IPv6-Mostly Networks: Deployment and Operations Considerations
draft-link-v6ops-6mops-00
| Document | Type | Active Internet-Draft (individual) | |
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| Author | Jen Linkova | ||
| Last updated | 2024-03-04 | ||
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draft-link-v6ops-6mops-00
IPv6 operations J. Linkova
Internet-Draft Google
Intended status: Informational 4 March 2024
Expires: 5 September 2024
IPv6-Mostly Networks: Deployment and Operations Considerations
draft-link-v6ops-6mops-00
Abstract
This document discusses an deployment scenario called "an IPv6-Mostly
network", when IPv6-only and IPv4-enabled endpoints coexist on the
same network (network segment, VLAN, SSID etc).
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4
4.1. IPv6-Only Capable Endpoints . . . . . . . . . . . . . . . 5
4.2. IPv6-Only and IPv4-enabled Endpoints Coexistence . . . . 5
4.3. Access to IPv4-only Destinations . . . . . . . . . . . . 5
4.3.1. NAT64 . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3.2. 464XLAT . . . . . . . . . . . . . . . . . . . . . . . 6
4.3.3. Signalling NAT64 Prefix to Hosts . . . . . . . . . . 6
4.3.4. DNS vs DNS64 . . . . . . . . . . . . . . . . . . . . 7
5. Solution Benefits . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Benefits Compared to Dual-Stack . . . . . . . . . . . . . 7
5.2. Benefits Compared to a Dedicated IPv6-Only Network . . . 8
6. Incremental Rollout Considerations . . . . . . . . . . . . . 9
6.1. Per-Device and Per-Subnet Incremental Rollout . . . . . . 9
6.2. Rollback Approach . . . . . . . . . . . . . . . . . . . . 9
6.3. Opt-In and Opt-Out Modes . . . . . . . . . . . . . . . . 9
7. Operational Considerations . . . . . . . . . . . . . . . . . 10
7.1. Address Assignment Policy . . . . . . . . . . . . . . . . 10
7.2. Extension Headers . . . . . . . . . . . . . . . . . . . . 10
7.3. Typical Issues . . . . . . . . . . . . . . . . . . . . . 10
7.3.1. Hosts with Disabled or Disfunctional IPv6 . . . . . . 11
7.3.2. Network Extension . . . . . . . . . . . . . . . . . . 11
7.3.3. Multiple Addresses per Device . . . . . . . . . . . . 11
7.3.4. Host Mobility and Renumbering . . . . . . . . . . . . 12
7.3.5. Fragmentation . . . . . . . . . . . . . . . . . . . . 12
7.3.6. Representing IPv6 Addresses by CLAT . . . . . . . . . 13
7.3.7. Custom DNS Configuration on Endpoints . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 15
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
While most network operators initially deploy IPv6 alongside their
existing IPv4 infrastructure, pure IPv6-only networks remain uncommon
outside of the mobile carrier space. This dual-stack approach is
seen as a necessary transition phase, allowing operators to gain
experience with IPv6 while minimizing disruption.
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However, dual-stack networks don't address the core problem driving
IPv6 adoption: IPv4 address exhaustion. They still require the same
amount of IPv4 resources as IPv4-only networks. Even worse, this
dual-stack approach often becomes a long-term crutch. Many
applications still rely on IPv4, creating a chicken-and-egg problem:
IPv6-only networks seem impractical with so many incompatible
applications, yet applications continue to rely on IPv4 because
IPv6-only networks are rare.
The less control a network operator has over devices and
applications, the more difficult it is to break IPv4 dependencies and
move to IPv6-only. This is particularly challenging in enterprise
networks with legacy IPv4-dependent applications and public WiFi
networks where operators cannot guarantee device compatibility.
To enable a gradual migration, operators need to identify which
devices can function in IPv6-only mode and which cannot. Creating
separate network segments for each type introduces complexity and
scalability issues – a major hurdle to IPv6-only adoption.
A more desirable approach is to deploy so-called "IPv6-mostly"
network that provides IPv4 on demand. This allows IPv6-capable
devices to remain IPv6-only while seamlessly supplying IPv4 to those
that require it.
This document explores the requirements, recommendations, and
challenges associated with deploying IPv6-mostly networks in
enterprise and public WiFi environments. While the principles
discussed may be applicable to other network types, this document's
focus remains on these specific use cases.
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
This document reuses most of Terminology section from [RFC8925].
Endpoint: A device connected to a network and considered a host From
the operator's perspective. However, some endpoint can also extend
the network to other physical or logical systems, thereby assuming
routing functions. Examples include:
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* Corporate laptop: While primarily a host, it might run virtual
systems and route traffic to them, extending the network and
acting as a router.
* Mobile phone with tethering enabled: Acts as a host on the WiFi
network, but also as a router for tethered devices, potentially
without the operator's knowledge or consent.
Network segment: a link (VLAN, a broadcast domain etc) where hosts
share the same IP subnet.
4. Solution Overview
In a nutshell, an IPv6-mostly network is very much similar to a dual-
stack one with two additional key elements:
* The network provides NAT64 ([RFC6146]) functionality ([RFC6146]),
enabling IPv6-only clients to communicate with IPv4-only
destinations.
* The DHCPv4 infrastructure processing DHCPv4 Option 108 as per
[RFC8925].
Upon connecting to an IPv6-mostly network segment, an endpoint
configures its IP stack based on its capabilities:
* IPv4-Only Endpoint: Acquires an IPv4 address through DHCPv4.
* Dual-Stack Endpoint (Not IPv6-Only Capable): Configures IPv6
addresses via Stateless Address Autoconfiguration (SLAAC) and,
optionally, DHCPv6. Additionally, it obtains an IPv4 address via
DHCPv4.
* IPv6-only capable endpoint configures its IPv6 addresses and,
while performing DHCPv4, includes option 108 ([RFC8925]) into the
Parameter Request List. The DHCP server returns the option and,
as per [RFC8925], the endpoint forgoes requesting an IPv4 address,
remaining in IPv6-only mode.
An IPv6-mostly network segment can support a mix of IPv4-only, dual-
stack, and IPv6-only devices. IPv6-only endpoints utilize the
network-provided NAT64 to reach IPv4-only destinations.
The following sections discussed the various solution elements in
more details.
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4.1. IPv6-Only Capable Endpoints
The term "IPv6-only capable endpoint" lacks a strict technical
definition. It broadly describes a device that can function without
native IPv4 connectivity/IPv4 addresses, providing the same user
experience. The most common way to achieve this is by implementing a
customer-side translator (CLAT) as specified in 464XLAT ([RFC6877]).
Devices which support CLAT (such as mobile phones) are known to
operate without issues in IPv6-only mode. In some cases, however, a
network administrator may consider a device IPv6-only capable even
without CLAT implementation. For example, if all applications run on
the device have been tested and confirmed to operate in NAT64
envinronment without any IPv4 dependencies.
4.2. IPv6-Only and IPv4-enabled Endpoints Coexistence
One effective way to restrict IPv4 addresses solely to devices that
require them is to enable support for the IPv6-Only Preferred DHCPv4
option (Option 108, [RFC8925]) on the network's DHCP infrastructure.
Most CLAT-enabled systems also support Option 108. By recognizing
this option, the network can configure those devices as IPv6-only,
allowing them to use CLAT fo providing IPv4 address to the local
endpoint's network stack.
Certain devices, such as resource-constrained embedded systems, may
operate in IPv6-only mode without CLAT if their communication is
limited to IPv6-enabled destinations. Since these systems often lack
Option 108 support, administrators may need alternative methods to
prevent IPv4 address assignment. One approach is to block IPv4
traffic at the switchport level. This could involve:
* Static ACL: Applying a static filter with a "deny ip any any"
rule.
* Dynamic ACL via RADIUS: If 802.1x authentication is in use, RADIUS
can provide an ACL blocking all IPv4 traffic.
The ACL-based approach has some scalability implications and
increases operational complexity, therefore it could only be
recommended as a stopgap solution.
4.3. Access to IPv4-only Destinations
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4.3.1. NAT64
IPv6-only endpoints require NAT64 to access IPv4-only destinations.
Quite often operators choose to combine NAT44 and NAT64 functions.
However, if not all internal services are IPv6-enabled, then NAT64
might need to be performed closer to the clients. If IPv4-only
internal destinations are using [RFC1918] address space, then the
operator MUST NOT use the well-known prefix 64:ff9b::/96 for NAT64
(see section 3.1 of [RFC6052]).
4.3.2. 464XLAT
Enabling CLAT (Customer-side translator) on endpoints is essential
for seamless operation of IPv4-only applications in IPv6-only
environments. CLAT provides an [RFC1918] address and IPv4 default
route, ensuring functionality even without a native IPv4 address from
the network. Without CLAT, IPv4-only applications would fail,
negatively impacting user experience and increasing support overhead.
Recommendations for Network Administrators controlling the endpoints:
* CLAT + DHCPv4 Option 108: If the network administrator can control
endpoint configuration, CLAT SHOULD be enabled on endpoints
sending DHCPv4 Option 108. This streamlines the transition.
* Option 108 Without CLAT MAY be enabled if the administrator is
willing to identify and fixIPv4-only systems/applications, or if
all applications are confirmed to work in IPv6-only mode.
4.3.3. Signalling NAT64 Prefix to Hosts
Hosts running 464XLAT need to discover the PREF64 (the IPv6 prefix
used by NAT64). The network administrator SHOULD configure the
first-hop routers to include PREF64 information in Router
Advertisements as per ([RFC8781]) even if the network provides DNS64
(so hosts can use DNS64-based prefix discovery, [RFC7050]). This is
required as hosts or individual applications might have custom DNS
configuration (or even run a local DNS server) and ignore DNS64
information provided by the network, so they can not use [RFC7050]
method to detect PREF64. In the absense of PREF64 information in
Router Advertisements such systems would not be able to run clat,
which would cause connectivity issues for all IPv4-only applications
running on the affected device. As such device wouldn't be able to
use the network-provided DNS64, access to IPv4-only destination would
be impacted as well. At the time of writing all major OSes
supporting DHCPv4 option 108 and enabling clat automatically also
support [RFC8781]. Therefore providing PREF64 information in RAs can
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reliably mitigate the impact of custom DNS configuration on those
systems.
Receiving PREF64 information in RAs also speeds up the clat start up
time, so an IPv4 address and default route become available for
applications much faster.
4.3.4. DNS vs DNS64
While DNS64 (with NAT64) enables IPv6-only endpoints to access
IPv4-only destinations, it has several drawbacks:
* DNSSEC Incompatibility: DNS64 responses fail DNSSEC validation.
* Custom Resolvers: Endpoints or applications configured with custom
resolvers can not benefit from the DNS64 provided by the network.
* Additional requirements for application: to benefit from DNS64,
applications need to be IPv6-enabled, use DNS (do not use IPv4
literals). Many applications do not satisfy those requirements
and therefore fail if the endpoint does not have an IPv4 address/
native IPv4 connectivity.
If the network provides PREF64 in RAs (Section 4.3.3) and all
endpoints are guaranteed to have CLAT enabled, DNS64 is unnecessary
and SHOULD NOT be enabled. However, if some IPv6-only devices might
lack CLAT support, the network MUST provide DNS64 unless those
endpoints are guaranteed never to need IPv4-only destinations (for
example, in case of a specialized network segment communicating
solely with IPv6-capable destinations).
5. Solution Benefits
5.1. Benefits Compared to Dual-Stack
IPv6-Mostly networks offer significant advantages over traditional
dual-stack models where endpoints have both IPv4 and IPv6 addresses:
* Drastically Reduced IPv4 Consumption: Dual-stack deployments don't
solve the core problem of IPv4 address exhaustion. IPv6-Mostly
allows to significantly reduce IPv4 consumption, as well as to
reclaim IPv4 space. This reduction depends on endpoint
capabilities (DHCPv4 Option 108 and CLAT support). In real-world
scenarios, like conference Wi-Fi, 60-70% of endpoints may support
IPv6-only operation, potentially allowing 2-4 times smaller IPv4
subnets.
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* Simplified Operations: Managing dual-stack networks means running
two network planes simultaneously, increasing complexity, costs,
and the potential for errors. IPv6-Mostly allows to phase out
IPv4 from many endpoints, streamlining operations and improving
overall network reliability.
* Reduced Dependency on DHCPv4: As more devices operate seamlessly
in IPv6-only mode, the criticality of DHCPv4 service diminishes
significantly. This allows operators to scale down DHCPv4
infrastructure or operate it with less stringent SLOs, optimizing
costs and resource allocation.
5.2. Benefits Compared to a Dedicated IPv6-Only Network
Traditional IPv6-only adoption involved separate networks alongside
dual-stack ones. IPv6-Mostly offers significant improvements:
* Enhanced Scalability: Separate IPv6-only networks double the
number of SSIDs in wireless environments, causing channel
congestion and degrading performance. IPv6-Mostly doesn't require
additional SSIDs. Similarly, it allows IPv4 and IPv6-only devices
to coexist on the same wired VLANs, eliminating the need of
additional VLANs.
* Operational Simplicity: Managing one network segment for all
clients (regardless of IPv4 needs) simplifies operations, improves
user experience (no more confusing SSID choices), and reduces
support tickets related to mismatched connections. Dynamic VLAN
assignment becomes easier without device-specific IPv6 capability
tracking.
* Optimized IPv4 Consumption: User-selected dual-stack networks
often lead to unnecessary IPv4 use, as users often connect
IPv6-only capable devices to a dual-stack network. IPv6-Mostly
network allocates IPv4 addresses only when devices don't advertise
IPv6-only capability (DHCPv4 Option 108).
* Improved Problem Visibility: User-selected fallback to dual-stack
networks can mask issues with IPv6-only operation, hindering
problem reporting and resolution. IPv6-Mostly forces users to
work through any issues, improving identification and enabling
fixes for smoother long-term migration.
* Flexible, Incremental Migration: IPv6-Mostly allows for gradual
device migration on a per-segment basis. Devices become IPv6-only
only when deemed fully compatible with that mode.
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6. Incremental Rollout Considerations
Migrating endpoints to IPv6-only fundamentally changes network
dynamics by removing the IPv4 safety net. This includes the masking
effect of Happy Eyeballs. IPv6 connectivity issues become far more
prominent, including those previously hidden within dual-stack
environments. Operators should be prepared to discover and
troubleshoot issues in both endpoints and network infrastructure,
even if the dual-stack network appeared problem-free.
Some rollout considerations are discussed in the following sections.
6.1. Per-Device and Per-Subnet Incremental Rollout
Limited control over endpoint configuration necessitates a per-subnet
rollout, incrementally enabling Option 108 processing in DHCP. If
endpoint control exists, per-device rollout is possible (at least for
OSes with configurable Option 108). Note that some OSes
unconditionally enable Option 108 support, becoming IPv6-only the
moment it's activated on the server side. The following approach is
RECOMMENDED:
* DHCP Server-Side Activation: Enable Option 108 processing. Some
OSes automatically switch to IPv6-only. Rollback at this stage
affects the entire subnet.
* Controlled Endpoint Activation: Enable Option 108 on managed
endpoints with per-device rollback possible.
6.2. Rollback Approach
For quick rollback, the administrator SHOULD start with a minimal
Option 108 value (300 seconds, Section 3.4 of [RFC8925]) and increase
this value as the IPv6-mostly network proves reliable, reducing the
likelihood of full-scale rollback.
6.3. Opt-In and Opt-Out Modes
Before user-facing deployment, the administrator SHOULD consider a
dedicated IPv6-mostly proof-of-concept network for early adopters.
While this temporarily sacrifices some IPv6-mostly benefits
(Section 5.2), it provides valuable operational experience and early
issue detection.
* Opt-In Phase: Invite tech-savvy early adopters to enable Option
108 and report issues. While response rates may be low, dedicated
participants provide valuable troubleshooting data.
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* Opt-Out Phase: Incrementally enable Option 108. Allow selective
disabling for problematic endpoints. Disabling Option 108 SHOULD
NOT be possible without a problem reports to ensure issue tracking
and resolution.
In some scenarios (see Section 7.3.1) the administrator MAY keep a
dual-stack network as a last resort fallback mechanism but SHOULD
prevent usesrs from connecting to it accidentially (e.g. it should be
a hidden protected SSID).
7. Operational Considerations
7.1. Address Assignment Policy
As outlined in Section 6.3 of [RFC6877], CLAT requires either a
dedicated IPv6 prefix or, if unavailable, a dedicated IPv6 address.
Currently (2024), all implementations use SLAAC for CLAT address
acquisition. Therefore, to enable CLAT functionality within
IPv6-mostly network segments, first-hop routers must advertise a
Prefix Information Option (PIO) containing a globally routable SLAAC-
suitable prefix with the 'Autonomous Address-Configuration' (A) flag
set to zero.
7.2. Extension Headers
Being an IPv6-specific concept, IPv6 extension headers are often
neglected or even explictly prohibited by security policies in dual-
stack networks. The issues caused by blockig extension headers might
be masked by the presense of Happy Eyeballs but become highly visible
when there is no IPv4 to fallback to.
The network SHOULD permit at least the following extension headers:
* Fragment Header (Section 4.5 of [RFC8200]). Section 7.3.5
discusses the fragmentation in more details.
* ESP Header, which is used for IPSec traffic, such as VPN and WiFi
Calling.
7.3. Typical Issues
IPv6-mostly networks expose hidden issues by removing the IPv4 safety
net. While implementation bugs vary greatly and are beyond the scope
of this document, this section focus on common problems caused by
configuration, topology, or design choices. It's crucial to note
that these issues likely pre-exist in dual-stack networks, but remain
unnoticed due to IPv4 fallback.
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7.3.1. Hosts with Disabled or Disfunctional IPv6
Historically, tech support often advised disabling IPv6 as a quick
workaround, leading to devices with disabled IPv6. Similarly,
corporate IT may have disabled or filtered IPv6 under the assumption
that it's not widely used. Such endpoints requesting Option 108 will
fail to connect in an IPv6-mostly network, as they won't receive IPv4
addresses and Ipv6 is disabled.
Administrators controlling endpoints SHOULD ensure those endpoints
have IPv6 enabled and operational before migrating the network to
IPv6-mostly mode.
7.3.2. Network Extension
IPv4's NAT44 allows endpoints to extend connectivity to downstream
systems without upstream network awareness or permission. This
creates challenges in IPv6-mostly deployments where endpoints lack
IPv4 addresses:
Solutions and trade-offs:
* Using DHCPv6-PD to allocate prefixes to endpoints
([I-D.ietf-v6ops-dhcp-pd-per-device]). Provides downstream
systems with IPv6 addresses and native connectivity.
* Enabling the CLAT function on the endpoint. This scenario is
similar to the Wireline Network Architecture described in
Section 4.1 of [RFC6877]. The downstream systems would receive
IPv4 addresses and their IPv4 traffic would be translated to IPv6
by the endpoint. However thios approach leads to the downstream
systems using IPv4 only and not benefiting from end2end IPv6
connectivity. To enable IPv6 benefits, combine this with IPv6
Prefix Delegation as above.
* Bridging and ND Proxy: The endpoint bridges IPv6 traffic and masks
downstream devices behind its MAC address. This can lead to
scalability issues ( Section 7.3.3) due to the single MAC being
mapped to many IPv6 addresses.
7.3.3. Multiple Addresses per Device
Unlike IPv4, where endpoints typically have a single IPv4 address per
interface, IPv6 endpoints inherently use multiple addresses:
* Link-local address.
* Temporary address (common on mobile devices for privacy)
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* Stable address (for long-term identification)
* CLAT address (in IPv6-mostly/IPv6-only networks)
Endpoints with containers, namespaces, or ND proxy functions can have
even more addresses. This poses challenges for network
infrastructure devices (SAVI switches, wireless access points etc)
that map MAC addresses to IPv6 addresses, often with limits to
prevent resource exhaustion or DoS attacks. When the number of IPs
per MAC limit is exceeded, infastructure devices behavior varies
across implementations, leading to inconsistent connectivity loss:
while some systems drop new addresses, others delete older entries,
causing previously functional addresses to lose connectivity. In all
those cases Endpoints and applications don't receive explicit
signalling about the address becoming unusable.
While allocating prefixes to endpoints via DHCP-PD
([I-D.ietf-v6ops-dhcp-pd-per-device]) alows to eliminate the issue
and corresponding scalability concerns, that solution migth not be
supported by all endpoints. The network administrator SHOULD ensure
that the deployed network infastructure devices allow sufficient
number of IPv6 addresses to be mapped to a client's MAC and SHOULD
monitor for events, indicating that the limit has been reached (such
as syslog messages etc).
7.3.4. Host Mobility and Renumbering
Networks employing dynamic VLAN assignment (e.g., based on 802.1x or
MAC-based authentication) can cause endpoints to move between VLANs
and IPv6 subnets. As client operating systems do not always handle
changes in link-layer state (e.g., VLAN changes) correctly, this
mobility often leads to inconsistent IP stack behavior on operating
systems, resulting in the persistence of old subnet addresses and
potential connectivity issues due to incorrect source address
selection. [I-D.link-v6ops-gulla] provides further analysis and
potential solutions.
7.3.5. Fragmentation
As the basic IPv6 header is 20 bytes longer than the IPv4 header,
transating from IPv4 to IPv6 can result in packets exceeding the path
MTU on the IPv6 side. In that case NAT64 creates IPv6 packets with
the Fragment Header (see Section 4 of [RFC6145] for more details. As
per [RFC6145], by default the translator fragments IPv4 packets so
that they fit in 1280-byte IPv6 packets. It means that all IPv4
packets larger than 1260 bytes are fragmented (or dropped if the DF
bit is set).
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Administrators SHOULD maximize the path MTU on the IPv6 side (from
the translator to IPv6-only hosts) to minimize fragmentation. NAT64
devices SHOULD be configured to use the actual path MTU on the IPv6
side when fragmenting IPv4 packets.
Another common case of IPv6 fragmentation is the use of protocols
like DNS and RADIUS, where the server response needs to be sent as a
single UDP datagram. Network security policies MUST allow IPv6
fragments for permitted UDP traffic (e.g., DNS, RADIUS) where single-
datagram responses are required. Allowing IPv6 fragments for
permitted TCP traffic is RECOMMENDED unless the network
infrastructure reliably performs TCP MSS clamping.
DISCUSSION: neither [RFC6145] nor [RFC6146] requires that NAT64
device performs MSS clamping, reducing MSS by 20 bytes while
translating IPv6 to IPv4. Sounds like a useful feature though.
7.3.6. Representing IPv6 Addresses by CLAT
Certain CLAT implementations face challenges when translating
incoming IPv6 packets with native (non-synthesized) source addresses
(e.g. ICMPv6 packets sent by intermediate hops on the path). This
lack of standardized translation mechanisms can lead to:
* Incomplete Traceroute: Omission of IPv6-only hops between the
endpoint and NAT64 translator, hindering troubleshooting.
* Path MTU Discovery Issues: Potential disruptions in the PMTU
discovery process.
DISCUSSION: shall the IETF consider standardizing a translation
mechanism for such packets?
7.3.7. Custom DNS Configuration on Endpoints
In IPv6-mostly networks without PREF64 in RAs, hosts rely on DNS64
([RFC7050]) to discover the NAT64 prefix for CLAT operation.
Endpoints or applications configured with custom DNS resolvers (e.g.,
public or corporate DNS) may bypass the network-provided DNS64,
preventing NAT64 prefix discovery and hindering CLAT functionality.
Where feasible, administrators SHOULD include PREF64 in RAs within
IPv6-mostly networks to minimize reliance on DNS64. Administrators
need to be aware of the potential for CLAT failures when endpoints
use custom resolvers in environments lacking PREF64.
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8. Security Considerations
9. Privacy Considerations
This document does not introduce any privacy considerations.
10. IANA Considerations
This memo does not introduce any requests to IANA.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
<https://www.rfc-editor.org/info/rfc6333>.
[RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
Combination of Stateful and Stateless Translation",
RFC 6877, DOI 10.17487/RFC6877, April 2013,
<https://www.rfc-editor.org/info/rfc6877>.
[RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis",
RFC 7050, DOI 10.17487/RFC7050, November 2013,
<https://www.rfc-editor.org/info/rfc7050>.
[RFC7335] Byrne, C., "IPv4 Service Continuity Prefix", RFC 7335,
DOI 10.17487/RFC7335, August 2014,
<https://www.rfc-editor.org/info/rfc7335>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8781] Colitti, L. and J. Linkova, "Discovering PREF64 in Router
Advertisements", RFC 8781, DOI 10.17487/RFC8781, April
2020, <https://www.rfc-editor.org/info/rfc8781>.
[RFC8585] Palet Martinez, J., Liu, H. M.-H., and M. Kawashima,
"Requirements for IPv6 Customer Edge Routers to Support
IPv4-as-a-Service", RFC 8585, DOI 10.17487/RFC8585, May
2019, <https://www.rfc-editor.org/info/rfc8585>.
[RFC8925] Colitti, L., Linkova, J., Richardson, M., and T.
Mrugalski, "IPv6-Only Preferred Option for DHCPv4",
RFC 8925, DOI 10.17487/RFC8925, October 2020,
<https://www.rfc-editor.org/info/rfc8925>.
11.2. Informative References
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
DOI 10.17487/RFC6052, October 2010,
<https://www.rfc-editor.org/info/rfc6052>.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
<https://www.rfc-editor.org/info/rfc6145>.
[RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the
Port Control Protocol (PCP)", RFC 7225,
DOI 10.17487/RFC7225, May 2014,
<https://www.rfc-editor.org/info/rfc7225>.
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[I-D.ietf-v6ops-dhcp-pd-per-device]
Colitti, L., Linkova, J., and X. Ma, "Using DHCPv6-PD to
Allocate Unique IPv6 Prefix per Client in Large Broadcast
Networks", Work in Progress, Internet-Draft, draft-ietf-
v6ops-dhcp-pd-per-device-07, 26 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-v6ops-
dhcp-pd-per-device-07>.
[I-D.link-v6ops-claton]
Linkova, J. and T. Jensen, "464 Customer-side Translator
(CLAT): Node Recommendations", Work in Progress, Internet-
Draft, draft-link-v6ops-claton-02, 28 February 2024,
<https://datatracker.ietf.org/doc/html/draft-link-v6ops-
claton-02>.
[I-D.link-v6ops-gulla]
Linkova, J., "Using Subnet-Specific Link-Local Addresses
to Improve SLAAC Robustness", Work in Progress, Internet-
Draft, draft-link-v6ops-gulla-01, 25 February 2024,
<https://datatracker.ietf.org/doc/html/draft-link-v6ops-
gulla-01>.
Acknowledgements
TBA
Author's Address
Jen Linkova
Google
1 Darling Island Rd
Pyrmont NSW 2009
Australia
Email: furry13@gmail.com, furry@google.com
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