IPv6 operations J. Linkova
Internet-Draft Google
Updates: 8585 (if approved) T. Jensen
Intended status: Informational Microsoft
Expires: 7 July 2024 4 January 2024
464 Customer-side Translator (CLAT): Node Recommendations
draft-link-v6ops-claton-01
Abstract
464XLAT ([RFC6877]) defines an arcitecture for providing IPv4
connectivity across an IPv6-only network. The solution contains two
key elements: provider-side translator (PLAT) and customer-side
translator (CLAT). This document provides recommendations on when a
node shall enable or disable CLAT.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Multiple Interfaces Considerations . . . . . . . . . . . . . 3
5. Enabling CLAT . . . . . . . . . . . . . . . . . . . . . . . . 3
5.1. Detecting IPv4 Presence . . . . . . . . . . . . . . . . . 4
6. CLAT Addresses Considerations . . . . . . . . . . . . . . . . 4
6.1. CLAT IPv6 Addresses . . . . . . . . . . . . . . . . . . . 4
6.2. CLAT IPv4 Addresses . . . . . . . . . . . . . . . . . . . 5
7. Disabling CLAT . . . . . . . . . . . . . . . . . . . . . . . 6
8. Updates to RFC8585 . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informative References . . . . . . . . . . . . . . . . . 10
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
464XLAT is widely deployed in 3GPP networks (as described in
Section 4.2 of [RFC6877]) where a mobile phone performs the CLAT
function, providing a private IPv4 address and IPv4 default route for
the applications and tethered devices. Enabling 464XLAT allowed
mobile operators to migrate User Equipment (UE) devices (also known
as mobile phones) to IPv6-only mode, where those devices are only
assigned IPv6 addresses.
Until recently, IPv6-only hosts were rather uncommon outside of
mobile networks and datacenters. Even if the network provides PLAT
in the form of NAT64, hosts like desktops and laptops still need the
network to provide IPv4 addresses, as otherwise IPv4-only
applications fail. However, as more and more operating systems
outside of the 3GPP world support CLAT, it becomes possible to
migrate those devices to IPv6-only mode. Networks such as public Wi-
Fi, enterprise networks, or even home networks can deploy 464XLAT as
described in Section 4.2 of [RFC6877]:
* PLAT functions are performed by NAT64 network devices.
* CLAT is performed by the host itself.
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Another 464XLAT deployment model is a Wireline one (section 4.1 of
[RFC6877]), when a CPE router is connected to an IPv6-only network
and provides CLAT functions for IPv4-enabled downstream devices.
[RFC8585] specifies 464XLAT support requirements for such devices.
For both scenarios to work, the node performing CLAT (such as a host
or a CPE router) need to enable the CLAT when connecting to an
IPv6-only network. This document complements [RFC6877] by providing
recommendations for the node developers on enabling and disabling
CLAT functions.
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
To be added
4. Multiple Interfaces Considerations
A node may have multiple IPv6-only interfaces (for example, a mobile
phone can be connected to an IPv6-only Wi-Fi network and to an
IPv6-only mobile network). In that case the node SHOULD run an
independent, dedicated CLAT instance on each interface connected to a
network equipped with PLAT. Consequently, each CLAT instance SHOULD
install a separate default IPv4 route on each CLAT-enabled interface.
The metrics of IPv4 routes SHOULD be consistent with the metrics of
IPv6 default routes.
5. Enabling CLAT
To enable CLAT, the node needs to discover the PLAT-side translation
IPv6 prefix, also known as the NAT64 prefix (see Section 6.3 of
[RFC6877]). The PREF64 Router Advertisement option ([RFC8781])
provides that information and can be used as a strong indication that
the network supports NAT64 (PLAT) functionality. Therefore the node
SHOULD enable CLAT if it receives an Router Advertisement containing
PREF64 option.
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If RAs received by the node do not contain a PREF64 option, the node
MAY use other mechanisms to detect the PLAT presence and obtain the
NAT64 prefix (such as [RFC7050]). In that case, the node SHOULD
enable CLAT after discovering the NAT64 prefix, unless by that time
the node has already obtained an IPv4 address.
The node MUST follow recommendations from Section 4 of [RFC7335] to
avoid IPv4 address space conflicts.
5.1. Detecting IPv4 Presence
From a performance perspective, native IPv4 connectivity is
preferrable over 464XLAT, so CLAT SHOULD NOT be enabled if the node
has IPv4 connectivity over the given interface. However, SLAAC might
complete faster than DHCPv4. The node SHOULD NOT wait for an
explicit (DHCPv4 Option 108, [RFC8925]) or an implicit (DHCPv4
timeouts) indication that native IPv4 connectivity is not available.
Such delay would be impactful for IPv4-only applications, as such
applications cannot benefit from 464XLAT until CLAT is operational.
Therefore, the node SHOULD enable CLAT as soon as network support for
PLAT is detected while IPv4 connectivity is not yet detected.
Clients SHOULD then disable CLAT if native IPv4 connectivity is
established whether or not PLAT support from the network remains
available.
6. CLAT Addresses Considerations
6.1. CLAT IPv6 Addresses
Section 6.3 of [RFC6877] recommends that the node acquires a
dedicated /64 for its CLAT functions, and only uses a single
interface IPv6 address if a dedicated prefix is not available via
DHCPv6-PD. However, deployments where each node can obtain a
dedicated /64 just for CLAT are rather uncommon, to say the least.
In most cases, the node uses a single IPv6 address as a source for
all IPv4 traffic translated bt CLAT.
The node SHOULD obtain a dedicated IPv6 address used exclusively for
CLAT functions. This is required as when the node receives a packet
from a NAT64 source, the node needs to differentiate between native
IPv6 traffic and traffic which needs to be passed to CLAT. For
example, an ICMPv6 Echo Reply packet from 64:ff9b::203.0.113.1 can be
a response to either an IPv6 ping to 64:ff9b::203.0.113.1, or an IPv4
ping to 203.0.113.1, translated by CLAT. Using a dedicated IPv6
source address for all CLAT traffic allows the node to make that
distinction without keeping state and operate in the stateless mode
(see Section 1.3 of [RFC6145].
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In accordance with Section 5.4 of [RFC4862], the node MUST perform
Duplicate Address Detection for its dedicated CLAT address.
If the dedicated CLAT address is obtained via SLAAC, the node SHOULD
ensure that the address is checksum-neutral for the given local IPv4
CLAT address and the NAT64 prefix (this means that the local IPv4
address needs to be assigned/known before the IPv6 one is
configured). Using a checksum-neutral CLAT address provides the
following benefits:
* Better performance as CLAT doesn't need to recalculate the
checksum.
* If a protocol uses the standard IP checksum, CLAT doesn't need to
recalculate the checksum. That improves the chances of the
protocol working via CLAT even if CLAT is not aware of the
protocol's semantics.
The node SHOULD generate a different interface id for the CLAT
address when connecting to different networks, even if the NAT64
prefix and the local IPv4 CLAT address do not change. To achieve
that, the node SHOULD generate a random checksum-neutral CLAT address
every time.
6.2. CLAT IPv4 Addresses
There are two different cases of IPv4 usage in 464XLAT deployments:
* Wireline network architecture, as defined in Section 4.1 of
[RFC6877]. In that case, the node performing CLAT functions also
extends the network downstream and provides network connectivity
services to other connected systems. Those systems can be
physical (e.g. various clients connected to a CPE router), or
logical (e.g. virtual systems running on a node, while the host
system acts as a router and performs CLAT). In all those cases,
systems behind the CLAT node usually use [RFC1918] addresses.
* Wireless network architecture, as defined in Section 4.2 of
[RFC6877]. In that case, the CLAT node provides an IPv4 address
and the default route to the local node's network stack only. It
should be noted that [RFC6877] implies that the second deployment
scenario is limited to 3GPP cases, while currently it is also
deployed in other types of networks, such as enterprise and public
Wi-Fi networks, where hosts (as mobile phones, laptops and
desktops) use CLAT to provide connectivity to IPv4-only local
applications. Despite the word "wireless" in the name, this
architecure is applicable for wired networks as well (e.g.
desktops or servers using wired connections).
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In the latter case, the CLAT node needs a single IPv4 address only.
The node providing CLAT functions to local applications SHOULD use
IPv4 addresses from the dedicated 192.0.0.0/29 range ([RFC7335]),
reserved for IPv4 continuity solutions including but not limited to
464XLAT. If the node runs multiple CLAT instances (see Section 4),
the node SHOULD use different local IPv4 addresses for each CLAT
instance. This means that it might not be possible to run more than
8 CLAT instances per node. The node MUST NOT send packets on wire
from the local CLAT address.
The host SHOULD use 255.255.255.255 as a netmask for the CLAT
address. That allows all 8 addresses from 192.0.0.0/29 to be used,
if needed.
It should be noted that 192.0.0.0/29 is shared between multiple IPv4
continuity solutions such as 464XLAT and DS-Lite (see [RFC7335]. For
example, Section 10 of [RFC6333] reserves 192.0.0.1 for the Dual-
Stack Lite default router. However, as per Section 4 of [RFC7335],
the host MUST NOT enable two active IPv4 continuity solutions
simultaneously in a way that would cause a node to have overlapping
192.0.0.0/29 address space. Therefore, as long as the host is not
using DS-Lite, it MAY use 192.0.0.1 as a CLAT address.
7. Disabling CLAT
The node MAY choose to turn CLAT off if an IPv4 address becomes
available after CLAT has started. However, turning it off would
affect all applications and traffic flows already utilizing CLAT.
8. Updates to RFC8585
This document makes the following changes to Section 3.2.1 of
[RFC8585]:
OLD TEXT:
===
464XLAT requirements:
===
NEW TEXT:
===
464XLAT requirements:
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464XLAT-0: The IPv6 Transition CE Router SHOULD follow
recommendations provided in draft-link-v6ops-claton.
===
OLD TEXT:
===
464XLAT-4: The IPv6 Transition CE Router MUST implement [RFC7050]
("Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis") in
order to discover the provider-side translator (PLAT) translation
IPv4 and IPv6 prefix(es)/suffix(es).
464XLAT-5: If PCP is implemented, the IPv6 Transition CE Router MUST
follow [RFC7225] ("Discovering NAT64 IPv6 Prefixes Using the Port
Control Protocol (PCP)") in order to learn the PLAT-side translation
IPv4 and IPv6 prefix(es)/suffix(es) used by an upstream PCP-
controlled NAT64 device.
464XLAT-6: If the network provides several choices for the discovery/
learning of the NAT64 prefix, the priority to use one or the other
MUST follow this order: 1) [RFC7225] and 2) [RFC7050].
The NAT64 prefix could be discovered by means of the method defined
in [RFC7050] only if the service provider uses DNS64 [RFC6147]. It
may be the case that the service provider does not use or does not
trust DNS64 [RFC6147] because the DNS configuration at the CE (or
hosts behind the CE) can be modified by the customer. In that case,
the service provider may opt to configure the NAT64 prefix by means
of the option defined in [RFC7225]. This can also be used if the
service provider uses DNS64 [RFC6147].
===
NEW TEXT
===
464XLAT-4: The IPv6 Transition CE Router MUST implement [RFC8781]
("Discovering PREF64 in Router Advertisements") and [RFC7050]
("Discovery of the IPv6 Prefix Used for IPv6 Address Synthesis") in
order to discover the provider-side translator (PLAT) translation
IPv4 and IPv6 prefix(es)/suffix(es).
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464XLAT-5: If PCP is implemented, the IPv6 Transition CE Router MUST
follow [RFC7225] ("Discovering NAT64 IPv6 Prefixes Using the Port
Control Protocol (PCP)") in order to learn the PLAT-side translation
IPv4 and IPv6 prefix(es)/suffix(es) used by an upstream PCP-
controlled NAT64 device.
464XLAT-6: If the network provides several choices for the discovery/
learning of the NAT64 prefix, the priority to use one or the other
MUST follow this order: 1)[RFC7225] 2)[RFC8781] and 3) [RFC7050].
[RFC8781] allows the service provider to signal NAT64 prefix
independently from DNS64 presence. At the same time the NAT64 prefix
could be discovered by means of the method defined in [RFC7050] only
if the service provider uses DNS64 [RFC6147]. It may be the case
that the service provider does not use or does not trust DNS64
[RFC6147] because the DNS configuration at the CE (or hosts behind
the CE) can be modified by the customer. In that case, the service
provider may opt to configure the NAT64 prefix by means of the option
defined in [RFC7225]. This can also be used if the service provider
uses DNS64 [RFC6147].
===
9. Security Considerations
If a malicious actor spoofs PLAT presence signals (such as an RA with
PREF64 option) or DNS responses for DNS-based NAT64 prefix detection
([RFC7050]), traffic of IPv4-only applications using CLAT can be
affected:
* if there is no PLAT (NAT64) devices, traffic to NAT64 destinations
would be dropped.
* If the attacker intercepts traffic for the NAT64 prefix (e.g. by
providing the victim with a bogus NAT64 prefix and steering
traffic for those destinations towards themselves), the attacker
might be able to perform man-in-the-middle attacks.
Using the PREF64 RA option to detect PLAT presence and the NAT64
prefix is less prone to such attacks, as the attacker needs to be on-
link and be able to bypass layer-2 security features such as RA
Guard.
10. Privacy Considerations
This document does not introduce any privacy considerations.
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11. IANA Considerations
This memo does not introduce any requests to IANA.
12. References
12.1. 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>.
[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>.
[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>.
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[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>.
12.2. 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>.
[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>.
Acknowledgements
Thanks to Ondrej Caletka, Lorenzo Colitti, Ted Lemon, Jordi Palet,
Dieter Siegmund for the discussions, the input and all contribution.
Authors' Addresses
Jen Linkova
Google
1 Darling Island Rd
Pyrmont NSW 2009
Australia
Email: furry13@gmail.com, furry@google.com
Tommy Jensen
Microsoft
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Email: tojens@microsoft.com
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