IS-IS Multi-Flooding Instances

Document Type Active Internet-Draft (individual)
Authors Yali Wang  , Aijun Wang  , Zhibo Hu , Tianran Zhou 
Last updated 2021-02-21
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Link State Routing Working Group                                 Y. Wang
Internet-Draft                                                    Huawei
Intended status: Standards Track                                 A. Wang
Expires: August 25, 2021                                   China Telecom
                                                                   Z. Hu
                                                                 T. Zhou
                                                       February 21, 2021

                     IS-IS Multi-Flooding Instances


   This document proposes a new IS-IS flooding mechanism which separates
   multiple flooding instances for dissemination of routing information
   and other types of application-specific information to minimizes the
   impact of non-routing information flooding on the routing convergence
   and stability.  Due to different flooding information has different
   requirements on the flooding rate, these multi-flooding instances
   should be given various priorities and flooding parameters.  An
   encoding format for IS-IS Multi-Flooding Instance Identifier (MFI-ID)
   TLV and Update Process are specified in this document.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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
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   This Internet-Draft will expire on August 25, 2021.

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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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   ( in effect on the date of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  IS-IS Multi-Flooding Instances  . . . . . . . . . . . . . . .   3
     2.1.  Multi-Flooding Instance Identifier  . . . . . . . . . . .   4
     2.2.  Update Process Operation  . . . . . . . . . . . . . . . .   4
     2.3.  Interoperability Considerations . . . . . . . . . . . . .   5
   3.  IS-IS Non-routing MFIs Omission of Routing Calculation  . . .   5
   4.  Applicability of IS-IS Multi-Flooding Instances . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   [ISO10589] specifies the IS-IS protocol, in which each Intermediate
   System (IS) (router) advertises one or more IS-IS Link State Protocol
   Data Units (LSPs) with routing topology and Traffic Engineering (TE)
   information.  As the one-octet LSP Number field, there are limited
   256 numbers of LSPs that may be assigned.  However, with the
   increasing amount of Topology information and TE information proposed
   to be advertised, for example, advertisement of Virtual Transport
   Networks (VTN) Topology, VTN Resource and VTN specific Data Plane
   Identifiers [I-D.dong-lsr-sr-enhanced-vpn], there will be huge
   consumption of LSPs.  In addition, with the increasing use the same
   mechanism for advertisement of application-specific information,
   therefore, a mechanism should be defined for advertisement of
   application-specific information that minimizes the impact on the
   operation of the IS-IS protocol.

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   This document proposes a new IS-IS flooding mechanism which separates
   multiple flooding instances for dissemination of routing information
   and other types of application-specific information in a single IS-IS
   protocol instance.  This document therefore defines an encoding
   format for IS-IS Multi-Flooding Instances Identifier (MFIs-ID) TLV
   and MFIs Update Process.

   For dissemination of generic information (GENINFO) not directly
   related to the operation of the IS-IS protocol within the domain,
   [RFC6823] defines a GENINFO TLV aand specifies that the advertisement
   of GENINFO must occur in a non-zero instance of IS-IS protocol as
   defined in [RFC8202] for minimizing the impact of advertisement of
   GENINFO on the operation of routing.  This document also recommends
   the use of GENINFO TLV in a specific MFI for advertisement of GENINFO
   in the zero IS-IS instance, which can isolate the impact of non-
   routing information on the standard IS-IS operation.

   Instead of using non-zero IS-IS instances, the advertisement of non-
   routing information in MFIs is implemented in the zero IS-IS
   instance, which simplifies the deployment.  MFIs mechanism has a
   lower cost to maintain neighbor because that all the MFIs share the
   standard IS-IS instance neighbor.  In addition, MFIs can be
   configured with customized MFIs-specific flooding parameters
   (including the retransmission interval, refresh timer, maximum age,

   Similarly, OSPF Multi-Flooding Instances will be proposed in the
   future work.

2.  IS-IS Multi-Flooding Instances

   An existing protocol limitation is that a given IS-IS instance in a
   single level supports a single update process operating on a single
   Link State Database (LSDB).  This document defines an extension to
   IS-IS to allow one standard instance of the protocol to support
   multiple update process operations.  This extension is referred to as
   "IS-IS Multi-Flooding Instances" (IS-IS MFIs).

   Each update process is associated with a unique MFI.  The behavior of
   the standard update process is not changed in any way by the
   extensions defined in this document.  MFI-specific prioritization for
   processing PDUs and MFI-specific flooding parameters should be
   defined so as to allow different MFIs to consume network-wide
   resources at different rates.  The use of MFIs can enhance the
   ability to isolate the resources associated with the standard update
   process and other application-specific update process.

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2.1.  Multi-Flooding Instance Identifier

   A Multi-Flooding Instance Identifier (MFI-ID) is introduced to
   uniquely identify an IS-IS Multi-Flooding Instance and the associated
   update process.  The protocol extension includes a new TLV (i.e.
   MFI-ID TLV) in each IS-IS PDU originated by an Intermediate System.
   It is recommended that the MFI-ID TLV be the first TLV in the PDU,
   which allows determination of the association of a PDU with a
   particular MFI more quickly.  Each IS-IS PDU is associated with only
   one IS-IS MFI.

   The MFI-ID TLV is carried in Link State PDUs (LSPs) and Sequence
   Number PDUs (SNPs).  MFI-IDs MUST be unique within the same routing
   domain.  The following format is used for the MFI-ID TLV:

                                     No. of octets
   |      Type     |      Length   |      2
   |            MFI-ID             |      2

   MFI-ID#0 is reserved for the routing flooding instance supported by
   legacy systems.  IS-IS LSPs and SNPs do not carry the MFI-ID TLV,
   which indicates these PDUs are associated with the routing flooding
   instance in the zero IS-IS instance.

2.2.  Update Process Operation

   In this document, MFIs can be created in a single IS-IS instance.
   Different application information can be advertised to all the other
   Intermediate systems in the corresponding MFI.

   The Update Process in an Intermediate system shall generate one or
   more new Link State PDUs.  Each Level 1/Level 2 Link State PDU
   associated with a specific MFI carries application information
   belonging to the specific MFI.  And Level 1/Level 2 PSNP and Level 1/
   Level 2 CSNP containing information about LSPs that transmitted in a
   specific MFI are generated to synchronize the LSDB corresponding to
   the specific MFI.

   In each MFI, update parameters can be customized differently.  As
   specified in [ISO10589], parameters include the LSP MaxAge, LSP
   Refresh time, LSP retransmission interval, Maximum LSP Generation
   interval, Minimum LSP Generation interval, Minimum LSP transmission
   interval, PSNP sending interval, and CSNP sending interval.  Note
   that besides of different update parameters, any other elements in
   these MFI-specific Update Process are same as the standard IS-IS

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   Update Process including Input and Output, Event driven LSP
   Generation, action on receipt of a link state PDU, etc.

2.3.  Interoperability Considerations

   In the scenario where some routers that do not support MFI are
   deployed in the same routing domain, it is recommended that all MFIs
   in an IS-IS protocol instance share one LSP Number space.  The total
   number of LSPs in all MFIs cannot exceed 256.  This implementation
   mode of MFI can coexist with routers that do not support MFI.  If
   routers that do not support MFI receive the LSPs and SNPs encoding
   MFI-ID TLV, then routers SHOULD ignore the MFI-ID TLV and continues
   processing other TLVs.

   In the scenario where all routers in the entire routing domain
   support MFI, it is recommended that each MFI can has its separate LSP
   Number space.  Each MFI can have a maximum of 256 LSPs.  Both LSP ID
   and MFI are used to uniquely identify an LSP.

   Note that the MFI mechanism does not affect neighbor relationship
   establishment, shortest-path-first (SPF) algorithm and TE routing
   calculation, but only affects IS-IS LSDB synchronization.

3.  IS-IS Non-routing MFIs Omission of Routing Calculation

   IS-IS standard routing related TLVs and TE related extended TLVs, for
   example, IS Neighbors TLV and IP Reachability, are not included in
   Non-routing Multi-flooding Instances.

4.  Applicability of IS-IS Multi-Flooding Instances

   In addition to IS-IS route flooding, more and more application
   information and node capabilities that are not directly related to
   IS-IS operations need to be advertised in the entire routing domain
   through the IS-IS flooding mechanism.  For example, the advertisement
   of supported In-situ Flow Information Telemetry (IFIT) capabilities
   at node and/or link granularity [].

5.  IANA Considerations

   IANA is requested to allocate values for the following new TLV.

                          | Type | Description |
                          | TBA  | MFI-ID TLV  |

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6.  Security Considerations

   It does not introduce any new security risks to IS-IS.

7.  Acknowledgements


8.  References

8.1.  Normative References

              "International Organization for Standardization,
              "Information technology -- Telecommunications and
              information exchange between systems -- Intermediate
              System to Intermediate System intra-domain routing
              information exchange protocol for use in conjunction with
              the protocol for providing the connectionless-mode network
              service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,
              November 2002.",

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

8.2.  Informative References

              "IGP Extensions for Segment Routing based Enhanced VPN",

              "IGP Extensions for In-situ Flow Information Telemetry
              (IFIT) Capability Advertisement",

   [RFC6823]  "Advertising Generic Information in IS-IS",

   [RFC8202]  "IS-IS Multi-Instance",

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Authors' Addresses

   Yali Wang
   156 Beiqing Rd., Haidian District


   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District


   Zhibo Hu
   156 Beiqing Rd., Haidian District


   Tianran Zhou
   156 Beiqing Rd., Haidian District


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