draft-ietf-6man-multi-homed-host-04.txt   draft-ietf-6man-multi-homed-host-05.txt 
IPv6 Maintenance F. Baker IPv6 Maintenance F. Baker
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Updates: 4861 (if approved) B. Carpenter Updates: 4861 (if approved) B. Carpenter
Intended status: Standards Track Univ. of Auckland Intended status: Standards Track Univ. of Auckland
Expires: August 21, 2016 February 18, 2016 Expires: August 25, 2016 February 22, 2016
Routing packets from hosts in a multi-prefix network Routing packets from hosts in a multi-prefix network
draft-ietf-6man-multi-homed-host-04 draft-ietf-6man-multi-homed-host-05
Abstract Abstract
This document describes expected IPv6 host behavior in a network that This document describes expected IPv6 host behavior in a network that
has more than one prefix, each allocated by an upstream network that has more than one prefix, each allocated by an upstream network that
implements BCP 38 ingress filtering, when the host has multiple implements BCP 38 ingress filtering, when the host has multiple
routers to choose from. It also applies to other scenarios such as routers to choose from. It also applies to other scenarios such as
the usage of stateful firewalls that effectively act as address-based the usage of stateful firewalls that effectively act as address-based
filters. This host behavior may interact with source address filters. This host behavior may interact with source address
selection in a given implementation, but logically follows it. Given selection in a given implementation, but logically follows it. Given
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 21, 2016. This Internet-Draft will expire on August 25, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2. Sending context expected by the host 2. Sending context expected by the host
2.1. Expectations the host has of the network 2.1. Expectations the host has of the network
A host receives prefixes in a Router Advertisement [RFC4861], which A host receives prefixes in a Router Advertisement [RFC4861], which
goes on to identify whether they are usable by SLAAC [RFC4862] goes on to identify whether they are usable by SLAAC [RFC4862]
[RFC4941] [RFC7217]. When no prefixes are usable for SLAAC, the [RFC4941] [RFC7217]. When no prefixes are usable for SLAAC, the
Router Advertisement would normally signal the availability of DHCPv6 Router Advertisement would normally signal the availability of DHCPv6
[RFC3315] and the host would use it to configure its addresses. In [RFC3315] and the host would use it to configure its addresses. In
the latter case (or if both SLAAC and DHCPv6 are used on the same the latter case (or if both SLAAC and DHCPv6 are used on the same
link for some reason) it will be generally the case that the link for some reason) it will generally be the case that the
configured addresses match one of the prefixes advertised in a Router configured addresses match one of the prefixes advertised in a Router
Advertisement that are supposed to be on-link for that link. Advertisement that are supposed to be on-link for that link.
The simplest multihomed network implementation in which a host makes The simplest multihomed network implementation in which a host makes
choices among routers might be a LAN with one or more hosts on it and choices among routers might be a LAN with one or more hosts on it and
two or more routers, one for each upstream network, or a host that is two or more routers, one for each upstream network, or a host that is
served by disjoint networks on separate interfaces. In such a served by disjoint networks on separate interfaces. In such a
network, especially the latter, there is not necessarily a routing network, especially the latter, there is not necessarily a routing
protocol, and the two routers may not even know that the other is a protocol, and the two routers may not even know that the other is a
router as opposed to a host, or may be configured to ignore its router as opposed to a host, or may be configured to ignore its
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different upstream network. different upstream network.
3. Reasonable expectations of the host 3. Reasonable expectations of the host
3.1. Interpreting Router Advertisements 3.1. Interpreting Router Advertisements
As described in [RFC4191] and [RFC4861], a Router Advertisement may As described in [RFC4191] and [RFC4861], a Router Advertisement may
contain zero or more Prefix information Options (PIOs), or zero or contain zero or more Prefix information Options (PIOs), or zero or
more Route Information Options (RIOs). In their original intent, more Route Information Options (RIOs). In their original intent,
these indicate general information to a host: "the router whose these indicate general information to a host: "the router whose
address is found in the source address field of this packet is your address is found in the source address field of this packet is one of
default router", "you might create an address in this prefix", or your default routers", "you might create an address in this prefix",
"this router would be a good place to send traffic directed to a or "this router would be a good place to send traffic directed to a
given destination prefix". In a multi-homed network implementing given destination prefix". In a multi-homed network implementing
source/destination routing, the interpretation of default router or source/destination routing, the interpretation of default router or
an RIO has to be modified with the words "if the source address is in an RIO has to be modified with the words "if the source address is in
one of the prefixes I advertise in a PIO". Additionally, the PIO one of the prefixes I advertise in a PIO". Additionally, the PIO
must be reinterpreted to also imply that the advertising router would must be reinterpreted to also imply that the advertising router would
be a reasonable first hop for any packet using a source address in be a reasonable first hop for any packet using a source address in
any advertised prefix. any advertised prefix.
+---------+ | +---------+ |
( ISP A ) - + Bob-A +--+ +-----+ ( ISP A ) - + Bob-A +--+ +-----+
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