Invalid TLV Handling in IS-IS
RFC 8918

Document Type RFC - Proposed Standard (September 2020; No errata)
Updates RFC 5305, RFC 6232
Authors Les Ginsberg  , Paul Wells  , Tony Li  , Tony Przygienda  , Shraddha Hegde 
Last updated 2020-09-24
Replaces draft-ginsberg-lsr-isis-invalid-tlv
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Internet Engineering Task Force (IETF)                       L. Ginsberg
Request for Comments: 8918                                      P. Wells
Updates: 5305, 6232                                        Cisco Systems
Category: Standards Track                                          T. Li
ISSN: 2070-1721                                          Arista Networks
                                                           T. Przygienda
                                                                S. Hegde
                                                  Juniper Networks, Inc.
                                                          September 2020

                     Invalid TLV Handling in IS-IS


   The key to the extensibility of the Intermediate System to
   Intermediate System (IS-IS) protocol has been the handling of
   unsupported and/or invalid Type-Length-Value (TLV) tuples.  Although
   there are explicit statements in existing specifications, deployment
   experience has shown that there are inconsistencies in the behavior
   when a TLV that is disallowed in a particular Protocol Data Unit
   (PDU) is received.

   This document discusses such cases and makes the correct behavior
   explicit in order to ensure that interoperability is maximized.

   This document updates RFCs 5305 and 6232.

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

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
   ( 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
     1.1.  Requirements Language
   2.  TLV Codepoints Registry
   3.  TLV Acceptance in PDUs
     3.1.  Handling of Disallowed TLVs in Received PDUs Other Than LSP
     3.2.  Special Handling of Disallowed TLVs in Received LSP Purges
     3.3.  Applicability to Sub-TLVs
     3.4.  Correction to POI "TLV Codepoints Registry" Entry
   4.  TLV Validation and LSP Acceptance
   5.  IANA Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Authors' Addresses

1.  Introduction

   The Intermediate System to Intermediate System (IS-IS) protocol
   [ISO10589] utilizes Type-Length-Value (TLV) encoding for all content
   in the body of Protocol Data Units (PDUs).  New extensions to the
   protocol are supported by defining new TLVs.  In order to allow
   protocol extensions to be deployed in a backwards compatible way, an
   implementation is required to ignore TLVs that it does not
   understand.  This behavior is also applied to sub-TLVs [RFC5305],
   which are contained within TLVs.

   Also essential to the correct operation of the protocol is having the
   validation of PDUs be independent from the validation of the TLVs
   contained in the PDU.  PDUs that are valid must be accepted
   [ISO10589] even if an individual TLV contained within that PDU is not
   understood or is invalid in some way (e.g., incorrect syntax, data
   value out of range, etc.).

   The set of TLVs (and sub-TLVs) that are allowed in each PDU type is
   documented in the "TLV Codepoints Registry" established by [RFC3563]
   and updated by [RFC6233] and [RFC7356].

   This document is intended to clarify some aspects of existing
   specifications and, thereby, reduce the occurrence of non-conformant
   behavior seen in real-world deployments.  Although behaviors
   specified in existing protocol specifications are not changed, the
   clarifications contained in this document serve as updates to
   [RFC5305] (see Section 3.3) and [RFC6232] (see Section 3.4).

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
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