Requirements for IPv6
Customer Edge Routers to Support IPv4 Connectivity as-a-ServiceThe IPv6 CompanyMolino de la Navata, 75La Navata - GalapagarMadrid28420Spainjordi.palet@theipv6company.comhttp://www.theipv6company.com/D-Link Systems, Inc.17595 Mount Herrmann St.Fountain ValleyCalifornia92708UShans.liu@dlinkcorp.comhttp://www.dlink.com/NEC Platforms, Ltd.800, ShimomataKakegawa-shiShizuoka436-8501Japankawashimam@vx.jp.nec.comhttps://www.necplatforms.co.jp/en/IPv6 Operations (v6ops)IPv6 transition CE requirements for IPv4aaSThis document specifies the IPv4 service continuity requirements
for an IPv6 Customer Edge (CE) router,
either provided by the service provider or thru the retail market.Specifically, this document extends the "Basic Requirements for
IPv6 Customer Edge Routers"
in order to allow the provisioning of IPv6 transition services for the
support of "IPv4 as-a-Service" (IPv4aaS) by means of new transition mechanisms.
The document only covers transition technologies for delivering IPv4 in
IPv6-only access networks, commonly called "IPv4 as-a-Service" (IPv4aaS),
as required in a world where IPv4 addresses are no longer available, so hosts
in the customer LANs with IPv4-only or IPv6-only applications or devices, requiring
to communicate with IPv4-only services at the Internet, are still able to do so.This document defines IPv4 service continuity features over an IPv6-only
network, for a residential or
small-office router, referred to as an "IPv6 Transition CE Router",
in order to establish an industry baseline for transition features
to be implemented on such a router.These routers are likely to rely upon "Basic Requirements for
IPv6 Customer Edge Routers" (), so the scope of
this document is to ensure the IPv4 "service continuity" support,
in the LAN side and the access to IPv4-only Internet services from
an IPv6-only access WAN even from IPv6-only applications
or devices in the LAN side.This document covers a set of IP transition techniques required when ISPs
have an IPv6-only access network. This is a common situation
in a world where IPv4 addresses are no longer available, so the service providers
need to provision IPv6-only WAN access. At the same time, they need to ensure that
both IPv4-only and IPv6-only devices or applications in the customer networks,
can still reach IPv4-only devices and applications in the Internet.This document specifies the IPv4 service continuity mechanisms
to be supported by an IPv6
Transition CE Router, and relevant provisioning or configuration information
differences from .This document is not a recommendation for service providers to use any specific
transition mechanism.Automatic provisioning of more complex
topology than a single router with multiple LAN interfaces may be handled by
means of HNCP (), which is out of the scope of this
document.Service providers who specify feature sets for IPv6 Transition CE Router MAY specify
a different set of features than those included in this document. Since
it is impossible to know prior to sale which transition mechanism a
device will need over the lifetime of the device, IPv6 Transition CE Router
intended for the retail market MUST support all of them.A complete description of "Usage Scenarios" and "End-User Network
Architecture" is provided in Annex A and B, respectively.
Unlike other IETF documents, the key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document are not used as
described in RFC 2119. This document uses
these keywords not
strictly for the purpose of interoperability, but rather for the
purpose of establishing industry-common baseline functionality. As
such, the document points to several other specifications
to provide additional guidance to implementers
regarding any protocol implementation required to produce a
successful IPv6 Transition CE Router that interoperates successfully with a
particular subset of currently deploying and planned common IPv6-only
access networks.
This document uses the same terms as in ,
with minor clarifications."IPv4aaS" stands for "IPv4 as-a-Service", meaning transition technologies
for delivering IPv4 in IPv6-only access networks.The term "IPv6 transition Customer Edge Router with IPv4aaS"
(shortened as "IPv6 Transition CE Router") is defined
as an "IPv6 Customer Edge Router" that provides features for the
delivery of IPv4 services over an IPv6-only WAN network
including IPv6-IPv4 communications.The "WAN Interface" term used across this document, means that can also support
link technologies based in Internet-layer (or higher-layers) "tunnels", such as
IPv4-in-IPv6 tunnels.The IPv6 Transition CE Router MUST comply with
(Basic Requirements for IPv6 Customer Edge Routers).A new general requirement is added, in order to ensure that the IPv6 Transition CE Router
respects the IPv6 prefix length as a parameter:G-6 The IPv6 Transition CE Router MUST comply with
(IPv6 Prefix Length Recommendation for Forwarding).A new LAN requirement is added, which in fact is common in regular IPv6 Transition CE Router,
and it is required by most of the transition mechanisms:L-15 The IPv6 Transition CE Router SHOULD implement a DNS proxy as described
in (DNS Proxy Implementation Guidelines).The main target of this document is the support of IPv6-only WAN
access. To enable legacy IPv4 functionality, this document also includes
the support of IPv4-only devices and applications in the customers LANs,
as well as IPv4-only services on the Internet. Thus, both IPv4-only
and the IPv6-only devices inside the IPv6 Transition CE Router are able to reach the
IPv4-only services.This document takes no position on simultaneous operation of any
transition mechanism and native IPv4.In order to seamlessly provide the IPv4 Service Continuity in Customer LANs,
allowing an automated IPv6 transition mechanism provisioning, general
transition requirements are added.General transition requirements: If more than one S46 mechanism is supported, the IPv6 Transition CE Router MUST
support the DHCPv6 S46 priority option described in
(Unified IPv4-in-IPv6 Softwire Customer
Premises Equipment (CPE): A DHCPv6-Based Prioritization Mechanism).The IPv6 Transition CE Router MUST verify if the WAN link supports native IPv4.
In that case, transition mechanisms SHOULD NOT be automatically
enabled for that interface.If native IPv4 is not available and 464XLAT
is supported, the IPv6 Transition CE Router MUST enable the CLAT (in order to
automatically configure 464XLAT ).
If 464XLAT is not supported, and more
than one S46 mechanism is supported, following Section 1.4 of
, MUST check for a valid match in
OPTION_S46_PRIORITY, which will allow configuring any
of the other transition mechanisms.The following sections describe the requirements for supporting
transition mechanisms.464XLAT is a technique
to provide IPv4 service over an IPv6-only access network
without encapsulation. This architecture assumes a NAT64
(Stateful NAT64: Network Address and Protocol
Translation from IPv6 Clients to IPv4 Servers) function
deployed at the service provider or a third-party network.The IPv6 Transition CE Router SHOULD support CLAT functionality.
If 464XLAT is supported, it MUST be implemented according to
.
The following IPv6 Transition CE Router requirements also apply:464XLAT requirements: The IPv6 Transition CE Router MUST perform IPv4 Network Address
Translation (NAT) on IPv4 traffic translated using the CLAT, unless
a dedicated /64 prefix has been acquired using DHCPv6-PD
(IPv6 Prefix Options for DHCPv6).The IPv6 Transition CE Router SHOULD support IGD-PCP IWF
(UPnP Internet Gateway Device - Port Control Protocol Interworking
Function).If PCP () is implemented, the IPv6 Transition CE Router MUST
also implement (DHCP Options for the PCP).
If no PCP server is configured, the IPv6 Transition CE Router MAY verify
if the default gateway, or the NAT64 is the PCP server.
A plain IPv6 mode is used to send PCP requests to the server.The IPv6 Transition CE Router MUST implement
(Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis)
in order to discover the PLAT-side translation IPv4 and IPv6
prefix(es)/suffix(es). The IPv6 Transition CE Router MUST follow
(Discovering NAT64 IPv6 Prefixes Using the PCP), in order to
learn the PLAT-side translation IPv4 and IPv6 prefix(es)/suffix(es)
used by an upstream PCP-controlled NAT64 device.Dual-Stack Lite enables both
continued support for IPv4 services and incentives for the
deployment of IPv6. It also de-couples IPv6 deployment in the
service provider network from the rest of the Internet, making
incremental deployment easier. Dual-Stack Lite enables a broadband
service provider to share IPv4 addresses among customers by
combining two well-known technologies: IP in IP (IPv4-in-IPv6) and
Network Address Translation (NAT). It is expected that DS-Lite
traffic is forwarded over the IPv6 Transition CE Router's native IPv6 WAN interface,
and not encapsulated in another tunnel.The IPv6 Transition CE Router SHOULD implement DS-Lite
functionality. If DS-Lite is supported, it MUST be implemented according
to .
The following IPv6 Transition CE Router requirements also apply:DS-Lite requirements: The IPv6 Transition CE Router MUST support configuration of DS-Lite via the
DS-Lite DHCPv6 option
(DHCPv6 Option for Dual-Stack Lite).
The IPv6 Transition CE Router MAY use other mechanisms to configure
DS-Lite parameters. Such mechanisms are outside the scope
of this document.The IPv6 Transition CE Router SHOULD support IGD-PCP IWF
(UPnP Internet Gateway Device - Port Control Protocol Interworking
Function).If PCP () is implemented, the IPv6 Transition CE Router SHOULD
also implement (DHCP Options for the PCP).
If PCP () is implemented and a PCP server
is not configured, the IPv6 Transition CE Router MUST assume, by default, that the AFTR
is the PCP server.
A plain IPv6 mode is used to send PCP requests to the server.The IPv6 Transition CE Router MUST NOT perform IPv4 Network Address
Translation (NAT) on IPv4 traffic encapsulated using
DS-Lite ().Lw4o6 specifies an extension to DS-Lite,
which moves the NAPT function from the DS-Lite tunnel concentrator to the
tunnel client located in the IPv6 Transition CE Router, removing the
requirement for a CGN function in the tunnel concentrator and reducing
the amount of centralized state.The IPv6 Transition CE Router SHOULD implement lw4o6 functionality.
If DS-Lite is implemented, lw4o6 SHOULD be supported as well. If lw4o6
is supported, it MUST be implemented according to .
The following IPv6 Transition CE Router requirements also apply:Lw4o6 requirements: The IPv6 Transition CE Router MUST support configuration of
lw4o6 via the lw4o6 DHCPv6 options (DHCPv6 Options
for Configuration of Softwire Address and Port-Mapped Clients).
The IPv6 Transition CE Router MAY use other mechanisms to configure
lw4o6 parameters. Such mechanisms are outside the scope
of this document.The IPv6 Transition CE Router MUST support the DHCPv4-over-DHCPv6
(DHCP 4o6) transport described in
(DHCPv4-over-DHCPv6 Transport).The IPv6 Transition CE Router MAY support Dynamic Allocation of
Shared IPv4 Addresses as described in
(Dynamic Allocation of Shared IPv4 Addresses).MAP-E is a mechanism for transporting IPv4
packets across an IPv6 network using IP encapsulation, including an
algorithmic mechanism for mapping between IPv6 addresses and IPv4
addresses as well as transport-layer ports.The IPv6 Transition CE Router SHOULD support MAP-E functionality.
If MAP-E is supported, it MUST be implemented according to
. The following IPv6 Transition CE Router requirements also apply:MAP-E requirements: The IPv6 Transition CE Router MUST support configuration of MAP-E
via the MAP-E DHCPv6 options (DHCPv6 Options for
Configuration of Softwire Address and Port-Mapped Clients).
The IPv6 Transition CE Router MAY use other mechanisms to configure
MAP-E parameters. Such mechanisms are outside the scope
of this document.The IPv6 Transition CE Router MAY support Dynamic Allocation of
Shared IPv4 Addresses as described in
(Dynamic Allocation of Shared IPv4 Addresses).MAP-T is a mechanism similar to MAP-E,
differing from it in that MAP-T uses IPv4-IPv6 translation, rather than
encapsulation, as the form of IPv6 domain transport.The IPv6 Transition CE Router SHOULD support MAP-T functionality.
If MAP-T is supported, it MUST be implemented according to
. The following IPv6 Transition CE Router requirements
also apply:MAP-T requirements: The IPv6 Transition CE Router MUST support configuration of MAP-T via the MAP-T
DHCPv6 options (DHCPv6 Options for Configuration
of Softwire Address and Port-Mapped Clients). The IPv6 Transition CE Router
MAY use other mechanisms to configure MAP-T parameters. Such mechanisms
are outside the scope of this document.The IPv6 Transition CE Router MAY support Dynamic Allocation of
Shared IPv4 Addresses as described in
(Dynamic Allocation of Shared IPv4 Addresses).Actual deployments support IPv4 multicast for services such as
IPTV. In the transition phase it is expected that multicast services
will still be provided using IPv4 to the customer LANs.If the IPv6 Transition CE Router supports delivery of IPv4 multicast services, then it
MUST support (Delivery of IPv4 Multicast Services
to IPv4 Clients over an IPv6 Multicast Network) and
(DHCPv6 Option for IPv4-Embedded Multicast and Unicast IPv6 Prefixes).UPnP SHOULD be disabled by default on the IPv6 Transition CE Router when using an IPv4aaS
transition mechanism.UPnP MAY be enabled when a IPv6 Transition CE Router is configured to use a
stateless mechanism that allows unsolicited inbound packets through to the CE,
such as MAP or LW4o6, or when configured with an a port set containing all
65535 ports, e.g. with an IPv4 address sharing ratio of 1.If UPnP is enabled on a IPv6 Transition CE Router, the UPnP agent MUST reject any port
mapping requests for ports outside of the port set allocated to the IPv6 Transition CE Router.UPnP MAY also be enabled on a IPv6 Transition CE Router configured for IPv4aaS mechanisms
that support PCP , if implemented
in conjunction with a method to control the external port mapping,
such as IGD-PCP IWF .A IPv6 Transition CE Router that implements a UPnP agent, SHOULD support the
Open Connectivity Foundation's IGD:2 specification,
including the AddAnyPortMapping() function.This document no longer consider the need to support 6rd
() and includes slightly different requirements
for DS-LITE .One of the apparent main issues for vendors to include new functionalities,
such as support for new transition mechanisms, is the lack of space in the flash
(or equivalent) memory. However, it has been confirmed from existing open source
implementations (OpenWRT/LEDE, Linux, others), that adding the support for
the new transitions mechanisms, requires around 10-12 Kbytes (because most
of the code base is shared among several transition mechanisms already
supported by ), as a single data plane
is common to all them, which typically means about 0,15% of the
existing code size in popular CEs already in the market.It is also clear that the new requirements don't have extra cost in terms of
RAM memory, neither other hardware requirements such as more powerful CPUs.The other issue seems to be the cost of developing the code for those new
functionalities. However, at the time of writing this document, it has been
confirmed that there are several open source versions of the required code for
supporting the new transition mechanisms, and even several vendors already
have implementations and provide it to ISPs, so the development cost is negligent,
and only integration and testing cost may become a minor issue.The IPv6 Transition CE Router must comply with the Security Considerations
as stated in , as well as those stated by
each transition mechanism implemented by the IPv6 Transition CE Router.This document has no actions for IANA.Thanks to Mikael Abrahamsson, Fred Baker, Mohamed Boucadair, Brian Carpenter,
Lee Howard, Richard Patterson, Barbara Stark, Ole Troan, James Woodyatt,
and "TBD", for their review and comments in this and
previous versions of this document.The situation previously described, where there is ongoing IPv6 deployment
and lack of IPv4 addresses, is not happening at the same pace at every country,
and even within every country, every ISP. For different technical, financial,
commercial/marketing and socio-economic reasons, each network is transitioning
at their own pace, and nobody has a magic crystal ball, to make a guess.Different studies (for example )
also show that this is a changing situation, because in a
single country, it may be that not all operators provide IPv6 support, and consumers
may switch ISPs and use the same IPv6 Transition CE Router with an ISP that provides IPv4-only
and an ISP that provides IPv6 plus IPv4aaS.So, it is clear that, to cover all those evolving situations, a IPv6 Transition CE Router is
required, at least from the perspective of the transition support,
which can accommodate those changes.Moreover, because some services will remain IPv4-only for an
undetermined time, and some service providers will remain IPv4-only
for an undetermined period of time, IPv4 will be needed for an
undetermined period of time. There will be a need for CEs
with support "IPv4 as-a-Service" for an undetermined period of time.This document is consequently, based on those premises, in order to
ensure the continued transition from networks that today may provide
access with dual-stack or IPv6-in-IPv4, as described in ,
and as an "extension" to it, evolving to an IPv6-only access with
IPv4-as-a-Service.Considering that situation and different possible usage cases, the
IPv6 Transition CE Router described in this document is expected to be
used typically, in the following scenarios:Residential/household, Small Office/Home Office (SOHO) and
Small/Medium Enterprise (SME). Common usage is any kind of Internet access
(web, email, streaming, online gaming, etc.).Residential/household and Small/Medium Enterprise (SME)
with advanced requirements. Same basic usage
as for the previous case, however there may be requirements for allowing
inbound connections (IP cameras, web, DNS, email, VPN, etc.).The above list is not intended to be comprehensive of all the possible usage
scenarios, just an overall view. In fact, combinations of the above usages are also
possible, as well as situations where the same CE is used at different times
in different scenarios or even different services providers that may use
a different transition mechanism.The mechanisms for allowing inbound connections are "naturally" available
in any IPv6 router, as when using GUA, unless they are blocked by firewall rules,
which may require some manual configuration by means of a GUI and/or CLI.However, in the case of IPv4aaS, because the usage of private addresses and
NAT and even depending on the specific transition mechanism, it typically
requires some degree of more complex manual configuration such as setting up a DMZ,
virtual servers, or port/protocol forwarding. In general, IPv4 CE Routers already
provide GUI and/or CLI to manually configure them, or the possibility to setup the
CE in bridge mode, so another CE behind it, takes care of that. It is out of the
scope of this document the definition of any requirements for that.The main difference for a CE Router to support the above indicated scenarios
and number of users, is related to the packet processing capabilities,
performance, even other details such as the number of WAN/LAN interfaces,
their maximum speed, memory for keeping tables or tracking connections, etc.
It is out of the scope of this document to classify them.The actual bandwidth capabilities of access technologies such as FTTH, cable
and even 3GPP/LTE, allows the support of such scenarios, and indeed, is a very
common situation that access networks and CE Router provided
by the service provider are the same for SMEs and residential users.There is also no difference in terms of who actually provides the
CE Router. In most of the cases is the service provider,
and in fact is responsible, typically, of provisioning/managing at least the
WAN side. However, commonly the user has access to configure the LAN interfaces,
firewall, DMZ, and many other features. In fact, in many cases, the user must
supply or may replace the CE Router; this makes even
more relevant that all the CE Routers, support the same
requirements defined in this document.The IPv6 Transition CE Router described in this document is not intended
for usage in other scenarios such as large Enterprises, Data Centers,
Content Providers, etc. So, even if the documented requirements meet
their needs, they may have additional requirements, which are out of
the scope of this document.According to the descriptions in the preceding sections, an end-user
network will likely support both IPv4 and IPv6. It is
not expected that an end user will change their existing network
topology with the introduction of IPv6. There are some differences in
how IPv6 works and is provisioned; these differences have implications
for the network architecture.A typical IPv4 end-user network consists of a "plug and play" router with
NAT functionality and a single link upstream, connected to the service
provider network.From the perspective of an "IPv4 user" behind an IPv6 transition Customer
Edge Router with IPv4aaS, this doesn't change.However, while a typical IPv4 NAT deployment by default blocks all incoming
connections and may allow opening of ports using a Universal
Plug and Play Internet Gateway Device (UPnP IGD) or some other firewall control protocol, in the
case of an IPv6-only access and IPv4aaS, that may not be feasible depending on
specific transition mechanism details. PCP (Port Control Protocol,
) may be an alternative solution.Another consequence of using IPv4 private address space in the end-user
network is that it provides stable addressing; that is, it never changes
even when you change service providers, and the addresses are always
there even when the WAN interface is down or the customer edge router
has not yet been provisioned. In the case of an IPv6-only access,
there is no change on that if the transition mechanism keeps running
the NAT interface towards the LAN side.More advanced routers support dynamic routing (which learns routes
from other routers), and advanced end-users can build arbitrary, complex
networks using manual configuration of address prefixes combined with a
dynamic routing protocol. Once again, this is true for both, IPv4 and IPv6.In general, the end-user network architecture for IPv6 should provide
equivalent or better capabilities and functionality than the current
IPv4 architecture.The end-user network is a stub network, in the sense that is not providing
transit to other external networks. However, HNCP ()
allows support for automatic provisioning of downstream routers.
Figure 1 illustrates the model topology for the end-user network.This architecture describes the:Basic capabilities of the IPv6 Transition CE RouterProvisioning of the WAN interface connecting to the service
providerProvisioning of the LAN interfacesThe IPv6 Transition CE Router may be manually configured in an arbitrary
topology with a dynamic routing protocol or using HNCP
(). Automatic provisioning and configuration
is described for a single IPv6 Transition CE Router only.Section to be removed for WGLC.
Significant updates are:ID-Nits: IANA section.ID-Nits: RFC7084 reference removed from Abstract.This document no longer updates RFC7084.UPnP section reworded."CE Router" changed to "IPv6 Transition CE Router".Reduced text in Annex A.InternetGatewayDevice:2 Device Template Version 1.01IPv6 Deployment SurveyThe IPv6 Company