Internet DRAFT - draft-gont-v6ops-ipv6-addressing-considerations
draft-gont-v6ops-ipv6-addressing-considerations
IPv6 Operations Working Group (v6ops) F. Gont
Internet-Draft G.G. Gont
Intended status: Informational SI6 Networks
Expires: 3 December 2022 1 June 2022
IPv6 Addressing Considerations
draft-gont-v6ops-ipv6-addressing-considerations-02
Abstract
IPv6 addresses can differ in a number of properties, such as scope,
stability, and intended usage type. This document analyzes the
impact of these properties on aspects such as security, privacy,
interoperability, and network operations, with the goal of providing
guidance about IPv6 address usage. Additionally, it identifies
challenges and gaps that currently prevent systems and applications
from leveraging the increased flexibility and availability of IPv6
addresses.
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 3 December 2022.
Copyright Notice
Copyright (c) 2022 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/
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Please review these documents carefully, as they describe your rights
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This document may not be modified, and derivative works of it may not
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Legacy Specifications and Schemes . . . . . . . . . . . . 4
3.2. Address Scope . . . . . . . . . . . . . . . . . . . . . . 5
4. IPv6 Address Properties . . . . . . . . . . . . . . . . . . . 5
4.1. Address Scope Considerations . . . . . . . . . . . . . . 6
4.2. Provider Dependency . . . . . . . . . . . . . . . . . . . 7
4.3. Address Reachability . . . . . . . . . . . . . . . . . . 8
4.4. Address Stability Considerations . . . . . . . . . . . . 9
5. IPv6 Address Usage . . . . . . . . . . . . . . . . . . . . . 12
5.1. Default IPv6 Address Selection . . . . . . . . . . . . . 12
5.2. Usage Type Considerations . . . . . . . . . . . . . . . . 13
5.2.1. Incoming communications . . . . . . . . . . . . . . . 13
5.2.2. Outgoing communications . . . . . . . . . . . . . . . 15
6. Current Issues Associated with IPv6 Addressing . . . . . . . 15
6.1. Sub-optimal Address Configuration . . . . . . . . . . . . 15
6.1.1. Number of Addresses . . . . . . . . . . . . . . . . . 15
6.1.2. SLAAC/DHCPv6 Interaction . . . . . . . . . . . . . . 16
6.2. Sub-optimal IPv6 Address Usage . . . . . . . . . . . . . 16
6.2.1. Correlation of Network Activity . . . . . . . . . . . 16
6.2.2. Host Tracking . . . . . . . . . . . . . . . . . . . . 17
6.2.3. Unintended Service Disclosure . . . . . . . . . . . . 17
6.2.4. Availability of Service Outside the Expected
Domain . . . . . . . . . . . . . . . . . . . . . . . 18
6.3. Operational Problems . . . . . . . . . . . . . . . . . . 18
6.3.1. Implications on Firewall Rules and Access Control Lists
(ACLs) . . . . . . . . . . . . . . . . . . . . . . . 18
6.3.2. Implications on Network Infrastructure . . . . . . . 19
6.3.3. Legitimate Network Activity Correlation . . . . . . . 19
6.3.4. Routing in Multi-Prefix/Multi-Router Networks . . . . 19
6.3.5. Renumbering . . . . . . . . . . . . . . . . . . . . . 20
7. Current Gaps that Prevent Leveraging IPv6 Addressing . . . . 21
7.1. Profile-based IPv6 Address Configuration . . . . . . . . 21
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7.2. Advice on IPv6 Address Usage . . . . . . . . . . . . . . 22
7.3. Protocol Improvements to Deal with Many Addresses . . . . 22
7.4. Improved Address Selection APIs . . . . . . . . . . . . . 23
7.5. Universal Support of RFC 8028 . . . . . . . . . . . . . . 23
7.6. Support for Firewall Traversal in CE Routers . . . . . . 24
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
9. Security Considerations . . . . . . . . . . . . . . . . . . . 24
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.1. Normative References . . . . . . . . . . . . . . . . . . 24
11.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
IPv6 addresses can differ in a number of properties, such as address
scope (e.g. link-local vs. global), stability (e.g. stable addresses
vs. temporary addresses), and intended usage type (outgoing
communications vs. incoming communications). While often overlooked,
these properties have direct impact on areas such as security,
privacy, interoperability, and network operations.
IPv6 hosts typically configure addresses based on local system
policy, which tends to be static and irrespective of the specific
network the host attaches to. For example, most IPv6 host
implementations configure one link-local address for each network
interface, and one stable and one (or more) temporary addresses per
each Stateless Address Auto-configuration (SLAAC) [RFC4862] prefix
for each network interface. However, this static policy for address
configuration might be inappropriate. For example, mobile nodes
might benefit from employing only temporary addresses, which
generally offer better privacy properties than stable addresses. On
the other hand, an enterprise network might prefer that local hosts
employ only stable addresses, which might be more convenient when
enforcing access control, performing network trouble-shooting, or
performing legitimate network activity correlation when e.g. hosts
become infected by malware.
Additionally, each application on a given host could have its own set
of requirements or expectations for the underlying IPv6 addresses.
For example, an application meaning to offer a public service might
expect to employ addresses that are both stable [RFC7721] [RFC8064]
and globally-reachable [RFC8190], while a privacy-sensible client
application might prefer short-lived temporary addresses [RFC8981],
or might even expect to employ single-use ("ephemeral") IPv6
addresses when connecting to public servers. However, the subtleties
associated with IPv6 address usage and with IPv6 addresses themselves
are often ignored or overlooked by application programmers. This
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means that applications could fail to signal their requirements and
preferences to the underlying host, or that the addresses configured
by the underlying host might be inappropriate to satisfy the
requirements of the corresponding applications.
Finally, a number of limitations in components that range from
network devices to Application Programming Interfaces (APIs) could
also prevent hosts and applications from leveraging the increased
flexibility of IPv6 addressing.
This document identifies a set of properties that can be associated
with IPv6 addresses (such as scope and stability), and analyzes the
impact of these properties on areas ranging from security and privacy
to network operations, with the goal of providing guidance about IPv6
address usage. Additionally, it identifies challenges and gaps that
currently prevent systems and applications from leveraging the
increased flexibility and availability of IPv6 addresses.
2. Terminology
This document employs the definitions of "public address", "stable
address", and "temporary address" from Section 2 of [RFC7721].
This document employs the definition of "globally reachable" from
Section 2.1 of [RFC8190].
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. Conventions
3.1. Legacy Specifications and Schemes
IPv6 SLAAC has traditionally employed schemes for generating
Interface Identifiers (IIDs) that have negatively affected the
security and privacy properties of IPv6 addresses. For example, IPv6
SLAAC originally generated stable addresses by embedding the
underlying link-layer address in the IPv6 Interface Identifier (IID),
thus negatively affecting the security and privacy properties of IPv6
addresses [RFC7721] [RFC7707]. Similarly, IPv6 temporary addresses
[RFC4941] reused the same randomized IID for different auto-
configuration prefixes [RFC4941], thus allowing for network activity
correlation across different addresses of the same host.
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These schemes have become formally superseded by other schemes, such
as [RFC7217] and [RFC8981], that mitigate the aforementioned issues.
Therefore, this document does not discuss issues arising from legacy
IID generation algorithms.
NOTE:
The security and privacy implications of such schemes are
discussed in [RFC7721], [RFC7707], and [RFC7217].
3.2. Address Scope
[RFC4007] defines the scope of an address as:
"[the] topological span within which the address may be used as a
unique identifier for an interface or set of interfaces"
And defines the "global scope" to be used for:
"uniquely identifying interfaces anywhere in the Internet"
However, the term "scope" is employed in conflicting ways in
different specifications (see [I-D.gont-6man-ipv6-ula-scope]).
Throughout this document, we employ the notion of "scope" defined in
[RFC4007]. As a result, addresses that do not uniquely identify
interfaces Internet-wide are considered to have "non-global" or
"limited" scope. Grouping addresses in such a way is simply useful
for the purpose of discussing address properties.
4. IPv6 Address Properties
There are, at least, four properties that can be associated with
every IPv6 address:
* Scope
* Reachability
* Stability
* Provider Dependency
The address scope essentially represents the topological span where
an address can be expected to uniquely identify an interface; i.e.,
the topological span where an given address is meaningful. For
example, link-local addresses are only meaningful within a given
network link, and are expected to be unique only within such network
link.
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Address reachability represents the topological span where an address
can be expected to be used for receiving and transmitting packets.
Reachability is implicitly constrained by the address scope, and may
also be affected by network devices: for example, Customer Edge
Routers (CE Routers) that enforce a filtering policy of "only
allowing outgoing communications" can render otherwise globally
reachable addresses as "unreachable from the public Internet, unless
communication is initiated from the customer's network".
The stability of an address is associated with the invariance of an
address over time. For example, a manually-configured address will
typically remain stable while the node remains attached to the same
subnet, while a temporary address will, by definition, change over
time. While address stability depends on the local policy of a node
(e.g. stable vs. temporary addresses), it may also be constrained by
other properties and external factors, such as provider dependency:
if a network employs a prefix that is assigned/leased by an upstream
provider, then the overall stability an address will also depend on
the stability corresponding network prefix.
Provider-dependency is typically discussed in the context of Global
Unicast Addresses, where the address space may be allocated by an
Internet Service Provider (ISP) (and hence "provider aggregatable")
or by a Regional Internet Registry (RIR) (and hence "provider
independent"). However, this document considers "provider
dependency" in a more general way: "provider aggregatable" address
space is assigned or leased by an upstream provider and carved out
from the provider's address space, and thus is topologically-related
to the upstream provider's address space; on the other hand,
"provider independent" address space is "owned" by the subnet in
question and thus is not necessarily topologically-related to the
upstream provider.
4.1. Address Scope Considerations
The IPv6 address scope [RFC4007] has a direct implication on address
reachability: the address scope essentially constrains address
reachability. For example, addresses that have a non-global/limited
scope are not, in principle, globally reachable.
NOTE:
This assumption becomes invalid if technologies such as Network
Prefix Translation (NPT) [RFC6296] are employed, though. However,
strictly speaking, in these scenarios the non-global addresses are
still not globally reachable, but rather the middle-box acts as an
interface with the "external realm" via globally-reachable
addresses (i.e., the middle-box provides an interface between two
topological spans).
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The IPv6 address scope can, in some scenarios, limit the attack
exposure of a node as a result of the implicit isolation provided by
non-global/limited address scopes. For example, a node that only
employs link-local addresses will, in principle, only be exposed to
attacks from other nodes on the same local link.
The potential protection provided by a non-global-scope 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 non-global scope addresses are normally usable by only a
limited number of applications/protocols that operate on a limited
scope (e.g., mDNS), or deployments where the intended participants
may be known to operate in a limited domain [RFC8799] (e.g., OpenSSH
client and server attached to the same link and employing link-local
addresses, or mDNS hosts employing link-local addresses).
The address scope can at times be somewhat related with the provider
dependency property. For example, link-local addresses are, by
definition, provider independent. In the same light, a locally-
generated ULA prefix will be, by definition, provider independent.
However, a router might also employ a ULA prefix leased by an
upstream router, in which case this prefix would be "provider
dependent". The possible implications of the address scope on
"provider dependency" may also affect address stability: for example,
a locally-generated ULA prefix is "provider independent", and will
not be subject to renumbering events triggered by the upstream
provider. However, a router (e.g. CE Router) might, in some
circumstances, be unable to guarantee prefix stability -- as in the
case where the locally-generated ULA prefix is not recorded on stable
storage, and thus cannot be guaranteed to remain stable across power
outages (see [RFC9096] for more details).
4.2. Provider Dependency
Provider-dependency is typically discussed in the context of Global
Unicast Addresses, where the address space may be allocated by an
Internet Service Provider (ISP) (and hence "provider agreggatable")
or by a Regional Internet Registry (RIR) (and hence "provider
independent"). However, this document considers "provider
dependency" in a more general way: "provider aggregatable" address
space is assigned or leased by an upstream provider and carved out
from the provider's address space, and thus is topologically-related
to the upstream provider's address space; on the other hand,
"provider independent" address space is "owned" by the network in
question and thus is not necessarily topologically-related to the
upstream provider.
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An implicit consequence of PA address space is that its use is tied
to the specific provider/upstream provider that provides the address
space. This has a number of consequences, including:
* Multi-homing (employing local address space with multiple upstream
providers) may not be possible.
* A renumbering event at the upstream provider will typically cause
the local network to be renumbered.
Some organizations have opted to employ NPT [RFC6296] such that:
* The local network is isolated of renumbering events caused by the
upstream provider.
* The local network employs the same address space regardless of the
upstream provider employed to communicate with the external realm.
While PA space may impact address stability, PI address space
generally has better stability properties. For example, a home
network could internally employ both ULAs and GUAs, where a ULA
prefix is locally generated by the CE Router (and hence resulting in
PI space), and a global prefix is leased by the ISP via DHCPv6 Prefix
Delegation [RFC8415] (hence PA space). If for some reason there was
an outage involving the connection with the upstream ISP, the lease
time for the GUA prefix would eventually expire, and therefore
addresses configured for such prefix would need to be invalidated.
Similarly, if upon prefix lease expiration the ISP were to lease a
new GUA prefix (rather than renew the existing prefix), the network
would need to be renumbered. On the other hand, locally-generated
ULA prefixes can be employed independently from the upstream ISP.
Similarly, an organizational network that employs PI global address
space obtained from a RIR would be able to employ the same address
space irrespective of renumbering events or outages involving the
upstream provider. However, if dynamic sub-prefixes were delegated
via DHCPv6-PD within the corresponding organization, such sub-
address-space would be considered "provider dependent" from the
perspective of such leaf networks.
4.3. Address Reachability
Address reachability represents the area of the network (and the
associated conditions), where an address can be used for receiving
and transmitting packets. As noted in Section 4.1, the address scope
has a direct implication on address reachability, since it constrains
the network span where the address is reachable.
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In addition to the inherent reachability semantics of each address
type, network filtering policies may also affect address
reachability. For example, there is widespread deployment of
Customer Edge Routers that implement a (stateful) filtering policy of
"only allowing outgoing communications" -- mimicking the filtering
policy enforced (as a side-effect) by IPv4 NATs. In such scenarios,
even otherwise globally-reachable addresses become unreachable,
unless:
* communication is initiated from the internal network, or,
* the CE Router is manually configured override the default
filtering policy, or,
* a technology to dynamically override the filtering policy (such as
UPnP [UPnP] or PCP [RFC6887]) is employed.
Address reachability is what ultimately determines the application
architecture that may be successfully employed by an IPv6 node.
NOTE:
Ironically, an IPv6-only host (with global-scope addresses)
attached to a home network where the CE Router "only allows
outgoing communications" and does not implement protocols such as
UPnP [UPnP] or PCP [RFC6887], will normally have a harder time
using peer-to-peer (P2P) applications than an IPv4-only host (with
a private address) attached to a home network where the CE Router
employs NAT but implements a protocols such as UPnP or PCP.
Address reachability has a direct impact on security, since the
ability to attack a system normally relies on the ability of the
attacker to reach the system in the first place. Firewalls
[I-D.gont-opsawg-firewalls-analysis] are, indeed, devices that can be
specifically devoted to administer address reachability.
4.4. Address Stability Considerations
Address stability typically depends on two factors:
* Stability of the network prefix
* Stability of the associated interface identifier (IID)
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Depending on whether the local prefix is PI or PA (see Section 4.2)
and whether the prefix is stable or dynamic (see [RFC8978]), the
resulting addresses will have different stability properties.
Additionally, even in the presence of stable prefixes, a host may use
stable and/or temporary IIDs, thus resulting in stable addresses
[RFC8064] and/or temporary addresses [RFC8981].
The stability of an address has two associated security/privacy
implications:
* Ability of an attacker to correlate network activity
* 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 remove) one new address for each communication instance
(e.g., TCP connection), network activity correlation would be
mitigated.
NOTE:
The security and privacy implications of predictable addresses are
discussed in [RFC7721] and [RFC7707].
Typically, the longer an address is employed the longer the window of
exposure of a host (via an address that becomes revealed as a result
of active communication). While such exposure is typically
associated with the stability of the address, the usage type of the
address may also have an impact on attack exposure (see Section 5.2).
A popular approach to mitigate network activity correlation is the
use of "temporary addresses" [RFC8981]. Temporary addresses are
typically employed along with stable addresses, with the temporary
addresses employed for outgoing communications, and the stable
addresses employed for incoming communications.
NOTE:
That latest revision of the "temporary addresses" RFC ([RFC8981])
allows the configuration and use of only temporary addresses
(i.e., removes the requirement to configure stable addresses).
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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
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 of interest. However,
temporary addresses do limit the window of exposure to network-based
attacks (including that of network activity correlation).
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 temporary addresses or, even better,
generate one new IPv6 address for each application or new transport
protocol instance (sometimes referred to as "ephemeral addresses").
However, reduced address lifetimes and the use of multiple IPv6
addresses may have a negative impact on the network (please see
Section 6.3).
Enforcing a maximum lifetime (versus "preferred lifetime") on IPv6
addresses may cause long-lived TCP connections to fail. For example,
an address becoming "Invalid" (after transitioning through the
"Preferred" and "Deprecated" states) would cause the TCP connections
employing them to break, which would in turn cause e.g. long-lived
SSH sessions to break/fail. Traditionally, many application
protocols have assumed or expected address stability. However, in
the light of mobile roaming nodes that may frequently switch among
different connections (e.g. Wi-Fi, 4G, etc.) or that may be subject
to renumbering events (see [RFC8978]), robust applications should
assume and expect "ephemeral" IPv6 addresses (i.e., gracefully handle
the case where the underlying IPv6 addresses change over short
periods of time).
In some scenarios, attack exposure may be further mitigated by
limiting the usage of temporary addresses to outgoing connections,
and preventing such addresses from being used for incoming
connections (please see Section 5.2).
Finally, we note that if a different single-use (i.e., "ephemeral")
IPv6 address is employed for each transport protocol instance, the
possibility of an attacker successfully performing off-path attacks
(such as the TCP reset attacks discussed in [RFC4953]) is reduced,
since the ephemeral IPv6 address will typically be unknown and
unpredictable to the off-path attacker.
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5. IPv6 Address Usage
5.1. Default IPv6 Address Selection
Applications use system API's to implicitly or explicitly select the
IPv6 addresses that will be used for incoming and outgoing
connections. These choices have consequences in terms of privacy,
security, performance, and interoperability.
Default Address Selection for IPv6 is specified in [RFC6724], and
only applies for outgoing connections, such as those made by clients
trying to use services offered by other hosts. The selection starts
with a set of potential destination addresses, such as returned by
getaddrinfo(3), and the set of potential source addresses currently
configured for the selected interfaces. For each potential
destination address, the algorithm will select the source address
that provides the best route to the destination, while choosing the
appropriate scope and preferring temporary addresses. The algorithm
will then select the destination address, while giving a preference
to reachable addresses with the smallest scope.
We note that [RFC6724] selects IPv6 addresses from all the currently
available addresses on the host, and there is currently no way for an
application to indicate expected or desirable properties for the IPv6
source addresses employed for such outgoing communications. For
example, a privacy-sensitive application might want that each
outgoing communication instance employs a new, single-use IPv6
address, or to employ a new reusable address that is not employed or
reusable by any other application on the host.
NOTE:
Reuse of an IPv6 address by an application would allow the
correlation of all network activities corresponding to such
application as being performed by the same host, while reuse of an
IPv6 address by multiple different applications would allow the
correlation of all such network activities as being performed by
the host with such IPv6 address (see Section 4.4 for further
details).
When a host provides a service, the common pattern is to just wait
for incoming connections over all configured addresses. For example,
applications using the BSD Sockets API will commonly bind(2) the
listening socket to the undefined address. This long-established
behavior is appropriate for hosts providing public services, but can
have unexpected results for hosts providing semi-private services,
such as various forms of peer-to-peer or local-only applications
(e.g. mDNS).
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This behavior leads to three problems: host tracking, discussed in
Section 6.2.2; unexpected address discovery, discussed in
Section 6.2.3; and availability outside the expected scope, discussed
in Section 6.2.4. These problems are caused in part by the
limitations of available address selection APIs, as discussed in
Section 7.4.
5.2. Usage Type Considerations
IPv6 hosts may configure stable [RFC8064] and/or temporary [RFC8981]
addresses, where stable addresses are typically employed for incoming
(server-like) communications, and temporary addresses are employed
for outgoing (client-like) communications. That is, the stability
properties of an address have an implicitly associated usage type.
A host that employs one of its addresses to communicate with a remote
server (i.e., that performs an "outgoing connection") will expose
that address to the target server (and to on-path nodes). Once the
remote server receives an incoming connection, it could readily
launch an attack against the host via the exposed address. A real-
world instance of this type of scenario has been documented in
[Hein].
However, we note that employing an IPv6 address for outgoing
communications need not increase the exposure of local services to
other parties. For example, nodes could employ temporary addresses
only for outgoing communications, and disallow their use for incoming
communications. Thus, nodes that learn about a client's addresses
could not really leverage such addresses for actively contacting
clients. Unfortunately, current APIs represent a challenge when
trying to leverage IPv6 addresses in this way (please see
Section 5.2.1 and Section 7.4 for further details).
The following subsections discuss possible techniques that could be
employed by applications to better leverage IPv6 addresses for both
incoming and outgoing communications
5.2.1. Incoming communications
There are a number of ways in which a system or network may affect
which addresses may be employed (and how) for different services and
cases. Namely,
* TCP/IP stack address filtering
* Application-based address filtering
* Firewall-based address filtering
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Clearly, the most elegant approach for address selection would be for
applications to be able to specify the properties of the addresses
they are willing to employ by means of an API, such the TCP/IP stack
itself could "filter" which addresses are allowed for the given
service/application. For example, an application could specify the
stability and scope properties of the addresses on which incoming
communications should be accepted, such that the application can be
relieved from dealing with low-level networking details, portability
is improved, and duplicate code in applications is avoided. However,
constraints in the current APIs (see Section 7.4) prevent application
programmers from leveraging this technique. Alternatively, 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 the underlying addresses and their
associated properties, something that tends to be non-trivial and
non-portable, and that also makes applications protocol-dependent,
unnecessarily. Secondly, the BSD Sockets API does not 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.
Another possible approach would be for applications to e.g. bind
services to all available addresses, and perform the associated
selection/filtering at the application level. While possible, this
would have a number of drawbacks. Firstly, it would require
applications to deal with low-level networking details, lead to
duplicated code in all applications, and also negatively affect
portability. Secondly, performing address/selection filtering at the
application level may not mitigate some possible attacks. For
example, port scanning would still be possible, since the
aforementioned filtering would be performed once UDP packets have
been received or TCP connections have been established.
A client could simply run a host-based firewall that only allows
incoming connections on the stable addresses. This would be more of
an operational approach for achieving the desired functionality, and
would require good firewall/host integration (e.g., the firewall
should be able to tell stable vs. temporary addresses), would require
the client to run additional firewall software for this specific
purpose, etc. In some scenarios, a network-based firewall could be
configured to allow outgoing communications from all internal
addresses, but only allow incoming communications to stable addresses
(either via manual configuration or via a helper protocol such as
[UPnP] or PCP [RFC6887]). For obvious reasons, this is generally
only applicable to networks where incoming communications are allowed
to a limited number of hosts/servers.
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5.2.2. Outgoing communications
An application might be able to obtain the list of currently-
configured addresses, and subsequently select an address with desired
properties, and explicitly "bind" the address to the socket, to
override the default source address selection.
However, this approach is problematic for a number of reasons.
Firstly, there is no portable way of obtaining the list of currently-
configured addresses on the local node, let alone checking the
properties of such addresses. Secondly, as discussed in
Section 5.2.1, it would require application programmers to understand
all the subtleties associated with IPv6 addressing, and would also
lead to duplicate code on all applications. Finally, applications
would be limited to use already-configured addresses and unable to
trigger the generation of new addresses where desirable (e.g. the
generation of a new single-use address for this application instance
or communication instance).
6. Current Issues Associated with IPv6 Addressing
The following subsections discuss current problems associated with
IPv6 addresses, namely:
* Sub-optimal Address Configuration (Section 6.1)
* Sub-optimal IPv6 Address Usage (Section 6.2)
* Operational Problems (Section 6.3)
6.1. Sub-optimal Address Configuration
6.1.1. Number of Addresses
Two mechanisms exist for automatic network configuration: SLAAC
[RFC4862] and DHCPv6 [RFC8415]. DHCPv6 centralizes network
configuration and address assignment, and may thus prevent hosts from
leveraging the increased flexibility and availability of IPv6
addresses. On the other hand, SLAAC may result in network
configuration anarchy, where hosts may e.g. configure and use
addresses in a way that may negatively affect the network (please see
Section 6.3.2).
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Most of the challenges associated with the use of multiple addresses
can be addressed by allocating one /64 per host via mechanisms such
as DHCPv6-PD [RFC8415]. However, support for such mechanisms in host
implementations and in the LAN-side of CE Routers is rather uncommon.
On the other hand, SLAAC lacks the means for conveying information
about e.g., the number of addresses per host that the network is able
or willing to support.
NOTE:
Use of a /64 prefix per host could also render techniques such as
temporary addresses [RFC8981] ineffective, since hosts would
become identified by corresponding /64 prefix.
6.1.2. SLAAC/DHCPv6 Interaction
Many CE Routers offer address configuration via both SLAAC and
DHCPv6, by including Prefix Information Options (PIOs) with the "A"
flag set in Router Advertisement messages, and also setting the "M"
flag in such RA messages. This has a number of implications:
* The outcome of the configuration process is non-deterministic,
difficulting network troubleshooting (see
[I-D.ietf-v6ops-dhcpv6-slaac-problem]).
* Nodes end up configuring more addresses than needed (or even
used), normally configuring multiple stable addresses for each
autoconfiguration prefix, with at least one address for each
configuration mechanism (SLAAC and DHCPv6).
* A host may end up employing predictable addresses resulting from
DHCPv6, thus thwarting the security and privacy improvements of
SLAAC-configured addresses (i.e., [RFC7217] and [RFC8981]).
6.2. Sub-optimal IPv6 Address Usage
6.2.1. Correlation of Network Activity
As discussed in [RFC7721], a node that reuses an IPv6 address for
multiple communication instances will enable the correlation of such
network activities. This could be the case when the same IPv6
address is employed by several instances of the same application
(e.g., a browser in "privacy" mode and a browser in "normal" mode),
or when the same IPv6 address is employed by two different
applications on the same node (e.g., a browser in "privacy" mode, and
an email client).
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Particularly in the case of privacy-sensitive applications, an
application or system might want to limit the usage of a given IPv6
address to a single communication instance, a single application, a
single user on the system, etc. However, as discussed in Section 5,
this is practically impossible achieve with currently-available APIs.
6.2.2. Host Tracking
The stable addresses recommended in [RFC8064] use stable IIDs defined
in [RFC7217]. One key part of that algorithm is that if a device
connects to a given network at different times, it will always
configure the same IPv6 addresses on that network. If the device
hosts a service ready to accept connections on that stable address,
adversaries can test the presence of the device on the network by
attempting connections to that stable address. Stable addresses will
thus enable testing whether a specific device is returning to a
particular network, which in a number of cases might be considered a
privacy issue.
6.2.3. Unintended Service Disclosure
Systems like DNS-Based Service Discovery [RFC6763] allow clients to
discover services within a limited domain (e.g. a local link). These
services are not advertised outside of that domain, and thus are not
expected to be discovered by random parties on the Internet.
However, such services may be easily discoverable if they allow
incoming connections on IPv6 addresses that client processes also use
when connecting to remote servers.
NOTE:
An example of such service disclosure is described in [Hein],
where a network manager observed port scanning traffic directed at
the temporary addresses of local host. The analysis in [Hein]
shows that the attackers (scanners) learned the addresses by
observing the device contact an NTP service ([RFC5905]). The
remote scanning attack was possible because the local services
were accepting connections on all configured addresses, including
temporary addresses.
Local services may be disclosed if they are bond to the same IPv6
addresses that are also used by clients for outgoing communications
with remote systems. But the overlap between "client" and "server"
addresses is only one part of the problem. Suppose that a host
operates both a video game server and a home automation application
server. The video game users will be able to discover the IPv6
address of the game server; if the home automation server listens to
the same IPv6 addresses, its address will be revealed to all these
users, thus increasing the exposure of the home automation server.
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We note that a host or network that wants to limit access to local
services should filter incoming connection attempts by affecting
address reachability (see Section 4.3) via firewalls
[I-D.gont-opsawg-firewalls-analysis] and/or the use of IPv6 addresses
of appropriate scope (see Section 4.1). However, it is also prudent
to avoid unintended service disclosure by avoiding the scenarios
discussed in this section altogether.
6.2.4. Availability of Service Outside the Expected Domain
IPv6 defines multiple address scopes [RFC4291] [RFC4007], with hosts
typically configuring Global Unicast Addresses (GUAs), link local
addresses, and Unique Local IPv6 Unicast Addresses (ULAs) [RFC4193].
Availability of a service outside the expected scope happens when a
service is expected to be available only in some limited domain, but
it inadvertently becomes available from outside of that domain. This
could happen, for example, if a service is meant to be accessible
only within a given link, but becomes reachable from outside that
link via ULAs or GUAs, or if a service is meant to be accessible only
within some organization's perimeter but becomes accessible from the
public Internet via GUAs. This will commonly happen if a service
intended for a limited domain is implemented by bind()ing the
listening socket to the "unspecified" addresses (please see
Section 7.4).
6.3. Operational Problems
6.3.1. Implications on Firewall Rules and Access Control Lists (ACLs)
Simple firewall rules have traditionally been specified in terms of
the associated IP addresses and transport protocol port numbers,
generally implying that the associated IP addresses are stable. In
the IPv4 world, IP addresses may be considered rather stable.
However, this is generally not the case with IPv6 addresses, which
tend to be less stale than IPv4 addresses. This may prevent the
enforcement of filtering policies based on specific IPv6 addresses,
or may lead to filtering based on a more coarse granularity (e.g. on
specific address prefixes, as opposed to specific IPv6 addresses).
In some scenarios, it may also encourage disabling features such as
IPv6 temporary addresses [RFC8981].
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NOTE:
In some scenarios, from the point of view of enforcing filtering
policies, it might be desirable to disable temporary addresses
altogether, whether at the system level or at the application
level (if possible). For example, an administrator might prefer
that a secondary DNS server performing DNS zone transfers, or an
MTA, always employ the same source IPv6 address, as opposed to the
different temporary addresses over times
[I-D.gont-opsawg-firewalls-analysis].
6.3.2. Implications on Network Infrastructure
Network deployments are currently recommended to provide multiple
IPv6 addresses to general-purpose hosts [RFC7934]. However, in some
scenarios, use of a large number of IPv6 addresses may have negative
implications on network devices that need to maintain entries for
each IPv6 address in network data structures (e.g., [RFC7039]).
Additionally, concurrent active use of multiple IPv6 addresses will
normally increase neighbour discovery traffic if Neighbour Caches in
network devices are not large enough to store all addresses on the
link. This can impact performance and energy efficiency on networks
on which multicast is expensive (e.g. [RFC9119]). Finally, network
devices may interpret the use of a number of addresses above a
certain threshold as a security event, and block the offending device
from using the network.
6.3.3. Legitimate Network Activity Correlation
The desires of protecting individual privacy versus the desire to
effectively maintain and debug a network can conflict with each
other. For example, having clients use addresses that change over
time will make it more difficult to track down and isolate
operational problems. When looking at packet traces, it could become
more difficult to determine whether one is seeing behavior caused by
a single errant machine, or by a number of them.
6.3.4. Routing in Multi-Prefix/Multi-Router Networks
If the network is provided with multiple upstream connections via
different providers and different local routers, each of them will
typically provide its own PA address space (see Section 4.2) and thus
local hosts will typically configure addresses for each of PA address
space. In this scenario, packets sourced from a given PA space
should only employ the local router of the corresponding upstream
provider, since otherwise packets might be dropped as a result of
ingress/egress filtering [RFC2827]. Unfortunately, traditional
Neighbor Discovery [RFC4861] can advertise routes only with a per-
destination granularity, irrespective of the source address/prefix.
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[RFC8028] addresses the most important challenges associated with
these scenarios. However, [RFC8028] is not yet widely implemented.
As a result, operating a multi-prefix/multi-router IPv6 network
represents a major challenge -- if at all possible.
6.3.5. Renumbering
The challenges posed by network renumbering have been known for a
very long time [RFC5887], with network renumbering typically being
assumed to be performed in a planned manner.
However, in scenarios where a host is moved to a different network
without the host detecting the network re-attachment event, or where
the network a host attaches to is moved to a different point of the
network topology (i.e., the network itself is migrated/"moved"), the
aforementioned host will also experience a renumbering event
[RFC8978]. In an era in which migrating virtual machines,
containers, and networks around a network topology is commonplace,
and where mobile systems changing network connectivity to and from
e.g. WiFi and 4G is also commonplace, renumbering events are
anything but rare.
One of the challenges represented by network renumbering is how hosts
can infer that an existing network prefix and associated address(es)
have become stale (such that stale prefixes and addresses can be
removed and replaced by new prefixes and addresses). In scenarios
where the network topology does not change and the network is
renumbered, network elements may be aware of the renumbering event
and signal this condition to attached systems (i.e., signal that
existing network configuration information should be removed and
replaced). However, in scenarios where it is the host, virtual
machine, container or network that move around the network topology,
the network might not be able to signal the "renumbering event", and
these events might be harder to infer and react to.
Unfortunately, both SLAAC and DHCPv6 assume that network
configuration information is somewhat stable. SLAAC has
traditionally employed long lifetimes for network configuration
information, meaning that stale information could be employed for an
unacceptably long period of time. DCHPv6 operates on the same
premise, and lacks widespread support for RECONFIGURE messages -- so
even if the network were in a position to signal a renumbering event,
hosts will normally rely on expiration of lease times for stale
information to be cleared up.
Some of these problems have been discussed in detail in [RFC8978],
and there have been a number of efforts (see
[I-D.ietf-6man-slaac-renum] and [RFC9096]) to mitigate this issue.
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7. Current Gaps that Prevent Leveraging IPv6 Addressing
The following subsections identify and discuss areas where further
work is needed. Namely,
* Profile-based IPv6 Address Configuration (see Section 7.1)
* Advice on IPv6 Address Usage (see Section 7.2)
* Protocol Improvements to Deal with Many Addresses (see
Section 7.3)
* Improved Address Selection APIs (see Section 7.4)
* Universal Support of RFC 8028 (see Section 7.5)
* Support for Firewall Traversal in CE Routers (see Section 7.6)
7.1. Profile-based IPv6 Address Configuration
Most operating systems configure the same type of addresses
regardless of the current "operating mode" or "profile" of the device
(e.g., device connected to an enterprise network vs. roaming across
untrusted networks). For example, many operating systems configure
both stable [RFC8064] and temporary [RFC8981] addresses for all
network types. However, this "one size fits all" approach tends to
be sub-optimal or even inappropriate for some scenarios. For
example, enterprise networks typically prefer the use of only stable
addresses, thus requiring the network administrator to configure each
host to disable the use of temporary addresses. On the other hand,
mobile devices typically configure both stable and temporary
addresses, even when their operating mode (client-like operation)
would allow for the more privacy-sensible option of configuring only
temporary addresses.
The lack of fine-grained address configuration policies forces nodes
to rely on a "one size fits all" approach that, as noted, usually
leads to suboptimal results. Advice in this area might help achieve
profile-based address configuration policies such that IPv6
addressing capabilities are fully leveraged.
NOTE:
One might envision a document that provides advice regarding IPv6
address generation for different typical scenarios (e.g., when to
configure stable-only, temporary-only, or stable+temporary). In
the most simple analysis, one might expect nodes in a typical
enterprise network to employ only stable addresses. General-
purpose nodes in a home or "trusted" network might want to employ
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both stable and temporary addresses. Finally, mobile nodes (e.g.
when roaming across non-trusted networks) might want to employ
only temporary addresses).
7.2. Advice on IPv6 Address Usage
Application programmers typically rely on the Default Source IPv6
Address Selection for IPv6 (see Section 5.1) for selected source
addresses for outgoing communications, and on accepting incoming
communications on any of the configured addresses. As discussed
throughout this document, this leads to sub-optimal or undesirable
results. All applications on a node share the same pool of
configured addresses, and currently available APIs prevent
applications from requesting the generation of new addresses (e.g. to
be employed for a particular application or communication instance).
Guidance in this area is warranted such that applications and systems
can fully leverage IPv6 addressing.
NOTE:
Such guidance would elaborate, among other things, on the usage of
IPv6 addresses for incoming communications and for outgoing
communications. For example, for incoming communications, hosts
might want to employ only the smallest-scope applicable addresses
(if available) and, if stable addresses were available, only
accept incoming connections on such addresses. For outgoing
communications, hosts might prefer temporary addresses, unless the
corresponding communication instances are expected to be long-
lived (e.g., SSH sessions).
7.3. Protocol Improvements to Deal with Many Addresses
Possible improvements to IPv6 SLAAC should be evaluated, including:
* Enabling IPv6 routers to convey information about network
constraints such as maximum number of addressees per node.
* Enabling hosts to register/de-register configured addresses, such
that e.g. routers need not tie resources to addresses that are no
longer used.
On the other hand, in order for DHCPv6-PD (or some alternative
protocol) to be employed to support the "one /64 per node" paradigm,
widespread support for DHCPv6-PD (or an alternative protocol) would
be necessary.
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7.4. Improved Address Selection APIs
Application developers using the BSD Sockets API can "bind()" a
listening socket to a specific address, and ensure that the
application is only reachable through that address. In theory,
careful selection of the binding address could mitigate the problems
described in Section 6.2. Binding services to temporary addresses
could mitigate the ability of an attacker from testing for the
presence of the node in the network. Binding different services to
different addresses could mitigate unexpected discovery. Binding
services to non-globally-reachable addresses (e.g. link-local
addresses or ULAs) could mitigate availability outside the expected
domain. However, explicitly managing addresses adds significant
complexity to application development. It requires that application
developers master IPv6 addressing architecture subtleties, and
implement logic that reacts adequately to connectivity events and
address changes. Experience shows that application developers would
probably prefer a much simpler solution.
In addition, we note that many application developers use high level
APIs that listen to TLS, HTTP, or some other application protocol.
These high level APIs seldomly provide detailed access to specific
IPv6 addresses, and typically default to listening on all available
addresses.
A more advanced API could allow application programmers to select
desired properties in an address (scope, stability, etc.), such that
the best-suitable addresses are selected, while relieving the
application from low-level IPv6 addressing details. Such API could
also trigger the generation of new IPv6 addresses if/when the
specified properties require so.
7.5. Universal Support of RFC 8028
To put it bluntly, multi-prefix/multi-router networks cannot possibly
work properly without implementation of [RFC8028]. Unfortunately,
[RFC8028] is not yet widely implemented. On the protocol
standardization side, the IETF should consider elevating the
requirement to support RFC8028 in the IPv6 Node Requirements RFC
[RFC8504] from "SHOULD" to "MUST".
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7.6. Support for Firewall Traversal in CE Routers
Customer Edge (CE) routers that implement a default filtering policy
of "only allowing outgoing communications" need to support helper
protocols such as [UPnP] or PCP [RFC6887], so that applications can
open holes in the CE router firewall to be able to receive incoming
communications. Otherwise, P2P applications that currently work in
IPv4 networks might not function in IPv6-only networks.
Support for these protocols is particularly important for IPv6
deployments since, as hosts will normally employ "provider
aggregatable" addresses (see Section 4.2), renumbering events will
result in host address changes, and thus static firewall rules will
be harder to implement than for the IPv4 networks. Similarly, use of
only temporary addresses [RFC8981] would require that incoming
connections be accepted on temporary addresses, thus requiring that
the associated firewall rules be updated.
NOTE:
One might argue that if a node is to receive incoming connections,
both stable and temporary addresses should be configured, though.
Thus, firewall rules to allow incoming connections would be
configured for the stable addresses rather than for the temporary
addresses.
8. IANA Considerations
This document has no IANA actions.
9. Security Considerations
The security and privacy implications associated with the IPv6
addresses have been analyzed in [RFC7217] [RFC7721], and [RFC7707].
This document complements and extends the aforementioned analysis by
also considering other IPv6 properties such as address scope and
address reachability, and the associated trade-offs.
10. Acknowledgements
The authors would like to thank (in alphabetical order) Mikael
Abrahamsson, Fred Baker, Brian Carpenter, Owen DeLong, Francis
Dupont, Tatuya Jinmei, Ted Lemon, and Dave Thaler for providing
valuable comments on earlier versions of this document.
11. References
11.1. 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>.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <https://www.rfc-editor.org/info/rfc2827>.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[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>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/info/rfc8981>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<https://www.rfc-editor.org/info/rfc6724>.
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[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<https://www.rfc-editor.org/info/rfc6887>.
[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,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<https://www.rfc-editor.org/info/rfc8028>.
[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
RFC 8064, DOI 10.17487/RFC8064, February 2017,
<https://www.rfc-editor.org/info/rfc8064>.
[RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
"Host Address Availability Recommendations", BCP 204,
RFC 7934, DOI 10.17487/RFC7934, July 2016,
<https://www.rfc-editor.org/info/rfc7934>.
[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>.
[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>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>.
11.2. Informative References
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[RFC9119] Perkins, C., McBride, M., Stanley, D., Kumari, W., and JC.
Zúñiga, "Multicast Considerations over IEEE 802 Wireless
Media", RFC 9119, DOI 10.17487/RFC9119, October 2021,
<https://www.rfc-editor.org/info/rfc9119>.
[I-D.ietf-6man-slaac-renum]
Gont, F., Zorz, J., and R. Patterson, "Improving the
Robustness of Stateless Address Autoconfiguration (SLAAC)
to Flash Renumbering Events", Work in Progress, Internet-
Draft, draft-ietf-6man-slaac-renum-02, 19 January 2021,
<https://www.ietf.org/archive/id/draft-ietf-6man-slaac-
renum-02.txt>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[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>.
[I-D.gont-6man-ipv6-ula-scope]
Gont, F., "Scope of Unique Local IPv6 Unicast Addresses",
Work in Progress, Internet-Draft, draft-gont-6man-ipv6-
ula-scope-00, 5 January 2021,
<https://www.ietf.org/archive/id/draft-gont-6man-ipv6-ula-
scope-00.txt>.
[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks",
RFC 4953, DOI 10.17487/RFC4953, July 2007,
<https://www.rfc-editor.org/info/rfc4953>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
[RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
Still Needs Work", RFC 5887, DOI 10.17487/RFC5887, May
2010, <https://www.rfc-editor.org/info/rfc5887>.
Gont & Gont Expires 3 December 2022 [Page 27]
Internet-Draft IPv6 Addressing Considerations June 2022
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
<https://www.rfc-editor.org/info/rfc6296>.
[RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
"Source Address Validation Improvement (SAVI) Framework",
RFC 7039, DOI 10.17487/RFC7039, October 2013,
<https://www.rfc-editor.org/info/rfc7039>.
[RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
<https://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,
<https://www.rfc-editor.org/info/rfc7721>.
[RFC8190] Bonica, R., Cotton, M., Haberman, B., and L. Vegoda,
"Updates to the Special-Purpose IP Address Registries",
BCP 153, RFC 8190, DOI 10.17487/RFC8190, June 2017,
<https://www.rfc-editor.org/info/rfc8190>.
[I-D.gont-opsawg-firewalls-analysis]
Gont, F. and F. Baker, "On Firewalls in Network Security",
Work in Progress, Internet-Draft, draft-gont-opsawg-
firewalls-analysis-02, 4 February 2016,
<https://www.ietf.org/archive/id/draft-gont-opsawg-
firewalls-analysis-02.txt>.
[I-D.ietf-v6ops-dhcpv6-slaac-problem]
Liu, B., Jiang, S., Gong, X., Wang, W., and E. Rey,
"DHCPv6/SLAAC Interaction Problems on Address and DNS
Configuration", Work in Progress, Internet-Draft, draft-
ietf-v6ops-dhcpv6-slaac-problem-07, 17 August 2016,
<https://www.ietf.org/archive/id/draft-ietf-v6ops-dhcpv6-
slaac-problem-07.txt>.
[UPnP] UPnP, "UPnP Device Architecture 2.0", April 17, 2020,
<https://openconnectivity.org/upnp-specs/UPnP-arch-
DeviceArchitecture-v2.0-20200417.pdf>.
[Hein] Hein, B., "The Rising Sophistication of Network
Scanning", January 2016,
<http://netpatterns.blogspot.be/2016/01/the-rising-
sophistication-of-network.html>.
Gont & Gont Expires 3 December 2022 [Page 28]
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Authors' Addresses
Fernando Gont
SI6 Networks
Evaristo Carriego 2644
1706 Haedo
Provincia de Buenos Aires
Argentina
Email: fgont@si6networks.com
URI: https://www.si6networks.com
Guillermo Gont
SI6 Networks
Evaristo Carriego 2644
1706 Haedo
Provincia de Buenos Aires
Argentina
Email: ggont@si6networks.com
URI: https://www.si6networks.com
Gont & Gont Expires 3 December 2022 [Page 29]
