Security Assessment of the Internet Protocol Version 4
RFC 6274

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Internet Engineering Task Force (IETF)                           F. Gont
Request for Comments: 6274                                       UK CPNI
Category: Informational                                        July 2011
ISSN: 2070-1721

         Security Assessment of the Internet Protocol Version 4

Abstract

   This document contains a security assessment of the IETF
   specifications of the Internet Protocol version 4 and of a number of
   mechanisms and policies in use by popular IPv4 implementations.  It
   is based on the results of a project carried out by the UK's Centre
   for the Protection of National Infrastructure (CPNI).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   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/rfc6274.

Copyright Notice

   Copyright (c) 2011 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.

Gont                          Informational                     [Page 1]
RFC 6274                IPv4 Security Assessment               July 2011

Table of Contents

   1. Preface .........................................................4
      1.1. Introduction ...............................................4
      1.2. Scope of This Document .....................................6
      1.3. Organization of This Document ..............................7
   2. The Internet Protocol ...........................................7
   3. Internet Protocol Header Fields .................................8
      3.1. Version ....................................................9
      3.2. IHL (Internet Header Length) ..............................10
      3.3. Type of Service (TOS) .....................................10
           3.3.1. Original Interpretation ............................10
           3.3.2. Standard Interpretation ............................12
                  3.3.2.1. Differentiated Services Field .............12
                  3.3.2.2. Explicit Congestion Notification (ECN) ....13
      3.4. Total Length ..............................................14
      3.5. Identification (ID) .......................................15
           3.5.1. Some Workarounds Implemented by the Industry .......16
           3.5.2. Possible Security Improvements .....................17
                  3.5.2.1. Connection-Oriented Transport Protocols ...17
                  3.5.2.2. Connectionless Transport Protocols ........18
      3.6. Flags .....................................................19
      3.7. Fragment Offset ...........................................21
      3.8. Time to Live (TTL) ........................................22
           3.8.1. Fingerprinting the Operating System in Use
                  by the Source Host .................................24
           3.8.2. Fingerprinting the Physical Device from
                  which the Packets Originate ........................24
           3.8.3. Mapping the Network Topology .......................24
           3.8.4. Locating the Source Host in the Network Topology ...25
           3.8.5. Evading Network Intrusion Detection Systems ........26
           3.8.6. Improving the Security of Applications That
                  Make Use of the Internet Protocol (IP) .............27
           3.8.7. Limiting Spread ....................................28
      3.9. Protocol ..................................................28
      3.10. Header Checksum ..........................................28
      3.11. Source Address ...........................................29
      3.12. Destination Address ......................................30
      3.13. Options ..................................................30
           3.13.1. General Issues with IP Options ....................31
                  3.13.1.1. Processing Requirements ..................31