Internet Engineering Task Force (IETF) B. Carpenter
Request for Comments: 6883 Univ. of Auckland
Category: Informational S. Jiang
ISSN: 2070-1721 Huawei Technologies Co., Ltd
March 2013
IPv6 Guidance for Internet Content Providers
and Application Service Providers
Abstract
This document provides guidance and suggestions for Internet Content
Providers and Application Service Providers who wish to offer their
service to both IPv6 and IPv4 customers. Many of the points will
also apply to hosting providers or to any enterprise network
preparing for IPv6 users.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6883.
Copyright Notice
Copyright (c) 2013 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
(
http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction ....................................................2
2. General Strategy ................................................3
3. Education and Skills ............................................5
4. Arranging IPv6 Connectivity .....................................6
5. IPv6 Infrastructure .............................................7
5.1. Address and Subnet Assignment ..............................7
5.2. Routing ....................................................8
5.3. DNS ........................................................9
6. Load Balancers .................................................10
7. Proxies ........................................................11
8. Servers ........................................................12
8.1. Network Stack .............................................12
8.2. Application Layer .........................................12
8.3. Logging ...................................................13
8.4. Geolocation ...............................................13
9. Coping with Transition Technologies ............................13
10. Content Delivery Networks .....................................15
11. Business Partners .............................................16
12. Possible Complexities .........................................16
13. Operations and Management .....................................17
14. Security Considerations .......................................18
15. Acknowledgements ..............................................20
16. References ....................................................20
16.1. Normative References .....................................20
16.2. Informative References ...................................22
1. Introduction
The deployment of IPv6 [RFC2460] is now in progress, and users
without direct IPv4 access are likely to appear in increasing numbers
in the coming years. Any provider of content or application services
over the Internet will need to arrange for IPv6 access or else risk
losing large numbers of potential users. For users who already have
dual-stack connectivity, direct IPv6 access might provide more
satisfactory performance than indirect access via NAT.
In this document, we often refer to the users of content or
application services as "customers" to clarify the part they play,
but this is not intended to limit the scope to commercial sites.
The time for action is now, while the number of IPv6-only customers
is small, so that appropriate skills, software, and equipment can be
acquired in good time to scale up the IPv6 service as demand
increases. An additional advantage of early support for IPv6
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customers is that it will reduce the number of customers connecting
later via IPv4 "extension" solutions such as double NAT or NAT64
[RFC6146], which will otherwise degrade the user experience.
Nevertheless, it is important that the introduction of IPv6 service
should not make service for IPv4 customers worse. In some
circumstances, technologies intended to assist in the transition from
IPv4 to IPv6 are known to have negative effects on the user
experience. A deployment strategy for IPv6 must avoid these effects
as much as possible.
The purpose of this document is to provide guidance and suggestions
for Internet Content Providers (ICPs) and Application Service
Providers (ASPs) who wish to offer their services to both IPv6 and
IPv4 customers but who are currently supporting only IPv4. For
simplicity, the term "ICP" is mainly used in the body of this
document, but the guidance also applies to ASPs. Any hosting
provider whose customers include ICPs or ASPs is also concerned.
Many of the points in this document will also apply to enterprise
networks that do not classify themselves as ICPs. Any enterprise or
department that runs at least one externally accessible server, such
as an HTTP server, may also be concerned. Although specific
managerial and technical approaches are described, this is not a rule
book; each operator will need to make its own plan, tailored to its
own services and customers.
2. General Strategy
The most important advice here is to actually have a general
strategy. Adding support for a second network-layer protocol is a
new experience for most modern organizations, and it cannot be done
casually on an unplanned basis. Even if it is impossible to write a
precisely dated plan, the intended steps in the process need to be
defined well in advance. There is no single blueprint for this. The
rest of this document is meant to provide a set of topics to be taken
into account in defining the strategy. Other documents about IPv6
deployment, such as [IPv6-NETWORK-DESIGN], should be consulted as
well.
In determining the urgency of this strategy, it should be noted that
the central IPv4 registry (IANA) ran out of spare blocks of IPv4
addresses in February 2011, and the various regional registries are
expected to exhaust their reserves over the next one to two years.
After this, Internet Service Providers (ISPs) will run out at dates
determined by their own customer base. No precise date can be given
for when IPv6-only customers will appear in commercially significant
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numbers, but -- particularly in the case of mobile users -- it may be
quite soon. Complacency about this is therefore not an option for
any ICP that wishes to grow its customer base over the coming years.
The most common strategy for an ICP is to provide dual-stack services
-- both IPv4 and IPv6 on an equal basis -- to cover both existing and
future customers. This is the recommended strategy in [RFC6180] for
straightforward situations. Some ICPs who already have satisfactory
operational experience with IPv6 might consider an IPv6-only
strategy, with IPv4 clients being supported by translation or proxy
in front of their IPv6 content servers. However, the present
document is addressed to ICPs without IPv6 experience, who are likely
to prefer the dual-stack model to build on their existing IPv4
service.
Due to the widespread impact of supporting IPv6 everywhere within an
environment, it is important to select a focused initial approach
based on clear business needs and real technical dependencies.
Within the dual-stack model, two approaches could be adopted,
sometimes referred to as "outside in" and "inside out":
o Outside in: Start by providing external users with an IPv6 public
access to your services, for example, by running a reverse proxy
that handles IPv6 customers (see Section 7 for details).
Progressively enable IPv6 internally.
o Inside out: Start by enabling internal networking infrastructure,
hosts, and applications to support IPv6. Progressively reveal
IPv6 access to external customers.
Which of these approaches to choose depends on the precise
circumstances of the ICP concerned. "Outside in" has the benefit of
giving interested customers IPv6 access at an early stage, and
thereby gaining precious operational experience, before meticulously
updating every piece of equipment and software. For example, if some
back-office system that is never exposed to users only supports IPv4,
it will not cause delay. "Inside out" has the benefit of completing
the implementation of IPv6 as a single project. Any ICP could choose
this approach, but it might be most appropriate for a small ICP
without complex back-end systems.
A point that must be considered in the strategy is that some
customers will remain IPv4-only for many years, others will have both
IPv4 and IPv6 access, and yet others will have only IPv6.
Additionally, mobile customers may find themselves switching between
IPv4 and IPv6 access as they travel, even within a single session.
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Services and applications must be able to deal with this, just as
easily as they deal today with a user whose IPv4 address changes (see
the discussion of cookies in Section 8.2).
Nevertheless, the end goal is to have a network that does not need
major changes when at some point in the future it becomes possible to
transition to IPv6-only, even if only for some parts of the network.
That is, the IPv6 deployment should be designed in such a way as to
more or less assume that IPv4 is already absent, so the network will
function seamlessly when it is indeed no longer there.
An important step in the strategy is to determine from hardware and
software suppliers details of their planned dates for providing
sufficient IPv6 support, with performance equivalent to IPv4, in
their products and services. Relevant specifications such as
[RFC6434] and [IPv6-CE-REQS] should be used. Even if complete
information cannot be obtained, it is essential to determine which
components are on the critical path during successive phases of
deployment. This information will make it possible to draw up a
logical sequence of events and identify any components that may cause
holdups.
3. Education and Skills
Some staff may have experience running multiprotocol networks, which
were common twenty years ago before the dominance of IPv4. However,
IPv6 will be new to them and also to staff brought up only on TCP/IP.
It is not enough to have one "IPv6 expert" in a team. On the
contrary, everybody who knows about IPv4 needs to know about IPv6,
from network architect to help desk responder. Therefore, an early
and essential part of the strategy must be education, including
practical training, so that all staff acquire a general understanding
of IPv6, how it affects basic features such as the DNS, and the
relevant practical skills. To take a trivial example, any staff used
to dotted-decimal IPv4 addresses need to become familiar with the
colon-hexadecimal format used for IPv6.
There is an anecdote of one IPv6 deployment in which prefixes
including the letters A to F were avoided by design, to avoid
confusing system administrators unfamiliar with hexadecimal notation.
This is not a desirable result. There is another anecdote of a help
desk responder telling a customer to "disable one-Pv6" in order to
solve a problem. It should be a goal to avoid having untrained staff
who don't understand hexadecimal or who can't even spell "IPv6".
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It is very useful to have a small laboratory network available for
training and self-training in IPv6, where staff may experiment and
make mistakes without disturbing the operational IPv4 service. This
lab should run both IPv4 and IPv6, to gain experience with a dual-
stack environment and new features such as having multiple addresses
per interface, and addresses with lifetimes and deprecation.
Once staff are trained, they will likely need to support IPv4, IPv6,
and dual-stack customers. Rather than having separate internal
escalation paths for IPv6, it generally makes sense for questions
that may have an IPv6 element to follow normal escalation paths;
there should not be an "IPv6 Department" once training is completed.
A final remark about training is that it should not be given too
soon, or it will be forgotten. Training has a definite need to be
done "just in time" in order to properly "stick". Training, lab
experience, and actual deployment should therefore follow each other
immediately. If possible, training should even be combined with
actual operational experience.
4. Arranging IPv6 Connectivity
There are, in theory, two ways to obtain IPv6 connectivity to the
Internet.
o Native. In this case, the ISP simply provides IPv6 on exactly the
same basis as IPv4 -- it will appear at the ICP's border
router(s), which must then be configured in dual-stack mode to
forward IPv6 packets in both directions. This is by far the
better method. An ICP should contact all its ISPs to verify when
they will provide native IPv6 support, whether this has any
financial implications, and whether the same service level
agreement will apply as for IPv4. Any ISP that has no definite
plan to offer native IPv6 service should be avoided.
o Managed Tunnel. It is possible to configure an IPv6-in-IPv4
tunnel to a remote ISP that offers such a service. A dual-stack
router in the ICP's network will act as a tunnel endpoint, or this
function could be included in the ICP's border router.
A managed tunnel is a reasonable way to obtain IPv6 connectivity
for initial testing and skills acquisition. However, it
introduces an inevitable extra latency compared to native IPv6,
giving customers a noticeably worse response time for complex web
pages. A tunnel may become a performance bottleneck (especially
if offered as a free service) or a target for malicious attack.
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It is also likely to limit the IPv6 MTU size. In normal
circumstances, native IPv6 will provide an MTU size of at least
1500 bytes, but it will almost inevitably be less for a tunnel,
possibly as low as 1280 bytes (the minimum MTU allowed for IPv6).
Apart from the resulting loss of efficiency, there are cases in
which Path MTU Discovery fails and IPv6 fragmentation therefore
fails; in this case, the lower tunnel MTU will actually cause
connectivity failures for customers.
For these reasons, ICPs are strongly recommended to obtain native
IPv6 service before attempting to offer a production-quality
service to their customers. Unfortunately, it is impossible to
prevent customers from using unmanaged tunnel solutions (see
Section 9).
Some larger organizations may find themselves needing multiple forms
of IPv6 connectivity, for their ICP data centers and for their staff
working elsewhere. It is important to obtain IPv6 connectivity for
both, as testing and supporting an IPv6-enabled service is
challenging for staff without IPv6 connectivity. This may involve
short-term alternatives to provide IPv6 connectivity to operations
and support staff, such as a managed tunnel or HTTP proxy server with
IPv6 connectivity. Note that unmanaged tunnels (such as 6to4 and
Teredo) are generally not useful for support staff, as recent client
software will avoid them when accessing dual-stack sites.
5. IPv6 Infrastructure
5.1. Address and Subnet Assignment
An ICP must first decide whether to apply for its own Provider
Independent (PI) address prefix for IPv6. This option is available
either from an ISP that acts as a Local Internet Registry or directly
from the relevant Regional Internet Registry. The alternative is to
obtain a Provider Aggregated (PA) prefix from an ISP. Both solutions
are viable in IPv6. However, the scaling properties of the wide-area
routing system (BGP-4) mean that the number of PI prefixes should be
limited, so only large content providers can justify obtaining a PI
prefix and convincing their ISPs to route it. Millions of enterprise
networks, including smaller content providers, will use PA prefixes.
In this case, a change of ISP would necessitate a change of the
corresponding PA prefix, using the procedure outlined in [RFC4192].
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An ICP that has connections via multiple ISPs but does not have a PI
prefix would therefore have multiple PA prefixes, one from each ISP.
This would result in multiple IPv6 addresses for the ICP's servers or
load balancers. If one address fails due to an ISP malfunction,
sessions using that address would be lost. At the time of this
writing, there is very limited operational experience with this
approach [MULTIHOMING-WITHOUT-NAT].
An ICP may also choose to operate a Unique Local Address prefix
[RFC4193] for internal traffic only, as described in [RFC4864].
Depending on its projected future size, an ICP might choose to obtain
/48 PI or PA prefixes (allowing 16 bits of subnet address) or longer
PA prefixes, e.g., /56 (allowing 8 bits of subnet address). Clearly,
the choice of /48 is more future-proof. Advice on the numbering of
subnets may be found in [RFC5375]. An ICP with multiple locations
will probably need a prefix per location.
An ICP that has its service hosted by a colocation provider, cloud
provider, or the like will need to follow the addressing policy of
that provider.
Since IPv6 provides for operating multiple prefixes simultaneously,
it is important to check that all relevant tools, such as address
management packages, can deal with this. In particular, the possible
need to allow for multiple PA prefixes with IPv6, and the possible
need to renumber, mean that the common technique of manually assigned
static addresses for servers, proxies, or load balancers, with
statically defined DNS entries, could be problematic [RFC6866]. An
ICP of reasonable size might instead choose to operate DHCPv6
[RFC3315] with standard DNS, to support stateful assignment. In
either case, a configuration management system is likely to be used
to support stateful and/or on-demand address assignment.
Theoretically, it would also be possible to operate an ICP's IPv6
network using only Stateless Address Autoconfiguration [RFC4862],
with Dynamic DNS [RFC3007] to publish server addresses for external
users.
5.2. Routing
In a dual-stack network, most IPv4 and IPv6 interior routing
protocols operate quite independently and in parallel. The common
routing protocols, such as OSPFv3 [RFC5340], IS-IS [RFC5308], and
even the Routing Information Protocol Next Generation (RIPng)
[RFC2080] [RFC2081], all support IPv6. It is worth noting that
whereas OSPF and RIP differ significantly between IPv4 and IPv6,
IS-IS has the advantage of handling them both in a single instance of
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the protocol, with the potential for operational simplification in
the long term. Some versions of OSPFv3 may also have this advantage
[RFC5838]. In any case, for trained staff, there should be no
particular difficulty in deploying IPv6 routing without disturbance
to IPv4 services. In some cases, firmware upgrades may be needed on
some network devices.
The performance impact of dual-stack routing needs to be evaluated.
In particular, what forwarding performance does the router vendor
claim for IPv6? If the forwarding performance is significantly
inferior compared to IPv4, will this be an operational problem?
Is extra memory or ternary content-addressable memory (TCAM) space
needed to accommodate both IPv4 and IPv6 tables? To answer these
questions, the ICP will need a projected model for the amount of IPv6
traffic expected initially and its likely rate of increase.
If a site has multiple PA prefixes as mentioned in Section 5.1,
complexities in routing configuration will appear. In particular,
source-based routing rules might be needed to ensure that outgoing
packets are routed to the appropriate border router and ISP link.
Normally, a packet sourced from an address assigned by ISP X should
not be sent via ISP Y, to avoid ingress filtering by Y [RFC2827]
[RFC3704]. Additional considerations may be found in
[MULTIHOMING-WITHOUT-NAT]. Note that the prefix translation
technique discussed in [RFC6296] does not describe a solution for
enterprises that offer publicly available content servers.
Each IPv6 subnet that supports end hosts normally has a /64 prefix,
leaving another 64 bits for the interface identifiers of individual
hosts. In contrast, a typical IPv4 subnet will have no more than
8 bits for the host identifier, thus limiting the subnet to 256 or
fewer hosts. A dual-stack design will typically use the same
physical or VLAN subnet topology for IPv4 and IPv6, and therefore the
same router topology. In other words, the IPv4 and IPv6 topologies
are congruent. This means that the limited subnet size of IPv4 (such
as 256 hosts) will be imposed on IPv6, even though the IPv6 prefix
will allow many more hosts. It would be theoretically possible to
avoid this limitation by implementing a different physical or VLAN
subnet topology for IPv6. This is not advisable, as it would result
in extremely complex fault diagnosis when something went wrong.
5.3. DNS
It must be understood that as soon as a AAAA record for a well-known
name is published in the DNS, the corresponding server will start to
receive IPv6 traffic. Therefore, it is essential that an ICP test
thoroughly to ensure that IPv6 works on its servers, load balancers,
etc., before adding their AAAA records to DNS. There have been
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numerous cases of ICPs breaking their sites for all IPv6 users during
a roll-out by returning AAAA records for servers improperly
configured for IPv6.
Once such tests have succeeded, each externally visible host (or
virtual host) that has an A record for its IPv4 address needs a AAAA
record [RFC3596] for its IPv6 address, and a reverse entry (in
ip6.arpa) if applicable. Note that if CNAME records are in use, the
AAAA record must be added alongside the A record at the end of the
CNAME chain. It is not possible to have the AAAA record on the same
name as used for a CNAME record, as per [RFC1912].
One important detail is that some clients (especially Windows XP) can
only resolve DNS names via IPv4, even if they can use IPv6 for
application traffic. Also, a dual-stack resolver might attempt to
resolve queries for A records via IPv6, or AAAA records via IPv4. It
is therefore advisable for all DNS servers to respond to queries via
both IPv4 and IPv6.
6. Load Balancers
Most available load balancers now support IPv6. However, it is
important to obtain appropriate assurances from vendors about their
IPv6 support, including performance aspects (as discussed for routers
in Section 5.2). The update needs to be planned in anticipation of
expected traffic growth. It is to be expected that IPv6 traffic will
initially be low, i.e., a small but growing percentage of total
traffic. For this reason, it might be acceptable to have IPv6
traffic bypass load balancing initially, by publishing a AAAA record
for a specific server instead of the load balancer. However, load
balancers often also provide for server fail-over, in which case it
would be better to implement IPv6 load balancing immediately.
The same would apply to Transport Layer Security (TLS) or HTTP
proxies used for load-balancing purposes.
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7. Proxies
An HTTP proxy [RFC2616] can readily be configured to handle incoming
connections over IPv6 and to proxy them to a server over IPv4.
Therefore, a single proxy can be used as the first step in an
outside-in strategy, as shown in the following diagram:
___________________________________________
( )
( IPv6 Clients in the Internet )
(___________________________________________)
|
-------------
| Ingress |
| router |
-------------
____________|_____________
|
-------------
| IPv6 stack|
|-----------|
| HTTP proxy|
|-----------|
| IPv4 stack|
-------------
____________|_____________
|
-------------
| IPv4 stack|
|-----------|
| HTTP |
| server |
-------------
In this case, the AAAA record for the service would provide the IPv6
address of the proxy. This approach will work for any HTTP or HTTPS
applications that operate successfully via a proxy, as long as IPv6
load remains low. Additionally, many load-balancer products
incorporate such a proxy, in which case this approach would be
possible at high load.
Note that in any proxy scenario, an ICP will need to make sure that
both IPv4 and IPv6 addresses are being properly passed to application
servers in any relevant HTTP headers and that those application
servers are properly handling the IPv6 addresses.
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8. Servers
8.1. Network Stack
The TCP/IP network stacks in popular operating systems have supported
IPv6 for many years. In most cases, it is sufficient to enable IPv6
and possibly DHCPv6; the rest will follow. Servers inside an ICP
network will not need to support any transition technologies beyond a
simple dual stack, with a possible exception for 6to4 mitigation
noted below in Section 9.
As some operating systems have separate firewall rule sets for IPv4
and IPv6, an ICP should also evaluate those rule sets and ensure that
appropriate firewall rules are configured for IPv6. More details are
discussed in Section 14.
8.2. Application Layer
Basic HTTP servers have been able to handle an IPv6-enabled network
stack for some years, so at the most it will be necessary to update
to a more recent software version. The same is true of generic
applications such as email protocols. No general statement can be
made about other applications, especially proprietary ones, so each
ASP will need to make its own determination. As changes to the
network layer to introduce IPv6 addresses can ripple through
applications, testing of both client and server applications should
be performed in IPv4-only, IPv6-only, and dual-stack environments
prior to dual-stacking a production environment.
One important recommendation here is that all applications should use
domain names, which are IP-version-independent, rather than IP
addresses. Applications based on middleware platforms that have
uniform support for IPv4 and IPv6, for example, Java, may be able to
support both IPv4 and IPv6 naturally without additional work.
Security certificates should also contain domain names rather than
addresses.
A specific issue for HTTP-based services is that IP address-based
cookie authentication schemes will need to deal with dual-stack
clients. Servers might create a cookie for an IPv4 connection or an
IPv6 connection, depending on the setup at the client site and on the
whims of the client operating system. There is no guarantee that a
given client will consistently use the same address family,
especially when accessing a collection of sites rather than a single
site, such as when cookies are used for federated authentication. If
the client is using privacy addresses [RFC4941], the IPv6 address
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(but usually not its /64 prefix) might change quite frequently. Any
cookie mechanism based on 32-bit IPv4 addresses will need significant
remodeling.
Generic considerations on application transition are discussed in
[RFC4038], but many of them will not apply to the dual-stack ICP
scenario. An ICP that creates and maintains its own applications
will need to review them for any dependency on IPv4.
8.3. Logging
The introduction of IPv6 clients will generally also result in IPv6
addresses appearing in the "client ip" field of server logs. It
might be convenient to use the same log field to hold a client's IP
address, whether it is IPv4 or IPv6. Downstream systems looking at
logs and client IP addresses may also need testing to ensure that
they can properly handle IPv6 addresses. This includes any of an
ICP's databases recording client IP addresses, such as for recording
IP addresses of online purchases and comment posters.
It is worth noting that accurate traceback from logs to individual
customers requires end-to-end address transparency. This is
additional motivation for an ICP to support native IPv6 connectivity,
since otherwise, IPv6-only customers will inevitably connect via some
form of translation mechanism, interfering with traceback.
8.4. Geolocation
Initially, ICPs may observe some weakness in geolocation for IPv6
clients. As time goes on, it is to be assumed that geolocation
methods and databases will be updated to fully support IPv6 prefixes.
There is no reason they will be more or less accurate in the long
term than those available for IPv4. However, we can expect many more
clients to be mobile as time goes on, so geolocation based on IP
addresses alone may in any case become problematic. A more robust
technique such as HTTP-Enabled Location Delivery (HELD) [RFC5985]
could be considered.
9. Coping with Transition Technologies
As mentioned above, an ICP should obtain native IPv6 connectivity
from its ISPs. In this way, the ICP can avoid most of the
complexities of the numerous IPv4-to-IPv6 transition technologies
that have been developed; they are all second-best solutions.
However, some clients are sure to be using such technologies. An ICP
needs to be aware of the operational issues this may cause and how to
deal with them.
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In some cases outside the ICP's control, clients might reach a
content server via a network-layer translator from IPv6 to IPv4.
ICPs who are offering a dual-stack service and providing both A and
AAAA records, as recommended in this document, should not normally
receive IPv4 traffic from NAT64 translators [RFC6146].
Exceptionally, however, such traffic could arrive via IPv4 from an
IPv6-only client whose DNS resolver failed to receive the ICP's AAAA
record for some reason. Such traffic would be indistinguishable from
regular IPv4-via-NAT traffic.
Alternatively, ICPs who are offering a dual-stack service might
exceptionally receive IPv6 traffic translated from an IPv4-only
client that somehow failed to receive the ICP's A record. An ICP
could also receive IPv6 traffic with translated prefixes [RFC6296].
These two cases would only be an issue if the ICP was offering any
service that depends on the assumption of end-to-end IPv6 address
transparency.
Finally, some traffic might reach an ICP that has been translated
twice en route (e.g., from IPv6 to IPv4 and back again). Again, the
ICP will be unable to detect this. It is likely that real-time
geolocation will be highly inaccurate for such traffic, since it will
at best indicate the location of the second translator, which could
be very distant from the customer.
In other cases, also outside the ICP's control, IPv6 clients may
reach the IPv6 Internet via some form of IPv6-in-IPv4 tunnel. In
this case, a variety of problems can arise, the most acute of which
affect clients connected using the Anycast 6to4 solution [RFC3068].
Advice on how ICPs may mitigate these 6to4 problems is given in
Section 4.5. of [RFC6343]. For the benefit of all tunneled clients,
it is essential to verify that Path MTU Discovery works correctly
(i.e., the relevant ICMPv6 packets are not blocked) and that the
server-side TCP implementation correctly supports the Maximum Segment
Size (MSS) negotiation mechanism [RFC2923] for IPv6 traffic.
Some ICPs have implemented an interim solution to mitigate transition
problems by limiting the visibility of their AAAA records to users
with validated IPv6 connectivity [RFC6589] (known as "DNS
whitelisting"). At the time of this writing, this solution seems to
be passing out of use, being replaced by "DNS blacklisting" of
customer sites known to have problems with IPv6 connectivity. In the
reverse direction, it is worth being aware that some ISPs with
significant populations of clients with broken IPv6 setups have begun
filtering AAAA record lookups by their clients. None of these
solutions are appropriate in the long term.
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Another approach taken by some ICPs is to offer IPv6-only support via
a specific DNS name, e.g., ipv6.example.com, if the primary service
is www.example.com. In this case, ipv6.example.com would have a AAAA
record only. This has some value for testing purposes but is
otherwise only of interest to hobbyist users willing to type in
special URLs.
There is little an ICP can do to deal with client-side or remote ISP
deficiencies in IPv6 support, but it is hoped that the "Happy
Eyeballs" [RFC6555] approach will improve the ability for clients to
deal with such problems.
10. Content Delivery Networks
DNS-based techniques for diverting users to Content Delivery Network
(CDN) points of presence (POPs) will work for IPv6, if AAAA records
as well as A records are provided. In general, the CDN should follow
the recommendations of this document, especially by operating a full
dual-stack service at each POP. Additionally, each POP will need to
handle IPv6 routing exactly like IPv4, for example, running BGP-4+
[RFC4760].
Note that if an ICP supports IPv6 but its external CDN provider does
not, its clients will continue to use IPv4 and any IPv6-only clients
will have to use a transition solution of some kind. This is not a
desirable situation, since the ICP's work to support IPv6 will be
wasted.
An ICP might face a complex situation if its CDN provider supports
IPv6 at some POPs but not at others. IPv6-only clients could only be
diverted to a POP supporting IPv6. There are also scenarios where a
dual-stack client would be diverted to a mixture of IPv4 and IPv6
POPs for different URLs, according to the A and AAAA records provided
and the availability of optimizations such as "Happy Eyeballs". A
related side effect is that copies of the same content viewed at the
same time via IPv4 and IPv6 may be different, due to latency in the
underlying data synchronization process used by the CDN. This effect
has in fact been observed in the wild for a major social network
supporting dual stack. These complications do not affect the
viability of relying on a dual-stack CDN, however.
The CDN itself faces related complexity: "As IPv6 rolls out, it's
going to roll out in pockets, and that's going to make the routing
around congestion points that much more important but also that much
harder," stated John Summers of Akamai in 2010 [CDN-UPGRADE].
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A converse situation that might arise is that an ICP has not yet
started its deployment of IPv6 but finds that its CDN provider
already supports IPv6. Then, assuming that the CDN provider
announces appropriate AAAA DNS Resource Records, dual-stack and
IPv6-only customers will obtain IPv6 access, and the ICP's content
may well be delivered to them via IPv6. In normal circumstances,
this should create no problems, but it is a situation that the ICP
and its support staff need to be aware of. In particular, support
staff should be given IPv6 connectivity in order to be able to
investigate any problems that might arise (see Section 4).
11. Business Partners
As noted earlier, it is in an ICP's or ASP's best interests that
their users have direct IPv6 connectivity, rather than indirect IPv4
connectivity via double NAT. If the ICP or ASP has a direct business
relationship with some of their clients, or with the networks that
connect them to their clients, they are advised to coordinate with
those partners to ensure that they have a plan to enable IPv6. They
should also verify and test that there is first-class IPv6
connectivity end-to-end between the networks concerned. This is
especially true for implementations that require IPv6 support in
specialized programs or systems in order for the IPv6 support on the
ICP/ASP side to be useful.
12. Possible Complexities
Some additional considerations come into play for some types of
complex or distributed sites and applications that an ICP may be
delivering. For example, an ICP may have a site spread across many
hostnames (not all under their control). Other ICPs may have their
sites or applications distributed across multiple locations for
availability, scale, or performance.
Many modern web sites and applications now use a collection of
resources and applications, some operated by the ICP and others by
third parties. While most clients support sites containing a mixture
of IPv4-only and dual-stack elements, an ICP should track the IPv6
availability of embedded resources (such as images), as otherwise
their site may only be partially functional or may have degraded
performance for IPv6-only users.
DNS-based load-balancing techniques for diverting users to servers in
multiple POPs will work for IPv6, if the load balancer supports IPv6
and if AAAA records are provided. Depending on the architecture of
the load balancer, an ICP may need to operate a full dual-stack
service at each POP. With other architectures, it may be acceptable
to initially only have IPv6 at a subset of locations. Some
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architectures will make it preferable for IPv6 routing to mirror IPv4
routing (for example, running BGP-4+ [RFC4760] if appropriate), but
this may not always be possible, as IPv6 and IPv4 connectivity can be
independent.
Some complexities may arise when a client supporting both IPv4 and
IPv6 uses different POPs for each IP version (such as when IPv6 is
only available in a subset of locations). There are also scenarios
where a dual-stack client would be diverted to a mixture of IPv4 and
IPv6 POPs for different URLs, according to the A and AAAA records
provided and the availability of optimizations such as "Happy
Eyeballs" [RFC6555]. A related side effect is that copies of the
same content viewed at the same time via IPv4 and IPv6 may be
different, due to latency in the underlying data synchronization
process used at the application layer. This effect has in fact been
observed in the wild for a major social network supporting dual
stack.
Even with a single POP, unexpected behavior may arise if a client
switches spontaneously between IPv4 and IPv6 as a performance
optimization [RFC6555] or if its IPv6 address changes frequently for
privacy reasons [RFC4941]. Such changes may affect cookies,
geolocation, load balancing, and transactional integrity. Although
unexpected changes of client address also occur in an IPv4-only
environment, they may be more frequent with IPv6.
13. Operations and Management
There is no doubt that, initially, IPv6 deployment will have
operational impact, and will also require education and training as
mentioned in Section 3. Staff will have to update network elements
such as routers, update configurations, provide information to end
users, and diagnose new problems. However, for an enterprise
network, there is plenty of experience, e.g., on numerous university
campuses, showing that dual-stack operation is no harder than
IPv4-only in the steady state.
Whatever management, monitoring, and logging are performed for IPv4
are also needed for IPv6. Therefore, all products and tools used for
these purposes must be updated to fully support IPv6 management data.
It is important to verify that tools have been fully updated to
support 128-bit addresses entered and displayed in hexadecimal format
[RFC5952]. Since an IPv6 network may operate with more than one IPv6
prefix and therefore more than one address per host, the tools must
deal with this as a normal situation. This includes any address
management tool in use (see Section 5.1) as well as tools used for
creating DHCP and DNS configurations. There is significant overlap
here with the tools involved in site renumbering [RFC6879].
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At an early stage of IPv6 deployment, it is likely that IPv6 will be
mainly managed via IPv4 transport. This allows network management
systems to test for dependencies between IPv4 and IPv6 management
data. For example, will reports mixing IPv4 and IPv6 addresses
display correctly?
In a second phase, IPv6 transport should be used to manage the
network. Note that it will also be necessary for an ICP to provide
IPv6 connectivity for its operations and support staff, even when
working remotely. As far as possible, mutual dependency between IPv4
and IPv6 should be avoided, for both the management data and the
transport. Failure of one should not cause a failure of the other.
One precaution to avoid this would be for network management systems
to be dual-stacked. It would then be possible to use IPv4
connectivity to repair IPv6 configurations, and vice versa.
Dual stack, while necessary, does have management scaling and
overhead considerations. As noted earlier, the long-term goal is to
move to single-stack IPv6, when the network and its customers can
support it. This is an additional reason why mutual dependency
between the address families should be avoided in the management
system in particular; a hidden dependency on IPv4 that had been
forgotten for many years would be highly inconvenient. In
particular, a management tool that manages IPv6 but itself runs only
over IPv4 would prove disastrous on the day that IPv4 is switched
off.
An ICP should ensure that any end-to-end availability monitoring
systems are updated to monitor dual-stacked servers over both IPv4
and IPv6. A particular challenge here may be monitoring systems
relying on DNS names, as this may result in monitoring only one of
IPv4 or IPv6, resulting in a loss of visibility to failures in
network connectivity over either address family.
As mentioned above, it will also be necessary for an ICP to provide
IPv6 connectivity for its operations and support staff, even when
working remotely.
14. Security Considerations
While many ICPs may still be in the process of experimenting with and
configuring IPv6, there is mature malware in the wild that will
launch attacks over IPv6. For example, if a AAAA DNS record is added
for a hostname, malware using client OS libraries may automatically
switch from attacking that hostname over IPv4 to attacking that
hostname over IPv6. As a result, it is crucial that firewalls and
other network security appliances protecting servers support IPv6 and
have rules tested and configured.
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Security experience with IPv4 should be used as a guide as to the
threats that may exist in IPv6, but they should not be assumed to be
equally likely nor should they be assumed to be the only threats that
could exist in IPv6. However, essentially every threat that exists
for IPv4 exists or will exist for IPv6, to a greater or lesser
extent. It is essential to update firewalls, intrusion detection
systems, denial-of-service precautions, and security auditing
technology to fully support IPv6. Needless to say, it is also
essential to turn on well-known security mechanisms such as DNS
Security and DHCPv6 Authentication. Otherwise, IPv6 will become an
attractive target for attackers.
When multiple PA prefixes are in use as mentioned in Section 5.1,
firewall rules must allow for all valid prefixes and must be set up
to work as intended even if packets are sent via one ISP but return
packets arrive via another.
Performance and memory size aspects of dual-stack firewalls must be
considered (as discussed for routers in Section 5.2).
In a dual-stack operation, there may be a risk of cross-contamination
between the two protocols. For example, a successful IPv4-based
denial-of-service attack might also deplete resources needed by the
IPv6 service, or vice versa. This risk strengthens the argument that
IPv6 security must be up to the same level as IPv4. Risks can also
occur with dual-stack Virtual Private Network (VPN) solutions
[VPN-LEAKAGES].
A general overview of techniques to protect an IPv6 network against
external attacks is given in [RFC4864]. Assuming that an ICP has
native IPv6 connectivity, it is advisable to block incoming
IPv6-in-IPv4 tunnel traffic using IPv4 protocol type 41. Outgoing
traffic of this kind should be blocked, except for the case noted in
Section 4.5 of [RFC6343]. ICMPv6 traffic should only be blocked in
accordance with [RFC4890]; in particular, Packet Too Big messages,
which are essential for Path MTU Discovery, must not be blocked.
Brute-force scanning attacks to discover the existence of hosts are
much less likely to succeed for IPv6 than for IPv4 [RFC5157].
However, this should not lull an ICP into a false sense of security,
as various naming or addressing conventions can result in IPv6
address space being predictable or guessable. In the extreme case,
IPv6 hosts might be configured with interface identifiers that are
very easy to guess; for example, hosts or subnets manually numbered
with consecutive interface identifiers starting from "1" would be
much easier to guess. Such practices should be avoided, and other
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useful precautions are discussed in [RFC6583]. Also, attackers might
find IPv6 addresses in logs, packet traces, DNS records (including
reverse records), or elsewhere.
Protection against rogue Router Advertisements (RA Guard) should also
be considered [RFC6105].
Transport Layer Security version 1.2 [RFC5246] and its predecessors
work correctly with TCP over IPv6, meaning that HTTPS-based security
solutions are immediately applicable. The same should apply to any
other transport-layer or application-layer security techniques.
If an ASP uses IPsec [RFC4301] and the Internet Key Exchange (IKE)
protocol [RFC5996] in any way to secure connections with clients,
these too are fully applicable to IPv6, but only if the software
stack at each end has been appropriately updated.
15. Acknowledgements
Valuable contributions were made by Erik Kline. Useful comments were
received from Tore Anderson, Cameron Byrne, Tassos Chatzithomaoglou,
Wesley George, Deng Hui, Joel Jaeggli, Roger Jorgensen, Victor
Kuarsingh, Bing Liu, Trent Lloyd, John Mann, Michael Newbery, Erik
Nygren, Arturo Servin, Mark Smith, and other participants in the
V6OPS working group.
Brian Carpenter was a visitor at the Computer Laboratory, Cambridge
University during part of this work.
16. References
16.1. Normative References
[RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
January 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
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[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", RFC 3596,
October 2003.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
January 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
October 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
[RFC5838] Lindem, A., Mirtorabi, S., Roy, A., Barnes, M., and R.
Aggarwal, "Support of Address Families in OSPFv3",
RFC 5838, April 2010.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, August 2010.
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[RFC5985] Barnes, M., "HTTP-Enabled Location Delivery (HELD)",
RFC 5985, September 2010.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
Requirements", RFC 6434, December 2011.
16.2. Informative References
[CDN-UPGRADE]
Marsan, C., "Akamai: Why our IPv6 upgrade is harder than
Google's", Network World, September 2010, <http://
www.networkworld.com/news/2010/091610-akamai-ipv6.html>.
[IPv6-CE-REQS]
Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", Work
in Progress, October 2012.
[IPv6-NETWORK-DESIGN]
Matthews, P., "Design Choices for IPv6 Networks", Work
in Progress, February 2013.
[MULTIHOMING-WITHOUT-NAT]
Troan, O., Ed., Miles, D., Matsushima, S., Okimoto, T.,
and D. Wing, "IPv6 Multihoming without Network Address
Translation", Work in Progress, February 2012.
[RFC1912] Barr, D., "Common DNS Operational and Configuration
Errors", RFC 1912, February 1996.
[RFC2081] Malkin, G., "RIPng Protocol Applicability Statement",
RFC 2081, January 1997.
[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery",
RFC 2923, September 2000.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, June 2001.
[RFC4038] Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E.
Castro, "Application Aspects of IPv6 Transition",
RFC 4038, March 2005.
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[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.
[RFC4890] Davies, E. and J. Mohacsi, "Recommendations for Filtering
ICMPv6 Messages in Firewalls", RFC 4890, May 2007.
[RFC5157] Chown, T., "IPv6 Implications for Network Scanning",
RFC 5157, March 2008.
[RFC5375] Van de Velde, G., Popoviciu, C., Chown, T., Bonness, O.,
and C. Hahn, "IPv6 Unicast Address Assignment
Considerations", RFC 5375, December 2008.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
February 2011.
[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.
[RFC6180] Arkko, J. and F. Baker, "Guidelines for Using IPv6
Transition Mechanisms during IPv6 Deployment", RFC 6180,
May 2011.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011.
[RFC6343] Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
RFC 6343, August 2011.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6583] Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
Neighbor Discovery Problems", RFC 6583, March 2012.
[RFC6589] Livingood, J., "Considerations for Transitioning Content
to IPv6", RFC 6589, April 2012.
[RFC6866] Carpenter, B. and S. Jiang, "Problem Statement for
Renumbering IPv6 Hosts with Static Addresses in Enterprise
Networks", RFC 6866, February 2013.
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[RFC6879] Jiang, S., Liu, B., and B. Carpenter, "IPv6 Enterprise
Network Renumbering Scenarios, Considerations, and
Methods", RFC 6879, February 2013.
[VPN-LEAKAGES]
Gont, F., "Virtual Private Network (VPN) traffic leakages
in dual-stack hosts/networks", Work in Progress,
December 2012.
Authors' Addresses
Brian Carpenter
Department of Computer Science
University of Auckland
PB 92019
Auckland 1142
New Zealand
EMail:
[email protected]
Sheng Jiang
Huawei Technologies Co., Ltd
Q14, Huawei Campus
No. 156 Beiqing Road
Hai-Dian District, Beijing 100095
P.R. China
EMail:
[email protected]
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