Improving the Robustness of Stateless Address Autoconfiguration (SLAAC) to Flash Renumbering Events
draft-ietf-6man-slaac-renum-08
| Document | Type | Active Internet-Draft (6man WG) | |
|---|---|---|---|
| Authors | Fernando Gont , Jan Zorz , Richard Patterson , Jen Linkova | ||
| Last updated | 2024-11-08 (Latest revision 2024-10-21) | ||
| Replaces | draft-gont-6man-slaac-renum | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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| Additional resources | Mailing list discussion | ||
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draft-ietf-6man-slaac-renum-08
IPv6 Maintenance (6man) Working Group F. Gont
Internet-Draft SI6 Networks
Updates: 4191, 4861, 4862, 8106 (if approved) J. Zorz
Intended status: Standards Track 6connect
Expires: 24 April 2025 R. Patterson
Sky UK
J. Linkova, Ed.
Google
21 October 2024
Improving the Robustness of Stateless Address Autoconfiguration (SLAAC)
to Flash Renumbering Events
draft-ietf-6man-slaac-renum-08
Abstract
In scenarios where network configuration information becomes invalid
without explicit notification to the local network, local hosts may
end up employing stale information for an unacceptably long period of
time, thus resulting in interoperability problems. This document
improves the reaction of IPv6 Stateless Address Autoconfiguration to
such configuration changes. It formally updates RFC 4191, RFC 4861,
RFC 4862, and RFC 8106.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 24 April 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. SLAAC reaction to Flash-renumbering Events . . . . . . . . . 4
4.1. Renumbering without Explicit Signaling . . . . . . . . . 4
4.2. Renumbering with Explicit Signaling . . . . . . . . . . . 5
5. Improvements to Stateless Address Autoconfiguration
(SLAAC) . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. More Appropriate Neighbor Discovery Option Lifetimes . . 7
5.2. Signaling Stale Configuration Information . . . . . . . . 9
5.3. Honor Small PIO Valid Lifetimes . . . . . . . . . . . . . 9
5.4. Interface Initialization . . . . . . . . . . . . . . . . 10
5.5. Conveying Information in Router Advertisement (RA)
Messages . . . . . . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 12
7.1. More Appropriate Lifetime Values . . . . . . . . . . . . 12
7.1.1. Router Configuration Variables . . . . . . . . . . . 12
7.2. Honor Small PIO Valid Lifetimes . . . . . . . . . . . . . 12
7.2.1. Linux Kernel . . . . . . . . . . . . . . . . . . . . 13
7.2.2. NetworkManager . . . . . . . . . . . . . . . . . . . 13
7.3. Conveying Information in Router Advertisement (RA)
Messages . . . . . . . . . . . . . . . . . . . . . . . . 13
7.4. Recovery from Stale Configuration Information without
Explicit Signaling . . . . . . . . . . . . . . . . . . . 13
7.4.1. dhcpcd(8) . . . . . . . . . . . . . . . . . . . . . . 13
7.5. Other mitigations implemented in products . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Selecting Neighbor Discovery Lifetimes . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
In scenarios where network configuration information becomes invalid
without explicit notification to the local network, local hosts may
end up employing stale information for an unacceptably long period of
time, resulting in interoperability problems. This issue has been
discussed in detail in [RFC8978].
This document updates the Neighbor Discovery specification [RFC4861],
the Stateless Address Autoconfiguration (SLAAC) specification
[RFC4862], and other associated specifications ([RFC4191] and
[RFC8106]), such that hosts can more gracefully deal with the so-
called flash renumbering events [RFC8978], thus improving the
robustness of SLAAC.
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
DHCPv6-PD:
DHCPv6 Prefix Delegation [RFC8415]; a mechanism to delegate IPv6
prefixes to clients.
Flash renumbering:
A network renumbering event, when an old prefix, used to address
hosts, becomes invalid and is replaced by a new prefix. Before
the flash renumbering event only the old prefix provides
connectivity, and after the flash renumbering only the new one can
be used. In other words, there is no period of time when
addresses from both prefixes provide connectivity. See [RFC8978]
for more detailed discussion of various flash-renumbering
scenarios. Note: typically, when flash-renumbering events occur,
other IPv6 netowrk configuration information (such as Recursive
DNS Server (RDNSS) information [RFC8106]) is affected in the same
manner, and thus the term "flash-renumbering" is also employed to
refer to a more general "flash-reconfiguration" event.
PIO:
Prefix Information Option, [RFC4861],
RA:
Router Advertisement, [RFC4861].
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SLAAC:
IPv6 Stateless Address AutoConfugration, [RFC4862].
SLAAC host:
A host which employs SLAAC for IPv6 network configuration.
SLAAC Router:
A IPv6 router that advertises configuration information via SLAAC.
4. SLAAC reaction to Flash-renumbering Events
In some flash-renumbering scenarios, the local router may try to
deprecate the stale information by explicitly signaling the network
about the renumbering event, whereas in other scenarios the
renumbering event may happen inadvertently, without the router
explicitly signaling the scenario to local hosts. The following
subsections analyze specific considerations for each of these
scenarios.
4.1. Renumbering without Explicit Signaling
In the absence of explicit signalling from SLAAC routers, stale SLAAC
configuration information will employed as allowed by the associated
lifetimes values. For example, stale prefixes will remain preferred
and valid according to the Preferred Lifetime and Valid Lifetime
parameters (respectively) of the last received Prefix Information
Option (PIO). [RFC4861] specifies the following default values for
PIOs:
* Preferred Lifetime (AdvPreferredLifetime): 604800 seconds (7 days)
* Valid Lifetime (AdvValidLifetime): 2592000 seconds (30 days)
This means that, in the absence of explicit signaling by a SLAAC
router to deprecate a prefix, it will take a host 7 days (one week)
to deprecate the corresponding addresses, and 30 days (one month) to
eventually remove any addresses configured for the stale prefix.
Clearly, employing such long default values is unacceptable for most
deployment scenarios that may experience flash-renumbering events.
NOTE:
[RFC8978] provides an operational recommendation for Customer Edge
(CE) routers to override the standard default Preferred Lifetime
(AdvPreferredLifetime) and Valid Lifetime (AdvValidLifetime) to
2700 seconds (45 minutes) and 5400 seconds (90 minutes),
respectively, thus improving the state of affairs for CE router
scenarios.
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Similarly, other Neighbor Discovery options employ long default
lifetimes that are unacceptable for most deployment scenarios where
flash-renumbering events may be experienced.
Use of more appropriate timers in Router Advertisement messages can
help limit the amount of time that hosts will maintain stale
configuration information. Thus, Section 5.1 specifies more
appropriate (i.e., shorter) default lifetimes for Neighbor Discovery
options. Section 5.5 provides recommendations about conveying
Neighbor Discovery information into RA messages, to help hosts infer
when information may have become stale.
4.2. Renumbering with Explicit Signaling
In scenarios where a local router is aware of the renumbering event,
it may try to phase out the stale network configuration information.
In these scenarios, there are two aspects to be considered:
* The amount of time during which the router should continue trying
to deprecate the stale network configuration information.
* The ability of SLAAC hosts to phase out stale configuration.
Since the network could become partitioned at any point in time and
for an arbitrarily long period of time, in order to reliably
deprecate stale information, a router should try to deprecate such
information for its maximum possible lifespan.
NOTE:
For example, a router should try to deprecate a prefix (via a PIO)
for a period of time equal to the "Preferred Lifetime" used when
advertising the prefix, and try to invalidate the prefix for a
period of time equal to the "Valid Lifetime" used when advertising
the prefix.
Once the number of seconds in the original "Preferred Lifetime"
have elapsed, all hosts will have deprecated the corresponding
addresses, while once the number of seconds in the "Valid
Lifetime" have elapsed, the corresponding addresses will have been
invalidated and removed.
Thus, use of more appropriate default lifetimes for Neighbor
Discovery options, as specified in Section 5.1, will reduce the
amount of time stale options would need to be advertised by a router
to ensure that the associated information is reliably phased out.
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In the case of PIOs, in scenarios where a router has positive
knowledge that a prefix has become invalid (and thus could signal
this condition to local hosts), the current specifications will
prevent SLAAC hosts from fully recovering from such stale
information: Item "e)" of Section 5.5.3 of [RFC4862] specifies that
an RA may never reduce the "RemainingLifetime" to less than 2 hours.
Additionally, if the "RemainingLifetime" of an address is less than 2
hours, then a "Valid Lifetime" less than 2 hours will be ignored.
The inability to invalidate a stale prefix may prevent communications
with the new "owners" of a prefix, and thus is highly undesirable.
On the other hand, the Preferred Lifetime of an address may be
reduced to any value to avoid the use of addresses from a stale
prefix for new communications.
Section 5.3 formally updates [RFC4862] to remove this restriction,
such that hosts may react to the advertised "Valid Lifetime" even if
it is less than 2 hours. Section 5.4 recommends that routers
disseminate network configuration information when a network
interface is initialized or reconfigured, such that configuration
information propagates in a timelier manner.
5. Improvements to Stateless Address Autoconfiguration (SLAAC)
The following subsections update [RFC4191], [RFC4861], [RFC4862], and
[RFC8106], such that the problem discussed in this document is
mitigated. Each of the following subsections improve different
aspects of SLAAC, and thus are mostly orthogonal:
* Reduce the default lifetimes of Neighbor Discovery options
(Section 5.1):
This helps limit the amount of time a host may employ stale
information, and also limits the amount of time a router should
try to deprecate stale information.
* Signal Stale Configuration Information (Section 5.2):
This allows local hosts to learn about stale configuration
information in a timelier manner.
* Honor PIOs with small Valid Lifetimes (Section 5.3):
This allows hosts to honor PIOs with a Valid Lifetime less than 2
hours, thus resulting in a timelier reaction to flash-renumbering
events.
* Recommend routers to retransmit configuration information upon
interface initialization/reconfiguration (Section 5.4):
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This helps spread the network configuration information in a
timelier manner.
* Recommend routers to always send all options (i.e. the complete
configuration information) in RA messages, and in the smallest
possible number of packets (Section 5.5):
This helps propagate the same information to all hosts.
5.1. More Appropriate Neighbor Discovery Option Lifetimes
This document defines the following variables to be employed for the
default lifetimes of Neighbor Discovery options:
* ND_DEFAULT_PREFERRED_LIFETIME: ND_RAS_PREFERRED *
MaxRtrAdvInterval
* ND_DEFAULT_VALID_LIFETIME: ND_RAS_VALID * MaxRtrAdvInterval
where:
ND_RAS_PREFERRED:
Number of RA messages sent during the
ND_DEFAULT_PREFERRED_LIFETIME period. It defaults to 3.
MaxRtrAdvInterval:
Maximum time allowed between sending unsolicited multicast Router
Advertisements from the interface, in seconds (as specified in
[RFC4861]. It defaults to 600 seconds.
ND_RAS_VALID:
Number of RA messages sent during the ND_DEFAULT_VALID_LIFETIME.
It defaults to 8.
NOTES:
ND_RAS_PREFERRED and ND_RAS_VALID should be computed with the
expression: n >= ln(1 - P)/ln(Loss), where P represents the
desired probability of receiving at least one RA for an RA loss
rate of "Loss". This expression is further discussed in
Appendix A.
ND_RAS_PREFERRED defaults to 3. We note that for e.g. for an RA
loss rate of 50% (Loss=0.50), this would result in a probability
hosts refreshing this timer before it expires of 0.87500. We note
that if the Preferred Lifetime expires, and the host has
configured addresses for other prefixes, it will start preferring
those other addresses instead. On the other hand, if the host has
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not configured addresses for other prefixes, it may still employ
addresses even if they are not "Preferred" (please see
Section 5.5.4 of [RFC4862]). Implementations MAY override the
default value of ND_RAS_PREFERRED according to the considerations
in Appendix A.
ND_RAS_VALID defaults to 8. We note that for e.g. an RA loss rate
of 50% (Loss=0.50), this would result in a probability of hosts
refreshing this timer before it expires of 0.99609.
Implementations MAY override the default value of ND_RAS_PREFERRED
according to the considerations in Appendix A.
This document formally updates [RFC4861] to modify the default value
of the Router Lifetime field of RA messages as follows:
* AdvDefaultLifetime: ND_DEFAULT_VALID_LIFETIME
NOTE:
This is to align the Router Lifetime with the recommendations in
[RFC7772].
This document formally updates [RFC4861] to modify the default values
of the Preferred Lifetime and the Valid Lifetime of PIOs as follows:
* AdvPreferredLifetime: ND_DEFAULT_PREFERRED_LIFETIME
* AdvValidLifetime: ND_DEFAULT_VALID_LIFETIME
This document formally updates [RFC4191] to specify the default Route
Lifetime of Route Information Options (RIOs) as follows:
* Route Lifetime: It defaults to ND_DEFAULT_VALID_LIFETIME
This document formally updates [RFC8106] to modify the default
Lifetime of Recursive DNS Server Options as:
* Lifetime: It defaults to ND_DEFAULT_VALID_LIFETIME
Additionally, this document formally updates [RFC8106] to modify the
default Lifetime of DNS Search List Options as:
* Lifetime: It defaults to ND_DEFAULT_VALID_LIFETIME
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5.2. Signaling Stale Configuration Information
In some scenarios, a SLAAC router may learn that previously
advertised information has become stale. For example, this may
happen when e.g. the advertised information is derived from
information that has been dynamically learned from an upstream router
via DHCPv6-PD, but the upstream router is no longer in use or
available. In such scenarios, it is paramount that the SLAAC router
signals the SLAAC configuration information change, to aid hosts in
quickly phasing out the stale network configuration information.
SLAAC routers MUST signal stale configuration information by
following the guidelines in Section 3.5 ("Signaling Stale
Configuration Information") of [RFC9096].
In scenarios where flash renumbering events or configuration changes
are frequent, a router may end up in a situation where multiple
pieces of information may need to be simultaneously deprecated, and
thus the size of Router Advertisement messages could substantially
increase. In such scenarios, routers MAY limit themselves to
deprecate the most recent configuration that would fit into a single
Router Advertisement message without fragmentation.
5.3. Honor Small PIO Valid Lifetimes
The entire item "e)" (pp. 19-20) from Section 5.5.3 of [RFC4862] is
replaced with the following text:
e) If the advertised prefix is equal to the prefix of an address
configured by stateless autoconfiguration in the list, the valid
lifetime and the preferred lifetime of the address should be
updated by processing the Valid Lifetime and the Preferred
Lifetime (respectively) in the received advertisement.
RATIONALE:
* This change allows hosts to react to the signal provided by a
router that has positive knowledge that a prefix has become
invalid.
* The behavior described in [RFC4862] had been incorporated
during the revision of the original IPv6 Stateless Address
Autoconfiguration specification ([RFC1971]). At the time, the
IPNG working group decided to mitigate the attack vector
represented by Prefix Information Options with very short
lifetimes, on the premise that these packets represented a
bigger risk than other ND-based attack vectors [IPNG-minutes].
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While reconsidering the trade-offs represented by such
decision, we conclude that the drawbacks of the aforementioned
mitigation outweigh the possible benefits.
In scenarios where RA-based attacks are of concern, proper
mitigations such as RA-Guard [RFC6105] [RFC7113] or SEND
[RFC3971] should be implemented.
5.4. Interface Initialization
When an interface is initialized or reconfigured, it is paramount
that network configuration information is propagated on the
corresponding network in a timely manner. Thus, this document
replaces the following text from Section 6.2.4 of [RFC4861]:
In such cases, the router MAY transmit up to
MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using
the same rules as when an interface becomes an advertising
interface.
with:
In such cases, the router MUST transmit
MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using
the same rules as when an interface becomes an advertising
interface.
RATIONALE:
* Use of stale information can lead to interoperability problems.
Therefore, it is important that new configuration information
propagates in a timelier manner to all hosts.
5.5. Conveying Information in Router Advertisement (RA) Messages
Intentionally omitting information in Router Advertisements may
prevent the propagation of such information, and may represent a
challenge for hosts that need to infer whether they have received a
complete set of SLAAC configuration information. As a result, this
section recommends that, to the extent that is possible, RA messages
contain a complete set of SLAAC information.
This document replaces the following text from Section 6.2.3 of
[RFC4861]:
A router MAY choose not to include some or all options when
sending unsolicited Router Advertisements. For example, if prefix
lifetimes are much longer than AdvDefaultLifetime, including them
every few advertisements may be sufficient. However, when
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responding to a Router Solicitation or while sending the first few
initial unsolicited advertisements, a router SHOULD include all
options so that all information (e.g., prefixes) is propagated
quickly during system initialization.
If including all options causes the size of an advertisement to
exceed the link MTU, multiple advertisements can be sent, each
containing a subset of the options.
with:
A router SHOULD include all options in a single Router
Advertisement. However, there are scenarios when routers MAY
split the information between multiple RAs. In particular:
* Routers MAY be explicitly or implicitly configured to send
multiple RAs and split information between them. For example,
a router could be configured to send information associated
with different provisional domains [RFC7556] in different RAs,
or to send multiple RAs, one per VRRPv3 [RFC9568] group.
* If including all options causes the size of an RA to exceed the
link MTU, multiple RAs SHOULD be sent, each containing a subset
of the options. Routers SHOULD whenever possible, split the
information between the fewest possible number of RAs.
RATIONALE:
* Sending information in the smallest possible number of packets
was somewhat already implied by the original text in [RFC4861].
Including all options when sending RAs leads to simpler code
(as opposed to dealing with special cases where specific
information is intentionally omitted), helps hosts infer when
they have received a complete set of SLAAC configuration
information, and reduces the probability of hosts learning only
a partial subset of SLAAC configuration information. Note that
while [RFC4861] allowed some RAs to omit some options, to the
best of the authors' knowledge, all SLAAC router
implementations always send all options in the smallest
possible number of packets. Therefore, this section simply
aligns the protocol specifications with existing implementation
practice.
* However in some scenarios (including, but not limited to
multihoming or having a router providing information from
multiple configuration or provisional domains (PvD) to non-PvD-
aware hosts) it might be desirable to send multiple sets of
network configuration information in multiple RAs.
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6. IANA Considerations
This document has no actions for IANA.
7. Implementation Status
[NOTE: This section is to be removed by the RFC-Editor before this
document is published as an RFC.]
This section summarizes the implementation status of the updates
proposed in this document. In some cases, they correspond to
variants of the mitigations proposed in this document (e.g., use of
reduced default lifetimes for PIOs, albeit using different values
than those recommended in this document). In such cases, we believe
these implementations signal the intent to deal with the problems
described in [RFC8978] while lacking any guidance on the best
possible approach to do it.
7.1. More Appropriate Lifetime Values
7.1.1. Router Configuration Variables
7.1.1.1. rad(8)
We have produced a patch for OpenBSD's rad(8) [rad] that employs
reduced lifetimes for Neighbor Discovery options, as recommended in
this document. The patch is available at:
<https://www.gont.com.ar/code/fgont-patch-rad-pio-lifetimes.txt>.
7.1.1.2. radvd(8)
The radvd(8) daemon [radvd], normally employed by Linux-based router
implementations, currently employs different default lifetimes than
those recommended in [RFC4861]. radvd(8) employs the following
default values [radvd.conf]:
* Preferred Lifetime: 14400 seconds (4 hours)
* Valid Lifetime: 86400 seconds (1 day)
These values do not follow the recommendations in this document, but
nevertheless represent a deviation and improvement from the current
standards.
7.2. Honor Small PIO Valid Lifetimes
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7.2.1. Linux Kernel
A Linux kernel implementation ohas been committed to the net-next
tree. The implementation was produced in April 2020 by Fernando Gont
<fgont@si6networks.com>. The corresponding patch can be found at:
<https://patchwork.ozlabs.org/project/netdev/
patch/20200419122457.GA971@archlinux-current.localdomain/>
7.2.2. NetworkManager
NetworkManager [NetworkManager] processes RA messages with a Valid
Lifetime less than 2 hours as recommended in this document.
7.3. Conveying Information in Router Advertisement (RA) Messages
We know of no implementation that splits network configuration
information into multiple RA messages.
7.4. Recovery from Stale Configuration Information without Explicit
Signaling
7.4.1. dhcpcd(8)
The dhcpcd(8) daemon [dhcpcd], a user-space SLAAC implementation
employed by some Linux-based and BSD-derived operating systems, will
set the Preferred Lifetime of addresses corresponding to a given
prefix to 0 when a single RA from the router that previously
advertised the prefix fails to advertise the corresponding prefix.
However, it does not affect the corresponding Valid Lifetime.
Therefore, it can be considered a partial implementation of this
feature.
7.5. Other mitigations implemented in products
[FRITZ] is a Customer Edge Router that tries to deprecate stale
prefixes by advertising stale prefixes with a Preferred Lifetime of
0, and a Valid Lifetime of 2 hours (or less). There are two things
to note with respect to this implementation:
* Rather than recording prefixes on stable storage (as recommended
in [RFC9096]), this implementation checks the source address of
IPv6 packets, and assumes that usage of any address that does not
correspond to a prefix currently-advertised by the Customer Edge
Router is the result of stale network configuration information.
Hence, upon receipt of a packet that employs a source address that
does not correspond to a currently-advertised prefix, this
implementation will start advertising the corresponding prefix
with small lifetimes, with the intent of deprecating it.
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* Possibly as a result of item "e)" (pp. 19-20) from Section 5.5.3
of [RFC4862] (discussed in Section 5.3 of this document), upon
first occurrence of a stale prefix, this implementation will
employ a decreasing Valid Lifetime, starting from 2 hours (7200
seconds), as opposed to a Valid Lifetime of 0.
8. Security Considerations
The protocol update in Section 5.3 could allow an on-link attacker to
perform a Denial of Service attack against local hosts, by sending a
forged RA with a PIO with a Valid Lifetime of 0. Upon receipt of
that packet, local hosts would invalidate the corresponding prefix,
and therefore remove any addresses configured for that prefix,
possibly terminating e.g. associated TCP connections. However, an
attacker may achieve similar effects via a number other Neighbor
Discovery (ND) attack vectors, such as directing traffic to a non-
existing node until ongoing TCP connections time out, or performing a
ND-based man-in-the-middle (MITM) attack and subsequently forging TCP
RST segments to cause on-going TCP connections to be reset. Thus,
for all practical purposes, this attack vector does not really
represent any greater risk than other ND attack vectors. As noted in
Section 5.3 , in scenarios where RA-based attacks are of concern,
proper mitigations such as RA-Guard [RFC6105] [RFC7113] or SEND
[RFC3971] should be implemented.
9. Acknowledgments
The authors would like to thank (in alphabetical order) Mikael
Abrahamsson, Tore Anderson, Luis Balbinot, Brian Carpenter, Lorenzo
Colitti, Owen DeLong, Gert Doering, Thomas Haller, Nick Hilliard, Bob
Hinden, Philip Homburg, Lee Howard, Christian Huitema, Tatuya Jinmei,
Erik Kline, Ted Lemon,Albert Manfredi, Roy Marples, Florian Obser,
Jordi Palet Martinez, Michael Richardson, Hiroki Sato, Mark Smith,
Hannes Frederic Sowa, Dave Thaler, Tarko Tikan, Ole Troan, Eduard
Vasilenko, and Loganaden Velvindron, for providing valuable comments
on earlier versions of this document.
Fernando would like to thank Alejandro D'Egidio and Sander Steffann
for a discussion of these issues, which led to the publication of
[RFC8978], and eventually to this document.
Fernando would also like to thank Brian Carpenter who, over the
years, has answered many questions and provided valuable comments
that has benefited his protocol-related work.
10. References
10.1. Normative References
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[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>.
[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>.
[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<https://www.rfc-editor.org/info/rfc7556>.
[RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy
Consumption of Router Advertisements", BCP 202, RFC 7772,
DOI 10.17487/RFC7772, February 2016,
<https://www.rfc-editor.org/info/rfc7772>.
[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>.
10.2. Informative References
[dhcpcd] Marples, R., "dhcpcd - a DHCP client",
<https://roy.marples.name/projects/dhcpcd/>.
[FRITZ] Gont, F., "Quiz: Weird IPv6 Traffic on the Local Network
(updated with solution)", SI6 Networks Blog, February
2016, <https://www.si6networks.com/2016/02/16/quiz-weird-
ipv6-traffic-on-the-local-network-updated-with-solution/>.
[IPNG-minutes]
IETF, "IPNG working group (ipngwg) Meeting Minutes",
Proceedings of the thirty-eightt Internet Engineering Task
Force , April 1997, <https://www.ietf.org/
proceedings/38/97apr-final/xrtftr47.htm>.
[NetworkManager]
NetworkManager, "NetworkManager web site",
<https://wiki.gnome.org/Projects/NetworkManager>.
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[rad] Obser, F., "OpenBSD Router Advertisement Daemon - rad(8)",
<https://cvsweb.openbsd.org/src/usr.sbin/rad/>.
[radvd] Hawkins, R. and R. Johnson, "Linux IPv6 Router
Advertisement Daemon (radvd)",
<http://www.litech.org/radvd/>.
[radvd.conf]
Hawkins, R. and R. Johnson, "radvd.conf - configuration
file of the router advertisement daemon",
<https://github.com/reubenhwk/radvd/blob/master/
radvd.conf.5.man>.
[RFC1971] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 1971, DOI 10.17487/RFC1971, August
1996, <https://www.rfc-editor.org/info/rfc1971>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
DOI 10.17487/RFC6105, February 2011,
<https://www.rfc-editor.org/info/rfc6105>.
[RFC7113] Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113,
DOI 10.17487/RFC7113, February 2014,
<https://www.rfc-editor.org/info/rfc7113>.
[RFC8106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 8106, DOI 10.17487/RFC8106, March 2017,
<https://www.rfc-editor.org/info/rfc8106>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
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[RFC8978] Gont, F., Žorž, J., and R. Patterson, "Reaction of IPv6
Stateless Address Autoconfiguration (SLAAC) to Flash-
Renumbering Events", RFC 8978, DOI 10.17487/RFC8978, March
2021, <https://www.rfc-editor.org/info/rfc8978>.
[RFC9096] Gont, F., Žorž, J., Patterson, R., and B. Volz, "Improving
the Reaction of Customer Edge Routers to IPv6 Renumbering
Events", BCP 234, RFC 9096, DOI 10.17487/RFC9096, August
2021, <https://www.rfc-editor.org/info/rfc9096>.
[RFC9568] Lindem, A. and A. Dogra, "Virtual Router Redundancy
Protocol (VRRP) Version 3 for IPv4 and IPv6", RFC 9568,
DOI 10.17487/RFC9568, April 2024,
<https://www.rfc-editor.org/info/rfc9568>.
Appendix A. Selecting Neighbor Discovery Lifetimes
Many default values in from the Neighbor Discovery specification
assumes fairly reliable communication of Neighbor Discovery messages.
However, as noted in [RFC7772], communication of multicasted RA
messages tends to be rather unreliable for battery-powered devices,
which tend to drop many of such messages to reduce the associated
effects on power consumption. This section provides an equation that
may be employed to override the default values of ND_RAS_PREFERRED
and ND_RAS_VALID from Section 5.1, by computing the number of RA
messages that a router should send, such that, given an RA-message
loss rate of "Loss", there is a probability of "P" that at least one
of such messages is received by the target hosts.
n >= ln(1 - P)/ln(Loss)
The following table tabulates the value of P (probability of
receiving at least one RA message) for a combination of "n" (number
of RA messages sent) and Loss (Loss rate for multicasted RA
messages):
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+------+---------+---------+---------+---------+---------+---------+
| n / | 0.10 | 0.20 | 0.30 | 0.40 | 0.50 | 0.60 |
| Loss | | | | | | |
+------+---------+---------+---------+---------+---------+---------+
| 3 | 0.99900 | 0.99200 | 0.97300 | 0.93600 | 0.87500 | 0.78400 |
+------+---------+---------+---------+---------+---------+---------+
| 4 | 0.99990 | 0.99840 | 0.99190 | 0.97440 | 0.93750 | 0.87040 |
+------+---------+---------+---------+---------+---------+---------+
| 5 | 0.99999 | 0.99968 | 0.99757 | 0.98976 | 0.96875 | 0.92224 |
+------+---------+---------+---------+---------+---------+---------+
| 6 | 1.00000 | 0.99994 | 0.99927 | 0.99590 | 0.98437 | 0.95334 |
+------+---------+---------+---------+---------+---------+---------+
| 7 | 1.00000 | 0.99999 | 0.99978 | 0.99836 | 0.99219 | 0.97201 |
+------+---------+---------+---------+---------+---------+---------+
| 8 | 1.00000 | 1.00000 | 0.99993 | 0.99934 | 0.99609 | 0.98320 |
+------+---------+---------+---------+---------+---------+---------+
| 9 | 1.00000 | 1.00000 | 0.99998 | 0.99974 | 0.99805 | 0.98992 |
+------+---------+---------+---------+---------+---------+---------+
| 10 | 1.00000 | 1.00000 | 0.99999 | 0.99989 | 0.99902 | 0.99395 |
+------+---------+---------+---------+---------+---------+---------+
Table 1: Sample values for P = 1 - (Loss)^n
Authors' Addresses
Fernando Gont
SI6 Networks
Segurola y Habana 4310, 7mo Piso
Villa Devoto
Ciudad Autonoma de Buenos Aires
Argentina
Email: fgont@si6networks.com
URI: https://www.si6networks.com
Jan Zorz
6connect
Email: jan@6connect.com
Richard Patterson
Sky UK
Email: richard.patterson@sky.uk
Jen Linkova (editor)
Google
Email: furry13@gmail.com, furry@google.com
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