Internet-Draft ASLA Any Application Bit August 2021
Hegde, et al. Expires 20 February 2022 [Page]
Workgroup:
LSR
Internet-Draft:
draft-hegde-lsr-asla-any-app-00
Published:
Intended Status:
Standards Track
Expires:
Authors:
S. Hegde
Juniper Networks
R. Bonica
Juniper Networks
C. Bowers
Juniper Networks
R. Raszuk
NTT Network Innovations
Z. Li
Huawei Technologies

The Application Specific Link Attribute (ASLA) Any Application Bit

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/.

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This Internet-Draft will expire on 20 February 2022.

Table of Contents

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 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 X require it.

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 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 [RFC8919] 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.

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:

7. Acknowledgements

Thanks to Xuesong Geng and Ram Santhanakrishnan for contributing to this document.

8. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8920>.

Authors' Addresses

Shraddha Hegde
Juniper Networks
Exora Business Park
Bangalore 560103
KA
India
Ron Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, Virginia 20171
United States of America
Chris Bowers
Juniper Networks
Robert Raszuk
NTT Network Innovations
Zhenbin Li
Huawei Technologies
People's Republic of China