wdiff rfc7707.original rfc7707.txt

opsec
Internet Engineering Task Force (IETF) F. Gont
Internet-Draft
Request for Comments: 7707 Huawei Technologies
Obsoletes: 5157 (if approved) T. Chown
Intended status:
Category: Informational University of Southampton
Expires: February 29, 2016 August 28,
ISSN: 2070-1721 November 2015

Network Reconnaissance in IPv6 Networks
draft-ietf-opsec-ipv6-host-scanning-08

Abstract

IPv6 offers a much larger address space than that of its IPv4
counterpart. An IPv6 subnet of size /64 can (in theory) accommodate
approximately 1.844 * 10^19 hosts, thus resulting in a much lower
host density (#hosts/#addresses) than is typical in IPv4 networks,
where a site typically has 65,000 or less fewer unique addresses. As a
result, it is widely assumed that it would take a tremendous effort
to perform address scanning address-scanning attacks against IPv6 networks, and
therefore brute-force networks; therefore,
IPv6 address scanning address-scanning attacks have been considered unfeasible. This
document formally obsoletes RFC 5157, which first discussed this
assumption, by providing further analysis on how traditional address address-
scanning techniques apply to IPv6
networks, networks and exploring some
additional techniques that can be employed for IPv6 network
reconnaissance.

Status of This Memo

This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a maximum candidate for any level of Internet
Standard; see Section 2 of RFC 5741.

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This Internet-Draft will expire on February 29, 2016.
http://www.rfc-editor.org/info/rfc7707.

This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements for the Applicability of Network Reconnaissance
Techniques . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IPv6 Address Scanning . . . . . . . . . . . . . . . . . . . . 5 6
3.1. Address Configuration in IPv6 . . . . . . . . . . . . . . 6
3.1.1. StateLess Stateless Address Auto-Configuration Autoconfiguration (SLAAC) . . . . . 6
3.1.2. Dynamic Host Configuration Protocol version 6 for IPv6 (DHCPv6) . . . . . . . . . . . . . . . . . . . . . . 11
3.1.3. Manually-configured Manually Configured Addresses . . . . . . . . . . . . 11 12
3.1.4. IPv6 Addresses Corresponding to Transition/Co-
existence
Transition/Coexistence Technologies . . . . . . . . . . . . . . . 14
3.1.5. IPv6 Address Assignment in Real-world Real-World Network
Scenarios . . . . . . . . . . . . . . . . . . . . . . 14
3.2. IPv6 Address Scanning of Remote Networks . . . . . . . . 17
3.2.1. Reducing the subnet Subnet ID search space Search Space . . . . . . . . . 17 18
3.3. IPv6 Address Scanning of Local Networks . . . . . . . . . 18 19
3.4. Existing IPv6 Address Scanning Address-Scanning Tools . . . . . . . . . . 19 20
3.4.1. Remote IPv6 Network Address Scanners . . . . . . . . . . . . 19 20
3.4.2. Local IPv6 Network Address Scanners . . . . . . . . . 21
3.5. Mitigations . . . . . . 20
3.5. Mitigations . . . . . . . . . . . . . . . . . 21
3.6. Conclusions . . . . . . 20 . . . . . . . . . . . . . . . . . 22
4. Leveraging the Domain Name System (DNS) for Network
Reconnaissance . . . . . . . . . . . . . . . . . . . . . . . 21 23
4.1. DNS Advertised Hosts . . . . . . . . . . . . . . . . . . 21 23
4.2. DNS Zone Transfers . . . . . . . . . . . . . . . . . . . 22 23
4.3. DNS Brute Forcing . . . . . . . . . . . . . . . . . . . . 22 23
4.4. DNS Reverse Mappings . . . . . . . . . . . . . . . . . . 22 23
5. Leveraging Local Name Resolution and Service Discovery
Services . . . . . . . . . . . . . . . . . . . . . . . . . . 23 24
6. Public Archives . . . . . . . . . . . . . . . . . . . . . . . 23 24
7. Application Participation . . . . . . . . . . . . . . . . . . 23 24
8. Inspection of the IPv6 Neighbor Cache and Routing Table . . . 23 25
9. Inspection of System Configuration and Log Files . . . . . . 24 25
10. Gleaning Information from Routing Protocols . . . . . . . . . 24 26
11. Gleaning Information from IP Flow Information Export (IPFIX) 24 26
12. Obtaining Network Information with traceroute6 . . . . . . . 24 26
13. Gleaning Information from Network Devices Using SNMP . . . . 25 26
14. Obtaining Network Information via Traffic Snooping . . . . . 25 26
15. Conclusions Security Considerations . . . . . . . . . . . . . . . . . . . 26
16. References . . . . . . 25
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
17. Security Considerations . . . . . . . . . . . . . . . . . . . 26
18. Acknowledgements 27
16.1. Normative References . . . . . . . . . . . . . . . . . . . . . . 26
19. 27
16.2. Informative References . . . . . . . . . . . . . . . . . . . . . . . . . 26
19.1. Normative References . 28
Appendix A. Implementation of a Full-Fledged IPv6 Address-
Scanning Tool . . . . . . . . . . . . . . . . . 26
19.2. Informative References . . 32
A.1. Host-Probing Considerations . . . . . . . . . . . . . . . 28
Appendix A. 32
A.2. Implementation of a full-fledged an IPv6 address-
scanning tool . . . . . . . . . . . Local Address-Scanning Tool . . 34
A.3. Implementation of an IPv6 Remote Address-Scanning Tool . 34
Acknowledgements . . . . . 31
A.1. Host-probing considerations . . . . . . . . . . . . . . . 31
A.2. Implementation of an IPv6 local address-scanning tool . . 33
A.3. Implementation of a IPv6 remote address-scanning tool . . 34 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 36

1. Introduction

The main driver for IPv6 [RFC2460] deployment is its larger address
space [CPNI-IPv6]. This larger address space not only allows for an
increased number of connected devices, devices but also introduces a number of
subtle changes in several aspects of the resulting networks. One of
these changes is the reduced host density (the number of hosts
divided by the number of addresses) of typical IPv6 subnetworks, when
compared to their IPv4 counterparts. [RFC5157] describes how this
significantly lower IPv6 host-density host density is likely to make classic
network address scans address-scanning attacks less feasible, since even by
applying various heuristics, the address space to be scanned remains
very large. RFC 5157 goes on to describe some alternative methods
for attackers to glean active IPv6 addresses, addresses and provides some
guidance for administrators and implementors, e.g. e.g., not using
sequential addresses with DHCPv6.

With the benefit of more than five years of additional IPv6
deployment experience, this document formally obsoletes RFC 5157. It
emphasises
emphasizes that while scanning address-scanning attacks are less feasible,
they may, with appropriate heuristics, remain possible. At the time
that RFC 5157 was written, observed scans address-scanning attacks were
typically across ports on the addresses of discovered servers; since
then, evidence that some classic address scanning is occurring is
being witnessed. This text thus updates the analysis on the
feasibility of "traditional" address-scanning attacks in IPv6 networks, and it
explores a number of additional techniques that can be employed for
IPv6 network reconnaissance. Practical examples and guidance are
also included in the Appendices. appendices.

On one hand, raising awareness about IPv6 network reconnaissance
techniques may allow (in some cases) network and security
administrators to prevent or detect such attempts. On the other
hand, network reconnaissance is essential for the so-called
"penetration tests" typically performed to assess the security of
production networks. As a result, we believe the benefits of a
thorough discussion of IPv6 network reconnaissance are two-fold. twofold.

Section 3 analyzes the feasibility of traditional address-scanning attacks (e.g. (e.g.,
ping sweeps) in IPv6 networks, networks and explores a number of possible
improvements to such techniques. Appendix A describes how the
aforementioned analysis can be leveraged to produce address-
scanning address-scanning
tools (e.g. (e.g., for penetration testing purposes). Section 4
analyzes network reconnaissance techniques that leverage the Domain
Name System (DNS). Finally, the rest of
this document discusses a number of other miscellaneous techniques that
could be leveraged for IPv6 network reconnaissance.

2. Requirements for the Applicability of Network Reconnaissance
Techniques

Throughout this document, a number of network reconnaissance
techniques are discussed. Each of these techniques have has different
requirements on the side of the practitioner, with respect to whether
they require local access to the target network, network and whether they
require login access (or similar access credentials) to the system on
which the technique is applied.

The following table tries to summarize the aforementioned
requirements,
requirements and serves as a cross index to the corresponding
sections.

+---------------------------------------------+----------+----------+
| Technique | Local | Login |
| | access | access |
+---------------------------------------------+----------+----------+
| Local address scans Remote Address Scanning (Section 3.3) 3.2) | Yes No | No |
+---------------------------------------------+----------+----------+
| Remote Local Address scans Scanning (Section 3.2) 3.3) | No Yes | No |
+---------------------------------------------+----------+----------+
| DNS Advertised Hosts (Section 4.1) | No | No |
+---------------------------------------------+----------+----------+
| DNS Zone Transfers (Section 4.2) | No | No |
+---------------------------------------------+----------+----------+
| DNS reverse mappings Brute Forcing (Section 4.3) | No | No |
+---------------------------------------------+----------+----------+
| DNS Reverse Mappings (Section 4.4) | No | No |
+---------------------------------------------+----------+----------+
| Leveraging Local Name Resolution and | Yes | No |
| Service Discovery Services (Section 5) | | |
+---------------------------------------------+----------+----------+
| Public archives Archives (Section 6) | No | No |
+---------------------------------------------+----------+----------+
| Application Participation (Section 7) | No | No |
+---------------------------------------------+----------+----------+
| Inspection of the IPv6 Neighbor Cache and | No | Yes |
| Routing Table (Section 8) | | |
+---------------------------------------------+----------+----------+
| Inspecting System Configuration and Log | No | Yes |
| Files (Section 9) | | |
+---------------------------------------------+----------+----------+
| Gleaning information Information from Routing Protocols | Yes | No |
| (Section 10) | | |
+---------------------------------------------+----------+----------+
| Gleaning Information from IP Flow | No | Yes |
| Information Export (IPFIX) (Section 11) | | |
+---------------------------------------------+----------+----------+
| Obtaining Network Information with | No | No |
| traceroute6 (Section 12) | | |
+---------------------------------------------+----------+----------+
| Gleaning Information from Network Devices | No | Yes |
| Using SNMP (Section 13) | | |
+---------------------------------------------+----------+----------+
| Obtaining Network Information via Traffic | Yes | No |
| Snooping (Section 14) | | |
+---------------------------------------------+----------+----------+

Table 1: Requirements for the Applicability of Network Reconnaissance
Techniques

3. IPv6 Address Scanning

This section discusses how traditional address scanning address-scanning techniques
(e.g.
(e.g., "ping sweeps") apply to IPv6 networks. Section 3.1 provides
an essential analysis of how address configuration is performed in
IPv6, identifying patterns in IPv6 addresses that can be leveraged to
reduce the IPv6 address search space when performing IPv6 address-
scanning attacks. Section 3.2 discusses IPv6 address scanning of
remote networks. Section 3.3 discusses IPv6 address
scans. scanning of
local networks. Section 3.4 discusses existing IPv6 address-scanning
tools. Section 3.5 provides advice on how to mitigate IPv6 address-
scanning attacks. Finally, Appendix A discusses how the insights
obtained in the
previous sub-sections following subsections can be incorporated into into a fully-fledged
fully fledged IPv6 address scanning address-scanning tool. Section 3.5 provides advice on how to
mitigate IPv6 address scans.

3.1. Address Configuration in IPv6

IPv6 incorporates two automatic address-configuration mechanisms:
SLAAC (StateLess
Stateless Address Auto-Configuration) Autoconfiguration (SLAAC) [RFC4862] and DHCPv6
(Dynamic Dynamic
Host Configuration Protocol version 6) for IPv6 (DHCPv6) [RFC3315]. SLAAC is
the mandatory mechanism for automatic address configuration, while
DHCPv6 is optional - -- however, most current versions of general-
purpose operating systems support both. In addition to automatic
address configuration, hosts, typically servers, may employ manual
configuration, in which all the necessary information is manually
entered by the host or network administrator into configuration files
at the host.

The following subsections describe each of the possible configuration
mechanisms/approaches in more detail.

3.1.1. StateLess Stateless Address Auto-Configuration Autoconfiguration (SLAAC)

The basic idea behind SLAAC is that every host joining a network will
send a multicasted solicitation requesting network configuration
information, and local routers will respond to the request providing
the necessary information. SLAAC employs two different ICMPv6
message types: ICMPv6 Router Solicitation and ICMPv6 Router
Advertisement messages. Router Solicitation messages are employed by
hosts to query local routers for configuration information, while
Router Advertisement messages are employed by local routers to convey
the requested information.

Router Advertisement messages convey a plethora of network
configuration information, including the IPv6 prefix that should be
used for configuring IPv6 addresses on the local network. For each
local prefix learned from a Router Advertisement message, an IPv6
address is configured by appending a locally-generated locally generated Interface
Identifier (IID) to the corresponding IPv6 prefix.

The following subsections describe currently-deployed currently deployed policies for
generating the IIDs used with SLAAC.

3.1.1.1. Interface-Identifiers Interface Identifiers Embedding IEEE Identifiers

The traditional SLAAC interface identifiers IIDs are based on the link-
layer link-layer address of the
corresponding network interface card. For example, in the case of
Ethernet addresses, the IIDs are constructed as follows:

1. The "Universal" bit (bit 6, from left to right) of the address is
set to 1 1.

2. The word 0xfffe is inserted between the OUI (Organizationally Organizationally Unique Identifier)
Identifier (OUI) and the rest of the Ethernet address address.

For example, the MAC Media Access Control (MAC) address 00:1b:38:83:88:3c
would lead to the IID 021b:38ff:fe83:883c.

NOTE:

NOTES:
[RFC7136] notes that all bits of an IID should be treated as
"opaque" bits. Furthermore, [I-D.ietf-6man-default-iids] [DEFAULT-IIDS] is currently in the
process of changing the default IID generation scheme to [RFC7217]. align
with [RFC7217], such that IIDs are semantically opaque and do not
follow any patterns. Therefore, the traditional IIDs based on
link-layer addresses are expected to become less common over time.

Throughout this document we consider that bits are numbered from
left to right, starting at 0, and that bytes are numbered from
left to right, starting at 0.

A number of considerations should be made about these identifiers.
Firstly, two bytes one 16-bit word (bytes 3-4) of the resulting address always have
has a fixed value (0xff, 0xfe), (0xfffe), thus reducing the search space for the
IID. Secondly, the first high-order three bytes of these identifiers the IID correspond to
the OUI of the network interface card vendor. Since not all possible
OUIs have been assigned, this further reduces the IID search space.
Furthermore, of the assigned OUIs, many could be regarded as
corresponding to legacy devices, devices and thus are unlikely to be used for
Internet-connected IPv6-enabled systems, yet further reducing the IID
search space. Finally, in some scenarios scenarios, it could be possible to
infer the OUI in use by the target network devices, yet narrowing
down the possible IIDs even more.

NOTES:

For example, an organization known for being provisioned by vendor
X is likely to have most of the nodes in its organizational
network with OUIs corresponding to vendor X.

These considerations mean that in some scenarios, the original IID
search space of 64 bits may be effectively reduced to 2^24 , or n *
2^24 (where "n" is the number of different OUIs assigned to the
target vendor).

Further,

Furthermore, if just one host address is detected or known within a
subnet, it is not unlikely that, if systems were ordered in a batch,
that
they may have sequential MAC addresses. Additionally, given a MAC
address observed in one subnet, sequential or nearby MAC addresses
may be seen in other subnets in the same site.

3.1.1.2. Interface-Identifiers Interface Identifiers of Virtualization Technologies

IIDs resulting from virtualization technologies can be considered a
specific sub-case subcase of IIDs embedding IEEE identifiers (please see
Section 3.1.1.1): they employ IEEE identifiers, but part of the lower
half of the IID
has specific patterns. The following subsections describe IIDs of
some popular virtualization technologies.

3.1.1.2.1. VirtualBox

All automatically-generated automatically generated MAC addresses in VirtualBox virtual
machines employ the OUI 08:00:27 [VBox2011]. This means that all
SLAAC-produced
addresses resulting from traditional SLAAC will have an IID of the
form a00:27ff:feXX:XXXX, thus effectively reducing the IID search
space from 64 bits to 24 bits.

3.1.1.2.2. VMWare VMware ESX server

VMWare Server

The VMware ESX server (versions 1.0 to 2.5) provides yet a more
interesting example. Automatically-generated Automatically generated MAC addresses have the
following pattern [vmesx2011]:

1. The OUI is set to 00:05:69 00:05:69.

2. The next 16 bits of the MAC address are set to the same value as
the last 16 bits of the console operating system's primary IPv4
address
address.

3. The final 8 bits of the MAC address are set to a hash value based
on the name of the virtual machine's configuration file.

This means that, assuming the console operating system's primary IPv4
address is known, the IID search space is reduced from 64 bits to 8
bits.

On the other hand, manually-configured manually configured MAC addresses in VMWare the VMware
ESX server employ the OUI 00:50:56, with the low-order three bytes of
the MAC address being in the range 00:00:00-3F:FF:FF (to avoid
conflicts with other VMware products). Therefore, even in the case
of manually-configured manually configured MAC addresses, the IID search space is reduced
from 64 bits to 22 bits.

3.1.1.2.3. VMWare VMware vSphere

VMWare

VMware vSphere [vSphere] supports these default MAC address
generation algorithms:

o Generated addresses

* Assigned by the vCenter Server server

* Assigned by the ESXi host

o Manually-configured Manually configured addresses

By default, MAC addresses assigned by the vCenter server use the OUI
00:50:56,
00:50:56 and have the format 00:50:56:XX:YY:ZZ, where XX is
calculated as (0x80 + vCenter Server ID (in the range 0x00-0x3F)),
and XX and YY are random two-digit hexadecimal numbers. Thus, the
possible IID range is 00:50:56:80:00:00-00:50:56:BF:FF:FF, and
therefore 00:50:56:80:00:00-00:50:56:BF:FF:FF; therefore,
the search space for the resulting SLAAC addresses will be
24 22 bits.

MAC addresses generated by the ESXi host use the OUI 00:0C:29, 00:0C:29 and
have the format 00:0C:29:XX:YY:ZZ, where XX, YY, and ZZ are the
lastthree last
three octets in hexadecimal format of the virtual machine UUID Universally
Unique Identifier (UUID) (based on a hash calculated by using with the UUID of
the ESXi physical machine and the path to a configuration file).
Thus, the MAC addresses will be in the range 00:0C:29:XX:YY:ZZ-00:0C:29:FF:FF:FF,
and therefore
00:0C:29:00:00:00-00:0C:29:FF:FF:FF; therefore, the search space for
the resulting SLAAC addresses will be 22 24 bits.

Finally, manually-configured manually configured MAC addresses employ the OUI 00:50:56,
with the low-order three bytes being in the range 0x000000-0x3fffff 00:00:00-3F:FF:FF
(to avoid conflicts with other VMware products). Therefore,
therefore the
resulting MAC addresses will be in the range
00:50:56:00:00:00-00:50:56:3F:FF:FF, and the search space for the resulting
corresponding SLAAC addresses will be 22 bits.

3.1.1.3. Temporary Addresses

Privacy concerns [Gont-DEEPSEC2011]
[I-D.ietf-6man-ipv6-address-generation-privacy] [RFC7721] regarding interface
identifiers IIDs
embedding IEEE identifiers led to the introduction of "Privacy
Extensions for Stateless Address Auto-configuration Autoconfiguration in IPv6"
[RFC4941], also known as "temporary addresses" or "privacy
addresses". Essentially, "temporary addresses" produce random
addresses by concatenating a random identifier to the auto-
configuration
autoconfiguration IPv6 prefix advertised in a Router Advertisement. Advertisement
message.

NOTE:
In addition to their unpredictability, these addresses are
typically short-lived, such that even if an attacker were to learn
of one of these addresses, they would be of use for a limited
period of time. A typical implementation may keep a temporary
address preferred for 24 hours, and configured but deprecated for
seven days.

It is important to note that "temporary addresses" are generated in
addition to the stable addresses [RFC7721] (such as the traditional
SLAAC addresses (i.e., based on IEEE identifiers): traditional stable SLAAC addresses
are meant to be employed for "server-like" inbound communications,
while "temporary addresses" are meant to be employed for "client-like" "client-
like" outbound communications. This means that implementation/use of
"temporary addresses" does not prevent an attacker from leveraging
the predictability of traditional stable SLAAC addresses, since "temporary
addresses" are generated in addition to (rather than as a replacement
of) the traditional stable SLAAC addresses (such as those derived from e.g. IEEE identifiers.
identifiers).

The benefit that temporary addresses offer in this context is that
they reduce the exposure of the SLAAC address host addresses to any third parties
that may observe traffic sent from a host where temporary addresses
are enabled and used by default. But, in the absence of firewall
protection for the host, its stable SLAAC address remains liable to
be scanned from offsite. off-site.

3.1.1.4. Constant, semantically opaque Semantically Opaque IIDs

In order to mitigate the security implications arising from the
predictable IPv6 addresses derived from IEEE identifiers, Microsoft
Windows produced an alternative scheme for generating "stable
addresses" (in replacement of the ones embedding IEEE identifiers).
The aforementioned scheme is believed to be an implementation of RFC
4941 [RFC4941], but without regenerating the addresses over time.
The resulting interface IDs IIDs are constant across system bootstraps, and also
constant across networks.

Assuming no flaws in the aforementioned algorithm, this scheme would
remove any patterns from the SLAAC addresses.

NOTE:
However, since the resulting interface IDs IIDs are constant across networks,
these addresses may still be leveraged for host tracking host-tracking purposes
[RFC7217]
[I-D.ietf-6man-ipv6-address-generation-privacy]. [RFC7721].

The benefit of this scheme is thus that the host may be less readily
detected by applying heuristics to a scan, an address-scanning attack, but,
in the absence of concurrent use of temporary addresses, the host is
liable to be tracked across visited networks.

3.1.1.5. Stable, semantically opaque Semantically Opaque IIDs

In response to the predictability issues discussed in Section 3.1.1.1
and the privacy issues discussed in
[I-D.ietf-6man-ipv6-address-generation-privacy], [RFC7721], the IETF has
standardized (in [RFC7217]) a method for generating IPv6 Interface
Identifiers IIDs to be
used with IPv6 Stateless Address Autoconfiguration
(SLAAC), SLAAC, such that addresses configured using this
method are stable within each subnet, but the Interface Identifier changes IIDs change when hosts
move from one subnet to another. The aforementioned method is meant
to be an alternative to generating Interface Identifiers IIDs based on IEEE identifiers,
such that the benefits of stable addresses can be achieved without
sacrificing the privacy of users.

Implementation of this method (in replacement of Interface
Identifiers IIDs based on IEEE
identifiers) would eliminate eliminates any patterns from the Interface ID, IID, thus benefiting
user privacy and reducing the ease with which addresses can be
scanned.

3.1.2. Dynamic Host Configuration Protocol version 6 for IPv6 (DHCPv6)

DHC

DHCPv6 can be employed as a stateful address configuration mechanism,
in which a server (the DHCPv6 server) leases IPv6 addresses to IPv6
hosts. As with the IPv4 counterpart, addresses are assigned
according to a configuration-defined address range and policy, with
some DHCPv6 servers assigning addresses sequentially, from a specific
range. In such cases, addresses tend to be predictable.

NOTE:
For example, if the prefix 2001:db8::/64 is used for assigning
addresses on the local network, the DHCPv6 server might
(sequentially) assign addresses from the range 2001:db8::1 -
2001:db8::100.

In most common scenarios, this means that the IID search space will
be reduced from the original 64 bits, bits to 8 or 16 bits. RFC 5157 [RFC5157]
recommended that DHCPv6 instead issue addresses randomly from a large
pool; that advice is repeated here.
[I-D.ietf-dhc-stable-privacy-addresses] [IIDS-DHCPv6] specifies an
algorithm that can be employed by DHCPv6 servers to produce stable
addresses which that do not follow any specific pattern, thus resulting in
an IID search space of 64 bits.

3.1.3. Manually-configured Manually Configured Addresses

In some scenarios, node addresses may be manually configured. This
is typically the case for IPv6 addresses assigned to routers (since
routers do not employ automatic address configuration) but also for
servers (since having a stable address that does not depend on the
underlying link-layer address is generally desirable).

While network administrators are mostly free to select the IID from
any value in the range 1 - 2^64, for the sake of simplicity (i.e.,
ease of remembering) remembering), they tend to select addresses with one of the
following patterns:

o "low-byte" low-byte addresses: in which most of the bytes of the IID are set
to 0 (except for the least significant byte). byte)

o IPv4-based addresses: in which the IID embeds the IPv4 address of
the network interface (as in 2001:db8::192.0.2.1)

o "service port" service port addresses: in which the IID embeds the TCP/UDP
service port of the main service running on that node (as in
2001:db8::80 or 2001:db8::25)

o wordy addresses: which encode words (as in 2001:db8::dead:beef)

Each of these patterns is discussed in detail in the following
subsections.

3.1.3.1. Low-byte Low-Byte Addresses

The most common form of low-byte addresses is that in which all the
the
bytes of the IID (except the least significant bytes) are set to zero
(as in 2001:db8::1, 2001:db8::2, etc.). However, it is also common
to find similar addresses in which the two lowest order lowest-order 16-bit words
(from the right to left) are set to small numbers (as in
2001::db8::1:10, 2001:db8::2:10, etc.). Yet it is not uncommon to
find IPv6 addresses in which the second lowest-order 16-bit word
(from right to left) is set to a small value in the range 0-255,
0x0000:0x00ff, while the lowest-order 16-bit word (from right to
left) varies in the range 0-65535. 0x0000:0xffff. It should be noted that all
of these address patterns are generally referred to as "low-byte
addresses", even when, strictly speaking, it is not only the lowest-order lowest-
order byte of the IPv6 address that varies from one address to
another.

In the worst-case scenario, the search space for this pattern is 2^24
(although most systems can be found by searching 2^16 or even 2^8
addresses).

3.1.3.2. IPv4-based IPv4-Based Addresses

The most common form of these addresses is that in which an IPv4
address is encoded in the lowest-order 32 bits of the IPv6 address
(usually as a result of the address notation of addresses in the form
2001:db8::192.0.2.1). However, it is also common for administrators
to encode one byte each of the bytes of the IPv4 address in each of the 16-bit
words of the IID (as in e.g. in, e.g., 2001:db8::192:0:2:1).

Therefore, the search space for addresses following this pattern is
that of the corresponding IPv4 prefix (or twice the size of that
search space if both forms of "IPv4-based addresses" are to be
searched).

3.1.3.3. Service-port Service-Port Addresses

Addresses

Address following this pattern include the service port (e.g. (e.g., 80
for HTTP) in the lowest-order byte of the IID, IID and set have the rest of
the bytes of the IID set to zero. There are a number of variants for
this address pattern:

o The lowest-order 16-bit word (from right to left) may contain the
service port, and the second lowest-order 16-bit word (from right
to left) may be set to a number in the range 0-255 0x0000-0x00ff (as in e.g. in,
e.g., 2001:db8::1:80).

o The lowest-order 16-bit word (from right to left) may be set to a
value in the range 0-255, 0x0000-0x00ff, while the second lowest-order
16-bit word (from right to left) may contain the service port (as in e.g.
in, e.g., 2001:db8::80:1).

o The service port itself might be encoded in decimal or in
hexadecimal notation (e.g., an address embedding the HTTP port
might be 2001:db8::80 or 2001:db8::50) -- with addresses encoding
the service port as a decimal number being more common.

Considering a maximum of 20 popular service ports, the search space
for addresses following this pattern is, in the worst-case scenario,
20 * 2^10.

3.1.3.4. Wordy Addresses

Since the IPv6 address notation allows for a number of hexadecimal
digits, it is not difficult to encode words into IPv6 addresses (as
in, e.g., 2001:db8::dead:beef).

Addresses following this pattern are likely to be explored by means
of "dictionary attacks", and therefore attacks"; therefore, computing the corresponding
search-space
search space is not straight-forward. straightforward.

3.1.4. IPv6 Addresses Corresponding to Transition/Co-existence Transition/Coexistence
Technologies

Some transition/co-existence transition/coexistence technologies might be leveraged to reduce
the target search space of remote address-scanning attacks, since
they specify how the corresponding IPv6 address must be generated.
For example, in the case of Teredo [RFC4380], the 64-bit
interface identifier IID is
generated from the IPv4 address observed at a Teredo server along
with a UDP port number.

For obvious reasons, the search space for these addresses will depend
on the specific transition/coexistence technology being employed.

3.1.5. IPv6 Address Assignment in Real-world Real-World Network Scenarios

Table

Figures 1, 2, Table 3 and Table 4 3 provide a summary of the results obtained by
[Gont-LACSEC2013] for when measuring the address patterns employed by web
servers, nameservers, name servers, and
mailservers, mail servers, respectively. Table 5 Figure 4
provides a rough summary of the results obtained by [Malone2008] for
IPv6 routers. Table 6 Figure 5 provides a summary of the results obtained by
[Ford2013] for clients.

+---------------+------------+
| Address type | Percentage |
+---------------+------------+
| IEEE-based | 1.44% |
+---------------+------------+
| Embedded-IPv4 | 25.41% |
+---------------+------------+
| Embedded-Port | 3.06% |
+---------------+------------+
| ISATAP | 0% 0.00% |
+---------------+------------+
| Low-byte | 56.88% |
+---------------+------------+
| Byte-pattern | 6.97% |
+---------------+------------+
| Randomized | 6.24% |
+---------------+------------+

Table 2:

Figure 1: Measured webserver addresses Web Server Addresses

+---------------+------------+
| Address type | Percentage |
+---------------+------------+
| IEEE-based | 0.67% |
+---------------+------------+
| Embedded-IPv4 | 22.11% |
+---------------+------------+
| Embedded-Port | 6.48% |
+---------------+------------+
| ISATAP | 0% 0.00% |
+---------------+------------+
| Low-byte | 56.58% |
+---------------+------------+
| Byte-pattern | 11.07% |
+---------------+------------+
| Randomized | 3.09% |
+---------------+------------+

Table 3:

Figure 2: Measured nameserver addresses Name Server Addresses
+---------------+------------+
| Address type | Percentage |
+---------------+------------+
| IEEE-based | 0.48% |
+---------------+------------+
| Embedded-IPv4 | 4.02% |
+---------------+------------+
| Embedded-Port | 1.07% |
+---------------+------------+
| ISATAP | 0% 0.00% |
+---------------+------------+
| Low-byte | 92.65% |
+---------------+------------+
| Byte-pattern | 1.20% |
+---------------+------------+
| Randomized | 0.59% |
+---------------+------------+

Table 4:

Figure 3: Measured mailserver addresses Mail Server Addresses

+--------------+------------+
| Address type | Percentage |
+--------------+------------+
| Low-byte | 70% 70.00% |
+--------------+------------+
| IPv4-based | 5% 5.00% |
+--------------+------------+
| SLAAC | 1% 1.00% |
+--------------+------------+
| Wordy | <1% <1.00% |
+--------------+------------+
| Randomized | <1% <1.00% |
+--------------+------------+
| Teredo | <1% <1.00% |
+--------------+------------+
| Other | <1% <1.00% |
+--------------+------------+

Table 5:

Figure 4: Measured router addresses Router Addresses
+---------------+------------+
| Address type | Percentage |
+---------------+------------+
| IEEE-based | 7.72% |
+---------------+------------+
| Embedded-IPv4 | 14.31% |
+---------------+------------+
| Embedded-Port | 0.21% |
+---------------+------------+
| ISATAP | 1.06% |
+---------------+------------+
| Randomized | 69.73% |
+---------------+------------+
| Low-byte | 6.23% |
+---------------+------------+
| Byte-pattern | 0.74% |
+---------------+------------+

Table 6:

Note that "ISATAP" stands for "Intra-Site
Automatic Tunnel Addressing Protocol".

Figure 5: Measured client addresses Client Addresses

It should be clear from these measurements that a very high
percentage of host and router addresses follow very specific
patterns.

Table 6

Figure 5 shows that while around 70% of clients observed in this
measurement appear to be using temporary addresses, there are still a significant amount exposing
number of clients still expose IEEE-based addresses, addresses and addresses
using embedded IPv4 (thus also revealing IPv4 addresses). Besides,
as noted in Section 3.1.1.3, temporary addresses are employed along
with stable IPv6 addresses; thus, hosts employing a temporary address
may still be the subject of address-scanning attacks that target
their stable address(es).

3.2. IPv6 Address Scanning of Remote Networks

While in IPv4 networks

Although attackers have been able to get away with
"brute force" scanning "brute-force"
address-scanning attacks in IPv4 networks (thanks to the reduced
search space), successfully performing a brute-force scan address-scanning
attack of an entire /64 network would be infeasible. As a result, it
is expected that attackers will leverage the IPv6 address patterns
discussed in Section 3.1 to reduce the IPv6 address search space.

IPv6 address scanning of remote area networks should consider an
additional factor not present for the IPv4 case: since the typical
IPv6 host subnet is a /64, scanning an entire /64 could, in theory, lead
to the creation of 2^64 entries in the Neighbor Cache of the last-hop
router. Unfortunately, a number of IPv6 implementations have been
found to be unable to properly handle a large number of entries in
the Neighbor Cache, and hence Cache; hence, these address-scan address-scanning attacks may have
the side effect of resulting in a Denial of Service Denial-of-Service (DoS) attack
[CPNI-IPv6] [RFC6583].

[RFC7421] discusses the "default" /64 boundary for host subnets, subnets and
the assumptions surrounding it. While there are reports of a handful
of sites
implementing host IPv6 subnets of size /112 or smaller to reduce concerns
about the above attack, such smaller subnets are likely to make address-based scanning
address-scanning attacks more feasible, in addition to encountering
the issues with non-/64 host subnets discussed in the
above draft. [RFC7421].

3.2.1. Reducing the subnet Subnet ID search space Search Space

When address scanning a remote network, consideration is required to
select which subnet IDs to choose. A typical site might have a /48
allocation, which would mean up to 65,000 or so host IPv6 /64 subnets to
be scanned.

However, in the same way the search space for the IID can be reduced,
we may also be able to reduce the subnet ID search space in a number
of ways, by guessing likely address plan schemes, schemes or using any
complementary clues that might exist from other sources or
observations. For example example, there are a number of documents available
online (e.g. (e.g., [RFC5375]) that provide recommendations for the
allocation of address space, which address various operational
considerations,
including: RIR including Regional Internet Registry (RIR) assignment
policy, ability to delegate reverse DNS zones to different servers,
ability to aggregate routes efficiently, address space preservation,
ability to delegate address assignment within the organization,
ability to add allocate add/allocate new sites/prefixes to existing entities
without updating ACLs, Access Control Lists (ACLs), and ability to de-
aggregate and advertise sub-spaces subspaces via various AS Autonomous System (AS)
interfaces.

Address plans might include use of subnets which: that:

o Run from low ID upwards, e.g. e.g., 2001:db8:0::/64, 2001:db8:1::/64,
etc.

o Use building numbers, in hex hexadecimal or decimal form.

o Use VLAN Virtual Local Area Network (VLAN) numbers.

o Use an IPv4 subnet number in a dual-stack target, e.g. e.g., a site
with a /16 for IPv4 might use /24 subnets, and the IPv6 address
plan may
re-use reuse the third byte of the IPv4 address as the IPv6
subnet ID.

o Use the service "colour", "color", as defined for service-based prefix
colouring,
coloring, or semantic prefixes. For example, a site using a
specific colouring coloring for a specific service such as VoIP Voice over IP
(VoIP) may reduce the subnet ID search space for those devices.

The net effect is that the address space of an organization may be
highly structured, and allocations of individual elements within this
structure may be predictable once other elements are known.

In general, any subnet ID address plan may convey information, or be
based on known information, which may in turn be of advantage to an
attacker.

3.3. IPv6 Address Scanning of Local Networks

IPv6 address scanning in Local Area Networks (LANs) could be
considered, to some extent, a completely different problem than that
of scanning a remote IPv6 network. The main difference is that use
of link-local multicast addresses can relieve the attacker of
searching for unicast addresses in a large IPv6 address space.

NOTE:
While a number of other network reconnaissance vectors (such as
network snooping, leveraging Neighbor Discovery traffic, etc.) are
available when scanning a local network, this section focuses only
on address-scanning attacks (a la "ping sweep").

An attacker can simply send probe packets to the all-nodes link-local
multicast address (ff02::1), such that responses are elicited from
all local nodes.

Since Windows systems (Vista, 7, etc.) do not respond to ICMPv6 Echo
Request messages sent to multicast addresses, IPv6 address-scanning
tools typically employ a number of additional probe packets to elicit
responses from all the local nodes. For example, unrecognized IPv6
options of type 10xxxxxx elicit ICMPv6 Internet Control Message Protocol
version 6 (ICMPv6) Parameter Problem, code 2, error messages.

Many address-scanning tools discover only IPv6 link-local addresses
(rather than e.g. than, e.g., the global addresses of the target systems):
since the probe packets are typically sent with the attacker's IPv6 link-
local
link-local address, the "victim" nodes send the response packets
using the IPv6 link-local address of the corresponding network
interface (as specified by the IPv6 address selection address-selection rules
[RFC6724]). However, sending multiple probe packets, with each
packet employing source addresses from different prefixes, typically
helps to overcome this limitation.

NOTE:
This technique is employed by the scan6 tool of the SI6 Network's
IPv6 Toolkit package [IPv6-Toolkit].

3.4. Existing IPv6 Address Scanning Address-Scanning Tools

3.4.1. Remote IPv6 Network Address Scanners

IPv4 address scanning address-scanning tools have traditionally carried out their task
for
by probing an entire address range (usually the entire address range of a
comprised by the target subnetwork). One might argue that the reason
for which we they have been able to get away with such somewhat
"rudimentary" techniques is that the scale or challenge of the task
is so small in the IPv4 world, world that a "brute-force" attack is "good
enough". However, the scale of the "address scanning" "address-scanning" task is so
large in
IPv6, IPv6 that attackers must be very creative to be "good
enough". Simply sweeping an entire /64 IPv6 subnet would just not be
feasible.

Many address scanning address-scanning tools such as nmap [nmap2012] do not even support sweeping an IPv6
address range. On the other hand, the alive6 tool from [THC-IPV6]
supports sweeping address ranges, thus being able to leverage some
patterns found in IPv6 addresses, such as the incremental addresses
resulting from some DHCPv6 setups. Finally, the scan6 tool from
[IPv6-Toolkit] supports sweeping address
ranges, ranges and can also leverage
all the address patterns described in Section 3.1 of this document.

Clearly, a limitation of many of the currently-available currently available tools for
IPv6 address scanning is that they lack of an appropriately tuned
"heuristics engine" that can help reduce the search space, such that
the problem of IPv6 address scanning becomes tractable.

It should be noted that IPv6 network monitoring and management tools
also need to build and maintain information about the hosts in their
network. Such systems can no longer scan internal systems in a
reasonable time to build a database of connected systems. Rather,
such systems will need more efficient approaches, e.g. e.g., by polling
network devices for data held about observed IP addresses, MAC
addresses, physical ports used, etc. Such an approach can also
enhance address accountability, by mapping IPv4 and IPv6 addresses to
observed MAC addresses. This of course implies that any access
control mechanisms for querying such network devices, e.g. e.g., community
strings for SNMP, should be set appropriately to avoid an attacker
being able to gather address information remotely.

3.4.2. Local IPv6 Network Address Scanners

There are a variety of publicly-available publicly available local IPv6 network address-
scanners:

o Current versions of nmap [nmap2012] [nmap2015] implement this functionality.

o THC's The Hacker's Choice (THC) IPv6 Attack Toolkit [THC-IPV6] includes
a tool (alive6) that implements this functionality.

o SI6 Network's IPv6 Toolkit [IPv6-Toolkit] includes a tool (scan6)
that implements this functionality.

3.5. Mitigations

IPv6 address-scanning attacks can be mitigated in a number of ways.
A non-exhaustive list of the possible mitigations includes:

o Employing [RFC7217] (stable, semantically opaque IIDs) in
replacement of addresses based on IEEE identifiers, such that any
address patterns are eliminated.

o Employing Intrusion Prevention Systems (IPS) (IPSs) at the perimeter,
such that address scanning attacks can be mitigated. perimeter.

o Enforce Enforcing IPv6 packet filtering where applicable (see e.g. (see, e.g.,
[RFC4890]).

o If Employing manually configured MAC addresses if virtual machines
are employed, employed and "resistance" to address
scanning address-scanning attacks is
deemed as desirable, manually-configured MAC
addresses can be employed, such that even if the virtual machines employ
IEEE-derived IIDs, they are generated from non-predictable MAC
addresses.

o When using DHCPv6, avoid Avoiding use of sequential addresses. addresses when using DHCPv6. Ideally,
the DHCPv6 server would allocate random addresses from a large
pool.
pool (see, e.g., [IIDS-DHCPv6]).

o Use Using the "default" /64 size IPv6 subnet prefixes.

o In general, avoid avoiding being predictable in the way addresses are
assigned.

It should be noted that some of the aforementioned mitigations are
operational, while others depend on the availability of specific
protocol features (such as [RFC7217]) on the corresponding nodes.

Additionally, while some resistance to address scanning address-scanning attacks is
generally desirable (particularly when lightweight mitigations are
available), there are scenarios in which mitigation of some address-
scanning vectors is unlikely to be a high-priority high priority (if at all
possible). And one should always remember that security by obscurity
is not a reasonable defence defense in itself; it may only be one (relatively
small) layer in a broader security environment.

Two of the techniques discussed in this document for local address-
scanning attacks are those that employ multicasted ICMPv6 Echo
Requests and multicasted IPv6 packets containing unsupported options
of type 10xxxxxx. These two vectors could be easily mitigated by
configuring nodes to not respond to multicasted ICMPv6 Echo Request Requests
(default on Windows systems), systems) and by updating the IPv6 specifications
(and/or possibly configuring local nodes) such that multicasted
packets never elicit ICMPv6 error messages (even if they contain
unsupported options of type 10xxxxxx).

[I-D.gont-6man-ipv6-smurf-amplifier] proposes

NOTE:
[SMURF-AMPLIFIER] proposed such an update to the IPv6
specifications.

In any case, when it comes to local networks, there are a variety of
network reconnaissance vectors. Therefore, even if address-scanning
vectors are were mitigated, an attacker could still rely on e.g. on, e.g.,
protocols employed for the so-called "opportunistic networking" (such
as mDNS
[RFC6762]), Multicast DNS (mDNS) [RFC6762]) or eventually rely on network
snooping as a last resort for network reconnaissance. There is
ongoing work in the IETF on extending mDNS, or at least DNS-based
service discovery, to work across a whole site, rather than in just a
single subnet, which will have associated security implications.

3.6. Conclusions

In the previous subsections, we have shown why a /64 host subnet may
be more vulnerable to address-based scanning than might intuitively
be thought and how an attacker might reduce the target search space
when performing an address-scanning attack.

We have described a number of mitigations against address-scanning
attacks, including the replacement of traditional SLAAC with stable
semantically opaque IIDs (which requires support from system
vendors). We have also offered some practical guidance in regard to
the principle of avoiding predictability in host addressing schemes.
Finally, examples of address-scanning approaches and tools are
discussed in the appendices.

While most early IPv6-enabled networks remain dual stack, they are
more likely to be scanned and attacked over IPv4 transport, and one
may argue that the IPv6-specific considerations discussed here are
not of an immediate concern. However, an early IPv6 deployment
within a dual-stack network may be seen by an attacker as a
potentially "easier" target if the implementation of security
policies is not as strict for IPv6 (for whatever reason). As
IPv6-only networks become more common, the above considerations will
be of much greater importance.

4. Leveraging the Domain Name System (DNS) for Network Reconnaissance

4.1. DNS Advertised Hosts

Any systems that are "published" in the DNS, e.g. MX mail relays, e.g., Mail Exchange (MX)
relays or web servers, will remain open to probing from the very fact
that their IPv6 addresses are publicly available. It is worth noting
that where the addresses used at a site follow specific patterns,
publishing just one address may lead to a threat an attack upon the other
hosts.
nodes.

Additionally, we note that publication of IPv6 addresses in the DNS
should not discourage the elimination of IPv6 address patterns: if
any address patterns are eliminated from addresses published in the
DNS, an attacker may have to rely on performing dictionary-based DNS
lookups in order to find all systems in a target network (which is
generally less reliable and more time/traffic consuming than mapping
nodes with predictable IPv6 addresses).

4.2. DNS Zone Transfers

A DNS zone transfer (DNS query type "AXFR") [RFC1034] [RFC1035] can
readily provide information about potential attack targets.
Restricting zone transfers is thus probably more important for IPv6,
even if it is already good practice to restrict them in the IPv4
world.

4.3. DNS Brute Forcing

Attackers may employ DNS brute-forcing techniques by testing for the
presence of DNS AAAA records against commonly used host names.

4.4. DNS Reverse Mappings

[van-Dijk] describes an interesting technique that employs DNS
reverse mappings for network reconnaissance. Essentially, the
attacker walks through the "ip6.arpa" zone looking up PTR records, in
the hopes of learning the IPv6 addresses of hosts in a given target
network (assuming that the reverse mappings have been configured, of
course). What is most interesting about this technique is that it
can greatly reduce the IPv6 address search space.

Basically, an attacker would walk the ip6.arpa zone corresponding to
a target network (e.g. (e.g., "0.8.0.0.8.b.d.0.1.0.0.2.ip6.arpa." for
"2001:db8:80::/48"), issuing queries for PTR records corresponding to
the domain names "0.0.8.0.0.8.b.d.0.1.0.0.2.ip6.arpa.",
"1.0.8.0.0.8.b.d.0.1.0.0.2.ip6.arpa.", etc. If, say, there were PTR
records for any hosts "starting" with the domain name
"0.0.8.0.0.8.b.d.0.1.0.0.2.ip6.arpa." (e.g., the ip6.arpa domain name
corresponding to the IPv6 address 2001:db8:80::1), the response would
contain an RCODE of 0 (no error). Otherwise, the response would
contain an RCODE of 4 (NXDOMAIN). As noted in [van-Dijk], this
technique allows for a tremendous reduction in the "IPv6 address"
search space.

[I-D.howard-isp-ip6rdns]

NOTE:
[IPv6-RDNS] analyzes different approaches and considerations for
ISPs in managing the ip6.arpa zone for IPv6 address space assigned
to many customers, which may affect the technique described in
this section.

5. Leveraging Local Name Resolution and Service Discovery Services

A number of protocols allow for unmanaged local name resolution and
service. For example, multicast DNS (mDNS) mDNS [RFC6762] and DNS Service Discovery (DNS-SD) (DNS-
SD) [RFC6763], or Link-Local Multicast Name Resolution (LLMNR)
[RFC4795], are examples of such protocols.

NOTE:
Besides the Graphical User Interfaces (GUIs) included in products
supporting such protocols, command-line tools such as mdns-scan
[mdns-scan] and mzclient [mzclient] can help discover IPv6 hosts
employing mDNS/DNS-SD.

6. Public Archives

Public mailing-list archives or Usenet news messages archives may
prove to be a useful channel for an attacker, since hostnames and/or
IPv6 addresses could be easily obtained by inspection of the (many)
"Received from:" or other header lines in the archived email or
Usenet news messages.

7. Application Participation

Peer-to-peer applications often include some centralized server which that
coordinates the transfer of data between peers. For example,
BitTorrent [BitTorrent] builds swarms of nodes that exchange chunks
of files, with a tracker passing information about peers with
available chunks of data between the peers. Such applications may
offer an attacker a source of peer addresses to probe.

8. Inspection of the IPv6 Neighbor Cache and Routing Table

Information about other systems connected to the local network might
be readily available from the Neighbor Cache [RFC4861] and/or the
routing table of any system connected to such network. SAVI Source
Address Validation Improvement (SAVI) [RFC6620] also builds a cache
of IPv6 and link-layer addresses (without actively participating in
the Neighbor Discovery packet
exchange), exchange) and hence is another source
of similar information.

These data structures could be inspected either via either "login" access or
via
SNMP. While this requirement may limit the applicability of this
technique, there are a number of scenarios in which this technique
might be of use. For example, security audit tools might be provided
with the necessary credentials such that the Neighbor Cache and the
routing table of all systems for which the tool has "login" or SNMP
access can be automatically gleaned. On the other hand, IPv6 worms
[V6-WORMS] could leverage this technique for the purpose of spreading
on the local network, since they will typically have access to the
Neighbor Cache and routing table of an infected system.

Section 2.5.1.4 of [I-D.ietf-opsec-v6] [OPSEC-IPv6] discusses additional considerations
for the inspection of the IPv6 Neighbor Cache.

9. Inspection of System Configuration and Log Files

Nodes are generally configured with the addresses of other important
local computers, such as email servers, local file servers, web proxy
servers, recursive DNS servers, etc. The /etc/hosts file in UNIX,
SSH UNIX-
like systems, Secure Shell (SSH) known_hosts files, or the Microsoft
Windows registry are just some examples of places where interesting
information about such systems might be found.

Additionally, system log files (including web server logs, etc.) may
also prove to be a useful channel source for an attacker.

While the required credentials to access the aforementioned
configuration and log files may limit the applicability of this
technique, there are a number of scenarios in which this technique
might be of use. For example, security audit tools might be provided
with the necessary credentials such that these files can be
automatically accessed. On the other hand, IPv6 worms could leverage
this technique for the purpose of spreading on the local network,
since they will typically have access to these files on an infected
system [V6-WORMS].

10. Gleaning Information from Routing Protocols

Some organizational IPv6 networks employ routing protocols to
dynamically maintain routing information. In such an environment, a
local attacker could become a passive listener of the routing
protocol, to determine other valid subnets/prefixes and some router
addresses within that organization [V6-WORMS].

11. Gleaning Information from IP Flow Information Export (IPFIX)

IPFIX [RFC7012] can aggregate the flows by source addresses, addresses and hence
may be leveraged for obtaining a list of "active" IPv6 addresses.
Additional discussion of IPFIX can be found in Section 2.5.1.2 of [I-D.ietf-opsec-v6].
[OPSEC-IPv6].

12. Obtaining Network Information with traceroute6

IPv6 traceroute [traceroute6] and similar tools (such as path6 from
[IPv6-Toolkit]) can be employed to find router addresses and valid
network prefixes.

13. Gleaning Information from Network Devices Using SNMP

SNMP can be leveraged to obtain information from a number of data
structures such as the Neighbor Cache [RFC4861], the routing table,
and the SAVI [RFC6620] cache of IPv6 and link-layer addresses. SNMP
access should be secured, such that unauthorized access to the
aforementioned information is prevented.

14. Obtaining Network Information via Traffic Snooping

Snooping network traffic can help in discovering active nodes in a
number of ways. Firstly, each captured packet will reveal the source
and destination of the packet. Secondly, the captured traffic may
correspond to network protocols that transfer information such as
host or router addresses, network topology information, etc.

15. Conclusions

In this document we have discussed issues around host-based scanning
of IPv6 networks. We have shown why a /64 host subnet may be more
vulnerable to address-based scanning that might intuitively be
thought, and how an attacker might reduce the target search space
when scanning.

We have described a number of mitigations against host-based
scanning, including the replacement of traditional SLAAC with stable
semantically-opaque IIDs (which will require support from system
vendors). We have also offered some practical guidance, around the
principle of avoiding having predictability in host addressing
schemes. Finally, examples of scanning approaches and tools are
discussed in the Appendices.

While most early IPv6-enabled networks remain dual-stack, they are
more likely to be scanned and attacked over IPv4 transport, and one
may argue that the IPv6-specific considerations discussed here are
not of an immediate concern. However, an early IPv6 deployment
within a dual-stack network may be seen by an attacker as a
potentially "easier" target, if the implementation of security
policies are not as strict for IPv6 (for whatever reason). As and
when IPv6-only networks become more common, the considerations in
this document will be of much greater importance.

16. 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.

17. Security Considerations

This Security Considerations

This document explores the topic of Network Reconnaissance network reconnaissance in IPv6
networks. It analyzes the feasibility of address-scan address-scanning attacks in
IPv6 networks, networks and showing shows that the search space for such attacks is
typically much smaller than the one traditionally assumed (64 bits).

Additionally, it this document explores a plethora of other network
reconnaissance techniques, ranging from inspecting the IPv6 Network
Cache of an attacker-controlled system, system to gleaning information about
IPv6 addresses from public mailing-list archives or Peer-To-Peer Peer-to-Peer
(P2P) protocols.

We expect traditional address-scanning attacks to become more and
more elaborated (i.e., less "brute force"), and other network
reconnaissance techniques to be actively explored, as global
deployment of IPv6 increases and. and, more specifically, as more
IPv6-only devices are deployed.

18. Acknowledgements

The authors would like to thank Ray Hunter, who provided valuable
text that was readily incorporated into Section 3.2.1 of this
document.

The authors would like to thank (in alphabetical order) Alissa
Cooper, Spencer Dawkins, Stephen Farrell, Wesley George, Marc Heuse,
Ray Hunter, Barry Leiba, Libor Polcak, Alvaro Retana, Tomoyuki
Sahara, Jan Schaumann, Arturo Servin, and Eric Vyncke, for providing
valuable comments on earlier versions of this document.

Part of the contents of this document are based on the results of the
project "Security Assessment of the Internet Protocol version 6
(IPv6)" [CPNI-IPv6], carried out by Fernando Gont on behalf of the UK
Centre for the Protection of National Infrastructure (CPNI).

19.

16. References

19.1.

16.1. Normative References

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.

[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>.

[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>.

[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.

[RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS
SAVI: First-Come, First-Served Source Address Validation
Improvement for Locally Assigned IPv6 Addresses",
RFC 6620, DOI 10.17487/RFC6620, May 2012,
<http://www.rfc-editor.org/info/rfc6620>.

[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,
<http://www.rfc-editor.org/info/rfc6724>.

[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
DOI 10.17487/RFC4380, February 2006,
<http://www.rfc-editor.org/info/rfc4380>.

[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,
<http://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,
<http://www.rfc-editor.org/info/rfc4862>.

[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>.

[RFC7012] Claise, B., Ed. and B. Trammell, Ed., "Information Model
for IP Flow Information Export (IPFIX)", RFC 7012,
DOI 10.17487/RFC7012, September 2013,
<http://www.rfc-editor.org/info/rfc7012>.

[RFC7136] Carpenter, B.
<http://www.rfc-editor.org/info/rfc7012>.

[RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6
Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
February 2014, <http://www.rfc-editor.org/info/rfc7136>.

[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>.

16.2. Informative References

[BitTorrent]
Wikipedia, "BitTorrent", November 2015,
<https://en.wikipedia.org/w/
index.php?title=BitTorrent&oldid=690381343>.

[CPNI-IPv6]
Gont, F., "Security Assessment of the Internet Protocol
version 6 (IPv6)", UK Centre for the Protection of
National Infrastructure, (available on request).

[DEFAULT-IIDS]
Gont, F., Cooper, A., Thaler, D., and S. LIU,
"Recommendation on Stable IPv6 Interface Identifiers",
Work in Progress, draft-ietf-6man-default-iids-08, October
2015.

[Ford2013]
Ford, M., "IPv6 Address Analysis - Privacy In, Transition
Out", May 2013,
<http://www.internetsociety.org/blog/2013/05/
ipv6-address-analysis-privacy-transition-out>.

[Gont-DEEPSEC2011]
Gont, F., "Results of a Security Assessment of the
Internet Protocol version 6 (IPv6)", DEEPSEC
Conference, Vienna, Austria, November 2011,
<http://www.si6networks.com/presentations/deepsec2011/
fgont-deepsec2011-ipv6-security.pdf>.

[Gont-LACSEC2013]
Gont, F., "IPv6 Network Reconnaissance: Theory &
Practice", LACSEC Conference, Medellin, Colombia, May
2013, <http://www.si6networks.com/presentations/lacnic19/
lacsec2013-fgont-ipv6-network-reconnaissance.pdf>.

[IIDS-DHCPv6]
Gont, F. and S. Jiang, "Significance of IPv6
Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
February 2014, <http://www.rfc-editor.org/info/rfc7136>.

[RFC7217] Gont, F., LIU, "A Method for Generating Semantically
Opaque Interface Identifiers with Dynamic Host
Configuration Protocol for IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217, (DHCPv6)", Work in
Progress, draft-ietf-dhc-stable-privacy-addresses-02,
April 2015.

[IPV6-EXT-HEADERS]
Gont, F., Linkova, J., Chown, T., and S. LIU,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", Work in Progress,
draft-ietf-v6ops-ipv6-ehs-in-real-world-01, October 2015.

[IPv6-RDNS]
Howard, L., "Reverse DNS in IPv6 for Internet Service
Providers", Work in Progress, draft-ietf-dnsop-isp-
ip6rdns-00, October 2015.

[IPv6-Toolkit]
SI6 Networks, "SI6 Networks' IPv6 Toolkit",
<http://www.si6networks.com/tools/ipv6toolkit>.

[Malone2008]
Malone, D., "Observations of IPv6 Addresses", Passive and
Active Network Measurement (PAM 2008, LNCS 4979),
DOI 10.17487/RFC7217, 10.1007/978-3-540-79232-1_3, April 2014,
<http://www.rfc-editor.org/info/rfc7217>.

19.2. Informative References 2008,
<http://www.maths.tcd.ie/~dwmalone/p/addr-pam08.pdf>.

[mdns-scan]
Poettering, L., "mdns-scan(1) Manual Page",
<http://manpages.ubuntu.com/manpages/precise/man1/
mdns-scan.1.html>.

[mzclient]
Bockover, A., "Mono Zeroconf Project -- mzclient command-
line tool",
<http://www.mono-project.com/archived/monozeroconf/>.

[nmap2015]
Lyon, Gordon "Fyodor", "Nmap 7.00", November 2015,
<http://insecure.org>.

[OPSEC-IPv6]
Chittimaneni, K., Kaeo, M., and E. Vyncke, "Operational
Security Considerations for IPv6 Networks", Work in
Progress, draft-ietf-opsec-v6-07, September 2015.

[RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local
Multicast Name Resolution (LLMNR)", RFC 4795,
DOI 10.17487/RFC4795, January 2007,
<http://www.rfc-editor.org/info/rfc4795>.

[RFC4890] Davies, E. and J. Mohacsi, "Recommendations for Filtering
ICMPv6 Messages in Firewalls", RFC 4890,
DOI 10.17487/RFC4890, May 2007,
<http://www.rfc-editor.org/info/rfc4890>.

[RFC5157] Chown, T., "IPv6 Implications for Network Scanning",
RFC 5157, DOI 10.17487/RFC5157, March 2008,
<http://www.rfc-editor.org/info/rfc5157>.

[RFC5375] Van de Velde, G., Popoviciu, C., Chown, T., Bonness, O.,
and C. Hahn, "IPv6 Unicast Address Assignment
Considerations", RFC 5375, DOI 10.17487/RFC5375, December
2008, <http://www.rfc-editor.org/info/rfc5375>.

[RFC6583] Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
Neighbor Discovery Problems", RFC 6583,
DOI 10.17487/RFC6583, March 2012,
<http://www.rfc-editor.org/info/rfc6583>.

[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.

[I-D.gont-6man-ipv6-smurf-amplifier]
Gont, F. and W. Liu, "Security Implications of IPv6
Options of Type 10xxxxxx", draft-gont-6man-ipv6-smurf-
amplifier-03 (work in progress), March 2013.

[I-D.howard-isp-ip6rdns]
Howard, L., "Reverse DNS in IPv6 for Internet Service
Providers", draft-howard-isp-ip6rdns-08 (work in
progress), May 2015.

[RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S.,
Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit
Boundary in IPv6 Addressing", RFC 7421,
DOI 10.17487/RFC7421, January 2015,
<http://www.rfc-editor.org/info/rfc7421>.

[I-D.ietf-6man-default-iids]
Gont, F., Cooper, A., Thaler, D., and S. LIU,
"Recommendation on Stable IPv6 Interface Identifiers",
draft-ietf-6man-default-iids-07 (work in progress), August
2015.

[I-D.ietf-6man-ipv6-address-generation-privacy]

[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Privacy "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
draft-ietf-6man-ipv6-address-generation-privacy-07 (work
in progress), June 2015.

[I-D.ietf-dhc-stable-privacy-addresses]
RFC 7721, DOI 10.17487/RFC7721, December 2015,
<http://www.rfc-editor.org/info/rfc7721>.

[SMURF-AMPLIFIER]
Gont, F. and S. LIU, "A Method for Generating Semantically
Opaque Interface Identifiers with Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", draft-ietf-dhc-
stable-privacy-addresses-02 (work in progress), April
2015.

[I-D.ietf-opsec-v6]
Chittimaneni, K., Kaeo, M., and E. Vyncke, "Operational
Security Considerations for IPv6 Networks", draft-ietf-
opsec-v6-06 (work in progress), March 2015.

[CPNI-IPv6]
Gont, F., W. Liu, "Security Assessment Implications of the Internet Protocol
version 6 (IPv6)", UK Centre for the Protection IPv6
Options of
National Infrastructure, (available on request). Type 10xxxxxx", Work in Progress, draft-gont-
6man-ipv6-smurf-amplifier-03, March 2013.

[THC-IPV6]
"THC-IPV6", <http://www.thc.org/thc-ipv6/>.

[traceroute6]
FreeBSD, "FreeBSD System Manager's Manual: traceroute6(8)
manual page", August 2009, <https://www.freebsd.org/cgi/
man.cgi?query=traceroute6>.

[V6-WORMS]
Bellovin, S., Cheswick, B., and A. Keromytis, "Worm
propagation strategies in an IPv6 Internet", ;login:,
pages Vol. 31, No.
1, pp. 70-76, February 2006,
<https://www.cs.columbia.edu/~smb/papers/v6worms.pdf>.

[Malone2008]
Malone, D., "Observations of IPv6 Addresses", Passive and
Active Measurement Conference (PAM 2008, LNCS 4979), April
2008,
<http://www.maths.tcd.ie/~dwmalone/p/addr-pam08.pdf>.

[mdns-scan]
Poettering, L., "mdns-scan(1) manual page", 2012,
<http://manpages.ubuntu.com/manpages/precise/man1/
mdns-scan.1.html>.

[nmap2012]
Fyodor, , "nmap - Network exploration tool and security /
port scanner",

[van-Dijk]
van Dijk, P., "Finding v6 hosts by efficiently mapping
ip6.arpa", March 2012, <http://insecure.org>. <http://7bits.nl/blog/2012/03/26/
finding-v6-hosts-by-efficiently-mapping-ip6-arpa>.

[VBox2011]
VirtualBox, , "Oracle VM VirtualBox User Manual, version
4.1.2", Manual",
Version 4.1.2, August 2011, <http://www.virtualbox.org>.

[vmesx2011]
vmware, ,
VMware, "Setting a static MAC address for a virtual
NIC", vmware NIC
(219)", VMware Knowledge Base, August 2011,
<http://kb.vmware.com/selfservice/microsites/
search.do?language=en_US&cmd=displayKC&externalId=219>.

[vSphere] vmware, , VMware, "vSphere Networking", vSphere 5.5, Update 2,
September 2014, <http://pubs.vmware.com/vsphere-
55/topic/com.vmware.ICbase/PDF/
vsphere-esxi-vcenter-server-552-networking-guide.pdf>.

[traceroute6]
FreeBSD, , "FreeBSD System Manager's Manual:
traceroute6(8) manual page", 2009,
<https://www.freebsd.org/cgi/man.cgi?query=traceroute6>.

[Gont-DEEPSEC2011]
Gont, F., "Results of a Security Assessment of the
Internet Protocol version 6 (IPv6)", DEEPSEC 2011
Conference, Vienna, Austria, November 2011, 2011,
<http://www.si6networks.com/presentations/deepsec2011/
fgont-deepsec2011-ipv6-security.pdf>.

[Gont-LACSEC2013]
Gont, F., "IPv6 Network Reconnaissance: Theory &
Practice", LACSEC 2013 Conference, Medellin, Colombia,
May 2013, 2013,
<http://www.si6networks.com/presentations/lacnic19/
lacsec2013-fgont-ipv6-network-reconnaissance.pdf>.

[Ford2013]
Ford, M., "IPv6 Address Analysis - Privacy In, Transition
Out", 2013, <http://www.internetsociety.org/blog/2013/05/
ipv6-address-analysis-privacy-transition-out>.

[THC-IPV6]
"THC-IPV6", <http://www.thc.org/thc-ipv6/>.

[IPv6-Toolkit]
"SI6 Networks' IPv6 Toolkit",
<http://www.si6networks.com/tools/ipv6toolkit>.

[BitTorrent]
"BitTorrent", <http://en.wikipedia.org/wiki/BitTorrent>.

[van-Dijk]
van Dijk, P., "Finding v6 hosts by efficiently mapping
ip6.arpa", 2012, <http://7bits.nl/blog/2012/03/26/
finding-v6-hosts-by-efficiently-mapping-ip6-arpa>.

Appendix A. Implementation of a full-fledged Full-Fledged IPv6 address-scanning tool Address-Scanning Tool

This section describes the implementation of a full-fledged IPv6
address scanning
address-scanning tool. Appendix A.1 discusses the selection of host
probes. Appendix A.2 describes the implementation of an IPv6 address
scanner for local area networks. Appendix A.3 outlines ongoing work
on the
implementation of a general (i.e., non-local) IPv6 host address scanner.

A.1. Host-probing considerations Host-Probing Considerations

A number of factors should be considered when selecting the probe
packet types and the probing-rate probing rate for an IPv6 address scanning address-scanning tool.

Firstly, some hosts (or border firewalls) might be configured to
block or rate-limit rate limit some specific packet types. For example, it is
usual for host and router implementations to rate-limit ICMPv6 error
traffic. Additionally, some firewalls might be configured to block
or rate-limit rate limit incoming ICMPv6 echo request packets (see e.g. (see, e.g.,
[RFC4890]).

NOTE:
As noted earlier in this document, Windows systems simply do not
respond to ICMPv6 echo requests sent to multicast IPv6 addresses.

Among the possible probe types are:

o ICMPv6 Echo Request packets (meant to elicit ICMPv6 Echo Replies),

o TCP SYN segments (meant to elicit SYN/ACK or RST segments),

o TCP segments that do not contain the ACK bit set (meant to elicit
RST segments),

o UDP datagrams (meant to elicit a UDP application response or an
ICMPv6 Port Unreachable),

o IPv6 packets containing any suitable payload and an unrecognized
extension header (meant to elicit ICMPv6 Parameter Problem error
messages), or, or

o IPv6 packets containing any suitable payload and an unrecognized
option of type 10xxxxxx (such that a (meant to elicit an ICMPv6 Parameter
Problem error message is elicited) message).

Selecting an appropriate probe packet might help conceal the ongoing
attack, but it may also be actually necessary if host or network
configuration causes certain probe packets to be dropped.

Some address-scanning tools (such as scan6 of [IPv6-Toolkit])
incorporate support for IPv6 extension headers. In some cases, it might be desirable to insert
inserting some IPv6 extension headers
before in the actual payload, such that probe packet may allow
some filtering policies can or monitoring devices to be circumvented.
However, it may also result in the probe packets being dropped, as a
result of the widespread dropping of IPv6 packets that employ IPv6
extension headers (see [IPV6-EXT-HEADERS]).

Another factor to consider is the host-probing address-probing rate. Clearly, the
higher the rate, the smaller the amount of time required to perform
the attack. However, the probing-rate probing rate should not be too high, or
else:

1. the attack might cause network congestion, thus resulting in
packet loss loss.

2. the attack might hit rate-limiting, rate limiting, thus resulting in packet loss
loss.

3. the attack might reveal underlying problems in the Neighbor Discovery implementation,
implementations, thus leading to packet loss and possibly even
Denial of Service

Packet-loss Service.

Packet loss is undesirable, since it would mean that an "alive" node
might remain undetected as a result of a lost probe or response.
Such losses could be the result of congestion (in case the attacker
is scanning a target network at a rate higher than the target network
can handle), handle) or may be the result of rate-limiting as rate limiting (as it would be
typically the case if ICMPv6 is employed for the probe packets. packets).
Finally, as discussed in [CPNI-IPv6] and [RFC6583], some IPv6 router
implementations have been found to be unable to perform decent
resource management when faced with Neighbor Discovery traffic
involving a large number of local nodes. This essentially means that
regardless of the type of probe packets, an address scanning address-scanning attack
might result in a Denial of Service (DoS) DoS of the target network, with the same (or worse)
effects as that of network congestion or rate- rate limiting.

The specific rates at which each of these issues may come into play
vary from one scenario to another, another and depend on the type of deployed
routers/firewalls, configuration parameters, etc.

A.2. Implementation of an IPv6 local address-scanning tool Local Address-Scanning Tool

scan6 [IPv6-Toolkit] is prototype a full-fledged IPv6 local address scanning address-scanning
tool, which has proven to be effective and efficient for the
discovery of IPv6 hosts on a local network.

The scan6 tool operates (roughly) as follows:

1. The tool learns the local prefixes used for auto-configuration,
an autoconfiguration and
generates/configures one address for each local prefix (in
addition to a link-local address).

2. An ICMPv6 Echo Request message destined to the all-nodes on-link
multicast address (ff02::1) is sent with from each of the addresses
"configured" in the previous step. Because of the different
Source Addresses,
source addresses, each probe packet causes the victim nodes to
use different Source Addresses source addresses for the response packets (this
allows the tool to learn virtually all the addresses in use in
the local network segment).

3. The same procedure of the previous bullet is performed, but this
time with ICMPv6 packets that contain an unrecognized option of
type 10xxxxxx, such that ICMPv6 Parameter Problem error messages
are elicited. This allows the tool to discover e.g. discover, e.g., Windows
nodes, which otherwise do not respond to multicasted ICMPv6 Echo
Request messages.

4. Each time a new "alive" address is discovered, the corresponding
Interface-ID
IID is combined with all the local prefixes, and the resulting
addresses are probed (with unicasted packets). This can help to
discover other addresses in use on the local network segment,
since the same Interface ID IID is typically used with all the available
prefixes for the local network.

NOTE:
The aforementioned scheme can fail to discover some addresses for
some implementation. implementations. For example, Mac OS X employs IPv6
addresses embedding IEEE-identifiers IEEE identifiers (rather than "temporary
addresses") when responding to packets destined to a link-local
multicast address, sourced from an on-link prefix.

A.3. Implementation of a an IPv6 remote address-scanning tool Remote Address-Scanning Tool

An IPv6 remote address scanning tool, address-scanning tool could be implemented with the
following features:

o The tool can be instructed to target specific address ranges (e.g.
2001:db8::0-10:0-1000)
(e.g., 2001:db8::0-10:0-1000).

o The tool can be instructed to scan for SLAAC addresses of a
specific vendor, such that only addresses embedding the
corresponding IEEE OUIs are probed.

o The tool can be instructed to scan for SLAAC addresses that employ
a specific IEEE OUI. OUI or set of OUIs corresponding to a specific
vector.

o The tool can be instructed to discover virtual machines, such that
a given IPv6 prefix is only scanned for the address patterns
resulting from virtual machines.

o The tool can be instructed to scan for low-byte addresses.

o The tool can be instructed to scan for wordy-addresses, wordy addresses, in which
case the tool selects addresses based on a local dictionary.

o The tool can be instructed to scan for IPv6 addresses embedding
TCP/UDP service ports, in which case the tool selects addresses
based on a list of well-known service ports.

o The tool can be specified to scan an IPv4 address range in use at
the target network, such that only IPv4-based IPv6 addresses are
scanned.

The scan6 tool of [IPv6-Toolkit] implements all these techniques/
features. Furthermore, when given a target domain name or sample
IPv6 address for a given prefix, the tool will try to infer the
address pattern in use at the target network, and reduce the address
search space accordingly.

Acknowledgements

The authors would like to thank Ray Hunter, who provided valuable
text that was readily incorporated into Section 3.2.1 of this
document.

The authors would like to thank (in alphabetical order) Alissa
Cooper, Spencer Dawkins, Stephen Farrell, Wesley George, Marc Heuse,
Ray Hunter, Barry Leiba, Libor Polcak, Alvaro Retana, Tomoyuki
Sahara, Jan Schaumann, Arturo Servin, and Eric Vyncke for providing
valuable comments on earlier draft versions of this document.

Fernando Gont would like to thank Jan Zorz of Go6 Lab
<http://go6lab.si/> and Jared Mauch of NTT America for providing
access to systems and networks that were employed to perform
experiments and measurements that helped to improve this document.

Additionally, he would like to thank SixXS <https://www.sixxs.net>
for providing IPv6 connectivity.

Authors' Addresses

Fernando Gont
Huawei Technologies
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina

Phone: +54 11 4650 8472
Email: fgont@si6networks.com
URI: http://www.si6networks.com

Tim Chown
University of Southampton
Highfield
Southampton , Hampshire SO17 1BJ
United Kingdom

Email: tjc@ecs.soton.ac.uk