Framework of Multi-domain IPv6-only Underlay Networks and IPv4-as-a-Service
draft-ietf-v6ops-framework-md-ipv6only-underlay-00
The information below is for an old version of the document.
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|---|---|---|---|
| Authors | Chongfeng Xie , Chenhao Ma , Xing Li , Gyan Mishra , Mohamed Boucadair , Thomas Graf | ||
| Last updated | 2023-01-18 (Latest revision 2023-01-09) | ||
| Replaces | draft-xie-v6ops-framework-md-ipv6only-underlay | ||
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draft-ietf-v6ops-framework-md-ipv6only-underlay-00
v6ops Working Group C. Xie
Internet-Draft C. Ma
Intended status: Informational China Telecom
Expires: 5 July 2023 X. Li
CERNET Center/Tsinghua University
G. Mishra
Verizon Inc
M. Boucadair
Orange
T. Graf
Swisscom
1 January 2023
Framework of Multi-domain IPv6-only Underlay Networks and IPv4-as-
a-Service
draft-ietf-v6ops-framework-md-ipv6only-underlay-00
Abstract
For the IPv6 transition, dual-stack deployments require both IPv4 and
IPv6 forwarding capabilities to be deployed in parallel. IPv6-only
is considered as the ultimate stage where only IPv6 forwarding
capabilities are used while ensuring global reachability for both
IPv6 and IPv4 service(usually known as IPv4aaS). This document
specifies requirements and proposes a framework for deploying
IPv6-only as the underlay in multi-domain networks, discusses the
requirements of service traffic, major components and interfaces,
IPv6 mapping prefix allocation, typical procedures for service
delivery. The document also discusses related considerations about
security.
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 https://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 5 July 2023.
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Copyright Notice
Copyright (c) 2023 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 (https://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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Focus on IPv6-only Networks . . . . . . . . . . . . . . . . . 4
4. Why Considering Multi-domain Factor When Implementing IPv6-only
Networks? . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Requirements from Service Traffic . . . . . . . . . . . . . . 9
6. Description of the Framework . . . . . . . . . . . . . . . . 11
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2. ADPT Description . . . . . . . . . . . . . . . . . . . . 13
6.2.1. Rule Management Layer . . . . . . . . . . . . . . . . 13
6.2.2. Routing Processing Layer . . . . . . . . . . . . . . 14
6.2.3. Data Forwarding Layer . . . . . . . . . . . . . . . . 15
6.3. Mapping Prefix Allocation . . . . . . . . . . . . . . . . 15
7. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8.1. Authenticity and Integrity of Packets . . . . . . . . . . 19
8.2. BGP-4 and Multiprotocol Extensions for BGP-4 . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. wledgement . . . . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
IPv6 capabilities have been widely deployed during the past decade
with IPv6 traffic growing faster than IPv4.
[I-D.ietf-v6ops-ipv6-deployment] provides an overview of IPv6
transition deployment status and how the transition to IPv6 is
progressing among network operators and enterprises.
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As of 2022, most IPv6 deployments rely on dual-stack[RFC4213]. Dual-
stack does have a few disadvantages in the long run, like the
duplication of the network resources and states and increased
complexity for network operation to maintain both stacks. For those
reasons, and furthermore when IPv6 usage is dominant, it makes more
sense to consider IPv6-only to reduce network resources and
operational complexity.
In 2016, the IAB announced that it "expects that the IETF will stop
requiring IPv4 compatibility in new or extended protocols. Future
IETF protocol work will then optimize for and depend on IPv6"
[IAB-statement] only. In order to provide the connectivity service
after IPv4 address depletion, operators need to provide IPv6 services
and preserve access to the global IPv4 Internet as a Service(IPv4aaS)
is therefore a natural consideration for IPv6-only network.
Several IPv4 service continuity mechanisms have been designed within
IETF during the past twenty
years[I-D.ietf-v6ops-transition-comparison]. Different types of IPv4
and IPv6 conversion technologies may be considered. For instance
464XLAT[RFC6877] uses stateful NAT64 translation, MAP-E[RFC7597]and
MAP-T [RFC7599] use stateless IPv4-IPv6 address translation for
encapsulation and translation respectively. DS-Lite[RFC6333] adopts
AFTR-based 4over6 tunneling technology.
This document specifies the requirements for multi-domain IPv6-only
underlay networks and proposes a general framework for network
operators. The objective of such a framework is to help large-scale
operators implement the transition to IPv6-only and support cross-
domain, end-to-end IPv4 service delivery over IPv6-only networks. In
this document, the term of "IPv6-only network" stands for "IPv6-only
underlay network", unless there is a specific statement. This
document does not introduce any new IPv6 transition mechanisms nor
IPv4aaS.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14[RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Terminology
The following terms are defined in this document:
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* Multi-domain IPv6-only network: An IPv6-only network which
consists of multiple ASes belonging to and operated by the same
operator.
* UE: User Equipment, e.g., mobile phone.
* CPE: Customer Premise Equipment.
* IXP: Internet Exchange Point.
* WKP: Well-Known Prefix.
* NSP: Network-Specific Prefix.
* PE : Provider Edge (Section 5.2 of [RFC4026]).
* IPv4-embedded IPv6 addresses: IPv6 addresses used to represent
IPv4 nodes in an IPv6 network, 32 bits in the IPv6 address contain
IPv4 address.[RFC6052]
* IPv4-embedded IPv6 packet: IPv6 packet which is generated from
IPv4 packet by algorithmically mapping of the source and
destination IPv4 addresses to IPv6 addresses.
* ASBR: A PE which runs eBGP routing protocol and peering with the
BGP router of external AS.
* AFBR: A type of PE which supports both IPv4 and IPv6 address
families and serves to provide transit services for the other in a
backbone network (Section 1 of [RFC5565]).
* ADPT: A function entity which implements the two-way IPv4 and IPv6
packet conversion for IPv4 service delivery over IPv6-only
underlay network.
* Conversion point: A function which provides conversion between
IPv4 and IPv6 realms. This is, for example, the XLAT function in
[RFC6144]
* GUA: IPv6 Global Unicast Address (Section 3 of [RFC3587]).
3. Focus on IPv6-only Networks
The global industry has not given a unified definition of IPv6-only
network so far. This document defines such a notion as a
IPv6-centric network in which data packets are forwarded upon IPv6
capability, An IPv6-only network may interconnect with external
networks, including IPv4-only networks.
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Generally, IPv6-only network should support the following scenarios,
Scenario 1: IPv6 user to IPv4 server, i.e., IPv6-only user accesses
IPv4 services hosted in cloud data centers.
Scenario 2: IPv4 user to IPv4 server, i.e., IPv4-only user accesses
IPv4 services hosted in cloud data centers.
Scenario 3: IPv6 user to IPv6 server, i.e., IPv6-only user accesses
IPv6 services hosted in cloud data centers.
Scenario 4: DC-to-DC, i.e., IPv6-only network provides communications
between VMs hosted in cloud data centers, despite they are IPv4, IPv6
or IPv4/IPv6 dual-stack.
Scenario 5: Transit for neighbor networks, i.e., IPv6-only network
serves as an interconnection between several segregated IPv4-only
networks, IPv4 packets are transported over the IPv6-only network
between IPv4 networks.
Scenario 6: IPv6-only eBGP Edge peering in Internet Exchange Point
(IXP)[I-D.ietf-bess-ipv6-only-pe-design], this serves to eliminate
IPv4 provisioning at the Edge of IXP that are facing IPv4 address
depletion at large peering points.
Scenario 7: 5G Transport service, SD-WAN, network slicing, etc.
It should be noted that the scenarios above are only a subset of the
scenarios that IPv6-only network will support in the future.
4. Why Considering Multi-domain Factor When Implementing IPv6-only
Networks?
Generally, the networks of large-scale operators comprise multiple
autonomous systems (ASes). Different ASes may serve different
scenarios, such as metro network, backbone network, 4G or 5G mobile
core, data center network and are often managed by different
departments or institutions, using different routing and security
policies.
A typical model of multi-domain network is depicted in figure 1.
Network 1, belonging to and operated by operator 1, is composed of
multiple inter-connected ASes, AS1, AS2 and AS3. Network 1 provides
access to multiple types of users, including mobile, home broadband
and enterprise customers, denoted by UE1, UE2 and UE3 in figure 1.
Routers that are outside the backbone but directly attached to it are
known as "Customer Edge" (CE) routers. [RFC8585] specifies the IPv4
service continuity requirements for IPv6 Customer Edge (CE) routers.
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Specifically, it extends the basic requirements for IPv6 CE routers
to allow for support of IPv4-as-a-Service (IPv4aaS) by means of
transition technologies for delivering IPv4 in IPv6-only access
networks. In addition, cloud services are hosted in data centers and
connected across multiple data centers, the edge, and public and
private clouds. The service instances in cloud data centers must be
able to communicate across these multiple sites, both on-premises and
in the cloud. Multi-domain Networks need to provide connections for
cloud data center. Network 1 supports two connection modes of cloud
data centers, the first one is between cloud data center and
individual users, for instance, the user of CPE1 accesses the service
hosted in DC1, the second one is the connection between cloud data
centers, for instance, communications between VMs hosted in DC1 and
DC2 separately.
Network 1 is open, it is interworking with external networks.
Operator 2 is one of the neighbor operators of operator 1, AS4 of
operator 2 and AS3 of operator 1 are interconnected through BGP
protocol. AS4 is an IPv4-only network, which means that it does not
run IPv6. The edge nodes of the Network 1 are often known as
"Provider Edge" (PE) routers. The term "ingress" (or "ingress PE")
refers to the router at which a packet enters the network, and the
term "egress" (or "egress PE") refers to the router at which it
leaves the backbone. Interior nodes are often known as "P routers"
(Provider Routers).
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----- -----
/ \ / \
| DC1 | | DC2 |
\ / \ /
----- -----
---------|--------------|---------
| | (Operator1) | |
| +---+ Network1+---+ |
| |PE3| |PE4| | (Operator2)
| +---+ +---+ | +--+
| / \ / \ | / \
+----+ | +---+ +--+ +--+ +---+ | +---+ +
|UE/ |---|PE1| AS1 |R1|-|R2| |PE5|---|BR1| AS4 |
|CPE1| | +---+ +--+ +--+ +---+ | +---+ +
+----+ | \ / | | | \ /
| +--+ | | | +--+
| |R5| | | |
| +--+ | AS3 | |
| | | | |
| +--+ | | |
+----+ | |R6| | | | (Operator3)
|UE/ | | +--+ | | | +--+
|CPE2|\| / \ | | | / \
+----+ \ +---+ +--+ +--+ +---+ | +---+ +
|-|PE2| AS2 |R3|-|R4| |PE6|---|BR2| AS5 |
+----+ / +---+ +--+ +--+ +---+ | +---+ +
|UE/ |/| \ / \ / | \ /
|CPE3| | ---- ----- | +--+
+----+ | |
----------------------------------
Figure 1. Multi-domain IPv6 Underlay Networks Model
For Network 1, transition to IPv6-only from dual-stack means some or
all the IPv4 protocol instances of dual-stack network will be
disabled gradually, thereby IPv6 will become the main network-layer
protocol. To be specific, the P routers in the core only support
IPv6, but the PEs support IPv4 on interfaces facing IPv4 client
networks and IPv6 on interfaces facing the core, in this case, the
PEs need to support both address families. Network 1 provides
transportation services for packets that originate outside the
network and whose destinations are outside the network. These
packets enter the IPv6 network at one of its PE routers. They are
routed through the network to another PE router, after which they
leave the network and continue their way.
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When IPv4 capabilities are disabled, the first question is how to
make remaining IPv4 services running normally and users' experience
does not deteriorate. The deployment of IPv6-only should not be
based on the premise of the extinction of all IPv4-only services, it
is very possible that some portion of the Internet service will
consistently be IPv4-based. In other words, IPv6-only network should
not only carry native IPv6 services, but also allow to reach
IPv4-only services. [RFC5565] describes the IPv4-over-IPv6 scenario,
where the network core is IPv6-only and the interconnected IPv4
networks are called IPv4 client networks. The P Routers in the core
only support IPv6, but the ASBRs support IPv4 on interfaces facing
IPv4 client networks and IPv6 on interfaces facing the core. The
routing solution defined in [RFC5565] is to run IBGP among AFBRs to
exchange IPv4 routing information in the core, and the IPv4 packets
are forwarded from one IPv4 client network to the other through a
softwire using tunneling technologies, such as MPLS, LSP, GRE, VXLAN,
L2TPv3, etc.
[RFC6992] describes a routing scenario where IPv4 packets are
transported over an IPv6 network, based on [RFC7915] and [RFC6052],
along with a separate OSPFv3 routing table for IPv4-embedded IPv6
routes in the IPv6 network.
For multi-domain networks, when introducing the IPv6-only scheme
without collaboration between ASes, different ASes adopt the IPv6
transition approach independently, the result is that multiple
IPv6-only islands are connected by IPv4 links between domains. As
shown in figure 2, there will be more IPv4-IPv6 packet conversion
gateways with different functions in the network. Under this
circumstance, IPv6 packets converted from IPv4 packets need to be
transformed back to IPv4 packets at the egress of one AS, and then
back to IPv6 in the next domain, and the number of conversion
gateways will increase along with the increasing of the number of
ASes. Excessive IPv4-IPv6 conversion gateways lead to complexity of
network and CAPEX increasing. Therefore, there is an urgent need for
multi-domain IPv6-only solution to eliminate unnecessary conversion
functions and improve data forwarding efficiency.
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+---+ +---+ +------+
|UE/|--|PGW| | IPv4 |
|CPE| +---+ |Server|
+---+ | +------+
| |
----------- -----------
/Mobile Core\ / \
| Network | | IPv4 |
| (IPv6-only) | | Internet |
\ / \ /
----------- -----------
| |
+-----+ +--------+
|PLAT/| |IPv4 BGP|
|NAT64| | Router |
+-----+ +--------+
| IPv4 link |IPv4 link
| ----------- |
+---------+ / Backbone \ +---------+
|Stateless|----| Network ----|Stateless|
| NAT64 | \(IPv6-only)/ | NAT64 |
+---------+ ----------- +---------+
XLAT-1 XLAT-2
Figure 2: IPv6-only Independent Deployment in Multi-domain Networks
5. Requirements from Service Traffic
Native-IPv6 traffic can be transported over an IPv6-only network
following legacy procedures.
In order to support IPv4 service continuity, the following
requirements should be met by multi-domain IPv6-only networks.
Requirement 1: beneficial to wider IPv6 adoption
It should largely reduce IPv4 public address consumption and
accelerate the deployment of IPv6, rather than prolonging the
lifecycle of IPv4 by introducing multiple layers of NAT44.
Requirement 2: IPv4-as-a-Service
It should provide IPv4 service delivery and there should be no
perceived degradation of customer experience when accessing the
remaining IPv4 services.
Requirement 3: optimized end-to-end
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For any given IPv4 traffic flow, there should be no IPv4-IPv6
conversion point in the middle of the IPv6 data path when traversing
multi-domain IPv6 networks, in other words, IPv4 packet should not
appear in the middle of the IPv6 data path, the quantity of the
conversion points should not exceed two. In addition, IPv6-only
network should support the following two types of IPv6 data path.
-From UE to egress, the packets of IPv4 service can be translated (or
encapsulated) into IPv6 packets within the UE or CPE, and there
should be no IPv6-IPv4 conversion before they reach the egress of the
network.
-From the ingress to egress, since the core of the network is
IPv6-based, so all IPv4 packets which reach the edge of the network
should be transformed into IPv6 packets by the ingress and forwarded
to the egress of the network.
The end-to-end requirement should also be valid for cloud-to-cloud
communications.
Requirement 4: support of double translation and encapsulation
The data-plane has two approaches for traversing the IPv6 provider
network: 4-6-4 translation and 4over6 encapsulation, at least one
mode should be supported by IPv6-only network, the core nodes do not
distinguish between translation-based IPv6 packet and encapsulation-
based IPv6 packet. At the egress, the PE can recover IPv4 packet by
reading the next-header field of the packet. Moreover, translation
mode and encapsulation mode should share the same IPv4-IPv6 address
mapping algorithm. Note that the double translation can reduce to
single translation, while the encapsulation cannot.
Requirement 5: user stateless at the border gateway
Maintaining user status will need great volume of storage and
computation power, so it is generally stored or managed at the edge
of network and close to the user side. It is unsuitable to store
user-related status at the inter-connection point. The border ASBR
that is interworking with external networks should be unaware of the
user-related information, it only needs to perform stateless
translation or encapsulation/decapsulation.
Requirement 6: high scalability
It should achieve high scalability, simplicity and availability,
especially for large-scale operators. When PE processes
IPv4-features at the edge of the network, the quantity of the
IPv4-related status should not increase linearly or exponentially
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along with the quantity of the user or traffic. Considering this, it
is better to adopt algorithm-based mapping approach to avoid
excessive status storage at the edge. It would also avoid
overloading of the IPv6 routing table.
Requirement 7: incremental deployment
It should deploy in an incremental fashion and the overall transition
process should be stable and operational.
Requirement 8: no security compromise
The technologies proposed must not introduce additional security
compromise.
6. Description of the Framework
6.1. Overview
Multi-domain IPv6-only networks should support the forwarding of IPv4
service data, after transforming IPv4 packets into IPv6 ones in the
UE/CPE or at the edge of the network. Take the latter case as an
example, when IPv4 packets that need to traverse lPv6-only network,
the ingress PE, i.e., PE1, will convert IPv4 packets into lPv6
packets by translation or encapsulation and send them into IPv6
network. After intra-domain and cross-domain transmission, the IPv6
packet reaches the egress PE, i.e., PE2, it can be restored to an
IPv4 packet.
As can be seen from the above, the routing of IPv4 data in the form
of IPv6 packet will follow topology of IPv6 network. With this
framework, each PE will be allocated and identified by at least one
IPv6 mapping prefix, denoted by Pref6(PE), it will also have one or
more associated IPv4 address blocks which are extracted from local
IPv4 routing table or address pool. The mapping relationship between
IPv4 address block and IPv6 mapping prefix is called mapping rule in
this context. The mapping rule announced by a given PE will have at
least the following data structure,
IPv4 address block: Pref6(PE)
Since this is prefix-level mapping, there is no need to maintain
user-related status or translation tables at the PE devices.
The mapping rule is used by the ingress to generate corresponding
IPv6 source and destination addresses from its IPv4 source and
destination address when its egress is the given PE, and vice versa.
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-The IPv6 source address is derived by appending the IPv4 source
address to the Pref6(ingress PE).
-The IPv6 destination address is derived by appending the IPv4
destination address to the Pref6(egress PE) in the mapping rule.
[RFC6052] illustrates the algorithmic translation of an IPv4 address
to a corresponding IPv6 address, and vice versa, using only
statically configured information. With this algorithm,
IPv4-embedded IPv6 addresses are composed by concatenating the
prefix, the 32 bits of the IPv4 address, and the suffix (if needed)
to obtain a 128-bit address. The prefixes can only have one of the
following lengths: 32, 40, 48,56, 64, or 96.
For the deployment scenario in this document, it proposed that IPv4
address is located at the last 32 bits of the IPv6 address, most
significant bits first. The bits between IPv6 mapping prefix and
IPv4 address are reserved for future extensions and SHOULD be set to
zero. Examples of such representations are presented in Table 1.
+-------------------+------------+--------------------------+
|IPv6-mapping prefix|IPv4 address|IPv4-embedded IPv6 address|
+-------------------+------------+--------------------------+
|2001:db8::/32 |192.0.2.33 |2001:db8::192.0.2.33 |
|2001:db8:100::/40 |192.0.2.33 |2001:db8:100::192.0.2.33 |
|2001:db8:122::/48 |192.0.2.33 |2001:db8:122::192.0.2.33 |
+-------------------+------------+--------------------------+
Table 1. Text Representation of IPv4-Embedded IPv6 Address
Using the mechanism of mapping rule exchange in IPv6-only network, an
egress PE can tell other PEs that IPv4 packet whose IPv4 destination
address is within the scope IPv4 address block of the mapping rule,
can be forwarded in the IPv6-only network through the egress PE
identified by the corresponding IPv6 mapping prefix of the mapping
rule. This mapping rule can be transmitted across domains.
Therefore, it gives the direction of IPv4 service data transmission
in multi-domain IPv6-only networks.
It should be noted that the mapping rule contains not only the data
structure above, but also other necessary information to support IPv4
service delivery over IPv6-only network, the detailed structure of
the mapping rule is out of the scope of this document.
Although this document illustrates the framework of multi-domain
IPv6-only networks operated by a single operator, this multi-domain
model can naturally be extended to IPv6-only networks which consist
of multiple ASes and are operated by different operators.
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6.2. ADPT Description
This section illustrates the framework of multi-domain IPv6 network
from the perspective of ADPT in PE devices. ADPT is the entity in PE
which accommodates the conversion of IPv4 packets into IPv6 ones for
IPv4 service delivery over IPv6-only network. ADPT comprises the
following components, as shown in figure 3.
+----- + +--------------------------------------------+
| | | PE1 /------------\ | +-------+
| | | | ADPT | | |PE2 |
| | |+-------+ | +-----+ | | | +---+ |
| | ||IPv4 | I3 | | | | I1 | | | | |
| +-++routing+--+--+------+ RM +-+-----+--------+-|-+RM | |
| | ||engine | | +---+ | | | | | | |
| | |+-------+ | | +--+--+ | | | +---+ |
| | | | | +I7 +I2 | | |_______|
| | | | | | +--+--+ | +-------+ |
| | | | |+-++ | | |I4|IPv6 | | +------+
|R1 | | | ||MD| | RP +-+-++routing+---+--+ |
|IPv4 | | | |+-++ | | | |engine | | | |
|Router| | | | | +-----+ | +---+---+ | |R2 |
| | | | | +I8 | | | |IPv6 |
| | |+----------+ | | +-----+ | +---+------+| |Router|
| | ||IPv4 |I5| +---+ | |I6|IPv6 || | |
| +-++packet +-++------+ DF +-+-++packet ++--+ |
| | ||forwarding| | | | | |forwarding|| | |
| | |+----------+ | +-----+ | +----------+| +------+
| | | |______________| |
+------+ +--------------------------------------------+
Figure 3. Framework of Multi-domain IPv6-only Networks
6.2.1. Rule Management Layer
The Rule Management Layer, i.e., RM, deals with the management of
mapping relationship between IPv4 address block and IPv6 mapping
prefix of PEs, as shown in figure 3.
In each PE, there is a mapping rule database, i.e., MD, to store all
the mapping rule records it receive from other PEs. Rule management
layer provides management functions to mapping rule database through
interface I7, for example, Rule Management Layer inserts, modifies,
or deletes mapping rules in the MD. The interface with the ADPT of
other PE is I1, which is used for the exchanging of mapping rule with
each other. The interface with Routing Processing Layer, which will
be illustrated in section 6.2.2, is I2, which is used for the
transmission of mapping rule through Routing Processing Layer. PE1
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can extract the IPv4 address blocks from its IPv4 BGP routing
instance through interface I3, and generate the mapping rules of the
device in combination with its own Pref6. When the mapping rules are
ready, they will be sent to Routing Processing Layer through
interface I2. Correspondingly, PE1 will receive the mapping rules of
other PEs through interface I2 and stores them in the local mapping
rule database.
For some IPv4 address blocks which are not announced explicitly by
any egress PEs to the ingress PE, there will be no corresponding
mapping rule in the rule database. To solve this problem, the
default egress PE is defined in this framework, which announces the
default IPv6 mapping rule with the default mapping prefix to other
PEs. The format of the mapping rule for default IPv4 address is as
follows,
0.0.0.0/0: Pref6(PE)
6.2.2. Routing Processing Layer
Routing Processing Layer, i.e., RP, is in charge of the exchanging of
mapping rule with other PEs and its related routing information at
the routing layer. The exchanging of the mapping rule should precede
to the process of IPv4 data transmission, otherwise, the data
originated from IPv4 network will be dropped due to the absence of
the IPv6 mapping prefix corresponding to its destination address.
When the request of the mapping rule from Rule Management Layer
through interface I2 is being received, Routing Processing Layer will
convert the mapping rule into data structure that is suitable for the
transmission in the IPv6 routing system and send it to the IPv6
routing engine through interface I4. In opposite direction, when
receiving the routing information from IPv6 routing engine through
interface I4, Routing Processing Layer will extract mapping rule from
the routing information and send it to the Rule management layer.
To support the transmission of mapping rules at the routing layer,
BGP4+ protocol or other control protocols needs to be extended.
However, this has been out of the scope of the draft and will be
discussed in other documents. In addition, routing process layer is
responsible for announcing the IPv6 route corresponding to each IPv6
mapping prefix throughout the multi-domain IPv6-only networks.
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6.2.3. Data Forwarding Layer
Data Forwarding Layer, i.e., DF, provides data forwarding function to
IPv6 packets, including native IPv6 packets and IPv4-embedded IPv6
packets. Multi-domain IPv6-only networks need to support both
translation and encapsulation technologies for IPv4 data delivery:
1. Translation
Translation refers to the conversion of IPv4 packets into IPv6
packets or reverse conversion. When receiving an IPv4 packet through
interface I5 from IPv4 packet forwarding module, the data forwarding
layer will look up the mapping rule database through the interface
I8, if the mapping rule corresponding to the IPv4 destination address
is found, the destination address of IPv6 header required for
translation is generated by appending the IPv4 address to the Pref6
in the mapping rule. Otherwise, the default IPv6 mapping prefix is
used to create the destination IPv6 address.
2. Encapsulation
Encapsulation means that PE encapsulates IPv4 packets in IPv6 packets
without changing the original IPv4 packets, and then transmits them
in multi-domain IPv6-only networks. Address mapping in encapsulation
mode is same to that in translation method, when receiving IPv4
packet through interface I5 from IPv4 packet forwarding module, the
data forwarding layer will look up the mapping rule database through
the interface I8, if the mapping rule corresponding to the IPv4
destination address is found, the destination address of IPv6 header
required for encapsulation is generated by appending the IPv4 address
to the Pref6 in the mapping rule. If the mapping prefix
corresponding to the destination IPv4 address is not found, the
default IPv6 mapping prefix is used.
For an IPv4-embedded IPv6 packet, whether it is based on translation
or encapsulation, the Pref6 part of the destination address can
identify the egress in the network, so the forwarding of the IPv6
packet can be implemented based on the Pref6 information of the
destination address.
6.3. Mapping Prefix Allocation
In order to support rule-based IPv4/IPv6 address mapping, a specific
IPv6 address range will be planned to represent IPv4 address space by
stateless mapping as with [RFC7915]. With this framework, there are
two options to allocate IPv6 mapping prefix:
1) WKP:
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A specific WKP can be allocated from the global IPv6 address prefix,
e.g., 64:ff9b:: /96.
Pros:
Service providers do not need to allocate IPv6 address prefixes
specially used for mapping IPv4 addresses from their own IPv6 address
resources.
Cons:
After the IPv4 address is converted into IPv6 address with WKP, the
IPv4 part of the IPv6 address is used for the routing of the origin
of the data packet. In this way, many fine routes with prefix length
greater than 96 will be introduced into the global IPv6 network. In
most networks, fine routing with long prefix length greater than 96
is not supported.
2) NSP:
Operator allocates a specific prefix from their existing IPv6 address
resources for IPv4 addresses mapping.
Pros:
The specific IPv6 prefix allocated by operators can be considered as
an parent prefix, and each PE can obtain IPv6 mapping prefixes
allocated from the parent prefix. Within the multi-domain networks,
the length of IPv6 mapping prefix can be easily tailored to meet the
requirements of IPv6 network for routing length, and the routing of
the packets can be based on the information of IPv6 mapping prefix
part of the IPv6 address. Outside the multi-domain network, because
the IPv6 mapping prefix has been included in its original IPv6
address prefix, it will not introduce any new routing items and
affect the global IPv6 routing system.
Cons:
Not found yet.
As mentioned earlier, each PE will be identified by at least one IPv6
mapping prefix, which is used as the basic routing information to
forward IPv4-embedded IPv6 packet to the right egress PE. For a
given operator, the selection of the length of IPv6 mapping prefix
should be given specific consideration. Firstly, the length of the
IPv6 mapping prefix should be smaller than the maximum length of the
routing prefix that the IPv6-only network specifies, so the PE can
successfully announce to its peers via BGP protocol. Secondly, the
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length of all the IPv6 mapping prefixes should be the same, to avoid
unnecessary processing cost and complexity induced by the prefix
length diversity.
7. Procedure
This section gives a brief overview of the procedures of the IPv4
service delivery over IPv6-only underlay network. The requisite of
IPv4 data delivery is that PEs have successfully exchanged the
mapping rules with each other. The end-to-end IPv4 data delivery by
IPv6-only network includes the following two cases,
1. IPv4 delivery from ingress PE to egress PE
When an ingress PE receives an IPv4 packet from a client-facing
interface destined to a remote IPv4 network, it looks up in its
mapping rule database to find the mapping rule which best matches the
packet's destination IP address. The IPv6 mapping prefix in the
mapping rule will help to find another PE, the egress PE. Since this
happens in multi-domain IPv6-only networks, the ingress and egress
may belong to different ASes, as shown in figure 4, the ingress PE1
is in AS 1 and egress is PE3 in AS 3. The ingress PE must convert
the IPv4 destination address into IPv6 destination address using the
IPv6 mapping prefix of PE3 and forward the IPv6 packet to PE3. When
PE3 receives the IPv6 packet, it derives the IPv4 source and
destination addresses from the IPv4-embedded IPv6 addresses
respectively and restore the original IPv4 packet[RFC6052].
Afterwards, the IPv4 packet will be further forwarded according to
the IPv4 routing table maintained on the egress. The IPv6 data-path
can be shown as below.
IPv6 Data Path
|<------------------------>|
| | (Operator2)
| ---- ----- | ----
| / \ / \ | / \
+----+ +---+ +--+ +--+ +---+ | |
|UE/ |---|PE1| AS1 |R1|-|R2| AS3 |PE3|---| AS4 |
|CPE1| +---+ +--+ +--+ +---+ | |
+----+ \ / \ / \ /
---- ----- ----
Figure 4. IPv6 Data Path from Ingress PE to Egress PE
In this case, there are only two IPv4-IPv6 conversion actions, which
occur in PE1 and PE3 respectively.
2. IPv4 delivery from UE/CPE to egress PE
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Another case is that IPv4 packets may have been transformed into IPv6
packet in UE/CPE, as done by CLAT of 464XLAT[RFC6877], before they
reach the edge of the network.
In this case, the PLAT of 464XLAT and ADPT will converge in ingress
PE, both the client-facing interface and the core-facing interface
are IPv6. When IPv6 packet reaches the ingress PE, the ingress PE
does not need to implement the conversion between IPv4 and IPv6
packets. For the source IPv6 address, because the address adopted by
UE is generally GUA, and the source address of the IPv4-embedded IPv6
packet is IPv4-embedded address in the core of this framework, it is
necessary to convert the source address from GUA to IPv4-embedded
IPv6 address. In addition, because the quantity of IPv4-embedded
IPv6 address is limited, it is necessary to take IPv6 address
multiplexing here, one or more IPv4-embedded IPv6 addresses are
shared among several IPv6-only clients with GUA addresses. For the
destination address, with 464XLAT, UE synthesizes the destination
IPv4 address into IPv6 address by appending IPv4 address to the IPv6
prefix provided by DNS64 server. When the IPv6 packet reaches the
edge the multi-domain IPv6 network, i.e. PE1, the destination IPv6
address is converted into IPv4-embedded IPv6 address. This process
is implemented by looking for the mapping rule corresponding to the
original destination IPv4 address in the MD database, and then
substituting the NAT64 prefix with the IPv6 mapping prefix of the
egress PE.
IPv6 Data Path
|<--------------------------------->|
| | (Operator2)
| ---- ----- | ----
| / \ / \ | / \
+----+ +---+ +--+ +--+ +---+ | |
|UE/ |---|PE1| AS1 |R1|-|R2| AS3 |PE3|---| AS4 |
|CPE1| +---+ +--+ +--+ +---+ | |
+----+ \ / \ / \ /
---- ----- ----
Figure 5. IPv6 Data Path from UE/CPE to Egress PE
In this case, there are only one stateless IPv4-IPv6 conversion
action, which occurs in PE3. Compared with the case of independent
deployment model mentioned in section 5, with the new framework the
quantity of IPv4-IPv6 conversion points has been reduced from three
to one.
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8. Security Considerations
Besides regular security checks on configured mapping rules, the
following two aspects need to be considered as well.
8.1. Authenticity and Integrity of Packets
In this framework, for each egress PE, they assume that all ingress
PEs are legal and authorized to convert the received IPv4 packets
into IPv6 packets and send them into IPv6-only network. If IPv6
packets cannot guarantee its authenticity or integrity, then there
may be a spoofing attack. Some faked ingress PEs can send IPv6 data
converted from IPv4 to attack the egress PE. After the egress PE
recovers the received IPv6 packets into IPv4 packets, it routes based
on the destination IPv4 address and enters the Internet. They use
global IPv4 address, not private address. Therefore, these attacks
cannot cause payload packets to be delivered to an address other than
the one appearing in the destination address field of the IP packet.
Since the PE in this framework is stateless, the effect of the attack
is limited.
8.2. BGP-4 and Multiprotocol Extensions for BGP-4
The framework allows BGP to propagate mapping rule information over
an IPv6-only underlay network, BGP is vulnerable to traffic diversion
attacks. The ability to advertise a mapping rule adds a new means by
which an attacker could cause traffic to be diverted from its normal
path. Such an attack differs from pre-existing vulnerabilities in
that traffic could be forwarded to a distant target across an
intervening network infrastructure (e.g., an IPv6 core), allowing an
attack to potentially succeed more easily since less infrastructure
would have to be subverted. The security issues already exist in
BGP-4 and MP-BGP for IPv6, the same security mechanisms are
applicable.
9. IANA Considerations
There are no other special IANA considerations.
10. wledgement
The authors would like to thank Brian E. Carpenter, Bob Harold, Fred
Baker, Xipeng Xiao, Giuseppe Fioccola, Vasilenko Eduard, Zhenbin Li,
Jen Linkova, Ron Bonica, Shuping Peng, Jingrong Xie, Eduard Metz, Wu
Qin, Dhruv Dhody, Nick Buraglio, Linda Dunbar, Guoliang Han, Weiqiang
Cheng, Aijun Wang, Tianran Zhou and Huaimo Chen for their review and
comments.
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11. References
11.1. Normative References
[I-D.ietf-bess-ipv6-only-pe-design]
Mishra, G. S., Mishra, M. P., Tantsura, J., Madhavi, S.,
Yang, Q., Simpson, A., and S. Chen, "IPv6-Only PE Design
for IPv4-NLRI with IPv6-NH", Work in Progress, Internet-
Draft, draft-ietf-bess-ipv6-only-pe-design-03, 24
September 2022, <https://www.ietf.org/archive/id/draft-
ietf-bess-ipv6-only-pe-design-03.txt>.
[RFC2119] Bradner, S. and RFC Publisher, "Key words for use in RFCs
to Indicate Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3587] Hinden, R., Deering, S., Nordmark, E., and RFC Publisher,
"IPv6 Global Unicast Address Format", RFC 3587,
DOI 10.17487/RFC3587, August 2003,
<https://www.rfc-editor.org/info/rfc3587>.
[RFC4026] Andersson, L., Madsen, T., and RFC Publisher, "Provider
Provisioned Virtual Private Network (VPN) Terminology",
RFC 4026, DOI 10.17487/RFC4026, March 2005,
<https://www.rfc-editor.org/info/rfc4026>.
[RFC5565] Wu, J., Cui, Y., Metz, C., Rosen, E., and RFC Publisher,
"Softwire Mesh Framework", RFC 5565, DOI 10.17487/RFC5565,
June 2009, <https://www.rfc-editor.org/info/rfc5565>.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., Li, X.,
and RFC Publisher, "IPv6 Addressing of IPv4/IPv6
Translators", RFC 6052, DOI 10.17487/RFC6052, October
2010, <https://www.rfc-editor.org/info/rfc6052>.
[RFC6144] Baker, F., Li, X., Bao, C., Yin, K., and RFC Publisher,
"Framework for IPv4/IPv6 Translation", RFC 6144,
DOI 10.17487/RFC6144, April 2011,
<https://www.rfc-editor.org/info/rfc6144>.
[RFC6877] Mawatari, M., Kawashima, M., Byrne, C., and RFC Publisher,
"464XLAT: Combination of Stateful and Stateless
Translation", RFC 6877, DOI 10.17487/RFC6877, April 2013,
<https://www.rfc-editor.org/info/rfc6877>.
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[RFC7915] Bao, C., Li, X., Baker, F., Anderson, T., Gont, F., and
RFC Publisher, "IP/ICMP Translation Algorithm", RFC 7915,
DOI 10.17487/RFC7915, June 2016,
<https://www.rfc-editor.org/info/rfc7915>.
[RFC8174] Leiba, B. and RFC Publisher, "Ambiguity of Uppercase vs
Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174,
DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References
[I-D.ietf-v6ops-ipv6-deployment]
Fioccola, G., Volpato, P., Martinez, J. P., Mishra, G. S.,
and C. Xie, "IPv6 Deployment Status", Work in Progress,
Internet-Draft, draft-ietf-v6ops-ipv6-deployment-10, 1
December 2022, <https://www.ietf.org/archive/id/draft-
ietf-v6ops-ipv6-deployment-10.txt>.
[I-D.ietf-v6ops-transition-comparison]
Lencse, G., Martinez, J. P., Howard, L., Patterson, R.,
and I. Farrer, "Pros and Cons of IPv6 Transition
Technologies for IPv4-as-a-Service (IPv4aaS)", Work in
Progress, Internet-Draft, draft-ietf-v6ops-transition-
comparison-04, 23 May 2022,
<https://www.ietf.org/archive/id/draft-ietf-v6ops-
transition-comparison-04.txt>.
[IAB-statement]
"IAB statement",
<https://www.iab.org/2016/11/07/iab-statement-on-ipv6/>.
[RFC4213] Nordmark, E., Gilligan, R., and RFC Publisher, "Basic
Transition Mechanisms for IPv6 Hosts and Routers",
RFC 4213, DOI 10.17487/RFC4213, October 2005,
<https://www.rfc-editor.org/info/rfc4213>.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., Lee, Y., and RFC
Publisher, "Dual-Stack Lite Broadband Deployments
Following IPv4 Exhaustion", RFC 6333,
DOI 10.17487/RFC6333, August 2011,
<https://www.rfc-editor.org/info/rfc6333>.
[RFC6992] Cheng, D., Boucadair, M., Retana, A., and RFC Publisher,
"Routing for IPv4-Embedded IPv6 Packets", RFC 6992,
DOI 10.17487/RFC6992, July 2013,
<https://www.rfc-editor.org/info/rfc6992>.
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[RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., Taylor, T., Ed., and RFC Publisher, "Mapping
of Address and Port with Encapsulation (MAP-E)", RFC 7597,
DOI 10.17487/RFC7597, July 2015,
<https://www.rfc-editor.org/info/rfc7597>.
[RFC7599] Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S.,
Murakami, T., and RFC Publisher, "Mapping of Address and
Port using Translation (MAP-T)", RFC 7599,
DOI 10.17487/RFC7599, July 2015,
<https://www.rfc-editor.org/info/rfc7599>.
[RFC8585] Palet Martinez, J., Liu, H. M.-H., Kawashima, M., and RFC
Publisher, "Requirements for IPv6 Customer Edge Routers to
Support IPv4-as-a-Service", RFC 8585,
DOI 10.17487/RFC8585, May 2019,
<https://www.rfc-editor.org/info/rfc8585>.
Authors' Addresses
Chongfeng Xie
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: xiechf@chinatelecom.cn
Chenhao Ma
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: machh@chinatelecom.cn
Xing Li
CERNET Center/Tsinghua University
Shuangqing Road No.30, Haidian District
Beijing
100084
China
Email: xing@cernet.edu.cn
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Gyan Mishra
Verizon Inc
Email: gyan.s.mishra@verizon.com
Mohamed Boucadair
Orange
France
Email: mohamed.boucadair@orange.com
Thomas Graf
Swisscom
Binzring 17
CH- CH-8045 Zurich
Switzerland
Email: thomas.graf@swisscom.com
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