v6ops Working Group C. Xie
Internet-Draft C. Ma
Intended status: Informational China Telecom
Expires: September 8, 2022 X. Li
CERNET Center/Tsinghua University
G. Mishra
Verizon Inc
M. Boucadair
Orange
March 7, 2022
Requirements to Multi-domain IPv6-only Network
draft-xie-v6ops-reqirements-multi-domain-ipv6only-01
Abstract
Dual-stack deployments require both IPv4 and IPv6 transfer
capabilities are deployed in parallel. IPv6-only is considered as
the ultimate stage where only IPv6 transfer capabilities are used
while ensuring global reachability. This document specifies
requirements when deploying IPv6-only in multi-domain networks.
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
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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on September 8, 2022.
Copyright Notice
Copyright (c) 2022 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
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publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. The reason to consider multi-domain factor when implementing
IPv6-only . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Requirements from IPv6-native traffic . . . . . . . . . . . . 8
7. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. Requirements from IPv4 service delivery . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
12.1. Normative References . . . . . . . . . . . . . . . . . . 12
12.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
IPv6 capabilities have been widely deployed during the past 10 years
and IPv6 traffic is growing faster than IPv4. Document
[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.
When most services and networks did not support IPv6, it was
straightforward to keep IPv4 function running when IPv6 was
introduced in early stages. Which is called IPv4/IPv6 dual-
stack[RFC4213]. Many IPv6 deployments rely on this dual-stack
approach. However, dual-stack does have a few disadvantages in the
long run, like the duplication of the network resources and states,
as well as other limitations for network operation. For this reason,
when IPv6 usage increases to a certain limit, it would be better to
consider IPv6-only. Generally, running an IPv6-only network would
reduce operational expenditures and optimize operations as compared
to an IPv4/IPv6 dual-stack environment. 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]
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In order to extend the service in the case of IPv4 address depletion,
operators need to provide IPv6 services and still keep the ability
for users to access the global IPv4 Internet. Therefore, IPv4 as a
Service (IPv4aaS) is a natural consideration for IPv6-only scheme.
Several IPv4 service continuity mechanisms have been designed within
IETF during the past twenty
years[I-D.ietf-v6ops-transition-comparison]. When these schemes
support the hosting of IPv4 service, different types of IPv4 and IPv6
conversion technologies are required, for example, 464XLAT[RFC6877]
uses stateful NAT64 translation technology, MAP-E[RFC7597]and MAP-T
[RFC7599] use stateless NAT64 translation. DS-Lite[RFC6333] adopts
AFTR-based 4over6 tunneling technology, while the backbone network
adopts GRE tunneling or stateless translation technology, etc. This
document specifies the requirements for multi-domain IPv6-only
network from the perspective of operators. It does not introduce any
new IPv6 transition mechanisms.
2. Conventions used in this document
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 [RFC2119] .
3. Terminology
The following terms are defined in this draft:
o Multi-domain IPv6-only network: An IPv6-only network which
consists of multiple ASes belonging to and operated by the same
operator.
o UE: User Equipment, e.g., mobile phone.
o CPE: Customer Premise Edge device.
o IXP: Internet Exchange Point.
o PE : Provider Edge device.
o 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.
o Border gateway: A PE router which run eBGP routing protocol and
peering with the BGP router of external AS.
o Conversion point: A function which provides conversion between
IPv4 and IPv6 realms.
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4. The reason to consider multi-domain factor when implementing
IPv6-only
In general, transition to IPv6-only from dual-stack means some or all
the IPv4 protocol instances of dual-stack network will closed
gradually, thereby IPv6 will become the main network-layer protocol.
When IPv4 is closed at the network layer, 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 in short time, it is very possible that some portion of the
Internet service will consistently be IPv4-based. In other words,
IPv6-only network should carry not only IPv6-capable services, but
also 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 (Provider Routers) in the core
only support IPv6, but the AFBRs support IPv4 on interfaces facing
IPv4 client networks and IPv6 on interfaces facing the core. The
routing solution defined in [RFC5565] for this scenario 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 technology, such as
MPLS, LSP, GRE, L2TPv3, etc.
[RFC6992] describes a routing scenario where IPv4 packets are
transported over an IPv6 network, based on [RFC6145] and [RFC6052],
along with a separate OSPFv3 routing table for IPv4-embedded IPv6
routes in the IPv6 network.
In general, the networks of large-scale operators are composed of
multiple autonomous system(AS)es, 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. 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 1,
there will be more IPv4-IPv6 packet conversion gateways with
different functions in the network. Under this circumstance,
IPv4-embedded IPv6 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 points will increases 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
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solutions to eliminate unnecessary conversion functions and improve
data forwarding efficiency.
+---+ +---+ +------+
|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 1: IPv6-only Independent Deployment in Multi-domain Network
5. Scenarios
This section describes scenarios where IPv4 packets are transported
over a multi-domain IPv6-only network. A typical model of multi-
domain IPv6 network is depicted in figure 2. Network 1, belonging to
and operated by operator A, runs IPv6 and is composed of multiple
inter-connected ASes, i.e., AS1, AS2 and AS3. In addition, network 1
provides access to different types of users, including mobile, home
broadband and enterprise customers, denoted by UE1, UE2 and UE3 in
figure 2. Routers that are outside the backbone but directly
attached to it are known as "Customer Edge" (CE) routers.
Network 1 is open, it is interworking with the external networks.
Operator 2 is one of the neighbor operators of Operator 1, AS4 of
operator 2 and AS3 of operator are interconnected through BGP
protocol. In order to illustrate "IPv4 As A service" , AS4 is an
IPv4-only network, which means that it does not run IPv6 protocol.
In addition, cloud services are hosted in data centers and connected
across multiple data centers, the edge, and public and private
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clouds. The data center must be able to communicate across these
multiple sites, both on-premises and in the cloud. IPv6-only network
need to provide connections for cloud data center. Network 1
supports two connections modes of cloud data centers, the first one
is between cloud data center and individual users, for instance, the
user of CPE1 access the service hosted in DC1, the second one is the
connection between cloud data centers, for instance, communications
between DC1 and DC2.
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". 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.
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 "edge routers".
They are routed through the network to another edge router, after
which they leave the network and continue on their way.
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----- -----
/ \ / \
| DC1 | | DC2 |
\ / \ /
----- -----
---------|--------------|---------
| | (Operator1) | |
| +---+ Network +---+ |
| |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 2. Multi-domain IPv6 Network Model
In order to illustrate the requirements of IPv6-only network, the
following scenarios should be considered,
Scenario 1: IPv6 user to IPv4 server, IPv6-only user accesses IPv4
services hosted in cloud data centers.
Scenario 2: IPv4 user to IPv4 server, IPv4-only user accesses IPv4
services hosted in cloud data centers.
Scenario 3: IPv6 user to IPv6 server, IPv6-only user accesses IPv6
services hosted in cloud data centers.
Scenario 4: DC-to-DC, IPv6-only provide communications between VMs
hosted cloud data centers, despite they are IPv4, IPv6 or IPv4/IPv6
dual-stack.
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Scenario 5: Transit for neighbor networks, IPv6-only network serves
as an interconnection between several segregated IPv4-only network,
IPv4 packets are transported over the IPv6 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, etc.
It should be noted that the aforementioned scenarios are only a
subset of the scenarios that multi-domain IPv6-only network will
support in the future.
6. Requirements from IPv6-native traffic
Since there is no IPv4-IPv6 transition issue, native-IPv6 traffic can
be transported by IPv6-only network naturally, the requirements are
not covered by this document.
7. Procedure
This section firstly gives a very brief overview of the procedures of
the IPv4 service delivery over IPv6-only network.
When an ingress PE receives an IPv4 packet from a client-facing
interface destined to a remote IPv4 network, it looks up the packet's
destination IP address. In the scenario of interest, the best match
will help to find another PE, the egress PE. Since this is a multi-
domain IPv6-only network, the ingress and egress may belong to
different ASes, for example the ingress is in AS 1 and egress is in
AS 2. The ingress PE must transform the IPv4 packet into IPv6 packet
and forward the packet to the egress PE. The egress PE then derives
the IPv4 source and destination addresses from the IPv4-embedded IPv6
addresses, respectively [RFC6052]and restore the original IPv4
packet, and forwards it further according to the IPv4 routing table
maintained on the egress. The IPv6 data-path can be shown as below,
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IPv6 Data Path
|<------------------------>|
| | (Operator2)
| ---- ----- | ----
| / \ / \ | / \
+----+ +---+ +--+ +--+ +---+ | |
|UE/ |---|PE1| AS1 |R1|-|R2| AS3 |PE3|---| AS4 |
|CPE1| +---+ +--+ +--+ +---+ | |
+----+ \ / \ / \ /
---- ----- ----
Figure 3. IPv6 Data Path from Ingress PE to Egress PE
Another case that IPv4 packets may have been transformed into IPv6
packet in UE/CPE, as done by CLAT of 464XLAT
[RFC6877][RFC6877]，before they reach the edge of the network.
In this case, the ingress PE receives an IPv6 packet from a client-
facing interface and looks up the packet's destination IPv6 address.
and forward the packet to the egress PE. The egress PE then restore
the original IPv4 packet, and forwards it further by looking up its
IP destination address. 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 UE/CPE to Egress PE
When PE of IPv6-only network UE/CPE need to implement IPv4-IPv6
conversion, a specific IPv6 address range will represent IPv4 systems
(IPv4-converted addresses), and the IPv6 systems have addresses
(IPv4-translatable addresses or IPv4-embedded IPv6 addresses) that
can be algorithmically mapped to a subset of the service provider's
IPv4 addresses. Note that IPv4-translatable addresses are a subset
of IPv4-converted addresses. In this way, there is no need to
concern oneself with translation tables, as the IPv4 and IPv6
counterparts are algorithmically related.
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8. Requirements from IPv4 service delivery
In order to support IPv4 service delivery, the following requirements
should be met by multi-domain IPv6-only network，
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 44NAT.
Requirement 2: IPv4-as-a-Service
IPv6 transition mechanisms should provide IPv4 service delivery and
there should be no perceived degradation of customer experience when
accessing the remaining IPv4 services.
Requirement 3: end-to-end
End-to-end means, 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 network, in other words, IPv4 packet
should not appear in the middle of the IPv6 data path, the maximum
number of the transition point should be two. In addition, IPv6-only
network should support the following two types of IPv6 data path, as
mentioned in section 7.
-From UE to egress, the packets of IPv4 service can be translated
into IPv6 packets within UE or CPE, and there should be no IPv4-IPv6
conversion before they reaches the egress of the network.
-From the ingress to egress, since the core of the network is
IPv6-based, so all IPv4 packets which reaches 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 also be
valid for cloud-to-cloud communications.
Requirement 4: support of translation and encapsulation
For the data-plane, there are two approaches for traversing the IPv6
provider network: 4-6-4 translation and 4-in6 encapsulation, both of
them can 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. It should be noted that
translation mode and encapsulation mode have the same IPv4-IPv6
address mapping algorithm.
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Requirement 5: controller independent
In order to forward an IPv4 packet to the right egress point, IPv4
reachability information must be exchanged in advance between the
IPv4 networks over in IPv6-only network. In general, BGP4+ is used
to distribute external IPv4 routing information among AFBRs. In the
scenarios of interest, the extension of BGP4+ sessions can be used to
pass IPv4 routing information. This would require that IPv4-embedded
IPv6 routes be flooded throughout the entire IPv6-only network and
stored on every router. It does not rely on the deployment of any
centralized controller. Note that with this routing solution, the
IPv4 and IPv6 header conversion performed in both directions by the
PE is stateless.
Requirement 6: 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
gateway with other networks should be unaware of the user-related
information, it only needs to perform stateless translation or
encapsulation/decapsulation.
Requirement 7: high scalability
It should achieve scalability, simplicity and high availability,
especially for large-scale SPs. When PE processes IPv4-features at
the edge of the network, the quantity of the IPv4-related status
should not increase linearly or exponentially 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 prevent overload of the IPv6 routing table.
Requirement 8: SRv6 applicable
SRv6 can be supported by inserting SRH in translated IPv6 packet, so
the network programming can be realized for IPv4 traffic flow.
Requirement 9: incremental deployment
It should deploy in an incremental fashion and the overall transition
process should be stable and operational.
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9. Security Considerations
There are no other special security considerations.
10. IANA Considerations
There are no other special IANA considerations.
11. Acknowledgement
This is under development by a large group of people. Those who have
posted to the list during the discussion.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "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>.
12.2. Informative References
[I-D.ietf-bess-ipv6-only-pe-design]
Mishra, G., Mishra, M., Tantsura, J., Madhavi, S., Yang,
Q., Simpson, A., and S. Chen, "IPv6-Only PE Design for
IPv4-NLRI with IPv6-NH", draft-ietf-bess-ipv6-only-pe-
design-00 (work in progress), September 2021.
[I-D.ietf-v6ops-ipv6-deployment]
Fioccola, G., Volpato, P., Elkins, N., Martinez, J. P.,
Mishra, G. S., and C. Xie, "IPv6 Deployment Status",
draft-ietf-v6ops-ipv6-deployment-04 (work in progress),
February 2022.
[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 IPv4aaS", draft-ietf-v6ops-transition-
comparison-02 (work in progress), March 2022.
[IAB-statement]
"IAB statement",
<https://www.iab.org/2016/11/07/iab-statement-on-ipv6/>.
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[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213,
DOI 10.17487/RFC4213, October 2005,
<https://www.rfc-editor.org/info/rfc4213>.
[RFC5565] Wu, J., Cui, Y., Metz, C., and E. Rosen, "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., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
DOI 10.17487/RFC6052, October 2010,
<https://www.rfc-editor.org/info/rfc6052>.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
<https://www.rfc-editor.org/info/rfc6145>.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
<https://www.rfc-editor.org/info/rfc6333>.
[RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
Combination of Stateful and Stateless Translation",
RFC 6877, DOI 10.17487/RFC6877, April 2013,
<https://www.rfc-editor.org/info/rfc6877>.
[RFC6992] Cheng, D., Boucadair, M., and A. Retana, "Routing for
IPv4-Embedded IPv6 Packets", RFC 6992,
DOI 10.17487/RFC6992, July 2013,
<https://www.rfc-editor.org/info/rfc6992>.
[RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, Ed., "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.,
and T. Murakami, "Mapping of Address and Port using
Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599, July
2015, <https://www.rfc-editor.org/info/rfc7599>.
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Authors' Addresses
Chongfeng Xie
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: xiechf@chinatelecom.cn
Chenhao Ma
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: machh@chinatelecom.cn
Xing Li
CERNET Center/Tsinghua University
Shuangqing Road No.30, Haidian District
Beijing, Beijing 100084
China
Email: xing@cernet.edu.cn
Gyan Mishra
Verizon Inc
Email: gyan.s.mishra@verizon.com
Mohamed Boucadair
Orange
France
Email: mohamed.boucadair@orange.com
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