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The Application Specific Link Attribute (ASLA) Any Application Bit
draft-hegde-lsr-asla-any-app-02

Document Type Active Internet-Draft (individual)
Authors Shraddha Hegde , Ron Bonica , Chris Bowers , Robert Raszuk , Zhenbin Li , Daniel Voyer
Last updated 2022-07-11
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draft-hegde-lsr-asla-any-app-02
LSR                                                             S. Hegde
Internet-Draft                                                 R. Bonica
Intended status: Standards Track                               C. Bowers
Expires: January 12, 2023                               Juniper Networks
                                                               R. Raszuk
                                                 NTT Network Innovations
                                                                   Z. Li
                                                     Huawei Technologies
                                                                D. Voyer
                                                             Bell Canada
                                                           July 11, 2022

   The Application Specific Link Attribute (ASLA) Any Application Bit
                    draft-hegde-lsr-asla-any-app-02

Abstract

   RFC 8919 and RFC 8920 define Application Specific Link Attributes
   (ASLA).  Each ASLA includes an Application Identifier Bit Mask.  The
   Application Identifier Bit Mask includes a Standard Application Bit
   Mask (SABM) and a User Defined Application Bit Mask (UDABM).  The
   SABM and UDABM determine which applications can use the ASLA as an
   input.

   This document introduces a new bit to the Standard Application
   Identifier Bit Mask.  This bit is called the Any Application Bit
   (i.e., the A-bit).  If the A-bit is set, the link attribute can be
   used by any application.  This includes currently defined
   applications as well as applications to be defined in the future.

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 January 12, 2023.

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Copyright Notice

   Copyright (c) 2022 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  The Any Application Bit . . . . . . . . . . . . . . . . . . .   4
     3.1.  IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  OSPF  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   [RFC8919] and [RFC8920] define Application Specific Link Attributes
   (ASLA).  Each ASLA includes an Application Identifier Bit Mask.  The
   Application Identifier Bit Mask includes a Standard Application Bit
   Mask (SABM) and a User Defined Application Bit Mask (UDABM).

   Each bit in the SABM represents a standard application while each bit
   in the UDABM represents a user defined application.  If a bit in the
   SABM or UDABM is set, the corresponding application can use the ASLA
   as an input.  If a bit in the SABM or UDABM is not set, the
   corresponding application cannot use the associated ASLA as an input.

   According to [RFC8919]:

   "If link attributes are advertised associated with zero-length
   Application Identifier Bit Masks for both standard applications and
   user-defined applications, then any standard application and/or any
   user-defined application is permitted to use that set of link

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   attributes so long as there is not another set of attributes
   advertised on that same link that is associated with a non-zero-
   length Application Identifier Bit Mask with a matching Application
   Identifier Bit set."

   This restriction introduces complexity.  For example, assume that a
   network runs many applications.  All applications use Attribute 1 as
   an input.  So, it would be convenient to advertise Attribute 1 with a
   zero-length SABM / UDABM.

   However, Applications X and Y also use Attribute 2 as an input.
   Because Applications X and Y required unique values for Attribute 2,
   Attribute 2 cannot be advertised with a zero-length SABM.  Therefore,
   Attribute 1 cannot be advertised with a zero-length SABM / UDABM
   either, because Applications X and Y require it.  This would result
   in having to set the application X and application Y bits on
   attribute 1 in the entire network on each link and is operationally
   complex.

   Zero length bitmasks also introduce LSP packing inefficiency.  From
   the example above, The attribute 1 has to be repeated for
   applications X and Y although application X and Y do not require
   different values for these applications.  When the attributes get
   advertised from IGP into BGP-LS, attributes from zero length bitmasks
   of ASLA and ASLA SRLG need to be collated to make it disambiguous.
   This collation introduces additional complexity.

   When a deployment requires link-attributes to be used by all
   applications instead of using the zero-length bitmasks one could use
   an ASLA advertisements with all known application bits set.  While
   this may work well for the current deployments for the current set of
   defined applications, it poses challenge when there are new
   applications to be deployed.  It would require all nodes in the
   network to support the new bit and require upgrade.

   This document reduces operational complexity by introducing a new bit
   to the Standard Application Identifier Bit Mask.  This bit is called
   the Any Application Bit (i.e., the A-bit).  If the A-bit is set, the
   link attribute can be used by any application.  This includes
   currently defined applications as well as applications to be defined
   in the future.

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

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   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  The Any Application Bit

   A new bit is defined in the Standard Application Identifier Bit Mask.
   This bit is called the Any Application Bit (i.e., the A-bit).  If the
   A-bit is set, the link attribute can be used by any application.
   This includes currently defined applications as well as applications
   to be defined in the future.

   If a link advertises an ASLA twice, once with the A-bit set and once
   with a more specific Application Identifier Bit set, the indicated
   application MUST use the value from the ASLA with the more specific
   Application Indicator Bit set.

3.1.  IS-IS

   IS-IS uses Bit 4 of the SABM to encode the A-bit.

3.2.  OSPF

   OSPF uses Bit 4 of the SABM to encode the A-bit.

4.  Backward Compatibility

   The solution described in this document is backward compatible with
   [RFC8919] and [RFC8920].  An implementation that does not recognize
   the A-bit will process the SABM as specified in [RFC8919] and
   [RFC8920].

   Implementations MAY advertise attributes under both A bit and with
   SABM and UDABM length set to zero for backward compatibility reasons.
   When same attributes are received with A bit set as well as in ASLA
   with SABM and UDABM set to zero, the attributes MUST be used from the
   ASLA with SABM and UDABM set to zero and procedures described in RFC
   8919 sec 6.2 MUST be followed.

5.  Security Considerations

   The security considerations discussed in [RFC8919] and [RFC8920] are
   applicable to this document.  This document does not introduce any
   new security risks.

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6.  IANA Considerations

   This document requests that IANA add the following entry to the
   registry titled "Link Attribute Application Identifiers" under the
   "Interior Gateway Protocol (IGP) Parameters" registry:

   o  Bit: 4

   o  Name: Any Application (A-bit)

   o  Reference: This document

7.  Acknowledgements

   TBD

8.  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>.

   [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>.

   [RFC8919]  Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
              J. Drake, "IS-IS Application-Specific Link Attributes",
              RFC 8919, DOI 10.17487/RFC8919, October 2020,
              <https://www.rfc-editor.org/info/rfc8919>.

   [RFC8920]  Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
              J., and J. Drake, "OSPF Application-Specific Link
              Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020,
              <https://www.rfc-editor.org/info/rfc8920>.

Authors' Addresses

   Shraddha Hegde
   Juniper Networks
   Exora Business Park
   Bangalore, KA  560103
   India

   Email: shraddha@juniper.net

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   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, Virginia  20171
   USA

   Email: rbonica@juniper.net

   Chris Bowers
   Juniper Networks

   Email: cbowers@juniper.net

   Robert Raszuk
   NTT Network Innovations

   Email: robert@raszuk.net

   Zenbin Li
   Huawei Technologies

   Email: lizhenbin@huawei.com

   Dan Voyer
   Bell Canada

   Email: daniel.voyer@bell.ca

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