Problem Statement for Default Address Selection in Multi-Prefix Environments: Operational Issues of RFC 3484 Default Rules
RFC 5220
Network Working Group A. Matsumoto
Request for Comments: 5220 T. Fujisaki
Category: Informational NTT
R. Hiromi
Intec Netcore
K. Kanayama
INTEC Systems
July 2008
Problem Statement for Default Address Selection in Multi-Prefix
Environments: Operational Issues of RFC 3484 Default Rules
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
A single physical link can have multiple prefixes assigned to it. In
that environment, end hosts might have multiple IP addresses and be
required to use them selectively. RFC 3484 defines default source
and destination address selection rules and is implemented in a
variety of OSs. But, it has been too difficult to use operationally
for several reasons. In some environments where multiple prefixes
are assigned on a single physical link, the host using the default
address selection rules will experience some trouble in
communication. This document describes the possible problems that
end hosts could encounter in an environment with multiple prefixes.
Matsumoto, et al. Informational [Page 1]
RFC 5220 Address Selection PS July 2008
Table of Contents
1. Introduction ....................................................2
1.1. Scope of This Document .....................................3
2. Problem Statement ...............................................4
2.1. Source Address Selection ...................................4
2.1.1. Multiple Routers on a Single Interface ..............4
2.1.2. Ingress Filtering Problem ...........................5
2.1.3. Half-Closed Network Problem .........................6
2.1.4. Combined Use of Global and ULA ......................7
2.1.5. Site Renumbering ....................................8
2.1.6. Multicast Source Address Selection ..................9
2.1.7. Temporary Address Selection .........................9
2.2. Destination Address Selection .............................10
2.2.1. IPv4 or IPv6 Prioritization ........................10
2.2.2. ULA and IPv4 Dual-Stack Environment ................11
2.2.3. ULA or Global Prioritization .......................12
3. Conclusion .....................................................13
4. Security Considerations ........................................14
5. Normative References ...........................................14
1. Introduction
In IPv6, a single physical link can have multiple prefixes assigned
to it. In such cases, an end host may have multiple IP addresses
assigned to an interface on that link. In the IPv4-IPv6 dual-stack
environment or in a site connected to both a Unique Local Address
(ULA) [RFC4193] and globally routable networks, an end host typically
has multiple IP addresses. These are examples of the networks that
we focus on in this document. In such an environment, an end host
may encounter some communication troubles.
Inappropriate source address selection at the end host causes
unexpected asymmetric routing, filtering by a router, or discarding
of packets because there is no route to the host.
Considering a multi-prefix environment, destination address selection
is also important for correct or better communication establishment.
RFC 3484 [RFC3484] defines default source and destination address
selection algorithms and is implemented in a variety of OSs. But, it
has been too difficult to use operationally for several reasons, such
as lack of an autoconfiguration method. There are some problematic
cases where the hosts using the default address selection rules
encounter communication troubles.
This document describes the possibilities of incorrect address
selection that lead to dropping packets and communication failure.
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RFC 5220 Address Selection PS July 2008
1.1. Scope of This Document
As other mechanisms already exist, the multi-homing techniques for
achieving redundancy are basically out of our scope.
We focus on an end-site network environment and unmanaged hosts in
such an environment. This is because address selection behavior at
these kinds of hosts is difficult to manipulate, owing to the users'
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