IS-IS Minimum Remaining Lifetime
RFC 7987

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Internet Engineering Task Force (IETF)                       L. Ginsberg
Request for Comments: 7987                                      P. Wells
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                              B. Decraene
                                                                  Orange
                                                           T. Przygienda
                                                                 Juniper
                                                              H. Gredler
                                                            RtBrick Inc.
                                                            October 2016

                    IS-IS Minimum Remaining Lifetime

Abstract

   Corruption of the Remaining Lifetime field in a Link State Protocol
   Data Unit (LSP) can go undetected.  In certain scenarios, this may
   cause or exacerbate flooding storms.  It is also a possible denial-
   of-service attack vector.  This document defines a backwards-
   compatible solution to this problem.

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
   http://www.rfc-editor.org/info/rfc7987.

Ginsberg, et al.             Standards Track                    [Page 1]
RFC 7987                IS-IS Remaining Lifetime            October 2016

Copyright Notice

   Copyright (c) 2016 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
   (http://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. Problem Statement ...............................................3
      1.1. Requirements Language ......................................4
   2. Solution ........................................................4
   3. Deployment Considerations .......................................5
      3.1. Inconsistent Values for MaxAge .............................5
      3.2. Reporting Corrupted Lifetime ...............................6
      3.3. Impact of Delayed LSP Purging ..............................7
   4. Security Considerations .........................................7
   5. References ......................................................7
      5.1. Normative References .......................................7
      5.2. Informative References .....................................8
   Acknowledgements ...................................................8
   Contributors .......................................................8
   Authors' Addresses .................................................9

Ginsberg, et al.             Standards Track                    [Page 2]
RFC 7987                IS-IS Remaining Lifetime            October 2016

1.  Problem Statement

   [ISO10589] defines the format of a Link State PDU (LSP) that includes
   a Remaining Lifetime field.  This field is set by the originator
   based on local configuration and then decremented by all systems once
   the entry is stored in their LSP Database (LSPDB) consistent with the
   passing of time.  This allows all Intermediate Systems (ISs) to age
   out the LSP at approximately the same time.

   Each LSP also has a checksum field to allow receiving systems to
   detect errors that may have occurred during transmission.  [ISO10589]
   mandates that the checksum is calculated by the originator of the LSP
   and cannot be modified by other routers.  Therefore, the Remaining
   Lifetime is deliberately excluded from the checksum calculation.  In
   cases where cryptographic authentication is included in an LSP
   ([RFC5304] or [RFC5310]), the Remaining Lifetime field is also
   excluded from the hash calculation.  If the Remaining Lifetime field
   gets corrupted during flooding, this corruption is therefore
   undetectable.  The consequences of such corruption depend upon how
   the Remaining Lifetime is altered.

   In cases where the Remaining Lifetime becomes larger than the