Internet DRAFT - draft-liu-sunset4-gapanalysis
draft-liu-sunset4-gapanalysis
Network Working Group W. Liu
Internet-Draft W. Xu
Intended status: Informational C. Zhou
Expires: April 21, 2019 Huawei Technologies
T. Tsou
Philips Lighting
S. Perreault
Jive Communications
P. Fan
R. Gu
China Mobile
C. Li
China Telecom
October 22, 2018
Gap Analysis for IPv4 Sunset
draft-liu-sunset4-gapanalysis-00
Abstract
Sunsetting IPv4 refers to the process of turning off IPv4
definitively. It can be seen as the final phase of the transition to
IPv6. This memo enumerates difficulties arising when sunsetting
IPv4, and identifies the gaps requiring additional work.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on April 21, 2019 .
Copyright Notice
Copyright (c) 2015 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
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Related Work . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Remotely Disabling IPv4 . . . . . . . . . . . . . . . . . . . 4
3.1. Indicating that IPv4 connectivity is unavailable . . . . 4
3.2. Disabling IPv4 in the LAN . . . . . . . . . . . . . . . . 4
4. Client Connection Establishment Behavior . . . . . . . . . . 5
5. Disabling IPv4 in Operating System and Applications . . . . . 5
6. On-Demand Provisioning of IPv4 Addresses . . . . . . . . . . 6
7. IPv4 Address Literals . . . . . . . . . . . . . . . . . . . . 6
8. Managing Router Identifiers . . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
12. Informative References . . . . . . . . . . . . . . . . . . . 7
Annex A. Solution Ideas . . . . . . . . . . . . . . . . . . . . 9
A.1. Remotely Disabling IPv4 . . . . . . . . . . . . . . . . . 9
A.1.1. Indicating that IPv4 connectivity is unavailable . . 9
A.1.2. Disabling IPv4 in the LAN . . . . . . . . . . . . . . 9
A.2. Client Connection Establishment Behavior . . . . . . . . 10
A.3. Disabling IPv4 in Operating System and Applications . . . 10
A.4. On-Demand Provisioning of IPv4 Address. . . . . . . . . . 10
A.5. Managing Router Identifiers . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The final phase of the transition to IPv6 is the sunset of IPv4, that
is turning off IPv4 definitively on the attached networks and on the
upstream networks.
Some current implementation behavior makes it hard to sunset IPv4.
Additionally, some new features could be added to IPv4 to make its
sunsetting easier. This document analyzes the current situation and
proposes new work in this area.
The decision about when to turn off IPv4 is out of scope. This
document merely attempts to enumerate the issues one might encounter
if that decision is made.
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2. Related Work
[RFC3789], [RFC3790],[RFC3791], [RFC3792], [RFC3793], [RFC3794],
[RFC3795] and [RFC3796] contain surveys of IETF protocols with their
IPv4 dependencies.
Additionally, although reviews in RFCs 3789-3796 ensured that IETF
standards then in use could support IPv6, no IETF-wide effort has
been undertaken to ensure that the issues identified in those drafts
are all addressed, nor to ensure that standards written after RFC3100
(where the previous review efforts stopped) function properly on
IPv6-only networks.
The IETF needs to ensure that existing standards and protocols have
been actively reviewed, and any parity gaps either identified so that
they can be fixed, or documented as unnecessary to address because it
is unused or superseded by other features.
First, the IETF must review RFCs 3789-3796 to ensure that any gaps in
specifications identified in these documents and still in active use
have been updated as necessary to enable operation in IPv6-only
environments (or if no longer in use, are declared historic).
Second, the IETF must review documents written after the existing
review stopped (according to RFC 3790, this review stopped with
approximately RFC 3100) to identify specifications where IPv6-only
operation is not possible, and update them as necessary and
appropriate, or document why an identified gap is not an issue i.e.
not necessary for functional parity with IPv4.
This document does not recommend excluding Informational and BCP RFCs
as the previous effort did, due to changes in the way that these
documents are used and their relative importance in the RFC Series.
Instead, any documents that are still active (i.e. not declared
historic or obsolete) and the product of IETF consensus (i.e. not a
product of the ISE Series) should be included. In addition, the
reviews undertaken by RFCs 3789-3796 were looking for "IPv4
dependency" or "usage of IPv4 addresses in standards". This document
recommends a slightly more specific set of criteria for review.
Reviews should include:
o Consideration of whether the specification can operate in an
environment without IPv4.
o Guidance on the use of 32-bit identifiers that are commonly
populated by IPv4 addresses.
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o Consideration of protocols on which specifications depend or
interact, to identify indirect dependencies on IPv4.
o Consideration of how to transit from an IPv4 environment to an
IPv6 environment.
3. Remotely Disabling IPv4
3.1. Indicating that IPv4 connectivity is unavailable
PROBLEM 1: When an IPv4 node boots and requests an IPv4 address
(e.g., using DHCP), it typically interprets the absence
of a response as a failure condition even when it is not.
PROBLEM 2: Home router devices often identify themselves as default
routers in DHCP responses that they send to requests
coming from the LAN, even in the absence of IPv4
connectivity on the WAN.
3.2. Disabling IPv4 in the LAN
PROBLEM 3: IPv4-enabled hosts inside an IPv6-only LAN can auto-
configure IPv4 addresses [RFC3927] and enable various
protocols over IPv4 such as mDNS [RFC6762] and LLMNR
[RFC4795]. This can be undesirable for operational or
security reasons, since in the absence of IPv4, no
monitoring or logging of IPv4 will be in place.
PROBLEM 4: IPv4 can be completely disabled on a link by filtering it
on the L2 switching device. However, this may not be
possible in all cases or may be too complex to deploy.
For example, an ISP is often not able to control the L2
switching device in the subscriber home network.
PROBLEM 5: A host with only Link-Local IPv4 addresses will "ARP for
everything", as described in Section 2.6.2 of [RFC3927].
Applications running on such a host connected to an
IPv6-only network will believe that IPv4 connectivity is
available, resulting in various bad or sub-optimal
behavior patterns. See
[I-D.yourtchenko-ipv6-disable-ipv4-proxyarp] for further
analysis.
Some of these problems were described in [RFC2563], which
standardized a DHCP option to disable IPv4 address auto-
configuration. However, using this option requires running an IPv4
DHCP server, which is contrary to the goal of IPv4 sunsetting.
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4. Client Connection Establishment Behavior
PROBLEM 6: Happy Eyeballs [RFC6555] refers to multiple approaches to
dual-stack client implementations that try to reduce
connection setup delays by trying both IPv4 and IPv6
paths simultaneously. Some implementations introduce
delays which provide an advantage to IPv6, while others
do not [Huston2012]. The latter will pick the fastest
path, no matter whether it is over IPv4 or IPv6,
directing more traffic over IPv4 than the other kind of
implementations. This can prove problematic in the
context of IPv4 sunsetting, especially for Carrier-Grade
NAT phasing out because CGN does not add significant
latency that would make the IPv6 path more preferable.
Traffic will therefore continue using the CGN path unless
other network conditions change.
PROBLEM 7: getaddrinfo() [RFC3493] sends DNS queries for both A and
AAAA records regardless of the state of IPv4 or IPv6
availability. The AI_ADDRCONFIG flag can be used to
change this behavior, but it relies on programmers using
the getaddrinfo() function to always pass this flag to
the function. The current situation is that in an
IPv6-only environment, many useless A queries are made.
5. Disabling IPv4 in Operating System and Applications
It is possible to completely remove IPv4 support from an operating
system as has been shown by the work of Bjoern Zeeb on FreeBSD.
[Zeeb] Removing IPv4 support in the kernel revealed many IPv4
dependencies in libraries and applications.
PROBLEM 8: Completely disabling IPv4 at runtime often reveals
implementation bugs. Hard-coded dependencies on IPv4
abound, such as on the 127.0.0.1 address assigned to the
loopback interface, and legacy IPv4-only APIs are widely
used by applications. It is hard for the administrators
and users to know what applications running on the
operating system have implementation problems of IPv4
dependency. It is therefore often operationally
impossible to completely disable IPv4 on individual
nodes.
PROBLEM 9: In an IPv6-only world, legacy IPv4 code in operating
systems and applications incurs a maintenance overhead
and can present security risks.
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6. On-Demand Provisioning of IPv4 Addresses
As IPv6 usage climbs, the usefulness of IPv4 addresses to subscribers
will become smaller. This could be exploited by an ISP to save IPv4
addresses by provisioning them on-demand to subscribers and
reclaiming them when they are no longer used. This idea is described
in [I-D.fleischhauer-ipv4-addr-saving] and [BBF.TR242] for the
context of PPP sessions. In these scenarios, the home router is
responsible for requesting and releasing IPv4 addresses, based on
snooping the traffic generated by the hosts in the LAN, which are
still dual-stack and unaware that their traffic is being snooped.
As described in TR-092 and TR-187, NAS(e.g., BRAS, BNG) stores pools of
IPv4 and IPv6 addresses, which are used for DHCP distribution to the
hosts in home network. IPv4 and IPv6 addresses of hosts can be dynamic
assignment from a pool of IPv4 and IPv6 prefixes in NAS.
As the IPv4 sunsets, the number of IPv4 hosts is reduced, therefore the
IPv4 address resource in NAS needs to be reduced too. These reduced
IPv4 addresses will be reclaimed by the address management system
(NMS, controller, IPAM, etc.). At the same time, as the number of IPv6
hosts increases, NAS need incrementally increase the number of IPv6
address resource. The increased IPv6 address resource can be assigned
by the address management system, which makes the transition more
smoothly by dynamically adding / releasing IP address resources in NAS.
In modern network systems, protocols such as NETCONF / RESTCONF / RADIUS
can be used for this process. With NETCONF, NAS acts as NETCONF server
mode with the opening port to listen for the client connection, while
the address management system as a netconf client that connects and
processes IP address request from NAS.
PROBLEM 10: Dual-stack hosts that implement Happy-Eyeballs [RFC6555]
will generate both IPv4 and IPv6 traffic even if the
algorithm end up chooosing IPv6. This means that an IPv4
address will always be requested by the home router,
which defeats the purpose of on-demand provisioning.
PROBLEM 11: Many operating systems periodically perform some kind of
network connectivity check as long as an interface is up.
Similarly, applications often send keep-alive traffic
continuously. This permanent "background noise" will
prevent an IPv4 address from being released by the home
router.
PROBLEM 12: Hosts in the LAN have no knowledge that IPv4 is available
to them on-demand only. If they had explicit knowledge
of this fact, they could tune their behaviour so as to be
more conservative in their use of IPv4.
PROBLEM 13: This mechanism is only being proposed for PPP even though
it could apply to other provisioning protocols (e.g.,
DHCP).
PROBLEM 14: When the number of IPv4 hosts connected to NAS is reduced,
the NAS releases the IPv4 address resource and the NAS
requests more IPv6 address resource for it to serve hosts
transitting from IPv4 to IPv6.
7. IPv4 Address Literals
IPv4 addresses are often used as resource locators. For example, it
is common to encounter URLs containing IPv4 address literals on web
sites [I-D.wing-behave-http-ip-address-literals]. IPv4 address
literals may be published on media other than web sites, and may
appear in various forms other than URLs. For the operating systems
which exhibit the behavior described in
[I-D.yourtchenko-ipv6-disable-ipv4-proxyarp], this also means an
increase in the broadcast ARP traffic, which may be undesirable.
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PROBLEM 14: IPv6-only hosts are unable to access resources identified
by IPv4 address literals.
8. Managing Router Identifiers
IPv4 addresses are often conventionally chosen to number a router ID,
which is used to identify a system running a specific protocol. The
common practice of tying an ID to an IPv4 address gives much
operational convenience. A human-readable ID is easy for network
operators to deal with, and it can be auto-configured, saving the
work of planning and assignment. It is also helpful to quickly
perform diagnosis and troubleshooting, and easy to identify the
availability and location of the identified router.
PROBLEM 15: In an IPv6 only network, there is no IP address that can
be directly used to number a router ID. IDs have to be
planned individually to meet the uniqueness requirement.
Tying the ID directly to an IP address which yields
human-friendly, auto-configured ID that helps with
troubleshooting is not possible.
9. IANA Considerations
None.
10. Security Considerations
It is believed that none of the problems identified in this draft are
security issues.
11. Acknowledgements
Thanks in particular to Andrew Yourtchenko, Jordi Palet Martinez,
Lee Howard, Nejc Skoberne, and Wes George for their thorough reviews
and comments.
Special thanks to Marc Blanchet who was the driving force behind this
work and to Jean-Philippe Dionne who helped with the initial version
of this document.
12. Informative References
[BBF.TR242]
Broadband Forum, "TR-242: IPv6 Transition Mechanisms for
Broadband Networks", August 2012.
[Huston2012]
Huston, G. and G. Michaelson, "RIPE 64: Analysing Dual
Stack Behaviour and IPv6 Quality", April 2012.
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[I-D.fleischhauer-ipv4-addr-saving]
Fleischhauer, K. and O. Bonness, "On demand IPv4 address
provisioning in Dual-Stack PPP deployment scenarios",
draft-fleischhauer-ipv4-addr-saving-05 (work in progress),
September 2013.
[I-D.wing-behave-http-ip-address-literals]
Wing, D., "Coping with IP Address Literals in HTTP URIs
with IPv6/IPv4 Translators", draft-wing-behave-http-ip-
address-literals-02 (work in progress), March 2010.
[I-D.yourtchenko-ipv6-disable-ipv4-proxyarp]
Yourtchenko, A. and O. Owen, "Disable "Proxy ARP for
Everything" on IPv4 link-local in the presence of IPv6
global address", draft-yourtchenko-ipv6-disable-
ipv4-proxyarp-00 (work in progress), May 2013.
[RFC2563] Troll, R., "DHCP Option to Disable Stateless Auto-
Configuration in IPv4 Clients", RFC 2563, May 1999.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6", RFC
3493, February 2003.
[RFC3789] Nesser, P. and A. Bergstrom, "Introduction to the Survey
of IPv4 Addresses in Currently Deployed IETF Standards
Track and Experimental Documents", RFC 3789, June 2004.
[RFC3790] Mickles, C. and P. Nesser, "Survey of IPv4 Addresses in
Currently Deployed IETF Internet Area Standards Track and
Experimental Documents", RFC 3790, June 2004.
[RFC3791] Olvera, C. and P. Nesser, "Survey of IPv4 Addresses in
Currently Deployed IETF Routing Area Standards Track and
Experimental Documents", RFC 3791, June 2004.
[RFC3792] Nesser, P. and A. Bergstrom, "Survey of IPv4 Addresses in
Currently Deployed IETF Security Area Standards Track and
Experimental Documents", RFC 3792, June 2004.
[RFC3793] Nesser, P. and A. Bergstrom, "Survey of IPv4 Addresses in
Currently Deployed IETF Sub-IP Area Standards Track and
Experimental Documents", RFC 3793, June 2004.
[RFC3794] Nesser, P. and A. Bergstrom, "Survey of IPv4 Addresses in
Currently Deployed IETF Transport Area Standards Track and
Experimental Documents", RFC 3794, June 2004.
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[RFC3795] Sofia, R. and P. Nesser, "Survey of IPv4 Addresses in
Currently Deployed IETF Application Area Standards Track
and Experimental Documents", RFC 3795, June 2004.
[RFC3796] Nesser, P. and A. Bergstrom, "Survey of IPv4 Addresses in
Currently Deployed IETF Operations & Management Area
Standards Track and Experimental Documents", RFC 3796,
June 2004.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, May
2005.
[RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local
Multicast Name Resolution (LLMNR)", RFC 4795, January
2007.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
February 2013.
[Zeeb] "FreeBSD Snapshots without IPv4 support",
<http://wiki.freebsd.org/IPv6Only>.
Annex A. Solution Ideas
A.1. Remotely Disabling IPv4
A.1.1. Indicating that IPv4 connectivity is unavailable
One way to address these issues is to send a signal to a dual-stack
node that IPv4 connectivity is unavailable. Given that IPv4 shall be
off, the message must be delivered through IPv6.
A.1.2. Disabling IPv4 in the LAN
One way to address these issues is to send a signal to a dual-stack
node that auto-configuration of IPv4 addresses is undesirable, or
that direct IPv4 communication between nodes on the same link should
not take place.
A signalling protocol equivalent to the one from [RFC2563] but over
IPv6 is necessary, using either Router Advertisements or DHCPv6.
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Furthermore, it could be useful to have L2 switches snoop this
signalling and automatically start filtering IPv4 traffic as a
consequence.
Finally, it could be useful to publish guidelines on how to safely
block IPv4 on an L2 switch.
A.2. Client Connection Establishment Behavior
Recommendations on client connection establishment behavior that
would facilitate IPv4 sunsetting would be appropriate.
A.3. Disabling IPv4 in Operating System and Applications
It would be useful for the IETF to provide guidelines to programmers
on how to avoid creating dependencies on IPv4, how to discover
existing dependencies, and how to eliminate them. It would be useful
if operating systems provide functions for users to see what
applications uses legacy IPv4-only APIs, so they can know it better
whether they can turn off IPv4 completely. Having programs and
operating systems that behave well in an IPv6-only environment is a
prerequisite for IPv4 sunsetting.
A.4. On-Demand Provisioning of IPv4 Address
As the sunset of IPv4 in NAS, parts of hosts no longer need IPv4
address. IPv4 address resources in NAS appears surplus, NAS
should obtain the unoccupied IPv4 address, generate a request
and send it to the address management system to release those IPv4
address resource. Meanwhile, NAS needs more IPv6 address resources for
the host transiting from IPv4 to IPv6. NAS judges whether the usage
status of the IPv6 address pool satisfies certain condition. If the
IPv6 address utilization is too high, the NAS generates
a resource request containing the IPv6 address information that needs
to be applied and sends it to the address management system. When the
address management system receives the IPv6 address resource request,
it allocates IPv6 address from its assignable IPv6 address resource
according the information of request, then sends a response message
with IPv6 address pools allocated for this NAS back to the NAS. Then
the NAS receives the response and get the information of allocated IPv6
address resource.
A.5. Managing Router Identifiers
Router IDs can be manually planned, possibly with some hierarchy or
design rule, or can be created automatically. A simple way of
automatic creation is to generate pseudo-random numbers, and one can
use another source of data such as the clock time at boot or
configuration time to provide additional entropy during the
generation of unique IDs. Another way is to hash an IPv6 address
down to a value as ID. The hash algorithm is supposed to be known
and the same across the domain. Since typically the number of
routers in a domain is far smaller than the value range of IDs, the
hashed IDs are hardly likely to conflict with each other, as long as
the hash algorithm is not designed too badly. It is necessary to be
able to override the automatically created value, and desirable if
the mechanism is provided by the system implementation.
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If the ID is created from IPv6 address, e.g. by hashing from an IPv6
address, then naturally it has relationship with the address. If the
ID is created regardless of IP address, one way to build association
with IPv6 address is to embed the ID into an IPv6 address that is to
be configured on the router, e.g. use a /96 IPv6 prefix and append it
with a 32-bit long ID. One can also use some record keeping
mechanisms, e.g. text file, DNS or other provisioning system like
network management system to manage the IDs and mapping relations
with IPv6 addresses, though extra record keeping does introduce
additional work.
Authors' Addresses
Will(Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
China
Email: liushucheng@huawei.com
Weiping Xu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
China
Email: xuweiping@huawei.com
Cathy Zhou
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
China
Email: cathy.zhou@huawei.com
Tina Tsou
Philips Lighting
United States of America
Email: tina.tsou@philips.com
Simon Perreault
Jive Communications
Quebec, QC
Canada
Email: sperreault@jive.com
Peng Fan
Beijing
China
Email: fanp08@gmail.com
Rong Gu
China Mobile
32 Xuanwumen West Ave, Xicheng District
Beijing 100053
China
Email: gurong_cmcc@outlook.com
Chen Li
China Telecom
No.118 Xizhimennei street, Xicheng District
Beijing 100035
China
Email: lichen.bri@chinatelecom.cn
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