC) plays an important role in 5G
   architecture.  MEC optimizes the performance for ultra-low latency
   and high bandwidth services by providing networking and computing at
   the edge of the network [ETSI-WP28-MEC].  To achieve this goal, it's
   important to expose the network capabilities and services of a MEC to
   UEs.

   The followings are an incomplete list of the kind of information that
   OSPF transport instance can help to disseminate:

   o  A network service is realized using one or more physical or
      virtualized hosts in MEC, and the locations of these service
      points might change.  The auto-discovery of these service
      locations can be achieved using an OSPF transport instance.

   o  UEs might be mobile, and MEC should support service continuity and
      application mobility.  This may require service state transferring




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      and synchronization.  OSPF transport instance can be used to
      synchronize these states.

   o  Network resources are limited, such as computing power, storage.
      The availability of such resources is dynamic, and OSPF transport
      instance can be used to populate such information, so applications
      can pick the right location of such resources, hence improve user
      experience and resource utilization.

3.2.  Application Data Dissemination

   Typically a network consists of routers from different vendors with
   different capabilities, and some applications may want to know
   whether a router supports certain functionality or where to find a
   router supports a functionality, so it will be ideal if such kind of
   information is known to all routers or a group of routers in the
   network.  For example, an ingress router needs to find an egress
   router that supports In-situ Flow Information Telemetry (IFIT)
   [I-D.wang-lsr-igp-extensions-ifit].

   OSPF transport instance can be used to populate such router
   capabilities/functionalities without impacting the performance of
   being a routing protocol.

4.  OSPF Transport Instance

   In order to isolate the effects of flooding and processing of non-
   routing information, it will be relegated to a separate protocol
   instance.  This instance should be given lower priority when
   contending for router resources including processing, backplane
   bandwidth, and line card bandwidth.  How that is realized is an
   implementation issue and is outside the scope of this document.

   Throughout the document, non-routing refers to routing information
   that is not used for IP or IPv6 routing calculations.  The OSPF
   transport instance is ideally suited for dissemination of routing
   information for other protocols and layers.

4.1.  OSPFv2 Transport Instance Packet Differentiation

   OSPFv2 currently does not offer a mechanism to differentiate
   Transport instance packets from normal instance packets sent and
   received on the same interface.  However, the [RFC6549] provides the
   necessary packet encoding to support multiple OSPF protocol
   instances.






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4.2.  OSPFv3 Transport Instance Packet Differentiation

   Fortunately, OSPFv3 already supports separate instances within the
   packet encodings.  The existing OSPFv3 packet header instance ID
   field will be used to differentiate packets received on the same link
   (refer to section 2.4 in [RFC5340]).

4.3.  Instance Relationship to Normal OSPF Instances

   There are basically two alternatives for the relationship between a
   normal OSPF instance and an OSPF transport instance.  In both cases,
   we must guarantee that any information we've received is treated as
   valid if and only if the router sending it is reachable.  We'll refer
   to this as the "condition of reachability" in this document.

   1.  Ships in the Night - The OSPF transport instance has no
       relationship or dependency on any other OSPF instance.

   2.  Child Instance - The OSPF transport instance has a child-parent
       relationship with a normal OSPF instance and is dependent on this
       for topology information and assuring the "condition of
       reachability".

4.3.1.  Ships in the Night Relationship to Normal OSPF Instances

   In this mode, the OSPF transport instance is not dependent on any
   other OSPF instance.  It does, however, have much of the same as
   topology information must be advertised to satisfy the "condition of
   reachability".

   Prefix information does not need to be advertised.  This implies that
   for OSPFv2, only router-LSAs, network-LSAs, and type 4 summary-LSAs
   need to be advertised.  In the router-LSAs, the stub (type 3) links
   may be suppressed.  For OSPFv3, this implies that router-LSAs,
   network-LSAs, and inter-area-router-LSAs must be advertised.

4.3.2.  Tighter Coupling with Normal OSPF Instances

   Further optimizations and coupling between an OSPF transport instance
   and a normal OSPF instance are beyond the scope of this document.
   This is an area for future study.

4.4.  Network Prioritization

   While OSPFv2 (section 4.3 in [RFC2328]) are normally sent with IP
   precedence Internetwork Control, any packets sent by an OSPF
   transport instance will be sent with IP precedence Flash (B'011').




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   This is only appropriate given that this is a pretty flashy
   mechanism.

   Similarly, OSPFv3 transport instance packets will be sent with the
   traffic class mapped to flash (B'011') as specified in ([RFC5340]).

   By setting the IP/IPv6 precedence differently for OSPF transport
   instance packets, normal OSPF routing instances can be given priority
   during both packet transmission and reception.  In fact, some router
   implementations map the IP precedence directly to their internal
   packet priority.  However, internal router implementation decisions
   are beyond the scope of this document.

4.5.  OSPF Transport Instance Omission of Routing Calculation

   Since the whole point of the transport instance is to separate the
   routing and non-routing processing and fate sharing, a transport
   instance SHOULD NOT install any IP or IPv6 routes.  OSPF routers
   SHOULD NOT advertise any transport instance LSAs containing IP or
   IPv6 prefixes and OSPF routers receiving LSAs advertising IP or IPv6
   prefixes SHOULD ignore them.  This implies that an OSPFv2 transport
   instance Link State Database should not include any summary-LSAs
   (type 3) , AS-external-LSAs (type 5), or NSSA-LSAs (type 7) and the
   router-LSAs should not include any stub (type 3) links.  An OSPFv3
   transport instance Link State database should not include any inter-
   area-prefix-LSAs (type 0x2003), AS-external-LSAs (0x4005), NSSA-LSAs
   (type 0x2007), or intra-area-prefix-LSAs (type 0x2009).  If they are
   erroneously advertised, they will be flooded as per standard OSPF but
   MUST be ignored by OSPF routers supporting this specification.

4.6.  Non-routing Instance Separation

   It has been suggested that an implementation could obtain the same
   level of separation between IP routing information and non-routing
   information in a single instance with slight modifications to the
   OSPF protocol.  The authors refute this contention for the following
   reasons:

   o  Adding internal and external mechanisms to prioritize routing
      information over non-routing information are much more complex
      than simply relegating the non-routing information to a separate
      instance as proposed in this specification.

   o  The instance boundary offers much better separation for allocation
      of finite resources such as buffers, memory, processor cores,
      sockets, and bandwidth.





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   o  The instance boundary decreases the level of fate sharing for
      failures.  Each instance may be implemented as a separate process
      or task.

   o  With non-routing information, many times not every router in the
      OSPF routing domain requires knowledge of every piece of non-
      routing information.  In these cases, groups of routers which need
      to share information can be segregated into sparse topologies
      greatly reducing the amount of non-routing information any single
      router needs to maintain.

4.7.  Non-Routing Sparse Topologies

   With non-routing information, many times not every router in the OSPF
   routing domain requires knowledge of every piece of non-routing
   information.  In these cases, groups of routers which need to share
   information can be segregated into sparse topologies.  This will
   greatly reduce the amount of information any single router needs to
   maintain with the core routers possibly not requiring any non-routing
   information at all.

   With normal OSPF, every router in an OSPF area must have every piece
   of topological information and every intra-area IP or IPv6 prefix.
   With non-routing information, only the routers needing to share a set
   of information need be part of the corresponding sparse topology.
   For directly attached routers, one only needs to configure the
   desired topologies on the interfaces with routers requiring the non-
   routing information.  When the routers making up the sparse topology
   are not part of a uniconnected graph, two alternatives exist.  The
   first alternative is configure tunnels to form a fully connected
   graph including only those routers in the sparse topology.  The
   second alternative is use remote neighbors as described in
   Section 4.7.1.

4.7.1.  Remote OSPF Neighbor

   With sparse topologies, OSPF routers sharing non-routing information
   may not be directly connected.  OSPF adjacencies with remote
   neighbors are formed exactly as they are with regular OSPF neighbors.
   The main difference is that a remote OSPF neighbor's address is
   configured and IP routing is used to deliver OSPF protocol packets to
   the remote neighbor.  Other salient feature of the remote neighbor
   include:

   o  All OSPF packets have the remote neighbor's configured IP address
      as the IP destination address.





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   o  The adjacency is represented in the router Router-LSA as a router
      (type-1) link with the link data set to the remote neighbor's
      configured IP address.

   o  Similar to NBMA networks, a poll-interval is configured to
      determine if the remote neighbor is reachable.  This value is
      normally much higher than the hello interval with 40 seconds
      RECOMMENDED as the default.

5.  OSPF Transport Instance Information Encoding

   The format of the TLVs within the body of an LSA containing non-
   routing information is the same as the format used by the Traffic
   Engineering Extensions to OSPF [RFC3630].  The LSA payload consists
   of one or more nested Type/Length/Value (TLV) triplets.  The format
   of each TLV is:


      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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Value...                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                                TLV Format

   However, each unique application using the mechanisms defined in this
   document will have it's own unique ID.  Whether to encode this ID as
   the top-level TLV or make it part of the OSPF LSA ID is open for
   debate.

   The specific TLVs and sub-TLVs relating to a given application and
   the corresponding IANA considerations MUST for standard applications
   MUST be specified in the document corresponding to that application.

5.1.  OSPFv2 Transport Instance Information Encoding

   Application specific information will be flooded in opaque LSAs as
   specified in [RFC5250].

5.2.  OSPFv3 Transport Instance Information Encoding

   Application specific information will be flooded in separate LSAs
   with separate function codes.  Refer to section A.4.2.1 of [RFC5340].
   for information on the LS Type encoding in OSPFv3.



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6.  Manageability Considerations

7.  Security Considerations

   The security considerations for the Transport Instance will not be
   different for those for OSPFv2 [RFC2328] and OSPFv3 [RFC5340].

8.  IANA Considerations

   No IANA actions are required.

9.  Acknowledgement

10.  References

10.1.  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>.

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

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC5250]  Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
              OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
              July 2008, <https://www.rfc-editor.org/info/rfc5250>.

   [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>.

   [RFC6549]  Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi-
              Instance Extensions", RFC 6549, DOI 10.17487/RFC6549,
              March 2012, <https://www.rfc-editor.org/info/rfc6549>.

   [RFC6823]  Ginsberg, L., Previdi, S., and M. Shand, "Advertising
              Generic Information in IS-IS", RFC 6823,
              DOI 10.17487/RFC6823, December 2012,
              <https://www.rfc-editor.org/info/rfc6823>.




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   [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>.

10.2.  Informative References

   [ETSI-WP28-MEC]
              Sami Kekki, etc., "MEC in 5G Networks", 2018,
              <https://www.etsi.org/images/files/ETSIWhitePapers/
              etsi_wp28_mec_in_5G_FINAL.pdf>.

   [I-D.wang-lsr-igp-extensions-ifit]
              Wang, Y., Zhou, T., Qin, F., Chen, H., and R. Pang, "IGP
              Extensions for In-situ Flow Information Telemetry (IFIT)
              Capability Advertisement", draft-wang-lsr-igp-extensions-
              ifit-01 (work in progress), July 2020.

Authors' Addresses

   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   CARY, NC 27513
   UNITED STATES

   Email: acee@cisco.com


   Yingzhen Qu
   Futurewei
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

   Email: yingzhen.qu@futurewei.com


   Abhay Roy
   Arrcus, Inc.

   Email: abhay@arrcus.com










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   Sina Mirtorabi
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: smirtora@cisco.com












































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