Evolution of the IP Model
RFC 6250
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
Show full document text