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draft-ietf-v6ops-ipv6-multihoming-without-ipv6nat-00.txt
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Internet Engineering Task Force O. Troan, Ed.
Internet-Draft Cisco
Intended status: Informational D. Miles
Expires: September 30, 2011 Alcatel-Lucent
S. Matsushima
SOFTBANK TELECOM Corp.
T. Okimoto
NTT West
D. Wing
Cisco
March 29, 2011
IPv6 Multihoming without Network Address Translation
draft-ietf-v6ops-ipv6-multihoming-without-ipv6nat-00
Abstract
Network Address and Port Translation (NAPT) works well for conserving
global addresses and addressing multihoming requirements, because an
IPv4 NAPT router implements three functions: source address
selection, next-hop resolution and optionally DNS resolution. For
IPv6 hosts one approach could be the use of IPv6 NAT. However, NAT
should be avoided, if at all possible, to permit transparent host-to-
host connectivity. In this document, we analyze the use cases of
multihoming. We also describe functional requirements for
multihoming without the use of NAT in IPv6 for hosts and small IPv6
networks that would otherwise be unable to meet minimum IPv6
allocation criteria.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 30, 2011.
Copyright Notice
Troan, et al. Expires September 30, 2011 [Page 1]
Internet-Draft IPv6 Multihoming without NAT March 2011
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IPv6 multihomed network scenarios . . . . . . . . . . . . . . 5
3.1. Classification of network scenarios for multihomed host . 5
3.2. Multihomed network environment . . . . . . . . . . . . . . 7
3.3. Problem Statement . . . . . . . . . . . . . . . . . . . . 8
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. End-to-End transparency . . . . . . . . . . . . . . . . . 9
4.2. Policy providing . . . . . . . . . . . . . . . . . . . . . 10
4.3. Scalability . . . . . . . . . . . . . . . . . . . . . . . 10
5. Problem statement and analysis . . . . . . . . . . . . . . . . 10
5.1. Source address selection . . . . . . . . . . . . . . . . . 11
5.2. Next-hop selection . . . . . . . . . . . . . . . . . . . . 11
5.3. DNS server selection . . . . . . . . . . . . . . . . . . . 12
6. Implementation approach . . . . . . . . . . . . . . . . . . . 13
6.1. Source address selection . . . . . . . . . . . . . . . . . 13
6.2. Next-hop selection . . . . . . . . . . . . . . . . . . . . 13
6.3. DNS resolver selection . . . . . . . . . . . . . . . . . . 14
7. Considerations for host without multi-prefix support . . . . . 14
7.1. IPv6 NAT . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.2. Co-exisitence consideration . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
Troan, et al. Expires September 30, 2011 [Page 2]
Internet-Draft IPv6 Multihoming without NAT March 2011
1. Introduction
IPv6 provides enough globally unique addresses to permit every
conceivable host on the Internet to be uniquely addressed without the
requirement for Network Address Port Translation (NAPT [RFC3022])
offering a renaissance in host-to-host transparent connectivity.
Unfortunately, this may not be possible due to the necessity of NAT
even in IPv6, because of multihoming. Though there are some
mechanisms to implement multihoming, such as BGP multihoming
[RFC4116] and SCTP based multihoming [RFC4960], there is no mechanism
in IPv6 that serves as a replacement for NAT based multihoming in
IPv4. In IPv4, for a host or a small network, NAT based multihoming
is easily deployable and already deployed technique. The same
situation that depends on NAT technique may be brought to the IPv6
world.
Whenever a host or small network (which does not meet minimum IPv6
allocation criteria) is connected to multiple upstream networks IPv6
address is assigned by each respective service provider resulting in
hosts with more than one active IPv6 addresses. As each service
provided is allocated a different address space from its Internet
Registry, it in-turn assigns a different address space to the end-
user network or host. For example, a remote access user's host or
router may use a VPN to simultaneously connect to a remote network
and retain a default route to the Internet for other purposes.
In IPv4 a common solution to the multihoming problem is to employ
NAPT on a border router and use private address space for individual
host addressing. The use of NAPT allows hosts to have exactly one IP
address visible on the public network and the combination of NAPT
with provider-specific outside addresses (one for each uplink) and
destination-based routing insulates a host from the impacts of
multiple upstream networks. The border router may also implement a
DNS cache or DNS policy to resolve address queries from hosts.
It is our goal to avoid the IPv6 equivalent of NAT. So, the goals
for IPv6 multihoming definced in [RFC3582] do not exactly match the
goals of us. Also regardless of what the IPv6 NAT's specification
is, we are trying to avoid any form of network address translation
technique that may not be visible for either of the end hosts. To
reach this goal, mechanisms are needed for end-user hosts to have
multiple address assignments and resolve issues such as which address
to use for sourcing traffic to which destination:
o If multiple routers exist on a single link the host must
appropriately select next-hop for each connected network. Each
router is in turn connected to a different service provider
Troan, et al. Expires September 30, 2011 [Page 3]
Internet-Draft IPv6 Multihoming without NAT March 2011
network, which provides independent address assignment and DNS
resolvers. Routing protocols that would normally be employed for
router-to-router network advertisement seem inappropriate for use
by individual hosts.
o Source address selection also becomes difficult whenever a host
has more than one address within the same address scope. Current
address selection criteria may result in hosts using an arbitrary
or random address when sourcing upstream traffic. Unfortunately,
for the host, the appropriate source address is a function of the
upstream network for which the packet is bound for. If an
upstream service provider uses IP anti-spoofing or uRPF, it is
conceivable that the packets that have inappropriate source
address for the upstream network would never reach their
destination.
o In a multihomed environment, different DNS scopes or partitions
may exist in each independent upstream network. A DNS query sent
to an arbitrary upstream resolver may result in incorrect or
poisoned responses
In short, while IPv6 facilitates hosts having more than one address
in the same address scope, the application of this causes significant
issues for a host from routing, source address selection and DNS
resolution perspectives. A possible consequence of assigning a host
multiple identical-scoped addresses is severely impaired IP
connectivity.
If a host connects to a network behind an IPv4 NAPT, the host has one
private address in the local network. There is no confusion. The
NAT becomes the gateway of the host and forwards the packet to an
appropriate network when it is multihomed. It also operates a DNS
cache server, which receives all DNS inquires, and gives a correct
answer to the host.
In this document, we identify the functions present in multihomed
IPv4 NAPT environments and propose requirements that address
multihomed IPv6 environments without using IPv6 NAT.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Troan, et al. Expires September 30, 2011 [Page 4]
Internet-Draft IPv6 Multihoming without NAT March 2011
IPv6 NAT The terms "NAT66" and "IPv6 NAT" refer to
[I-D.mrw-nat66].
NAPT Network Address Port Translation as described
in [RFC3022]. In other contexts, NAPT is often
pronounced "NAT" or written as "NAT".
Multihomed with multi-prefix (MHMP) A host implementation which
supports the mechanisms described in this
document. Namely source address selection
policy, next-hop selection and DNS selection
policy.
3. IPv6 multihomed network scenarios
In this section, we classify three scenarios of the multihoming
environment.
3.1. Classification of network scenarios for multihomed host
Scenario 1:
In this scenario, two or more routers are present on a single link
shared with the host(s). Each router is in turn connected to a
different service provider network, which provides independent
address assignment and DNS resolvers. A host in this environment
would be offered multiple prefixes and DNS resolvers advertised from
the two different routers.
+------+ ___________
| | / \
+---| rtr1 |=====/ network \
| | | \ 1 /
+------+ | +------+ \___________/
| | |
| host |-----+
| | |
+------+ | +------+ ___________
| | | / \
+---| rtr2 |=====/ network \
| | \ 2 /
+------+ \___________/
Figure 1: single uplink, multiple next-hop, multiple prefix
(Scenario 1)
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Figure 1 illustrates the host connecting to rtr1 and rtr2 via a
shared link. Networks 1 and 2 are reachable via rtr1 and rtr2
respectively. When the host sends packets to network 1, the next-hop
to network 1 is rtr1. Similarly, rtr2 is the next-hop to network 2.
- e.g., broadband service (Internet, VoIP, IPTV, etc.)
Scenario 2:
In this scenario, a single gateway router connects the host to two or
more upstream service provider networks. This gateway router would
receive prefix delegations from each independent service provider
network and a different set of DNS resolvers. The gateway in turn
advertises the provider prefixes to the host, and for DNS, may either
act as a lightweight DNS resolver/cache or may advertise the complete
set of service provider DNS resolvers to the hosts.
+------+ ___________
| | / \
+---| rtr1 |=====/ network \
| | | \ 1 /
+------+ +-----+ | +------+ \___________/
| | | | |
| host |-----| GW |---+
| | | rtr | |
+------+ +-----+ | +------+ ___________
| | | / \
+---| rtr2 |=====/ network \
| | \ 2 /
+------+ \___________/
Figure 2: single uplink, single next-hop, multiple prefix
(Scenario 2)
Figure 2 illustrates the host connected to GW rtr. GW rtr connects
to networks 1 and 2 via rtr1 and rtr2, respectively. When the host
sends packets to either network 1 or 2, the next-hop is GW rtr. When
the packets are sent to network 1 (network 2), GW rtr forwards the
packets to rtr1 (rtr2).
- e.g, Internet + VPN/ASP
Scenario 3:
In this scenario, a host has more than one active interface that
connects to different routers and service provider networks. Each
router provides the host with a different address prefix and set of
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DNS resolvers, resulting in a host with a unique address per link/
interface.
+------+ +------+ ___________
| | | | / \
| |-----| rtr1 |=====/ network \
| | | | \ 1 /
| | +------+ \___________/
| |
| host |
| |
| | +------+ ___________
| | | | / \
| |=====| rtr2 |=====/ network \
| | | | \ 2 /
+------+ +------+ \___________/
Figure 3: Multiple uplink, multiple next-hop, multiple prefix
(Scenario 3)
Figure 3 illustrates the host connecting to rtr1 and rtr2 via a
direct connection or a virtual link. When the host sends packets
network 1, the next-hop to network 1 is rtr1. Similarly, rtr2 is the
next-hop to network 2.
- e.g., Mobile Wifi + 3G, ISP A + ISP B
3.2. Multihomed network environment
In an IPv6 multihomed network, a host is assigned two or more IPv6
addresses and DNS resolvers from independent service provider
networks. When this multihomed host attempts to connect with other
hosts, it may incorrectly resolve the next-hop router, use an
inappropriate source address, or use a DNS response from an incorrect
service provider that may result in impaired IP connectivity.
Multihomed networks in IPv4 have been commonly implemented through
the use of a gateway router with NAPT function (scenario 2 with
NAPT). An analysis of the current IPv4 NAPT and DNS functions within
the gateway router should provide a baseline set of requirements for
IPv6 multihomed environments. A destination prefix/route is often
used on the gateway router to separate traffic between the networks.
Troan, et al. Expires September 30, 2011 [Page 7]
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+------+ ___________
| | / \
+---| rtr1 |=====/ network \
| | | \ 1 /
+------+ +-----+ | +------+ \___________/
| IPv4 | | | |
| host |-----| GW |---+
| | | rtr | |
+------+ +-----+ | +------+ ___________
(NAPT&DNS) | | | / \
(private +---| rtr2 |=====/ network \
address | | \ 2 /
space) +------+ \___________/
Figure 4: IPv4 Multihomed environment with Gateway Router performing
NAPT
3.3. Problem Statement
A multihomed IPv6 host has one or more assigned IPv6 addresses and
DNS resolvers from each upstream service provider, resulting in the
host having multiple valid IPv6 addresses and DNS resolvers. The
host must be able to resolve the appropriate next-hop, the correct
source address and DNS resolver to use based on the destination
prefix. To prevent IP spoofing, operators will often implement IP
filters and uRPF to discard traffic with an inappropriate source
address, making it essential for the host to correctly resolve these
three criteria before sourcing the first packet.
IPv6 has mechanisms for the provision of multiple routers on a single
link and multiple address assignments to a single host. However,
when these mechanisms are applied to the three scenarios in
Section 3.1 a number of connectivity issues are identified:
Scenario 1:
The host has been assigned an address from each router and recognizes
both rtr1 and rtr2 as valid default routers (in the default routers
list).
o The source address selection policy on the host does not
deterministically resolve a source address. Upstream uRPF or
filter policies will discard traffic with source addresses that
the operator did not assign.
o The host will select one of the two routers as the active default
router. No traffic is sent to the other router.
Troan, et al. Expires September 30, 2011 [Page 8]
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Scenario 2:
The host has been assigned two different addresses from the single
gateway router. The gateway router is the only default router on the
link.
o The source address selection policy on the host does not
deterministically resolve a source address. Upstream uRPF or
filter policies will discard traffic with source addresses that
the operator did not assign.
o The gateway router does not have a mechanism for determining which
traffic should be sent to which network. If the gateway router is
implementing host functions (ie, processing RA) then two valid
default routers may be recognized.
Scenario 3:
A host has two separate interfaces and on each interface a different
address is assigned. Each link has its own router.
o The host does not have enough information for determining which
traffic should be sent to which upstream routers. The host will
select one of the two routers as the active default router, and no
traffic is sent to the other router.
o The default address selection rules select the address assigned to
the outgoing interface as the source address. So, if a host has
an appropriate routing table, an appropriate source address will
be selected.
All scenarios:
o The host may use an incorrect DNS resolver for DNS queries.
4. Requirements
This section describes requirements that any solution multi-address
and multi-uplink architectures need to meet.
4.1. End-to-End transparency
End-to-end transparency is a basic concept of the Internet.
[RFC4966] states, "One of the major design goals for IPv6 is to
restore the end-to-end transparency of the Internet. Therefore,
because IPv6 is expected to remove the need for NATs and similar
impediments to transparency, developers creating applications to work
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with IPv6 may be tempted to assume that the complex mechanisms
employed by an application to work in a 'NATted' IPv4 environment are
not required." The IPv6 multihoming solution SHOULD guarantee end-
to-end transparency by avoiding IPv6 NAT.
4.2. Policy providing
The solution SHOULD have a function to provide a policy on sites/
nodes. In particular, in a managed environment such as enterprise
networks, an administrator has to control all nodes in his or her
network.
The providing mechanisms should have:
o a function to distribute policies to nodes dynamically to update
their behavior. When the network environment changes and the
nodes' behavior has to be changed, a network administrator can
modify the behavior of the nodes.
o a function to control every node centrally. A site administrator
or a service provider could determine or could have an effect on
the behavior at their users' hosts.
o a function to control node-specific behavior. Even when multiple
nodes are on the same subnet, the mechanism should be able to
provide a method for the network administrator to make nodes
behave differently. For example, each node may have a different
set of assigned prefixes. In such a case, the appropriate
behavior may be different.
4.3. Scalability
The solution will have to be able to manage a large number of sites/
nodes. In services for residential users, provider edge devices have
to manage thousands of sites. In such environments, sending packets
periodically to each site may affect edge system performance.
5. Problem statement and analysis
The problems described in Section 3 can be classified into these
three types:
o Wrong source address selection
o Wrong next-hop selection
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o Wrong DNS server selection
This section reviews the problem statements presented above and the
proposed functional requirements to resolve the issues.
5.1. Source address selection
A multihomed IPv6 host will typically have different addresses
assigned from each service provider either on the same link
(scenarios 1 & 2) or different links (scenario 3). When the host
wishes to send a packet to any given destination, the current source
address selection rules [RFC3484] may not deterministically resolve
the correct source address when the host addressing was via RA or
DHCPv6. [I-D.ietf-6man-addr-select-sol] describes the use of the
policy table [RFC3484] to resolve this problem, but there is no
mechanism defined to disseminate the policy table information to a
host. A proposal is in [I-D.ietf-6man-addr-select-opt] to provide a
DHCPv6 mechanism for host policy table management.
Again, by employing DHCPv6, the server could restrict address
assignment (of additional prefixes) only to hosts that support policy
table management.
Scenario 1: "Host" needs to support the solution for this problem
Scenario 2: "Host" needs to support the solution for this problem
Scenario 3: If "Host" support the next-hop selection solution, there
is no need to support the address selection functionality on the
host.
5.2. Next-hop selection
A multihomed IPv6 host or gateway may have multiple uplinks to
different service providers. Here each router would use Router
Advertisements [RFC4861] for distributing default route/next-hop
information to the host or gateway router.
In this case, the host or gateway router may select any valid default
router from the default routers list, resulting in traffic being sent
to the wrong router and discarded by the upstream service provider.
Using the above scenarios as an example, whenever the host wishes to
reach a destination in network 2 and there is no connectivity between
networks 1 and 2 (as is the case for a walled-garden or closed
service), the host or gateway router does not know whether to forward
traffic to rtr1 or rtr2 to reach a destination in network 2. The
host or gateway router may choose rtr1 as the default router, and
traffic fails to reach the destination server. The host or gateway
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router requires route information for each upstream service provider,
but the use of a routing protocol between a host and router causes
both configuration and scaling issues. For IPv4 hosts, the gateway
router is often pre-configured with static route information or uses
of Classless Static Route Options [RFC3442] for DHCPv4. Extensions
to Router Advertisements through Default Router Preference and More-
Specific Routes [RFC4191] provides for link-specific preferences but
does not address per-host configuration in a multi-access topology
because of its reliance on Router Advertisements. A DHCPv6 option,
such as that in [I-D.ietf-mif-dhcpv6-route-option], is preferred for
host-specific configuration. By employing a DHCPv6 solution, a
DHCPv6 server could restrict address assignment (of additional
prefixes) only to hosts that support more advanced next-hop and
address selection requirements.
Scenario 1: "Host" needs to support the solution for this problem
Scenario 2: "GW rtr" needs to support the solution for this problem
Scenario 3: "Host" needs to support the solution for this problem
5.3. DNS server selection
A multihomed IPv6 host or gateway router may be provided multiple DNS
resolvers through DHCPv6 or RA [RFC6106]. When the host or gateway
router sends a DNS query, it would normally choose one of the
available DNS resolvers for the query.
In the IPv6 gateway router scenario, the Broadband Forum [TR124]
required that the query be sent to all DNS resolvers, and the gateway
waits for the first reply. In IPv6, given our use of specific
destination-based policy for both routing and source address
selection, it is desirable to extend a policy-based concept to DNS
resolver selection. Doing so can minimize DNS resolver load and
avoid issues where DNS resolvers in different networks have
connectivity issues, or the DNS resolvers are not publicly
accessible. In the worst case, a DNS query may be unanswered if sent
towards an incorrect resolver, resulting in a lack of connectivity.
An IPv6 multihomed host or gateway router should have the ability to
select appropriate DNS resolvers for each service based on the domain
space for the destination, and each service should provide rules
specific to that network. [I-D.ietf-mif-dns-server-selection]
proposes a solution for DNS server selection policy providing
solution with a DHCPv6 option.
Scenario 1: "Host" needs to support the solution for this problem
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Scenario 2: "GW rtr" needs to support the solution for this problem
Scenario 3: "Host" needs to support the solution for this problem
6. Implementation approach
As mentioned in Section 5, in the multi-prefix environment, we have
three problems in source address selection, next-hop selection, and
DNS resolver selection. In this section, possible solution
mechanisms for each problem are introduced and evaluated against the
requirements in Section 4.
6.1. Source address selection
Possible solutions and their evaluation are summarized in
[I-D.ietf-6man-addr-select-sol]. When those solutions are examined
against the requirements in Section 4, the proactive approaches, such
as the policy table distribution mechanism and the routing system
assistance mechanism, are more appropriate in that they can propagate
the network administrator's policy directly. The policy distribution
mechanism has an advantage with regard to the host's protocol stack
impact and the staticness of the assumed target network environment.
6.2. Next-hop selection
As for the source address selection problem, both a policy-based
approach and a non policy-based approach are possible with regard to
the next-hop selection problem. Because of the same requirements,
the policy propagation-based solution mechanism, whatever the policy,
should be more appropriate.
Routing information is a typical example of policy related to next-
hop selection. If we assume source address-based routing at hosts or
intermediate routers, the pairs of source prefixes and next-hops can
be another example of next-hop selection policy.
The routing information-based approach has a clear advantage in
implementation and is already commonly used.
The existing proposed or standardized routing information
distribution mechanisms are routing protocols, such as RIPng and
OSPFv3, the router advertisement (RA) extension option defined in
[RFC4191], the DHCPv6 route information option proposed in
[I-D.ietf-mif-dhcpv6-route-option], and the [TR069] standardized at
BBF.
The RA-based mechanism has difficulty in per-host routing information
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distribution. The dynamic routing protocols such as RIPng are not
usually used between the residential users and ISP networks because
of their scalability implications. The DHCPv6 mechanism does not
have these difficulties and has the advantages of its relaying
functionality. It is commonly used and is thus easy to deploy.
[TR069], mentioned above, is a possible solution mechanism for
routing information distribution to customer-premises equipment
(CPE). It assumes, however, IP reachability to the Auto
Configuration Server (ACS) is established. Therefore, if the CPE
requires routing information to reach the ACS, [TR069] cannot be used
to distribute this information.
6.3. DNS resolver selection
As in the above two problems, a policy-based approach and non policy-
based approach are possible. In a non policy-based approach, a host
or a home gateway router is assumed to send DNS queries to several
DNS servers at once or to select one of the available servers.
In the non policy-based approach, by making a query to a resolver in
a different service provider to that which hosts the service, a user
could be directed to unexpected IP address or receive an invalid
response, and thus cannot connect to the service provider's private
and legitimate service. For example, some DNS servers reply with
different answers depending on the source address of the DNS query,
which is sometimes called split-horizon. When the host mistakenly
makes a query to a different provider's DNS to resolve a FQDN of
another provider's private service, and the DNS resolver adopts the
split-horizon configuration, the queried server returns an IP address
of the non-private side of the service. Another problem with this
approach is that it causes unnecessary DNS traffic to the DNS
resolvers that are visible to the users.
The alternative of a policy-based approach is documented in
[I-D.ietf-mif-dns-server-selection],where several pairs of DNS
resolver addresses and DNS domain suffixes are defined as part of a
policy and conveyed to hosts in a new DHCP option. In an environment
where there is a home gateway router, that router can act as a DNS
proxy, interpret this option and distribute DNS queries to the
appropriate DNS servers according to the policy.
7. Considerations for host without multi-prefix support
This section presents an alternative approach to mitigate the problem
in a multihomed network. This approach will help IPv6 hosts that are
not capable of the enhancements for the source address selection
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policy, next-hop selection policy, and DNS selection policy described
in Section 6.
7.1. IPv6 NAT
In a typical IPv4 multihomed network deployment, IPv4 NAPT is
practically used and it can eventually avoid assigning multiple
addresses to the hosts and solve the next-hop selection problem. In
a similar fashion, IPv6 NAT can be used as a last resort for IPv6
multihomed network deployments where one needs to assign a single
IPv6 address to a host.
__________
/ \
+---/ Internet \
gateway router | \ /
+------+ +---------------------+ | \__________/
| | | | | WAN1 +--+
| host |-----|LAN| Router |--------|
| | | | |NAT|WAN2+--+
+------+ +---------------------+ | __________
| / \
+---/ ASP \
\ /
\__________/
Figure 5: Legacy Host
The gateway router also has to support the two features, next-hop
selection and DNS server selection, shown in Section 6.
The implementation and issues of IPv6 NAT are out of the scope of
this document. They may be covered by another document under
discussion [I-D.mrw-nat66].
7.2. Co-exisitence consideration
To allow the coexistence of non-MHMP hosts and MHMP hosts (i.e. hosts
supporting multi-prefix with the enhancements for the source address
selection), GW-rtr may need to treat those hosts separately.
An idea to achieve this is that GW-rtr identifies the hosts, and then
assigns single prefix to non-MHMP hosts and assigns multiple prefix
to MHMP hosts. In this case, GW-rtr can perform IPv6 NAT only for
the traffic from MHMP hosts if its source address is not appropriate.
Another idea is that GW-rtr assigns multiple prefix to the both
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hosts, and it performs IPv6 NAT for the traffic from non-MHMP hosts
if its source address is not appropriate.
In scenario 1 and 3, the non-MHMP hosts can be placed behind the NAT
box. In this case, non-MHMP host can access the service through the
NAT box.
The implementation of identifying non-MHMP hosts and NAT policy is
outside the scope of this document.
8. Security Considerations
This document requires that the solutions for MHMP should have a
policy providing function. So, new security risks can be introduced
depending on what kind and what form of the policy. The threats can
be categorized in two parts: the policy receiver side and the policy
distributer side. A policy receiver may receive an evil policy from
a policy distributor. A policy distributor should expect some hosts
in his network do not follow the distributed policy. The security
threats related to IPv6 multihoming are described in [RFC4218].
9. IANA Considerations
This document has no IANA actions.
10. Contributors
The following people contributed to this document: Akiko Hattori,
Arifumi Matsumoto, Frank Brockners, Fred Baker, Tomohiro Fujisaki,
Jun-ya Kato, Shigeru Akiyama, Seiichi Morikawa, Mark Townsley,
Wojciech Dec, Yasuo Kashimura, Yuji Yamazaki. This document has
greatly benefited from inputs by Randy Bush, Brian Carpenter, and
Teemu Savolainen.
11. References
11.1. Normative References
[I-D.ietf-6man-addr-select-opt]
Matsumoto, A., Fujisaki, T., and J. Kato, "Distributing
Address Selection Policy using DHCPv6",
draft-ietf-6man-addr-select-opt-00 (work in progress),
December 2010.
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[I-D.ietf-6man-addr-select-sol]
Matsumoto, A., Fujisaki, T., and R. Hiromi, "Solution
approaches for address-selection problems",
draft-ietf-6man-addr-select-sol-03 (work in progress),
March 2010.
[I-D.ietf-mif-dhcpv6-route-option]
Dec, W., Mrugalski, T., Sun, T., and B. Sarikaya, "DHCPv6
Route Option", draft-ietf-mif-dhcpv6-route-option-01 (work
in progress), March 2011.
[I-D.ietf-mif-dns-server-selection]
Savolainen, T. and J. Kato, "Improved DNS Server Selection
for Multi-Homed Nodes",
draft-ietf-mif-dns-server-selection-01 (work in progress),
March 2011.
[I-D.mrw-nat66]
Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", draft-mrw-nat66-12 (work in progress),
March 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
11.2. Informative References
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
January 2001.
[RFC3442] Lemon, T., Cheshire, S., and B. Volz, "The Classless
Static Route Option for Dynamic Host Configuration
Protocol (DHCP) version 4", RFC 3442, December 2002.
[RFC3582] Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site-
Multihoming Architectures", RFC 3582, August 2003.
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[RFC4116] Abley, J., Lindqvist, K., Davies, E., Black, B., and V.
Gill, "IPv4 Multihoming Practices and Limitations",
RFC 4116, July 2005.
[RFC4218] Nordmark, E. and T. Li, "Threats Relating to IPv6
Multihoming Solutions", RFC 4218, October 2005.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007.
[RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
Address Translator - Protocol Translator (NAT-PT) to
Historic Status", RFC 4966, July 2007.
[RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 6106, November 2010.
[TR069] The BroadBand Forum, "TR-069, CPE WAN Management Protocol
v1.1, Version: Issue 1 Amendment 2", December 2007.
[TR124] The BroadBand Forum, "TR-124i2, Functional Requirements
for Broadband Residential Gateway Devices (work in
progress)", May 2010.
Authors' Addresses
Ole Troan (editor)
Cisco
Bergen
Norway
Email: ot@cisco.com
David Miles
Alcatel-Lucent
Melbourne
Australia
Email: david.miles@alcatel-lucent.com