Internet Engineering Task Force B. Liu
Internet-Draft S. Jiang
Intended status: Informational Huawei Technologies
Expires: November 3, 2015 May 2, 2015
Considerations For Using Unique Local Addresses
draft-ietf-v6ops-ula-usage-recommendations-05
Abstract
This document provides considerations for using IPv6 Unique Local
Addresses (ULAs). It identifies cases where ULA addresses are
helpful as well as potential problems that their use could introduce,
based on an analysis of different ULA usage scenarios.
Status of This Memo
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This Internet-Draft will expire on November 3, 2015.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Analysis of ULA Features . . . . . . . . . . . . . . . . . . 3
3.1. Automatically Generated . . . . . . . . . . . . . . . . . 3
3.2. Globally Unique . . . . . . . . . . . . . . . . . . . . . 3
3.3. Independent Address Space . . . . . . . . . . . . . . . . 3
3.4. Well Known Prefix . . . . . . . . . . . . . . . . . . . . 4
3.5. Stable or Temporary Prefix . . . . . . . . . . . . . . . 4
4. Analysis and Operational Considerations of Scenarios Using
ULAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Isolated Networks . . . . . . . . . . . . . . . . . . . . 4
4.2. Connected Networks . . . . . . . . . . . . . . . . . . . 5
4.2.1. ULA-Only Deployment . . . . . . . . . . . . . . . . . 5
4.2.2. ULAs along with PA Addresses . . . . . . . . . . . . 7
4.3. IPv4 Co-existence Considerations . . . . . . . . . . . . 9
5. General Considerations For Using ULAs . . . . . . . . . . . . 10
5.1. Do Not Treat ULA Equal to RFC1918 . . . . . . . . . . . . 10
5.2. Using ULAs in a Limited Scope . . . . . . . . . . . . . . 10
6. ULA Usages Considered Helpful . . . . . . . . . . . . . . . . 10
6.1. Used in Isolated Networks . . . . . . . . . . . . . . . . 11
6.2. ULA along with PA . . . . . . . . . . . . . . . . . . . . 11
6.3. Some Specific Use Cases . . . . . . . . . . . . . . . . . 11
6.3.1. Special Routing . . . . . . . . . . . . . . . . . . . 11
6.3.2. Used as NAT64 Prefix . . . . . . . . . . . . . . . . 11
6.3.3. Used as Identifier . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . 13
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
Unique Local Addresses (ULAs) are defined in [RFC4193] as provider-
independent prefixes that can be used locally, for example, on
isolated networks, internal networks, or VPNs. Although ULAs may be
treated like addresses of global scope by applications, normally they
are not used on the public Internet. ULAs are a possible alternative
to site-local addresses (deprecated in [RFC3879]) in some situations,
but there are differences between the two address types.
The use of ULAs in various types of networks has been confusing to
network operators. This document aims to clarify the advantages and
disadvantages of ULAs and how they can be most appropriately used.
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2. 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
[RFC2119] when they appear in ALL CAPS. When these words are not in
ALL CAPS (such as "should" or "Should"), they have their usual
English meanings, and are not to be interpreted as [RFC2119] key
words.
3. Analysis of ULA Features
3.1. Automatically Generated
ULA prefixes can be automatically generated using the algorithms
described in [RFC4193]. This feature allows automatic prefix
allocation. Thus one can get a network working immediately without
applying for prefix(es) from an RIR/LIR (Regional Internet Registry/
Local Internet Registry).
3.2. Globally Unique
ULAs are intended to have an extremely low probability of collision.
Since multiple networks in which the hosts have been assigned with
ULAs may occasionally be merged into one network, this uniqueness is
necessary. The randomization of 40 bits in a ULA prefix is
considered sufficient enough to ensure a high degree of uniqueness
(refer to [RFC4193] Section 3.2.3 for details) and simplifies merging
of networks by avoiding the need to renumber overlapping IP address
space. Such overlapping was a major drawback to the deployment of
private [RFC1918] addresses in IPv4.
Note that, as described in [RFC4864], applications may treat ULAs in
practice like global-scope addresses, but address selection
algorithms may need to distinguish between ULAs and Global-scope
Unicast Addresses (GUAs) to ensure bidirectional communications. As
a further note, the default address selection policy table in
[RFC6724]) responds to this requirement.
3.3. Independent Address Space
ULAs provide internal address independence in IPv6 since they can be
used for internal communications even without Internet connectivity.
They need no registration, so they can support on-demand usage and do
not carry any RIR/LIR burden of documentation or fees.
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3.4. Well Known Prefix
The prefixes of ULAs are well known thus they are easily identified
and filtered.
This feature is convenient for management of security policies and
troubleshooting. For example, network administrators can segregate
packets containing data which must stay in the internal network by
assigning ULAs to internal servers. Externally-destined data can be
sent to the Internet or telecommunication network by a separate
function, through an appropriate gateway/firewall.
3.5. Stable or Temporary Prefix
A ULA prefix can be generated once, at installation time or factory
reset, and then possibly never be changed. Alternatively, it can be
regenerated regularly, depending on deployment requirements.
4. Analysis and Operational Considerations of Scenarios Using ULAs
4.1. Isolated Networks
IP is used ubiquitously. Some networks like industrial control bus
(e.g. [RS-485], [SCADA], or even non-networked digital interfaces
like [MIL-STD-1397] have begun to use IP. In these kinds of
networks, the system may lack the ability to communicate with the
public networks.
As another example, there may be some networks in which the equipment
has the technical capability to connect to the Internet, but is
prohibited by administration or just temporarily not connected.
These networks may include separate financial networks, lab networks.
machine-to-machine (e.g. vehicle networks), sensor networks, or even
normal LANs, and can include very large numbers of addresses.
Serious disadvantages and impact on applications due to the use of
ambiguous address space have been well documented in [RFC1918].
However, ULA is a straightforward way to assign the IP addresses in
the kinds of networks just described, with minimal administrative
cost or burden. Also, ULAs fit in multiple subnet scenarios, in
which each subnet has its own ULA prefix. For example, when we
assign vehicles with ULA addresses, it is then possible to separate
in-vehicle embedded networks into different subnets depending on
real-time requirements, device types, services and more.
However, each isolated network has the possibility to be connected in
the future. Administrators need to consider the following before
deciding whether to use ULAs:
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o If the network eventually connects to another isolated or private
network, the potential for address collision arises. However, if
the ULAs were generated in the standard way, this will not be a
big problem.
o If the network eventually connects to the global Internet, then
the operator will need to add a new global prefix and ensure that
the address selection policy is properly set up on all interfaces.
If these further considerations are unacceptable for some reason,
then the administrator needs to be careful about using ULAs in
currently isolated networks.
Operational considerations:
o Prefix generation: Randomly generated according to the algorithms
defined in [RFC4193] or manually assigned. Normally, automatic
generation of the prefixes is recommended, following [RFC4193].
If there are some specific reasons that call for manual
assignment, administrators have to plan the prefixes carefully to
avoid collision.
o Prefix announcement: In some cases, networks may need to announce
prefixes to each other. For example, in vehicle networks with
infrastructure-less settings such as Vehicle-to-Vehicle (V2V)
communication, prior knowledge of the respective prefixes is
unlikely. Hence, a prefix announcement mechanism is needed to
enable inter-vehicle communications based on IP. As one
possibility, such announcements could rely on extensions to the
Router Advertisement message of the Neighbor Discovery Protocol
(e.g., [I-D.petrescu-autoconf-ra-based-routing] and
[I-D.jhlee-mext-mnpp]).
4.2. Connected Networks
4.2.1. ULA-Only Deployment
In some situations, hosts and interior interfaces are assigned ULAs
and not GUAs, but the network needs to communicate with the outside.
Two models can be considered:
o Using Network Prefix Translation
Network Prefix Translation (NPTv6) [RFC6296] is an experimental
specification that provides a stateless one-to-one mapping
between internal addresses and external addresses. The
specification considers translating ULA prefixes into GUA
prefixes as an use case. Although NPTv6 works differently from
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traditional stateful NAT/NAPT (which is discouraged in
[RFC5902]), it introduces similar additional complexity to
applications, which may cause applications to break.
Thus this document does not recommend the use of ULA+NPTv6.
Rather, this document considers ULA+PA (Provider Aggregated) as
a better approach to connect to the global network when ULAs
are expected to be retained. The use of ULA+PA is discussed in
detail in Section 4.2.2 below.
o Using Application-Layer Proxies
The proxies terminate the network-layer connectivity of the
hosts and associate separate internal and external connections.
In some environments (e.g., information security sensitive
enterprise or government), central control is exercised by
allowing the endpoints to connect to the Internet only through
a proxy. With IPv4, using private address space with proxies
is an effective and common practice for this purpose, and it is
natural to pick ULA as its counterpart in IPv6.
Benefits of using ULAs in this scenario:
o Allowing minimal management burden on address assignment for some
specific environments.
Drawbacks:
o The serious disadvantages and impact on applications imposed by
NATs have been well documented in [RFC2993] and [RFC3027].
Although NPTv6 is a mechanism that has fewer architectural
problems than a traditional stateful Network Address Translator in
an IPv6 environment [RFC6296], it still breaks end-to-end
transparency and hence in general is not recommended by the IETF.
Operational considerations:
o Firewall deployment: [RFC6296] points out that an NPTv6 translator
does not have the same security properties as a traditional NAT44,
and hence needs be supplemented with a firewall if security at the
boundary is an issue. The operator has to decide where to locate
the firewall.
- If the firewall is located outside the NPTv6 translator, then
filtering is based on the translated GUA prefixes, and when the
internal ULA prefixes are renumbered, the filtering rules do
not need to be changed. However, when the GUA prefixes of the
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NPTv6 are renumbered, the filtering rules need to be updated
accordingly.).
- If the firewall is located inside the NPTv6 translator, the
filtering is then based on the ULA prefixes, and the rules need
to be updated correspondingly. There is no need to update when
the NPTv6 GUA prefixes are renumbered.
4.2.2. ULAs along with PA Addresses
Two classes of network might need to use ULA with PA (Provider
Aggregated) addresses:
o Home network. Home networks are normally assigned with one or
more globally routed PA prefixes to connect to the uplink of an
ISP. In addition, they may need internal routed networking even
when the ISP link is down. Then ULA is a proper tool to fit the
requirement. [RFC7084] requires the CPE to support ULA. Note:
ULAs provide more benefit for multiple-segment home networks; for
home networks containing only one segment, link-local addresses
are better alternatives.
o Enterprise network. An enterprise network is usually a managed
network with one or more PA prefixes or with a PI prefix, all of
which are globally routed. The ULA can be used to improve
internal connectivity and make it more resilient, or to isolate
certain functions like OAM for servers.
Benefits of Using ULAs in this scenario:
o Separated local communication plane: for either home networks or
enterprise networks, the main purpose of using ULAs along with PA
addresses is to provide a logically local routing plane separated
from the global routing plane. The benefit is to ensure stable
and specific local communication regardless of the ISP uplink
failure. This benefit is especially meaningful for the home
network or for private OAM function in an enterprise.
o Renumbering: in some special cases such as renumbering, enterprise
administrators may want to avoid the need to renumber their
internal-only, private nodes when they have to renumber the PA
addresses of the rest of the network because they are changing
ISPs, because the ISP has restructured its address allocations, or
for some other reason. In these situations, ULA is an effective
tool for addressing internal-only nodes. Even public nodes can
benefit from ULA for renumbering, on their internal interfaces.
When renumbering, as [RFC4192] suggests, old prefixes continue to
be valid until the new prefix(es) is(are) stable. In the process
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of adding new prefix(es) and deprecating old prefix(es), it is not
easy to keep local communication disentangled from global routing
plane change. If we use ULAs for local communication, the
separated local routing plane can isolate the effects of global
routing change.
Drawbacks:
o Operational Complexity: there are some arguments that in practice
the use of ULA+PA creates additional operational complexity. This
is not a ULA-specific problem; the multiple-addresses-per-
interface is an important feature of IPv6 protocol. Nevertheless,
running multiple prefixes needs more operational consideration
than running a single one.
Operational considerations:
o Default Routing: connectivity may be broken if ULAs are used as
default route. When using RIO (Route Information Option) in
[RFC4191], specific routes can be added without a default route,
thus avoiding bad user experience due to timeouts on ICMPv6
redirects. This behavior was well documented in [RFC7084] as rule
ULA-5 "An IPv6 CE router MUST NOT advertise itself as a default
router with a Router Lifetime greater than zero whenever all of
its configured and delegated prefixes are ULA prefixes." and along
with rule L-3 "An IPv6 CE router MUST advertise itself as a router
for the delegated prefix(es) (and ULA prefix if configured to
provide ULA addressing) using the "Route Information Option"
specified in Section 2.3 of [RFC4191]. This advertisement is
independent of having or not having IPv6 connectivity on the WAN
interface.". However, it needs to be noticed that current OSes
don't all support [RFC4191].
o SLAAC/DHCPv6 co-existing: Since SLAAC and DHCPv6 might be enabled
in one network simultaneously; the administrators need to
carefully plan how to assign ULA and PA prefixes in accordance
with the two mechanisms. The administrators need to know the
current issue of the SLAAC/DHCPv6 interaction (please refer to
[I-D.ietf-v6ops-dhcpv6-slaac-problem] for details).
o Address selection: As mentioned in [RFC5220], there is a
possibility that the longest matching rule will not be able to
choose the correct address between ULAs and global unicast
addresses for correct intra-site and extra-site communication.
[RFC6724] claims that a site-specific policy entry can be used to
cause ULAs within a site to be preferred over global addresses.
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o DNS relevant: if administrators choose not to do reverse DNS
delegation inside of their local control of ULA prefixes, a
significant amount of information about the ULA population may
leak to the outside world. Because reverse queries will be made
and naturally routed to the global reverse tree, so external
parties will be exposed to the existence of a population of ULA
addresses. [ULA-IN-WILD] provides more detailed situations on
this issue. Administrators may need a split DNS to separate the
queries from internal and external for ULA entries and GUA
entries.
4.3. IPv4 Co-existence Considerations
Generally, this document does not consider IPv4 to be in scope. But
regarding ULA, there is a special case needs to be recognized, which
is described in Section 3.2.2 of [RFC5220]. When an enterprise has
IPv4 Internet connectivity but does not yet have IPv6 Internet
connectivity, and the enterprise wants to provide site-local IPv6
connectivity, a ULA is the best choice for site-local IPv6
connectivity. Each employee host will have both an IPv4 global or
private address and a ULA. Here, when this host tries to connect to
an outside node that has registered both A and AAAA records in the
DNS, the host will choose AAAA as the destination address and the ULA
for the source address according to the IPv6 preference of the
default policy table defined in the old address selection standard
[RFC3484]. This will clearly result in a connection failure. The
new address selection standard [RFC6724] has corrected this behavior
by preferring IPv4 than ULAs in the default policy table. However,
there are still lots of hosts using the old standard [RFC3484], thus
this could be an issue in real networks.
Happy Eyeballs [RFC6555] solves this connection failure problem, but
unwanted timeouts will obviously lower the user experience. One
possible approach to eliminating the timeouts is to deprecate the
IPv6 default route and simply configure a scoped route on hosts (in
the context of this document, only configure the ULA prefix routes).
Another alternative is to configure IPv4 preference on the hosts, and
not include DNS A records but only AAAA records for the internal
nodes in the internal DNS server. Then outside nodes have both A and
AAAA records and can be connected through IPv4 as default and
internal nodes can always connect through IPv6. But since IPv6
preference is default, changing the default in all nodes is not
suitable at scale.
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5. General Considerations For Using ULAs
5.1. Do Not Treat ULA Equal to RFC1918
ULA and [RFC1918] are similar in some aspects. The most obvious one
is as described in Section 3.1.3 that ULA provides an internal
address independence capability in IPv6 that is similar to how
[RFC1918] is commonly used. ULA allows administrators to configure
the internal network of each platform the same way it is configured
in IPv4. Many organizations have security policies and architectures
based around the local-only routing of [RFC1918] addresses and those
policies may directly map to ULA [RFC4864].
But this does not mean that ULA is equal to an IPv6 version of
[RFC1918] deployment. [RFC1918] usually combines with NAT/NAPT for
global connectivity. But it is not necessary to combine ULAs with
any kind of NAT. Operators can use ULA for local communications
along with global addresses for global communications (see
Section 4.2.2). This is a big advantage brought by default support
of multiple-addresses-per-interface feature in IPv6. (People may
still have a requirement for NAT with ULA, this is discussed in
Section 4.2.1. But people also need to keep in mind that ULA is not
intentionally designed for this kind of use case.)
Another important difference is the ability to merge two ULA networks
without renumbering (because of the uniqueness), which is a big
advantage over [RFC1918].
5.2. Using ULAs in a Limited Scope
A ULA is by definition a prefix that is never advertised outside a
given domain, and is used within that domain by agreement of those
networked by the domain.
So when using ULAs in a network, the administrators need to clearly
set the scope of the ULAs and configure ACLs on relevant border
routers to block them out of the scope. And if internal DNS is
enabled, the administrators might also need to use internal-only DNS
names for ULAs and might need to split the DNS so that the internal
DNS server includes records that are not presented in the external
DNS server.
6. ULA Usages Considered Helpful
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6.1. Used in Isolated Networks
As analyzed in Section 4.1, ULA is very suitable for isolated
networks. Especially when there are subnets in the isolated network,
ULA is a reasonable choice.
6.2. ULA along with PA
As described in Section 4.2.2, using ULAs along with PA addresses to
provide a logically separated local plane can benefit OAM functions
and renumbering.
6.3. Some Specific Use Cases
Along with the general scenarios, this section provides some specific
use cases that could benefit from using ULA.
6.3.1. Special Routing
For various reasons the administrators may want to have private
routing be controlled and separated from other routing. For example,
in the business-to-business case described in
[I-D.baker-v6ops-b2b-private-routing], two companies might want to
use direct connectivity that only connects stated machines, such as a
silicon foundry with client engineers that use it. A ULA provides a
simple way to assign prefixes that would be used in accordance with
an agreement between the parties.
6.3.2. Used as NAT64 Prefix
The NAT64 PREF64 is just a group of local fake addresses for the
DNS64 to point traffic to a NAT64. Using a ULA prefix as the PREF64
easily ensures that only local systems can use the translation
resources of the NAT64 system since the ULA is not intended to be
globally routable. The ULA helps clearly identify traffic that is
locally contained and destined to a NAT64. Using ULA for PREF64 is
deployed and it is an operational model.
But there is an issue needs to be noted. The NAT64 standard
[RFC6146] specifies that the PREF64 should align with [RFC6052], in
which the IPv4-Embedded IPv6 Address format was specified. If we
pick a /48 for NAT64, it happens to be a standard 48/ part of ULA
(7bit ULA well-known prefix+ 1 "L" bit + 40bit Global ID). Then the
40bit of ULA is not violated by being filled with part of the 32bit
IPv4 address. This is important, because the 40bit assures the
uniqueness of ULA. If the prefix is shorter than /48, the 40bit
would be violated, and this could cause conformance issues. But it
is considered that the most common use case will be a /96 PREF64, or
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even /64 will be used. So it seems this issue is not common in
current practice.
It is most common that ULA PREF64 will be deployed on a single
internal network, where the clients and the NAT64 share a common
internal network. ULA will not be effective as PREF64 when the
access network must use an Internet transit to receive the
translation service of a NAT64 since the ULA will not route across
the Internet.
According to the default address selection table specified in
[RFC6724], the host would always prefer IPv4 over ULA. This could be
a problem in NAT64-CGN scenario as analyzed in Section 8 of
[RFC7269]. So administrators need to add additional site-specific
address selection rules to the default table to steer traffic flows
going through NAT64-CGN. However, updating the default policy tables
in all hosts involves significant management cost. This may be
possible in an enterprise (using a group policy object, or other
configuration mechanisms), but it is not suitable at scale for home
networks.
6.3.3. Used as Identifier
ULAs could be self-generated and easily grabbed from the standard
IPv6 stack. And ULAs don't need to be changed as the GUA prefixes
do. So they are very suitable to be used as identifiers by the up
layer applications. And since ULA is not intended to be globally
routed, it is not harmful to the routing system.
Such kind of benefit has been utilized in real implementations. For
example, in [RFC6281], the protocol BTMM (Back To My Mac) needs to
assign a topology-independent identifier to each client host
according to the following considerations:
o TCP connections between two end hosts wish to survive in network
changes.
o Sometimes one needs a constant identifier to be associated with a
key so that the Security Association can survive the location
changes.
It needs to be noticed again that in theory ULA has the possibility
of collision. However, the probability is desirably small enough and
can be ignored in most cases when ULAs are used as identifiers.
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7. Security Considerations
Security considerations regarding ULAs, in general, please refer to
the ULA specification [RFC4193]. Also refer to [RFC4864], which
shows how ULAs help with local network protection.
As mentioned in Section 4.2.2, when using NPTv6, the administrators
need to know where the firewall is located to set proper filtering
rules.
Also as mentioned in Section 4.2.2, if administrators choose not to
do reverse DNS delegation inside their local control of ULA prefixes,
a significant amount of information about the ULA population may leak
to the outside world.
8. IANA Considerations
This memo has no actions for IANA.
9. Acknowledgements
Many valuable comments were received in the IETF v6ops WG mail list,
especially from Cameron Byrne, Fred Baker, Brian Carpenter, Lee
Howard, Victor Kuarsingh, Alexandru Petrescu, Mikael Abrahamsson, Tim
Chown, Jen Linkova, Christopher Palmer Jong-Hyouk Lee, Mark Andrews,
Lorenzo Colitti, Ted Lemon, Joel Jaeggli, David Farmer, Doug Barton,
Owen Delong, Gert Doering, Bill Jouris, Bill Cerveny, Dave Thaler,
Nick Hilliard, Jan Zorz, Randy Bush, Anders Brandt, , Sofiane Imadali
and Wesley George.
Some test of using ULA in the lab was done by our research partner
BNRC-BUPT (Broad Network Research Centre in Beijing University of
Posts and Telecommunications). Thanks for the work of Prof.
Xiangyang Gong and student Dengjia Xu.
Tom Taylor did a language review and revision throught the whole
document. The authors appreciate a lot for his help.
This document was produced using the xml2rfc tool [RFC2629]
(initially prepared using 2-Word-v2.0.template.dot.).
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
10.2. Informative References
[I-D.baker-v6ops-b2b-private-routing]
Baker, F., "Business to Business Private Routing", draft-
baker-v6ops-b2b-private-routing-00 (work in progress),
July 2007.
[I-D.ietf-v6ops-dhcpv6-slaac-problem]
Liu, B., Jiang, S., Bonica, R., Gong, X., and W. Wang,
"DHCPv6/SLAAC Address Configuration Interaction Problem
Statement", draft-ietf-v6ops-dhcpv6-slaac-problem-03 (work
in progress), October 2014.
[I-D.jhlee-mext-mnpp]
Tsukada, M., Ernst, T., and J. Lee, "Mobile Network Prefix
Provisioning", draft-jhlee-mext-mnpp-00 (work in
progress), October 2009.
[I-D.petrescu-autoconf-ra-based-routing]
Petrescu, A., Janneteau, C., Demailly, N., and S. Imadali,
"Router Advertisements for Routing between Moving
Networks", draft-petrescu-autoconf-ra-based-routing-05
(work in progress), July 2014.
[MIL-STD-1397]
"Military Standard, Input/Output Interfaces, Standard
Digital Data, Navy Systems (MIL-STD-1397B), 3 March 1989".
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.
[RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993,
November 2000.
[RFC3027] Holdrege, M. and P. Srisuresh, "Protocol Complications
with the IP Network Address Translator", RFC 3027, January
2001.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
Liu & Jiang Expires November 3, 2015 [Page 14]
Internet-Draft Considerations For Using ULAs May 2015
[RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879, September 2004.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC4864] Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
E. Klein, "Local Network Protection for IPv6", RFC 4864,
May 2007.
[RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Problem Statement for Default Address Selection in Multi-
Prefix Environments: Operational Issues of RFC 3484
Default Rules", RFC 5220, July 2008.
[RFC5902] Thaler, D., Zhang, L., and G. Lebovitz, "IAB Thoughts on
IPv6 Network Address Translation", RFC 5902, July 2010.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6281] Cheshire, S., Zhu, Z., Wakikawa, R., and L. Zhang,
"Understanding Apple's Back to My Mac (BTMM) Service", RFC
6281, June 2011.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012.
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
November 2013.
Liu & Jiang Expires November 3, 2015 [Page 15]
Internet-Draft Considerations For Using ULAs May 2015
[RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64
Deployment Options and Experience", RFC 7269, June 2014.
[RS-485] "Electronic Industries Association (1983). Electrical
Characteristics of Generators and Receivers for Use in
Balanced Multipoint Systems. EIA Standard RS-485.".
[SCADA] "Boyer, Stuart A. (2010). SCADA Supervisory Control and
Data Acquisition. USA: ISA - International Society of
Automation.".
[ULA-IN-WILD]
"G. Michaelson, "conference.apnic.net/data/36/apnic-
36-ula_1377495768.pdf"".
Authors' Addresses
Bing Liu
Huawei Technologies
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: leo.liubing@huawei.com
Sheng Jiang
Huawei Technologies
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: jiangsheng@huawei.com
Liu & Jiang Expires November 3, 2015 [Page 16]
