IPv6 Address Usage Recommendations
draft-gont-6man-address-usage-recommendations-01
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| Authors | Fernando Gont , Guillermo Gont , Madelen Garcia Corbo | ||
| Last updated | 2017-02-28 | ||
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draft-gont-6man-address-usage-recommendations-01
IPv6 maintenance Working Group (6man) F. Gont
Internet-Draft SI6 Networks / UTN-FRH
Intended status: Best Current Practice G. Gont
Expires: September 1, 2017 SI6 Networks
M. Garcia Corbo
SITRANS
February 28, 2017
IPv6 Address Usage Recommendations
draft-gont-6man-address-usage-recommendations-01
Abstract
This document analyzes the security and privacy implications of IPv6
addresses based on a number of properties such as address scope,
stability, and usage type. It analyzes what properties are desirable
for some popular scenarios, and provides advice regarding the
configuration and usage of such addresses.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 1, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Predictability Considerations . . . . . . . . . . . . . . . . 3
4. Address Scope Considerations . . . . . . . . . . . . . . . . 3
5. Address Stability Considerations . . . . . . . . . . . . . . 4
6. Usage Type Considerations . . . . . . . . . . . . . . . . . . 5
7. Advice on IPv6 Address Configuration . . . . . . . . . . . . 6
8. Advice on IPv6 Address Usage . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
12.1. Normative References . . . . . . . . . . . . . . . . . . 7
12.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
IPv6 hosts typically configure a number of IPv6 addresses, which may
differ in multiple aspects, such as address scope and stability (e.g.
stable addresses vs. temporary addresses). For example, a host may
configure one stable and one temporary address per each
autoconfiguration prefix advertised on the local network. The
addresses to be configured typically depend on local system
configuration, with the aforementioned configuration being static and
irrespective of the network the host attaches to.
There are three parameters that affect the security and privacy
properties of an address:
o Scope
o Stability
o Usage type (client-like "outgoing connections" vs. server-like
"incoming connections")
Section 3, Section 4, Section 5, and Section 6 discuss the security
and privacy implications (and associated tradeoffs) of the scope,
stability and usage type properties of IPv6 addresses, respectively.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Predictability Considerations
Predictable IPv6 addresses result in a number of security and privacy
implications. For example, [Barnes2012] discusses how patterns in
network prefixes can be leveraged for IPv6 address scanning. On the
other hand, [RFC7707], [RFC7721] and [RFC7217] discuss the security
and privacy implications of predictable IPv6 Interface Identifiers
(IIDs).
Given the aforementioned previous work in this area, and the formal
specification update produced by [RFC8064], we expect (and assume in
the rest of this document) that implementations have replaced any
schemes that produce predictable addresses with alternative schemes
that avoid such patterns (e.g., RFC7217 in replacement of the
traditional SLAAC addresses that embed link-layer addresses).
4. Address Scope Considerations
The IPv6 address scope can, in some scenarios, limit the attack
exposure of a node as a result of the implicit isolation provided by
a non-global address scope. For example, a node that only employs
link-local addresses may, in principle, only be exposed to attack
from other nodes in the local link. Hosts employing only Unique
Local Addresses (ULAs) may be more isolated from attack than those
employing Global Unicast Addresses (GUAs), assuming that proper
packet filtering is enforced at the network edge.
The potential protection provided by a non-global addresses should
not be regarded as a complete security strategy, but rather as a form
of "prophylactic" security (see
[I-D.gont-opsawg-firewalls-analysis]).
We note that the use of non-global addresses is usually limited to a
reduced type of applications/protocols that e.g. are only meant to
operate on a reduced scope, and hence their applicability may be
limited.
A discussion of ULA usage considerations can be found in
[I-D.ietf-v6ops-ula-usage-considerations].
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5. Address Stability Considerations
The stability of an address has two associated security/privacy
implications:
o Ability of an attacker to correlate network activity
o Exposure to attack
For obvious reasons, an address that is employed for multiple
communication instances allows the aforementioned network activities
to be correlated. The longer an address is employed (i.e., the more
stable it is), the longer such correlation will be possible. In the
worst-case scenario, a stable address that is employed for multiple
communication instances over time will allow all such activities to
be correlated. On the other hand, if a host were to generate (and
eventually "throw away") one new address for each communication
instance (e.g., TCP connection), network activity correlation would
be mitigated.
NOTE: the use of constant IIDs (as in traditional SLAAC) result in
addresses that, while not constant as a whole (since the prefix
changes), contain a globally-unique value that leaks out the node
"identity". Such addresses result in the worst possible security
and privacy implications, and their use has been deprecated by
[RFC8064].
Typically, when it comes to attack exposure, the longer an address is
employed the longer an attacker is exposed to attacks (e.g. an
attacker has more time to find the address in the first place
[RFC7707]). While such exposure is traditionally associated with the
stability of the address, the usage type of the address (see
Section 6) may also have an impact on attack exposure.
A popular approach to mitigate network activity correlation is the
use of "temporary addresses" [RFC4941]. Temporary addresses are
typically configured and employed along with stable addresses, with
the temporary addresses employed for outgoing communications, and the
stable addresses employed for incoming communications.
NOTE: Ongoing work [I-D.gont-6man-non-stable-iids] aims at
updating [RFC4941] such that temporary addresses can be employed
without the need to configure stable addresses.
We note that the extent to which temporary addresses provide improved
mitigation of network activity correlation and/or reduced attack
exposure may be questionable and/or limited in some scenarios. For
example, a temporary address that is reachable for, say, a few hours
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has a questionable "reduced exposure" (particularly when automated
attack tools do not typically require such a long period of time to
complete their task). Similarly, if network activity can be
correlated for the life of such address (e.g., on the order of
several hours), such period of time might be long enough for the
attacker to correlate all the network activity he is meaning to
correlate.
In order to better mitigate network activity correlation and/or
possibly reduce host exposure, an implementation might want to either
reduce the preferred lifetime of a temporary address, or even better,
generate one new temporary address for each new transport protocol
instance. However, the associated lifetime/stability of an address
may have a negative impact on the network. For example, if a node
were to employ "throw away" IPv6 addresses, or employ temporary
addresses [RFC4941] with a short preferred lifetime, local nodes
might need to maintain too many entries in their Neighbor Cache, and
a number of devices (possibly enforcing security policies) might also
need to keep such additional state.
Additionally, enforcing a maximum lifetime on IPv6 addresses may
cause long-lived TCP connections to fail. For example, an address
becoming "Invalid" (after transiting through the "Preferred" and
"Deprecated" states) would cause the TCP connections employing them
to break. This, in turn, would cause e.g. long-lived SSH sessions to
break/fail.
In some scenarios, attack exposure may be reduced by limiting the
usage of temporary addresses to outbound connections, and prevent
such addresses from being used for inbound connections (please see
Section 6).
6. Usage Type Considerations
A node that employs one of its addresses to communicate with an
external server (i.e., to perform an "outgoing connection") may cause
such address to become exposed to attack. For example, once the
external server receives an incoming connection, the corresponding
server might launch an attack against the aforementioned address. A
real-world instance of this type of scenario has been documented in
[Hein].
However, we note that employing an IPv6 address for an outgoing
communications need not increase the exposure of local services to
other parties. For example, nodes could employ temporary addresses
only for outgoing connections, but not for incoming connections.
Thus, external nodes that learn about client's addresses could not
really leverage such addresses for actively contacting the clients.
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There are multiple ways in which this could possibly be achieved,
with different implications. Namely:
Run a host-based or network-based firewall
Bind services to specific (explicit) addresses
Bind services only to stable addresses
A client could simply run a host-based firewall that only allows
incoming connections on the stable addresses. This is clearly more
of an operational way of achieving the desired functionality, and may
require good firewall/host integration (e.g., the firewall should be
able to tell stable vs. temporary addresses), may require the client
to run additional firewall software for this specific purpose, etc.
In other scenarios, a network-based firewalls could be configured to
allow outgoing communications from all internal addresses, but only
allow incoming communications to stable addresses. For obvious
reasons, this is generally only applicable to networks where incoming
communications are allowed to a limited number of hosts/servers.
Services could be bound to specific (explicit) addresses, rather than
to all locally-configured addresses. However, there are a number of
short-comings associated with this approach. Firstly, an application
would need to be able to learn all of its addresses and associated
stability properties, something that tends to be non-trivial and non-
portable, and that also makes applications protocol-dependent,
unnecessarily. Secondly, the Sockets API does not really allow a
socket to be bound to a subset of the node's addresses. That is,
sockets can be bound to a single address or to all available
addresses (wildcard), but not to a subset of all the configured
addresses.
Binding services only to stable addresses provides a clean separation
between addresses employed for client-like outgoing connections and
server-like incoming connections. However, we currently lack an
appropriate API for nodes to be able to specify that a socket should
only be bound to stable addresses. Development of such an API should
be considered for future work.
7. Advice on IPv6 Address Configuration
[TBD]
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8. Advice on IPv6 Address Usage
[TBD]
9. IANA Considerations
There are no IANA registries within this document. The RFC-Editor
can remove this section before publication of this document as an
RFC.
10. Security Considerations
This document discusses address usage considerations, and also
describes possible future standards-track work to allow for greater
flexibility in IPv6 address usage.
11. Acknowledgements
The authors would like to thank [TBD] for providing valuable comments
on earlier versions of this document.
Fernando Gont would like to thank Nelida Garcia and Jorge Oscar Gont
for their love and support, and Ivan Arce and Diego Armando Maradona
for their inspiration.
12. References
12.1. Normative References
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<http://www.rfc-editor.org/info/rfc4941>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<http://www.rfc-editor.org/info/rfc7217>.
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[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
February 2017, <https://tools.ietf.org/rfc/rfc8064.txt>.
12.2. Informative References
[RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
<http://www.rfc-editor.org/info/rfc7707>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<http://www.rfc-editor.org/info/rfc7721>.
[I-D.ietf-v6ops-ula-usage-considerations]
Liu, B. and S. Jiang, "Considerations For Using Unique
Local Addresses", draft-ietf-v6ops-ula-usage-
considerations-01 (work in progress), August 2016.
[I-D.gont-6man-non-stable-iids]
Gont, F. and S. LIU, "Recommendation on Non-Stable IPv6
Interface Identifiers", draft-gont-6man-non-stable-iids-00
(work in progress), May 2016.
[I-D.gont-opsawg-firewalls-analysis]
Gont, F. and F. Baker, "On Firewalls in Network Security",
draft-gont-opsawg-firewalls-analysis-02 (work in
progress), February 2016.
[Barnes2012]
Barnes, R., Altmann, R., and D. Kerr, "Mapping the Great
Void Smarter scanning for IPv6", ISMA 2012 AIMS-4 -
Workshop on Active Internet Measurements, February 2012,
<https://www.caida.org/workshops/isma/1202/slides/
aims1202_rbarnes.pdf>.
[Hein] Hein, B., "The Rising Sophistication of Network Scanning",
January 2016, <http://netpatterns.blogspot.be/2016/01/
the-rising-sophistication-of-network.html>.
Authors' Addresses
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Fernando Gont
SI6 Networks / UTN-FRH
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
Email: fgont@si6networks.com
URI: http://www.si6networks.com
Guillermo Gont
SI6 Networks
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
Email: ggont@si6networks.com
URI: https://www.si6networks.com
Madeleine Garcia Corbo
Servicios de Informacion del Transporte
Neptuno 358
Havana City 10400
Cuba
Email: madelen.garcia16@gmail.com
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