Evolution of the IP Model
RFC 6250

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Internet Architecture Board (IAB)                              D. Thaler
Request for Comments: 6250                                      May 2011
Category: Informational
ISSN: 2070-1721

                       Evolution of the IP Model

Abstract

   This RFC attempts to document various aspects of the IP service model
   and how it has evolved over time.  In particular, it attempts to
   document the properties of the IP layer as they are seen by upper-
   layer protocols and applications, especially properties that were
   (and, at times, still are) incorrectly perceived to exist as well as
   properties that would cause problems if changed.  The discussion of
   these properties is organized around evaluating a set of claims, or
   misconceptions.  Finally, this document provides some guidance to
   protocol designers and implementers.

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 Architecture Board (IAB)
   and represents information that the IAB has deemed valuable to
   provide for permanent record.  Documents approved for publication by
   the IAB are not 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/rfc6250.

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.

Thaler & IAB                  Informational                     [Page 1]
RFC 6250                Evolution of the IP Model               May 2011

Table of Contents

   1. Introduction ....................................................3
   2. The IP Service Model ............................................4
      2.1. Links and Subnets ..........................................5
   3. Common Application Misconceptions ...............................5
      3.1. Misconceptions about Routing ...............................5
           3.1.1. Claim: Reachability is symmetric ....................5
           3.1.2. Claim: Reachability is transitive ...................6
           3.1.3. Claim: Error messages can be received in
                  response to data packets ............................7
           3.1.4. Claim: Multicast is supported within a link .........7
           3.1.5. Claim: IPv4 broadcast is supported ..................8
           3.1.6. Claim: Multicast/broadcast is less expensive
                  than replicated unicast .............................8
           3.1.7. Claim: The end-to-end latency of the first
                  packet to a destination is typical ..................8
           3.1.8. Claim: Reordering is rare ...........................9
           3.1.9. Claim: Loss is rare and probabilistic, not
                  deterministic .......................................9
           3.1.10. Claim: An end-to-end path exists at a
                   single point in time ..............................10
           3.1.11. Discussion ........................................10
      3.2. Misconceptions about Addressing ...........................11
           3.2.1. Claim: Addresses are stable over long
                  periods of time ....................................11
           3.2.2. Claim: An address is four bytes long ...............12
           3.2.3. Claim: A host has only one address on one interface 12
           3.2.4. Claim: A non-multicast/broadcast address
                  identifies a single host over a long period of time 13
           3.2.5. Claim: An address can be used as an
                  indication of physical location ....................14
           3.2.6. Claim: An address used by an application is
                  the same as the address used for routing ...........14
           3.2.7. Claim: A subnet is smaller than a link .............14
           3.2.8. Claim: Selecting a local address selects
                  the interface ......................................15
           3.2.9. Claim: An address is part of an on-link
                  subnet prefix ......................................15
           3.2.10. Discussion ........................................15
      3.3. Misconceptions about Upper-Layer Extensibility ............16
           3.3.1. Claim: New transport-layer protocols can
                  work across the Internet ...........................16
           3.3.2. Claim: If one stream between a pair of
                  addresses can get through, then so can another .....17