Network Working Group S. Perreault
Internet-Draft Jive Communications
Intended status: Informational T. Tsou
Expires: July 30, 2015 Huawei Technologies (USA)
C. Zhou
Huawei Technologies
P. Fan
China Mobile
January 26, 2015
Gap Analysis for IPv4 Sunset
draft-ietf-sunset4-gapanalysis-05
Abstract
Sunsetting IPv4 refers to the process of turning off IPv4
definitively. It can be seen as the final phase of the migration to
IPv6. This memo enumerates difficulties arising when sunsetting
IPv4, and identifies the gaps requiring additional work.
Status of This Memo
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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
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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 . . . . . . . . . . . . . . . . . . . 3
3.1. Indicating that IPv4 connectivity is unavailable . . . . 3
3.2. Disabling IPv4 in the LAN . . . . . . . . . . . . . . . . 3
4. Client Connection Establishment Behavior . . . . . . . . . . 4
5. Disabling IPv4 in Operating System and Applications . . . . . 4
6. On-Demand Provisioning of IPv4 Addresses . . . . . . . . . . 4
7. IPv4 Address Literals . . . . . . . . . . . . . . . . . . . . 5
8. Managing Router Identifiers . . . . . . . . . . . . . . . . . 5
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. Security Considerations . . . . . . . . . . . . . . . . . . . 6
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
12. Informative References . . . . . . . . . . . . . . . . . . . 6
Appendix A. Solution Ideas . . . . . . . . . . . . . . . . . . . 8
A.1. Remotely Disabling IPv4 . . . . . . . . . . . . . . . . . 8
A.1.1. Indicating that IPv4 connectivity is unavailable . . 8
A.1.2. Disabling IPv4 in the LAN . . . . . . . . . . . . . . 8
A.2. Client Connection Establishment Behavior . . . . . . . . 9
A.3. Disabling IPv4 in Operating System and Applications . . . 9
A.4. On-Demand Provisioning of IPv4 Addresses . . . . . . . . 9
A.5. Managing Router Identifiers . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The final phase of the migration 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.
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
[I-D.cheshire-dnsext-multicastdns] 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. 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.
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
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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.
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).
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.
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
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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, 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.
[I-D.cheshire-dnsext-multicastdns]
Cheshire, S. and M. Krochmal, "Multicast DNS", draft-
cheshire-dnsext-multicastdns-15 (work in progress),
December 2011.
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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-03 (work in progress),
August 2012.
[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.
[Zeeb] "FreeBSD Snapshots without IPv4 support",
<http://wiki.freebsd.org/IPv6Only>.
Appendix 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.
Furthermore, it could be useful to have L2 switches snoop this
signalling and automatically start filtering IPv4 traffic as a
consequence.
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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. 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 Addresses
No idea.
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.
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.
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Authors' Addresses
Simon Perreault
Jive Communications
Quebec, QC
Canada
Email: sperreault@jive.com
Tina Tsou
Huawei Technologies (USA)
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1 408 330 4424
Email: tina.tsou.zouting@huawei.com
Cathy Zhou
Huawei Technologies
Huawei Industrial Base
Bantian, Shenzhen
China
Email: cathy.zhou@huawei.com
Peng Fan
China Mobile
32 Xuanwumen West Street
Beijing, Beijing
China
Email: fanp08@gmail.com
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