OPSEC                                                          E. Vyncke
Internet-Draft                                                     Cisco
Intended status: Informational                           K. Chittimaneni
Expires: October 11, 2021                                         WeWork
                                                                 M. Kaeo
                                                    Double Shot Security
                                                                  E. Rey
                                                                    ERNW
                                                           April 9, 2021


         Operational Security Considerations for IPv6 Networks
                         draft-ietf-opsec-v6-26

Abstract

   Knowledge and experience on how to operate IPv4 networks securely is
   available: whether it is an Internet Service Provider or an
   enterprise internal network.  However, IPv6 presents some new
   security challenges.  RFC 4942 describes security issues in the
   protocol, but network managers also need a more practical,
   operations-minded document to enumerate advantages and/or
   disadvantages of certain choices.

   This document analyzes the operational security issues associated
   with several types of network and proposes technical and procedural
   mitigation techniques.  This document is only applicable to managed
   networks, such as enterprise networks.  The recommendations in this
   document are not applicable to residential user cases, even in cases
   where a Service Provider may be managing the home gateway.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 11, 2021.




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Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Applicability Statement . . . . . . . . . . . . . . . . .   4
   2.  Generic Security Considerations . . . . . . . . . . . . . . .   4
     2.1.  Addressing Architecture . . . . . . . . . . . . . . . . .   4
       2.1.1.  Use of ULAs . . . . . . . . . . . . . . . . . . . . .   5
       2.1.2.  Point-to-Point Links  . . . . . . . . . . . . . . . .   5
       2.1.3.  Loopback Addresses  . . . . . . . . . . . . . . . . .   5
       2.1.4.  Stable Addresses  . . . . . . . . . . . . . . . . . .   5
       2.1.5.  Temporary Addresses for SLAAC . . . . . . . . . . . .   6
       2.1.6.  DHCP and DNS Considerations . . . . . . . . . . . . .   7
       2.1.7.  Using a /64 per host  . . . . . . . . . . . . . . . .   8
       2.1.8.  Privacy consideration of Addresses  . . . . . . . . .   8
     2.2.  Extension Headers . . . . . . . . . . . . . . . . . . . .   8
       2.2.1.  Order and Repetition of Extension Headers . . . . . .   9
       2.2.2.  Hop-by-Hop Options Header . . . . . . . . . . . . . .   9
       2.2.3.  Fragment Header . . . . . . . . . . . . . . . . . . .  10
       2.2.4.  IP Security Extension Header  . . . . . . . . . . . .  10
     2.3.  Link-Layer Security . . . . . . . . . . . . . . . . . . .  10
       2.3.1.  Neighbor Solicitation Rate-Limiting . . . . . . . . .  11
       2.3.2.  Router and Neighbor Advertisements Filtering  . . . .  11
       2.3.3.  Securing DHCP . . . . . . . . . . . . . . . . . . . .  13
       2.3.4.  3GPP Link-Layer Security  . . . . . . . . . . . . . .  13
       2.3.5.  Impact of Multicast Traffic . . . . . . . . . . . . .  14
       2.3.6.  SeND and CGA  . . . . . . . . . . . . . . . . . . . .  15
     2.4.  Control Plane Security  . . . . . . . . . . . . . . . . .  16
       2.4.1.  Control Protocols . . . . . . . . . . . . . . . . . .  17
       2.4.2.  Management Protocols  . . . . . . . . . . . . . . . .  17
       2.4.3.  Packet Exceptions . . . . . . . . . . . . . . . . . .  18
     2.5.  Routing Security  . . . . . . . . . . . . . . . . . . . .  19
       2.5.1.  BGP Security  . . . . . . . . . . . . . . . . . . . .  19
       2.5.2.  Authenticating OSPFv3 Neighbors . . . . . . . . . . .  19



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       2.5.3.  Securing Routing Updates  . . . . . . . . . . . . . .  20
       2.5.4.  Route Filtering . . . . . . . . . . . . . . . . . . .  20
     2.6.  Logging/Monitoring  . . . . . . . . . . . . . . . . . . .  21
       2.6.1.  Data Sources  . . . . . . . . . . . . . . . . . . . .  22
       2.6.2.  Use of Collected Data . . . . . . . . . . . . . . . .  26
       2.6.3.  Summary . . . . . . . . . . . . . . . . . . . . . . .  29
     2.7.  Transition/Coexistence Technologies . . . . . . . . . . .  29
       2.7.1.  Dual Stack  . . . . . . . . . . . . . . . . . . . . .  29
       2.7.2.  Encapsulation Mechanisms  . . . . . . . . . . . . . .  30
       2.7.3.  Translation Mechanisms  . . . . . . . . . . . . . . .  34
     2.8.  General Device Hardening  . . . . . . . . . . . . . . . .  36
   3.  Enterprises Specific Security Considerations  . . . . . . . .  37
     3.1.  External Security Considerations  . . . . . . . . . . . .  37
     3.2.  Internal Security Considerations  . . . . . . . . . . . .  38
   4.  Service Providers Security Considerations . . . . . . . . . .  39
     4.1.  BGP . . . . . . . . . . . . . . . . . . . . . . . . . . .  39
       4.1.1.  Remote Triggered Black Hole Filtering (RTBH)  . . . .  39
     4.2.  Transition/Coexistence Mechanism  . . . . . . . . . . . .  39
     4.3.  Lawful Intercept  . . . . . . . . . . . . . . . . . . . .  39
   5.  Residential Users Security Considerations . . . . . . . . . .  40
   6.  Further Reading . . . . . . . . . . . . . . . . . . . . . . .  41
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  41
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  41
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  41
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  41
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  56

1.  Introduction

   Running an IPv6 network is new for most operators not only because
   they are not yet used to large-scale IPv6 networks but also because
   there are subtle but critical and important differences between IPv4
   and IPv6, especially with respect to security.  For example, all
   layer-2 interactions are now done using Neighbor Discovery Protocol
   [RFC4861] rather than using Address Resolution Protocol [RFC0826].
   Also, there is no Network Address Port Translation (NAPT) defined in
   [RFC2663] for IPv6 even if [RFC6296] specifies a Network Prefix
   Translation for IPv6 (NPTv6) which is a 1-to-1 mapping of IPv6
   addresses.

   IPv6 networks are deployed using a variety of techniques, each of
   which have their own specific security concerns.

   This document complements [RFC4942] by listing all security issues
   when operating a network (including various transition technologies).
   It also provides more recent operational deployment experiences where
   warranted.



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1.1.  Applicability Statement

   This document is applicable to managed networks, i.e., when the
   network is operated by the user organization itself.  Indeed, many of
   the recommended mitigation techniques must be configured with
   detailed knowledge of the network (which are the default routers, the
   switch trunk ports, etc.).  This covers Service Provider (SP),
   enterprise networks and some knowledgeable-home-user-managed
   residential network.  This applicability statement especially applies
   to Section 2.3 and Section 2.5.4.

2.  Generic Security Considerations

2.1.  Addressing Architecture

   IPv6 address allocations and overall architecture are an important
   part of securing IPv6.  Initial designs, even if intended to be
   temporary, tend to last much longer than expected.  Although
   initially IPv6 was thought to make renumbering easy, in practice it
   may be extremely difficult to renumber without a proper IP Address
   Management (IPAM) system.  [RFC7010] introduces the mechanisms that
   could be utilized for IPv6 site renumbering and tries to cover most
   of the explicit issues and requirements associated with IPv6
   renumbering.

   A key task for a successful IPv6 deployment is to prepare an
   addressing plan.  Because an abundance of address space is available,
   structuring an address plan around both services and geographic
   locations allow address space to become a basis for more structured
   security policies to permit or deny services between geographic
   regions.  [RFC6177] documents some operational considerations of
   using different prefix sizes for address assignments at end sites.

   A common question is whether companies should use Provider
   Independent (PI) vs. Provider Allocated (PA) space [RFC7381], but
   from a security perspective there is little difference.  However, one
   aspect to keep in mind is who has administrative ownership of the
   address space and who is technically responsible if/when there is a
   need to enforce restrictions on routability of the space, e.g., due
   to malicious criminal activity originating from it.  Relying on PA
   address may also increase the perceived need for NPTv6 and therefore
   augmenting the complexity of the operations including the security
   operations.

   In [RFC7934], it is recommended that IPv6 network deployments provide
   multiple IPv6 addresses from each prefix to general-purpose hosts and
   it specifically does not recommend limiting a host to only one IPv6
   address per prefix.  It also recommends that the network give the



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   host the ability to use new addresses without requiring explicit
   requests (for example by using SLAAC).  Having by default multiple
   IPv6 addresses per interface is a major change compared to the unique
   IPv4 address per interface for hosts (secondary IPv4 addresses are
   not common); especially for audits (see section Section 2.6.2.3).

2.1.1.  Use of ULAs

   Unique Local Addresses (ULAs) [RFC4193] are intended for scenarios
   where interfaces are not globally reachable, despite being routed
   within a domain.  They formally have global scope, but [RFC4193]
   specifies that they must be filtered at domain boundaries.  ULAs are
   different from [RFC1918] addresses and have different use cases.  One
   use of ULA is described in [RFC4864], another one is for internal
   communication stability in networks where external connectivity may
   come and go (e.g., some ISPs provide ULAs in home networks connected
   via a cable modem).  It should further be kept in mind that ULA /48s
   from the fd00::/8 space (L=1) MUST be generated with a pseudo-random
   algorithm, per [RFC4193] section 3.2.1.

2.1.2.  Point-to-Point Links

   [RFC6164] in section 5.1 specifies the rationale of using /127 for
   inter-router point-to-point links; a /127 prevents the ping-pong
   attack between routers not correctly implementing [RFC4443] and also
   prevents a DoS attack on the neighbor cache.  The previous
   recommendation of [RFC3627] has been obsoleted and marked Historic by
   [RFC6547]).

   Some environments are also using link-local addressing for point-to-
   point links.  While this practice could further reduce the attack
   surface of infrastructure devices, the operational disadvantages also
   need to be carefully considered; see also [RFC7404].

2.1.3.  Loopback Addresses

   Many operators reserve a /64 block for all loopback addresses in
   their infrastructure and allocate a /128 out of this reserved /64
   prefix for each loopback interface.  This practice facilitates
   configuration of Access Control List (ACL) rules to enforce a
   security policy for those loopback addresses.

2.1.4.  Stable Addresses

   When considering how to assign stable addresses for nodes (either by
   static configuration or by pre-provisioned DHCPv6 lease
   Section 2.1.6), it is necessary to take into consideration the
   effectiveness of perimeter security in a given environment.



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   There is a trade-off between ease of operation (where some portions
   of the IPv6 address could be easily recognizable for operational
   debugging and troubleshooting) versus the risk of trivial scanning
   used for reconnaissance.  [SCANNING] shows that there are
   scientifically based mechanisms that make scanning for IPv6 reachable
   nodes more feasible than expected; see also [RFC7707].

   Stable addresses also allow easy enforcement of a security policy at
   the perimeter based on IPv6 addresses.  [RFC8520] is a mechanism
   where the perimeter defense can retrieve security policy template
   based on the type of internal device.

   The use of well-known IPv6 addresses (such as ff02::1 for all link-
   local nodes) or the use of commonly repeated addresses could make it
   easy to figure out which devices are name servers, routers, or other
   critical devices; even a simple traceroute will expose most of the
   routers on a path.  There are many scanning techniques possible and
   operators should not rely on the 'impossible to find because my
   address is random' paradigm (a.k.a. "security by obscurity"), even if
   it is common practice to have the stable addresses randomly
   distributed across /64 subnets and to always use DNS (as IPv6
   addresses are hard for human brains to remember).

   While in some environments obfuscating addresses could be considered
   an added benefit, it does not preclude enforcement of perimeter rules
   and that stable addresses follow some logical allocation scheme for
   ease of operation (as simplicity always helps security).

   Typical deployments will have a mix of stable and non-stable
   addresses; the stable addresses being either predictable (e.g., ::25
   for a mail server) or obfuscated (i.e., appearing as a random 64-bit
   number).

2.1.5.  Temporary Addresses for SLAAC

   Historically, stateless address autoconfiguration (SLAAC) makes up
   the globally unique IPv6 address based on an automatically generated
   64-bit interface identifier (IID) based on the EUI-64 MAC address
   combined with the /64 prefix (received in the Prefix Information
   Option (PIO) of the Router Advertisement (RA)).  The EUI-64 address
   is generated from the stable 48-bit MAC address and does not change
   even if the host moves to another network; this is of course bad for
   privacy as a host can be traced from network (home) to network
   (office or Wi-Fi in hotels).  [RFC8064] recommends against the use of
   EUI-64 addresses; and it must be noted that most host operating
   systems do not use EUI-64 addresses anymore and rely on either
   [RFC8981] or [RFC8064].




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   Randomly generating an interface ID, as described in [RFC8981], is
   part of SLAAC with so-called privacy extension addresses and is used
   to address some privacy concerns.  Privacy extension addresses,
   a.k.a., temporary addresses may help to mitigate the correlation of
   activities of a node within the same network and may also reduce the
   attack exposure window.  But using [RFC8981] privacy extension
   addresses might prevent the operator from building host specific
   access control lists (ACLs).  The [RFC8981] privacy extension
   addresses could also be used to obfuscate some malevolent activities
   and specific user attribution/accountability procedures should be put
   in place as described in Section 2.6.

   [RFC8064] combined with the address generation mechanism of [RFC7217]
   specifies another way to generate an address while still keeping the
   same IID for each network prefix; this allows SLAAC nodes to always
   have the same stable IPv6 address on a specific network while having
   different IPv6 addresses on different networks.

   In some specific use cases where user accountability is more
   important than user privacy, network operators may consider disabling
   SLAAC and relying only on DHCPv6; but not all operating systems
   support DHCPv6 so some hosts will not get any IPv6 connectivity.
   Disabling SLAAC and privacy extension addresses can be done for most
   operating systems by sending RA messages with a hint to get addresses
   via DHCPv6 by setting the M-bit but also disabling SLAAC by resetting
   all A-bits in all prefix information options.  However, attackers
   could still find ways to bypass this mechanism if not enforced at the
   switch/router level.

   However, in scenarios where anonymity is a strong desire (protecting
   user privacy is more important than user attribution), privacy
   extension addresses should be used.  When [RFC8064] is available, the
   stable privacy address is probably a good balance between privacy
   (among different networks) and security/user attribution (within a
   network).

2.1.6.  DHCP and DNS Considerations

   Some environments use DHCPv6 to provision addresses and other
   parameters in order to ensure auditability and traceability (see
   Section 2.6.1.5 for the limitations of DHCPv6 for auditability).

   A main security concern is the ability to detect and counteract rogue
   DHCP servers (Section 2.3.3).  It must be noted that as opposed to
   DHCPv4, DHCPv6 can lease several IPv6 addresses per client.  For
   DHCPv4, the lease is bound to the 'client identifier', which may
   contain a hardware address, or it may contain another type of
   identifier, such as a DNS name.  For DHCPv6, the lease is bound to



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   the client DHCP Unique ID (DUID), which may, or may not, be bound to
   the client link-layer address.  [RFC7824] describes the privacy
   issues associated with the use of DHCPv6 by Internet users.  The
   anonymity profiles [RFC7844] are designed for clients that wish to
   remain anonymous to the visited network.  [RFC7707] recommends that
   DHCPv6 servers issue addresses randomly from a large pool.

   While there are no fundamental differences with IPv4 and IPv6 DNS
   security concerns, there are specific considerations in DNS64
   [RFC6147] environments that need to be understood.  Specifically, the
   interactions and the potential of interference with DNSSEC
   ([RFC4033]) implementation need to be understood - these are pointed
   out in more detail in Section 2.7.3.2.

2.1.7.  Using a /64 per host

   An interesting approach is using a /64 per host as proposed in
   [RFC8273] especially in a shared environment.  This allows for easier
   user attribution (typically based on the host MAC address) as its /64
   prefix is stable even if applications within the host can change
   their IPv6 address within this /64 prefix.

   This can also be useful for the generation of ACLs once individual
   systems (e.g. admin workstations) have their own prefixes.

2.1.8.  Privacy consideration of Addresses

   Beside the security aspects of IPv6 addresses, there are also privacy
   considerations: mainly because they are of global scope and visible
   globally.  [RFC7721] goes into more detail on the privacy
   considerations for IPv6 addresses by comparing the manually
   configured IPv6 address, DHCPv6, and SLAAC.

2.2.  Extension Headers

   Extension headers are an important difference between IPv4 and IPv6.
   In IPv4-based packets, it's trivial to find the upper-layer protocol
   type and protocol header, while in IPv6 it is more complex since the
   extension header chain must be parsed completely (even if not
   processed) in order to find the upper-layer protocol header.  IANA
   has closed the existing empty "Next Header Types" registry to new
   entries and is redirecting its users to a new "IPv6 Extension Header
   Types" registry per [RFC7045].

   Extension headers have also become a very controversial topic since
   forwarding nodes that discard packets containing extension headers
   are known to cause connectivity failures and deployment problems
   [RFC7872].  Understanding the role of various extension headers is



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   important and this section enumerates the ones that need careful
   consideration.

   A clarification on how intermediate nodes should handle packets with
   existing or future extension headers is found in [RFC7045].  The
   uniform TLV format to be used for defining future extension headers
   is described in [RFC6564].  Sections 5.2 and 5.3 of [RFC8504] provide
   more information on the processing of extension headers by IPv6
   nodes.

   Vendors of filtering solutions and operations personnel responsible
   for implementing packet filtering rules should be aware that the
   'Next Header' field in an IPv6 header can both point to an IPv6
   extension header or to an upper layer protocol header.  This has to
   be considered when designing the user interface of filtering
   solutions or during the creation of filtering rule sets.

   There is IETF work in progress regarding filtering rules for those
   extension headers: [I-D.ietf-opsec-ipv6-eh-filtering] for transit
   routers.

2.2.1.  Order and Repetition of Extension Headers

   While [RFC8200] recommends the order and the maximum repetition of
   extension headers, there are still IPv6 implementations, at the time
   of writing, which support a non-recommended order of headers (such as
   ESP before routing) or an illegal repetition of headers (such as
   multiple routing headers).  The same applies for options contained in
   the extension headers (see [I-D.kampanakis-6man-ipv6-eh-parsing]).
   In some cases, it has led to nodes crashing when receiving or
   forwarding wrongly formatted packets.

   A firewall or edge device should be used to enforce the recommended
   order and the maximum occurrences of extension headers.

2.2.2.  Hop-by-Hop Options Header

   In the previous IPv6 specification [RFC2460], the hop-by-hop options
   header, when present in an IPv6 packet, forced all nodes to inspect
   and possibly process this header.  This enabled denial-of-service
   attacks as most, if not all, routers cannot process this type of
   packet in hardware but have to process these packets in software and
   hence compete with other software tasks, such as handling the control
   and management plane processing.

   Section 4.3 of the current Internet Standard for IPv6, [RFC8200], has
   taken this attack vector into account and made the processing of hop-




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   by-hop options headers by intermediate routers explicitly
   configurable.

2.2.3.  Fragment Header

   The fragment header is used by the source (and only the source) when
   it has to fragment packets.  [RFC7112] and section 4.5 of [RFC8200]
   explain why it is important that:

      Firewall and security devices should drop first fragments that do
      not contain the entire IPv6 header chain (including the transport-
      layer header).

      Destination nodes should discard first fragments that do not
      contain the entire IPv6 header chain (including the transport-
      layer header).

   If those requirements are not met, stateless filtering could be
   bypassed by a hostile party.  [RFC6980] applies a stricter rule to
   Neighbor Discovery Protocol (NDP) by enforcing the drop of fragmented
   NDP packets.  [RFC7113] describes how the RA-guard function described
   in [RFC6105] should behave in the presence of fragmented RA packets.

2.2.4.  IP Security Extension Header

   The IPsec [RFC4301] [RFC4301] extension headers (AH [RFC4302] and ESP
   [RFC4303]) are required if IPsec is to be utilized for network level
   security.  But IPsec is no longer required for normal IPv6 nodes: in
   the updated IPv6 Nodes Requirement standard [RFC8504], IPsec is a
   'SHOULD' and not a 'MUST' implement.

2.3.  Link-Layer Security

   IPv6 relies heavily on NDP [RFC4861] to perform a variety of link
   operations such as discovering other nodes on the link, resolving
   their link-layer addresses, and finding routers on the link.  If not
   secured, NDP is vulnerable to various attacks, such as router/
   neighbor message spoofing, redirect attacks, Duplicate Address
   Detection (DAD) DoS attacks, etc.  Many of these security threats to
   NDP have been documented in IPv6 ND Trust Models and Threats
   [RFC3756] and in [RFC6583].

   Most of the issues are only applicable when the attacker is on the
   same link but NDP also has security issues when the attacker is off-
   link, see the section below Section 2.3.1.






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2.3.1.  Neighbor Solicitation Rate-Limiting

   NDP can be vulnerable to remote denial of service (DoS) attacks; for
   example, when a router is forced to perform address resolution for a
   large number of unassigned addresses, i.e., a neighbor cache
   exhaustion attack.  This can keep new devices from joining the
   network or render the last-hop router ineffective due to high CPU
   usage.  Easy mitigative steps include rate-limiting Neighbor
   Solicitations, restricting the amount of state reserved for
   unresolved solicitations, and clever cache/timer management.

   [RFC6583] discusses the potential for off-link DoS in detail and
   suggests implementation improvements and operational mitigation
   techniques that may be used to mitigate or alleviate the impact of
   such attacks.  Here are some feasible mitigation options that can be
   employed by network operators today:

   o  Ingress filtering of unused addresses by ACL.  These require
      stable configuration of the addresses; for example, allocating the
      addresses out of a /120 and using a specific ACL to only allow
      traffic to this /120 (of course, the actual hosts are configured
      with a /64 prefix for the link).

   o  Tuning of NDP process (where supported), e.g., enforcing limits on
      data structures such as the number of neighbor cache entries in
      'incomplete' state.

   o  Using a /127 on point-to-point link per [RFC6164].

   o  Using link-local addresses only on links where there are only
      routers, see [RFC7404]

2.3.2.  Router and Neighbor Advertisements Filtering

2.3.2.1.  Router Advertisement Filtering

   Router Advertisement spoofing is a well-known on-link attack vector
   and has been extensively documented.  The presence of rogue RAs,
   either unintentional or malicious, can cause partial or complete
   failure of operation of hosts on an IPv6 link.  For example, a node
   can select an incorrect router address which can then be used for an
   on-path attack or the node can assume wrong prefixes to be used for
   SLAAC.  [RFC6104] summarizes the scenarios in which rogue RAs may be
   observed and presents a list of possible solutions to the problem.
   [RFC6105] (RA-Guard) describes a solution framework for the rogue RA
   problem where network segments are designed around switching devices
   that are capable of identifying invalid RAs and blocking them before
   the attack packets actually reach the target nodes.



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   However, several evasion techniques that circumvent the protection
   provided by RA-Guard have surfaced.  A key challenge to this
   mitigation technique is introduced by IPv6 fragmentation.  Attackers
   can conceal their attack by fragmenting their packets into multiple
   fragments such that the switching device that is responsible for
   blocking invalid RAs cannot find all the necessary information to
   perform packet filtering of the same packet.  [RFC7113] describes
   such evasion techniques and provides advice to RA-Guard implementers
   such that the aforementioned evasion vectors can be eliminated.

   Given that the IPv6 Fragmentation Header can be leveraged to
   circumvent some implementations of RA-Guard, [RFC6980] updates
   [RFC4861] such that use of the IPv6 Fragmentation Header is forbidden
   in all Neighbor Discovery messages except "Certification Path
   Advertisement", thus allowing for simple and effective measures to
   counter fragmented NDP attacks.

2.3.2.2.  Neighbor Advertisement Filtering

   The Source Address Validation Improvements (SAVI) working group has
   worked on other ways to mitigate the effects of such attacks.
   [RFC7513] helps in creating bindings between a DHCPv4 [RFC2131]
   /DHCPv6 [RFC8415] assigned source IP address and a binding anchor
   [RFC7039] on a SAVI device.  Also, [RFC6620] describes how to glean
   similar bindings when DHCP is not used.  The bindings can be used to
   filter packets generated on the local link with forged source IP
   addresses.

2.3.2.3.  Host Isolation

   Isolating hosts for the NDP traffic can be done by using a /64 per
   host, refer to Section 2.1.7, as NDP is only relevant within a /64
   on-link prefix; 3GPP Section 2.3.4 uses a similar mechanism.

   A more drastic technique to prevent all NDP attacks is based on
   isolation of all hosts with specific configurations.  Hosts (i.e.,
   all nodes that are not routers) are unable to send data-link layer
   frames to other hosts, therefore, no host-to-host attacks can happen.
   This specific setup can be established on some switches or Wi-Fi
   access points.  This is not always feasible when hosts need to
   communicate with other hosts in the same subnet, e.g., for access to
   file shares.

2.3.2.4.  NDP Recommendations

   It is still recommended that RA-Guard and SAVI be employed as a first
   line of defense against common attack vectors including misconfigured
   hosts.  This recommendation also applies when DHCPv6 is used as RA



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   messages are used to discover the default router(s) and for on-link
   prefix determination.  This line of defense is most effective when
   incomplete fragments are dropped by routers and switches as described
   in Section 2.2.3.  The generated log should also be analyzed to
   identify and act on violations.  Network operators should be aware
   that RA-Guard and SAVI do not work or could even be harmful in
   specific network configurations (notably when there could be multiple
   routers).

   Enabling RA-Guard by default in Wi-Fi networks or enterprise campus
   networks should be strongly considered unless specific use cases such
   as the presence of devices Homenet devices emitting router
   advertisements preclude this.

2.3.3.  Securing DHCP

   Dynamic Host Configuration Protocol for IPv6 (DHCPv6), as described
   in [RFC8415], enables DHCP servers to pass configuration parameters
   such as IPv6 network addresses and other configuration information to
   IPv6 nodes such as a recursive DNS server.  DHCP plays an important
   role in most large networks by providing robust stateful
   configuration in the context of automated system provisioning.

   The two most common threats to DHCP clients come from malicious
   (a.k.a., rogue) or unintentionally misconfigured DHCP servers.  A
   malicious DHCP server is established with the intent of providing
   incorrect configuration information to the clients to cause a denial-
   of-service attack or to mount on path attack.  While unintentional, a
   misconfigured DHCP server can have the same impact.  Additional
   threats against DHCP are discussed in the security considerations
   section of [RFC8415].

   DHCPv6-Shield, [RFC7610], specifies a mechanism for protecting
   connected DHCPv6 clients against rogue DHCPv6 servers.  This
   mechanism is based on DHCPv6 packet-filtering at the layer-2 device,
   i.e., the administrator specifies the interfaces connected to DHCPv6
   servers.  However, extension headers could be leveraged to bypass
   DHCPv6-Shield unless [RFC7112] is enforced.

   It is recommended to use DHCPv6-Shield and to analyze the
   corresponding log messages.

2.3.4.  3GPP Link-Layer Security

   The 3GPP link is a point-to-point like link that has no link-layer
   address.  This implies there can only be an end host (the mobile
   hand-set) and the first-hop router (i.e., a GPRS Gateway Support Node
   (GGSN) or a Packet Gateway (PGW)) on that link.  The GGSN/PGW never



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   configures a non link-local address on the link using the advertised
   /64 prefix on it; see Section 2.1.7.  The advertised prefix must not
   be used for on-link determination.  There is no need for address
   resolution on the 3GPP link, since there are no link-layer addresses.
   Furthermore, the GGSN/PGW assigns a prefix that is unique within each
   3GPP link that uses IPv6 stateless address autoconfiguration.  This
   avoids the necessity to perform DAD at the network level for every
   address generated by the mobile host.  The GGSN/PGW always provides
   an IID to the cellular host for the purpose of configuring the link-
   local address and ensures the uniqueness of the IID on the link
   (i.e., no collisions between its own link-local address and the
   mobile host's address).

   The 3GPP link model itself mitigates most of the known NDP-related
   Denial-of-Service attacks.  In practice, the GGSN/PGW only needs to
   route all traffic to the mobile host that falls under the prefix
   assigned to it.  As there is also a single host on the 3GPP link,
   there is no need to defend that IPv6 address.

   See Section 5 of [RFC6459] for a more detailed discussion on the 3GPP
   link model, NDP on it and the address configuration details.  In some
   mobile networks, DHCPv6 and DHCP-PD are also used.

2.3.5.  Impact of Multicast Traffic

   IPv6 uses multicast extensively for signaling messages on the local
   link to avoid broadcast messages for on-the-wire efficiency.

   The use of multicast has some side effects on wireless networks, such
   as a negative impact on battery life of smartphones and other
   battery-operated devices that are connected to such networks.
   [RFC7772], [RFC6775] (for specific wireless networks) discuss methods
   to rate-limit RAs and other ND messages on wireless networks in order
   to address this issue.

   The use of link-layer multicast addresses (e.g., ff02::1 for the all
   nodes link-local multicast address) could also be misused for an
   amplification attack.  Imagine, a hostile node sending an ICMPv6
   ECHO_REQUEST to ff02::1 with a spoofed source address, then, all
   link-local nodes will reply with ICMPv6 ECHO_REPLY packets to the
   source address.  This could be a DoS attack for the address owner.
   This attack is purely local to the layer-2 network as packets with a
   link-local destination are never forwarded by an IPv6 router.

   This is the reason why large Wi-Fi network deployments limit the use
   of link-layer multicast either from or to the uplink of the Wi-Fi
   access point, i.e., Wi-Fi stations cannot send link-local multicast
   to their direct neighboring Wi-Fi stations.



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2.3.6.  SeND and CGA

   SEcure Neighbor Discovery (SeND), as described in [RFC3971], is a
   mechanism that was designed to secure ND messages.  This approach
   involves the use of new NDP options to carry public key-based
   signatures.  Cryptographically Generated Addresses (CGA), as
   described in [RFC3972], are used to ensure that the sender of a
   Neighbor Discovery message is the actual "owner" of the claimed IPv6
   address.  A new NDP option, the CGA option, was introduced and is
   used to carry the public key and associated parameters.  Another NDP
   option, the RSA Signature option, is used to protect all messages
   relating to neighbor and Router discovery.

   SeND protects against:

   o  Neighbor Solicitation/Advertisement Spoofing

   o  Neighbor Unreachability Detection Failure

   o  Duplicate Address Detection DoS Attack

   o  Router Solicitation and Advertisement Attacks

   o  Replay Attacks

   o  Neighbor Discovery DoS Attacks

   SeND does NOT:

   o  Protect statically configured addresses

   o  Protect addresses configured using fixed identifiers (i.e., EUI-
      64)

   o  Provide confidentiality for NDP communications

   o  Compensate for an unsecured link - SeND does not require that the
      addresses on the link and Neighbor Advertisements correspond.

   However, at this time and over a decade since their original
   specifications, CGA and SeND do not have support from widely deployed
   IPv6 devices; hence, their usefulness is limited and should not be
   relied upon.








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2.4.  Control Plane Security

   [RFC6192] defines the router control plane and provides detailed
   guidance to secure it for IPv4 and IPv6 networks.  This definition is
   repeated here for the reader's convenience.  Please note that the
   definition is completely protocol-version agnostic (most of this
   section applies to IPv6 in the same way as to IPv4).

   Preamble: IPv6 control plane security is vastly congruent with its
   IPv4 equivalent with the exception of OSPFv3 authentication
   (Section 2.4.1) and some packet exceptions (see Section 2.4.3) that
   are specific to IPv6.

   Modern router architecture design maintains a strict separation of
   forwarding and router control plane hardware and software.  The
   router control plane supports routing and management functions.  It
   is generally described as the router architecture hardware and
   software components for handling packets destined to the device
   itself, as well as, building and sending packets originated locally
   on the device.  The forwarding plane is typically described as the
   router architecture hardware and software components responsible for
   receiving a packet on an incoming interface, performing a lookup to
   identify the packet's IP next hop and best outgoing interface towards
   the destination, and forwarding the packet through the appropriate
   outgoing interface.

   While the forwarding plane is usually implemented in high-speed
   hardware, the control plane is implemented by a generic processor
   (referred to as the route processor (RP)) and cannot process packets
   at a high rate.  Hence, this processor can be attacked by flooding
   its input queue with more packets than it can process.  The control
   plane processor is then unable to process valid control packets and
   the router can lose OSPF or BGP adjacencies which can cause a severe
   network disruption.

   [RFC6192] provides detailed guidance to protect the router control
   plane in IPv6 networks.  The rest of this section contains simplified
   guidance.

   The mitigation techniques are:

   o  To drop non-legit or potentially harmful control packets before
      they are queued to the RP (this can be done by a forwarding plane
      ACL) and

   o  To rate-limit the remaining packets to a rate that the RP can
      sustain.  Protocol-specific protection should also be done (for
      example, a spoofed OSPFv3 packet could trigger the execution of



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      the Dijkstra algorithm, therefore, the frequency of Dijsktra
      calculations should be also rate-limited).

   This section will consider several classes of control packets:

   o  Control protocols: routing protocols: such as OSPFv3, BGP, RIPng,
      and by extension NDP and ICMP

   o  Management protocols: SSH, SNMP, NETCONF, RESTCONF, IPFIX, etc.

   o  Packet exceptions: normal data packets which requires a specific
      processing such as generating a packet-too-big ICMP message or
      processing the hop-by-hop options header.

2.4.1.  Control Protocols

   This class includes OSPFv3, BGP, NDP, ICMP.

   An ingress ACL to be applied on all the router interfaces for packets
   to be processed by the RP should be configured to:

   o  drop OSPFv3 (identified by Next-Header being 89) and RIPng
      (identified by UDP port 521) packets from a non link-local address
      (except for OSPFv3 virtual links)

   o  allow BGP (identified by TCP port 179) packets from all BGP
      neighbors and drop the others

   o  allow all ICMP packets (transit and to the router interfaces)

   Note: dropping OSPFv3 packets which are authenticated by IPsec could
   be impossible on some routers that are unable to parse the IPsec ESP
   or AH extension headers during ACL classification.

   Rate-limiting of the valid packets should be done, see also [RFC8541]
   for a side benefit for OSPv3.  The exact configuration will depend on
   the available resources of the router (CPU, TCAM, ...).

2.4.2.  Management Protocols

   This class includes: SSH, SNMP, RESTCONF, NETCONF, gRPC, syslog, NTP,
   etc.

   An ingress ACL to be applied on all the router interfaces (or at
   ingress interfaces of the security perimeter or by using specific
   features of the platform) should be configured for packets destined
   to the RP such as:




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   o  Drop packets destined to the routers except those belonging to
      protocols which are used (for example, permit TCP 22 and drop all
      others when only SSH is used);

   o  Drop packets where the source does not match the security policy,
      for example, if SSH connections should only be originated from the
      Network Operation Center (NOC), then the ACL should permit TCP
      port 22 packets only from the NOC prefix.

   Rate-limiting of valid packets should be done.  The exact
   configuration will depend on the available router resources.

2.4.3.  Packet Exceptions

   This class covers multiple cases where a data plane packet is punted
   to the route processor because it requires specific processing:

   o  generation of an ICMP packet-too-big message when a data plane
      packet cannot be forwarded because it is too large (required to
      discover the Path MTU);

   o  generation of an ICMP hop-limit-expired message when a data plane
      packet cannot be forwarded because its hop-limit field has reached
      0 (also used by the traceroute utility);

   o  generation of an ICMP destination-unreachable message when a data
      plane packet cannot be forwarded for any reason;

   o  processing of the hop-by-hop options header, new implementations
      follow section 4.3 of [RFC8200] where this processing is optional;

   o  or more specific to some router implementation: an oversized
      extension header chain which cannot be processed by the hardware
      and force the packet to be punted to the RP.

   On some routers, not everything can be done by the specialized data
   plane hardware which requires some packets to be 'punted' to the
   generic RP.  This could include for example the processing of a long
   extension header chain in order to apply an ACL based on layer-4
   information.  [RFC6980] and more generally [RFC7112] highlight the
   security implications of oversized extension header chains on routers
   and updates the original IPv6 specifications, [RFC2460], such that
   the first fragment of a packet is required to contain the entire IPv6
   header chain.  Those changes are incorporated in the IPv6 standard
   [RFC8200]

   An ingress ACL cannot mitigate a control plane attack using these
   packet exceptions.  The only protection for the RP is to rate-limit



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   those packet exceptions that are forwarded to the RP, this means that
   some data plane packets will be dropped without an ICMP message sent
   to the source which may delay Path MTU discovery and cause drops.

   In addition to limiting the rate of data plane packets queued to the
   RP, it is also important to rate-limit the generation of ICMP
   messages.  This is important both to preserve RP resources and also
   to prevent an amplification attack using the router as a reflector.
   It is worth noting that some platforms implement this rate-limiting
   in hardware.  Of course, a consequence of not generating an ICMP
   message will break some IPv6 mechanisms such as Path MTU discovery or
   a simple traceroute.

2.5.  Routing Security

   Preamble: IPv6 routing security is congruent with IPv4 routing
   security with the exception of OSPv3 neighbor authentication (see
   Section 2.5.2).

   Routing security in general can be broadly divided into three
   sections:

   1.  Authenticating neighbors/peers

   2.  Securing routing updates between peers

   3.  Route filtering

   [RFC5082] is also applicable to IPv6 and can ensure that routing
   protocol packets are coming from the local network; it must also be
   noted that in IPv6 all interior gateway protocols use link-local
   addresses.

   As for IPv4, it is recommended to enable a routing protocol only on
   interfaces where it is required.

2.5.1.  BGP Security

   As BGP is identical for IPv4 and IPv6 and as [RFC7454] covers all the
   security aspects for BGP in detail, [RFC7454] is also applicable to
   IPv6.

2.5.2.  Authenticating OSPFv3 Neighbors

   OSPFv3 can rely on IPsec to fulfill the authentication function.
   However, it should be noted that IPsec support is not standard on all
   routing platforms.  In some cases, this requires specialized hardware
   that offloads crypto over to dedicated ASICs or enhanced software



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   images (both of which often come with added financial cost) to
   provide such functionality.  An added detail is to determine whether
   OSPFv3 IPsec implementations use AH or ESP-Null for integrity
   protection.  In early implementations, all OSPFv3 IPsec
   configurations relied on AH since the details weren't specified in
   [RFC5340].  However, the document which specifically describes how
   IPsec should be implemented for OSPFv3 [RFC4552] specifically states
   that "ESP-Null MUST and AH MAY be implemented" since it follows the
   overall IPsec standards wording.  OSPFv3 can also use normal ESP to
   encrypt the OSPFv3 payload to provide confidentiality for the routing
   information.

   [RFC7166] changes OSPFv3 reliance on IPsec by appending an
   authentication trailer to the end of the OSPFv3 packets; it does not
   specifically authenticate the specific originator of an OSPFv3
   packet; rather, it allows a router to confirm that the packet has
   been issued by a router that had access to the shared authentication
   key.

   With all authentication mechanisms, operators should confirm that
   implementations can support re-keying mechanisms that do not cause
   outages.  There have been instances where any re-keying causes
   outages and therefore, the tradeoff between utilizing this
   functionality needs to be weighed against the protection it provides.

2.5.3.  Securing Routing Updates

   IPv6 initially mandated the provisioning of IPsec capability in all
   nodes.  However, in the updated IPv6 Nodes Requirement standard
   [RFC8504], IPsec is a 'SHOULD' and not a 'MUST' implement.
   Theoretically, it is possible that all communication between two IPv6
   nodes, especially routers exchanging routing information, is
   encrypted using IPsec.  In practice however, deploying IPsec is not
   always feasible given hardware and software limitations of the
   various platforms deployed.

   Many routing protocols support the use of cryptography to protect the
   routing updates, the use of this protection is recommended; [RFC8177]
   is a YANG data model key chains including the renewal.

2.5.4.  Route Filtering

   Route filtering policies will be different depending on whether they
   pertain to edge route filtering vs. internal route filtering.  At a
   minimum, IPv6 routing policy as it pertains to routing between
   different administrative domains should aim to maintain parity with
   IPv4 from a policy perspective, e.g.,




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   o  Filter internal-use, non-globally routable IPv6 addresses at the
      perimeter;

   o  Discard routes for bogon [CYMRU] and reserved space (see
      [RFC8190]);

   o  Configure ingress route filters that validate route origin, prefix
      ownership, etc. through the use of various routing databases,
      e.g., [RADB].  There is additional work being done in this area to
      formally validate the origin ASs of BGP announcements in
      [RFC8210].

   Some good guidance can be found at [RFC7454].

   A valid routing table can also be used to apply network ingress
   filtering (see [RFC2827]).

2.6.  Logging/Monitoring

   In order to perform forensic research in the cases of a security
   incident or detecting abnormal behavior, network operators should log
   multiple pieces of information.  In some cases, this requires a
   frequent poll of devices via a Network Management Station.

   This logging should include:

   o  logs of all applications using the network (including user space
      and kernel space) when available (for example web servers);

   o  data from IP Flow Information Export [RFC7011] also known as
      IPFIX;

   o  data from various SNMP MIBs [RFC4293] or YANG data via RESTCONF
      [RFC8040] or NETCONF [RFC6241];

   o  historical data of Neighbor Cache entries;

   o  stateful DHCPv6 [RFC8415] lease cache, especially when a relay
      agent [RFC6221] is used;

   o  Source Address Validation Improvement (SAVI) [RFC7039] events,
      especially the binding of an IPv6 address to a MAC address and a
      specific switch or router interface;

   o  RADIUS [RFC2866] accounting records.

   Please note that there are privacy issues or regulations related to
   how these logs are collected, stored, and safely discarded.



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   Operators are urged to check their country legislation (e.g., General
   Data Protection Regulation GDPR [GDPR] in the European Union).

   All those pieces of information can be used for:

   o  forensic (Section 2.6.2.1) investigations such as who did what and
      when?

   o  correlation (Section 2.6.2.3): which IP addresses were used by a
      specific node (assuming the use of privacy extensions addresses
      [RFC8981])

   o  inventory (Section 2.6.2.2): which IPv6 nodes are on my network?

   o  abnormal behavior detection (Section 2.6.2.4): unusual traffic
      patterns are often the symptoms of an abnormal behavior which is
      in turn a potential attack (denial-of-service, network scan, a
      node being part of a botnet, etc.)

2.6.1.  Data Sources

   This section lists the most important sources of data that are useful
   for operational security.

2.6.1.1.  Application Logs

   Those logs are usually text files where the remote IPv6 address is
   stored in clear text (not binary).  This can complicate the
   processing since one IPv6 address, for example 2001:db8::1 can be
   written in multiple ways, such as:

   o  2001:DB8::1 (in uppercase)

   o  2001:0db8::0001 (with leading 0)

   o  and many other ways including the reverse DNS mapping into a FQDN
      (which should not be trusted).

   [RFC5952] explains this problem in detail and recommends the use of a
   single canonical format.  This document recommends the use of
   canonical format [RFC5952] for IPv6 addresses in all possible cases.
   If the existing application cannot log using the canonical format,
   then it is recommended to use an external post-processing program in
   order to canonicalize all IPv6 addresses.

   For example, this perl script can be used:





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   <CODE BEGINS>
   #!/usr/bin/perl -w
   use strict ;
   use warnings ;
   use Socket ;
   use Socket6 ;

   my (@words, $word, $binary_address) ;

   ## go through the file one line at a time
   while (my $line = <STDIN>) {
     chomp $line;
     foreach my $word (split /[\s+]/, $line) {
       $binary_address = inet_pton AF_INET6, $word ;
       if ($binary_address) {
         print inet_ntop AF_INET6, $binary_address ;
       } else {
         print $word ;
       }
       print " " ;
     }
     print "\n" ;
   }
   <CODE ENDS>

2.6.1.2.  IP Flow Information Export by IPv6 Routers

   IPFIX [RFC7012] defines some data elements that are useful for
   security:

   o  in section 5.4 (IP Header fields): nextHeaderIPv6 and
      sourceIPv6Address;

   o  in section 5.6 (Sub-IP fields): sourceMacAddress.

   The IP version is the ipVersion element defined in [IANA-IPFIX].

   Moreover, IPFIX is very efficient in terms of data handling and
   transport.  It can also aggregate flows by a key such as
   sourceMacAddress in order to have aggregated data associated with a
   specific sourceMacAddress.  This memo recommends the use of IPFIX and
   aggregation on nextHeaderIPv6, sourceIPv6Address, and
   sourceMacAddress.








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2.6.1.3.  SNMP MIB and NETCONF/RESTCONF YANG Modules data by IPv6
          Routers

   RFC 4293 [RFC4293] defines a Management Information Base (MIB) for
   the two address families of IP.  This memo recommends the use of:

   o  ipIfStatsTable table which collects traffic counters per
      interface;

   o  ipNetToPhysicalTable table which is the content of the Neighbor
      cache, i.e., the mapping between IPv6 and data-link layer
      addresses.

   There are also YANG modules relating to the two IP addresses families
   and can be used with [RFC6241] and [RFC8040].  This memo recommends
   the use of:

   o  interfaces-state/interface/statistics from ietf-
      interfaces@2018-02-20.yang [RFC8343] which contains counters for
      interface .

   o  ipv6/neighbor from ietf-ip@2018-02-22.yang [RFC8344] which is the
      content of the Neighbor cache, i.e., the mapping between IPv6 and
      data-link layer addresses.

2.6.1.4.  Neighbor Cache of IPv6 Routers

   The neighbor cache of routers contains all mappings between IPv6
   addresses and data-link layer addresses.  There are multiple ways to
   collect the current entries in the Neighbor Cache, notably but not
   limited to:

   o  the SNMP MIB (Section 2.6.1.3) as explained above;

   o  using streaming telemetry or NETCONF [RFC6241] and [RFC8040] to
      collect the operational state of the neighbor cache;

   o  also, by connecting over a secure management channel (such as SSH)
      and explicitly requesting a neighbor cache dump via the Command
      Line Interface (CLI) or another monitoring mechanism.

   The neighbor cache is highly dynamic as mappings are added when a new
   IPv6 address appears on the network.  This could be quite frequently
   with privacy extension addresses [RFC8981] or when they are removed
   when the state goes from UNREACH to removed (the default time for a
   removal per Neighbor Unreachability Detection [RFC4861] algorithm is
   38 seconds for a host using Windows 7).  This means that the content
   of the neighbor cache must periodically be fetched at an interval



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   which does not exhaust the router resources and still provides
   valuable information (suggested value is 30 seconds but this should
   be verified in the actual deployment) and stored for later use.

   This is an important source of information because it is trivial (on
   a switch not using the SAVI [RFC7039] algorithm) to defeat the
   mapping between data-link layer address and IPv6 address.  Let us
   rephrase the previous statement: having access to the current and
   past content of the neighbor cache has a paramount value for the
   forensic and audit trail.

   When using one /64 per host (Section 2.1.7) or DHCP-PD, it is
   sufficient to keep the history of the allocated prefixes when
   combined with strict source address prefix enforcement on the routers
   and layer-2 switches to prevent IPv6 spoofing.

2.6.1.5.  Stateful DHCPv6 Lease

   In some networks, IPv6 addresses/prefixes are managed by a stateful
   DHCPv6 server [RFC8415] that leases IPv6 addresses/prefixes to
   clients.  It is indeed quite similar to DHCP for IPv4 so it can be
   tempting to use this DHCP lease file to discover the mapping between
   IPv6 addresses/prefixes and data-link layer addresses as is commonly
   used in IPv4 networking.

   It is not so easy in the IPv6 networks because not all nodes will use
   DHCPv6 (there are nodes which can only do stateless
   autoconfiguration) but also because DHCPv6 clients are identified not
   by their hardware-client address as in IPv4 but by a DHCP Unique ID
   (DUID) which can have several formats: some being the data-link layer
   address, some being data-link layer address prepended with time
   information, or even an opaque number which is useless for
   operational security.  Moreover, when the DUID is based on the data-
   link address, this address can be of any client interface (such as
   the wireless interface while the client actually uses its wired
   interface to connect to the network).

   If a lightweight DHCP relay agent [RFC6221] is used in a layer-2
   switch, then the DHCP servers also receive the Interface-ID
   information which could be saved in order to identify the interface
   on which the switch received a specific leased IPv6 address.  Also,
   if a 'normal' (not lightweight) relay agent adds the data-link layer
   address in the option for Relay Agent Remote-ID [RFC4649] or
   [RFC6939], then the DHCPv6 server can keep track of the data-link and
   leased IPv6 addresses.

   In short, the DHCPv6 lease file is less interesting than for IPv4
   networks.  If possible, it is recommended to use DHCPv6 servers that



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   keep the relayed data-link layer address in addition to the DUID in
   the lease file as those servers have the equivalent information to
   IPv4 DHCP servers.

   The mapping between data-link layer address and the IPv6 address can
   be secured by deploying switches implementing the SAVI [RFC7513]
   mechanisms.  Of course, this also requires that the data-link layer
   address is protected by using a layer-2 mechanism such as
   [IEEE-802.1X].

2.6.1.6.  RADIUS Accounting Log

   For interfaces where the user is authenticated via a RADIUS [RFC2866]
   server, and if RADIUS accounting is enabled, then the RADIUS server
   receives accounting Acct-Status-Type records at the start and at the
   end of the connection which include all IPv6 (and IPv4) addresses
   used by the user.  This technique can be used notably for Wi-Fi
   networks with Wi-Fi Protected Address (WPA) or any other IEEE 802.1X
   [IEEE-802.1X] wired interface on an Ethernet switch.

2.6.1.7.  Other Data Sources

   There are other data sources for log information that must be
   collected (as currently collected in IPv4 networks):

   o  historical mapping of IPv6 addresses to users of remote access
      VPN;

   o  historical mappings of MAC addresses to switch ports in a wired
      network.

2.6.2.  Use of Collected Data

   This section leverages the data collected as described before
   (Section 2.6.1) in order to achieve several security benefits.
   Section 9.1 of [RFC7934] contains more details about host tracking.

2.6.2.1.  Forensic and User Accountability

   The forensic use case is when the network operator must locate an
   IPv6 address that was present in the network at a certain time or is
   currently in the network.

   To locate an IPv6 address in an enterprise network where the operator
   has control over all resources, the source of information can be the
   neighbor cache, or, if not found, the DHCP lease file.  Then, the
   procedure is:




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   1.  Based on the IPv6 prefix of the IPv6 address, find the router(s)
       which is(are) used to reach this prefix (assuming that anti-
       spoofing mechanisms are used).

   2.  Based on this limited set of routers, on the incident time and on
       the IPv6 address, retrieve the data-link address from the live
       neighbor cache, from the historical neighbor cache data, or from
       SAVI events, or retrieve the data-link address from the DHCP
       lease file (Section 2.6.1.5).

   3.  Based on the data-link layer address, look-up the switch
       interface associated with the data-link layer address.  In the
       case of wireless LAN with RADIUS accounting (see
       Section 2.6.1.6), the RADIUS log has the mapping between the user
       identification and the MAC address.  If a Configuration
       Management Data Base (CMDB) is used, then it can be used to map
       the data-link layer address to a switch port.

   At the end of the process, the interface of the host originating, or
   the subscriber identity associated with, the activity in question has
   been determined.

   To identify the subscriber of an IPv6 address in a residential
   Internet Service Provider, the starting point is the DHCP-PD leased
   prefix covering the IPv6 address; this prefix can often be linked to
   a subscriber via the RADIUS log.  Alternatively, the Forwarding
   Information Base of the CMTS or BNG indicates the CPE of the
   subscriber and the RADIUS log can be used to retrieve the actual
   subscriber.

   More generally, a mix of the above techniques can be used in most, if
   not all, networks.

2.6.2.2.  Inventory

   RFC 7707 [RFC7707] describes the difficulties for an attacker to scan
   an IPv6 network due to the vast number of IPv6 addresses per link
   (and why in some cases it can still be done).  While the huge
   addressing space can sometimes be perceived as a 'protection', it
   also makes the inventory task difficult in an IPv6 network while it
   was trivial to do in an IPv4 network (a simple enumeration of all
   IPv4 addresses, followed by a ping and a TCP/UDP port scan).  Getting
   an inventory of all connected devices is of prime importance for a
   secure network operation.

   There are many ways to do an inventory of an IPv6 network.





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   The first technique is to use the IPFIX information and extract the
   list of all IPv6 source addresses to find all IPv6 nodes that sent
   packets through a router.  This is very efficient but, alas, will not
   discover silent nodes that never transmitted packets traversing the
   IPFIX target router.  Also, it must be noted that link-local
   addresses will never be discovered by this means.

   The second way is again to use the collected neighbor cache content
   to find all IPv6 addresses in the cache.  This process will also
   discover all link-local addresses.  See Section 2.6.1.4.

   Another way that works only for a local network, consists of sending
   a ICMP ECHO_REQUEST to the link-local multicast address ff02::1 which
   addresses all IPv6 nodes on the network.  All nodes should reply to
   this ECHO_REQUEST per [RFC4443].

   Other techniques involve obtaining data from DNS, parsing log files,
   leveraging service discovery such as mDNS [RFC6762] and [RFC6763].

   Enumerating DNS zones, especially looking at reverse DNS records and
   CNAMES, is another common method employed by various tools.  As
   already mentioned in [RFC7707], this allows an attacker to prune the
   IPv6 reverse DNS tree, and hence enumerate it in a feasible time.
   Furthermore, authoritative servers that allow zone transfers (AXFR)
   may be a further information source.

2.6.2.3.  Correlation

   In an IPv4 network, it is easy to correlate multiple logs, for
   example to find events related to a specific IPv4 address.  A simple
   Unix grep command is enough to scan through multiple text-based files
   and extract all lines relevant to a specific IPv4 address.

   In an IPv6 network, this is slightly more difficult because different
   character strings can express the same IPv6 address.  Therefore, the
   simple Unix grep command cannot be used.  Moreover, an IPv6 node can
   have multiple IPv6 addresses.

   In order to do correlation in IPv6-related logs, it is advised to
   have all logs in a format with only canonical IPv6 addresses
   [RFC5952].  Then, the neighbor cache current (or historical) data set
   must be searched to find the data-link layer address of the IPv6
   address.  Then, the current and historical neighbor cache data sets
   must be searched for all IPv6 addresses associated to this data-link
   layer address to derive the search set.  The last step is to search
   in all log files (containing only IPv6 address in canonical format)
   for any IPv6 addresses in the search set.




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   Moreover, [RFC7934] recommends using multiple IPv6 addresses per
   prefix, so, the correlation must also be done among those multiple
   IPv6 addresses, for example by discovering in the NDP cache
   (Section 2.6.1.4) all IPv6 addresses associated with the same MAC
   address and interface.

2.6.2.4.  Abnormal Behavior Detection

   Abnormal behavior (such as network scanning, spamming, denial-of-
   service) can be detected in the same way as in an IPv4 network.

   o  Sudden increase of traffic detected by interface counter (SNMP) or
      by aggregated traffic from IPFIX records [RFC7012].

   o  Change in traffic pattern (number of connections per second,
      number of connections per host...) observed with the use of IPFIX
      [RFC7012].

2.6.3.  Summary

   While some data sources (IPFIX, MIB, switch CAM tables, logs, ...)
   used in IPv4 are also used in the secure operation of an IPv6
   network, the DHCPv6 lease file is less reliable and the neighbor
   cache is of prime importance.

   The fact that there are multiple ways to express the same IPv6
   address in a character string renders the use of filters mandatory
   when correlation must be done.

2.7.  Transition/Coexistence Technologies

   As it is expected that some networks will not run in a pure IPv6-only
   mode, the different transition mechanisms must be deployed and
   operated in a secure way.  This section proposes operational
   guidelines for the most known and deployed transition techniques.

2.7.1.  Dual Stack

   Dual stack is often the first deployment choice for network
   operators.  Dual stacking the network offers some advantages over
   other transition mechanisms.  Firstly, the impact on existing IPv4
   operations is reduced.  Secondly, in the absence of tunnels or
   address translation, the IPv4 and IPv6 traffic are native (easier to
   observe and secure) and should have the same network processing
   (network path, quality of service, ...).  Dual stack enables a
   gradual termination of the IPv4 operations when the IPv6 network is
   ready for prime time.  On the other hand, the operators have to
   manage two network stacks with the added complexities.



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   From an operational security perspective, this now means that the
   network operator has twice the exposure.  One needs to think about
   protecting both protocols now.  At a minimum, the IPv6 portion of a
   dual-stacked network should be consistent with IPv4 from a security
   policy point of view.  Typically, the following methods are employed
   to protect IPv4 networks at the edge or security perimeter:

   o  ACLs to permit or deny traffic;

   o  Firewalls with stateful packet inspection.

   It is recommended that these ACLs and/or firewalls be additionally
   configured to protect IPv6 communications.  The enforced IPv6
   security must be congruent with the IPv4 security policy, otherwise
   the attacker will use the protocol version having the more relaxed
   security policy.  Maintaining the congruence between security
   policies can be challenging (especially over time); it is recommended
   to use a firewall or an ACL manager that is dual-stack, i.e., a
   system that can apply a single ACL entry to a mixed group of IPv4 and
   IPv6 addresses.

   Also, given the end-to-end connectivity that IPv6 provides, it is
   recommended that hosts be fortified against threats.  General device
   hardening guidelines are provided in Section 2.8.

   For many years, all host operating systems have IPv6 enabled by
   default, so, it is possible even in an 'IPv4-only' network to attack
   layer-2 adjacent victims via their IPv6 link-local address or via a
   global IPv6 address when the attacker provides rogue RAs or a rogue
   DHCPv6 service.

   [RFC7123] discusses the security implications of native IPv6 support
   and IPv6 transition/coexistence technologies on "IPv4-only" networks
   and describes possible mitigations for the aforementioned issues.

2.7.2.  Encapsulation Mechanisms

   There are many tunnels used for specific use cases.  Except when
   protected by IPsec [RFC4301], all those tunnels have a couple of
   security issues as described in RFC 6169 [RFC6169];

   o  tunnel injection: a malevolent actor knowing a few pieces of
      information (for example the tunnel endpoints and the
      encapsulation protocol) can forge a packet which looks like a
      legitimate and valid encapsulated packet that will gladly be
      accepted by the destination tunnel endpoint.  This is a specific
      case of spoofing;




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   o  traffic interception: no confidentiality is provided by the tunnel
      protocols (without the use of IPsec or alternative encryption
      methods), therefore anybody on the tunnel path can intercept the
      traffic and have access to the clear-text IPv6 packet; combined
      with the absence of authentication, an on-path attack can also be
      mounted;

   o  service theft: as there is no authorization, even a non-authorized
      user can use a tunnel relay for free (this is a specific case of
      tunnel injection);

   o  reflection attack: another specific use case of tunnel injection
      where the attacker injects packets with an IPv4 destination
      address not matching the IPv6 address causing the first tunnel
      endpoint to re-encapsulate the packet to the destination... Hence,
      the final IPv4 destination will not see the original IPv4 address
      but only the IPv4 address of the relay router.

   o  bypassing security policy: if a firewall or an IPS is on the path
      of the tunnel, then it may neither inspect nor detect malevolent
      IPv6 traffic transmitted over the tunnel.

   To mitigate the bypassing of security policies, it is recommended to
   block all default configuration tunnels by denying IPv4 packets
   matching:

   o  IP protocol 41: this will block ISATAP (Section 2.7.2.2), 6to4
      (Section 2.7.2.7), 6rd (Section 2.7.2.3), as well as, 6in4
      (Section 2.7.2.1) tunnels;

   o  IP protocol 47: this will block GRE (Section 2.7.2.1) tunnels;

   o  UDP protocol 3544: this will block the default encapsulation of
      Teredo (Section 2.7.2.8) tunnels.

   Ingress filtering [RFC2827] should also be applied on all tunnel
   endpoints if applicable to prevent IPv6 address spoofing.

   As several of the tunnel techniques share the same encapsulation
   (i.e., IPv4 protocol 41) and embed the IPv4 address in the IPv6
   address, there are a set of well-known looping attacks described in
   RFC 6324 [RFC6324].  This RFC also proposes mitigation techniques.

2.7.2.1.  Site-to-Site Static Tunnels

   Site-to-site static tunnels are described in RFC 2529 [RFC2529] and
   in GRE [RFC2784].  As the IPv4 endpoints are statically configured
   and are not dynamic, they are slightly more secure (bi-directional



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   service theft is mostly impossible) but traffic interception and
   tunnel injection are still possible.  Therefore, the use of IPsec
   [RFC4301] in transport mode and protecting the encapsulated IPv4
   packets is recommended for those tunnels.  Alternatively, IPsec in
   tunnel mode can be used to transport IPv6 traffic over a non-trusted
   IPv4 network.

2.7.2.2.  ISATAP

   ISATAP tunnels [RFC5214] are mainly used within a single
   administrative domain and to connect a single IPv6 host to the IPv6
   network.  This often implies that those systems are usually managed
   by a single entity; therefore, audit trail and strict anti-spoofing
   are usually possible and this raises the overall security.

   Special care must be taken to avoid a looping attack by implementing
   the measures of [RFC6324] and [RFC6964].

   IPsec [RFC4301] in transport or tunnel mode can be used to secure the
   IPv4 ISATAP traffic to provide IPv6 traffic confidentiality and
   prevent service theft.

2.7.2.3.  6rd

   While 6rd tunnels share the same encapsulation as 6to4 tunnels
   (Section 2.7.2.7), they are designed to be used within a single SP
   domain, in other words, they are deployed in a more constrained
   environment than 6to4 tunnels and have few security issues other than
   lack of confidentiality.  The security considerations (Section 12) of
   [RFC5969] describes how to secure 6rd tunnels.

   IPsec [RFC4301] for the transported IPv6 traffic can be used if
   confidentiality is important.

2.7.2.4.  6PE, 6VPE, and LDPv6

   Organizations using MPLS in their core can also use 6PE [RFC4798] and
   6VPE [RFC4659] to enable IPv6 access over MPLS.  As 6PE and 6VPE are
   really similar to BGP/MPLS IP VPNs described in [RFC4364], the
   security properties of these networks are also similar to those
   described in [RFC4381].  They rely on:

   o  Address space, routing, and traffic separation with the help of
      VRFs (only applicable to 6VPE);

   o  Hiding the IPv4 core, hence removing all attacks against
      P-routers;




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   o  Securing the routing protocol between CE and PE; in the case of
      6PE and 6VPE, link-local addresses (see [RFC7404]) can be used and
      as these addresses cannot be reached from outside of the link, the
      security of 6PE and 6VPE is even higher than an IPv4 BGP/MPLS IP
      VPN.

   LDPv6 itself does not induce new risks, see also [RFC7552].

2.7.2.5.  DS-Lite

   DS-lite is also a translation mechanism and is therefore analyzed
   further (Section 2.7.3.3) in this document as it includes IPv4 NAPT.

2.7.2.6.  Mapping of Address and Port

   With the encapsulation and translation versions of mapping of Address
   and Port (MAP) (MAP-E [RFC7597] and MAP-T [RFC7599]), the access
   network is purely an IPv6 network and MAP protocols are used to
   provide IPv4 hosts on the subscriber network access to IPv4 hosts on
   the Internet.  The subscriber router does stateful operations in
   order to map all internal IPv4 addresses and layer-4 ports to the
   IPv4 address and the set of layer-4 ports received through MAP
   configuration process.  The SP equipment always does stateless
   operations (either decapsulation or stateless translation).
   Therefore, as opposed to Section 2.7.3.3, there is no state-
   exhaustion DoS attack against the SP equipment because there is no
   state and there is no operation caused by a new layer-4 connection
   (no logging operation).

   The SP MAP equipment should implement all the security considerations
   of [RFC7597]; notably, ensuring that the mapping of the IPv4 address
   and port are consistent with the configuration.  As MAP has a
   predictable IPv4 address and port mapping, the audit logs are easier
   to manage.

2.7.2.7.  6to4

   6to4 tunnels [RFC3056] require a public routable IPv4 address in
   order to work correctly.  They can be used to provide either single
   IPv6 host connectivity to the IPv6 Internet or multiple IPv6 networks
   connectivity to the IPv6 Internet.  The 6to4 relay was historically
   the anycast address defined in [RFC3068] which has been deprecated by
   [RFC7526] and is no longer used by recent Operating Systems.  Some
   security considerations are explained in [RFC3964].

   [RFC6343] points out that if an operator provides well-managed
   servers and relays for 6to4, non-encapsulated IPv6 packets will pass
   through well-defined points (the native IPv6 interfaces of those



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   servers and relays) at which security mechanisms may be applied.
   Client usage of 6to4 by default is now discouraged, and significant
   precautions are needed to avoid operational problems.

2.7.2.8.  Teredo

   Teredo tunnels [RFC4380] are mainly used in a residential environment
   because Teredo easily traverses an IPv4 NAPT device thanks to its UDP
   encapsulation.  Teredo tunnels connect a single host to the IPv6
   Internet.  Teredo shares the same issues as other tunnels: no
   authentication, no confidentiality, possible spoofing and reflection
   attacks.

   IPsec [RFC4301] for the transported IPv6 traffic is recommended.

   The biggest threat to Teredo is probably for an IPv4-only network as
   Teredo has been designed to easily traverse IPv4 NAT-PT devices which
   are quite often co-located with a stateful firewall.  Therefore, if
   the stateful IPv4 firewall allows unrestricted UDP outbound and
   accepts the return UDP traffic, then Teredo actually punches a hole
   in this firewall for all IPv6 traffic to the Internet and from the
   Internet.  While host policies can be deployed to block Teredo in an
   IPv4-only network in order to avoid this firewall bypass, it would be
   enough to block all UDP outbound traffic at the IPv4 firewall if
   deemed possible (of course, at least port 53 should be left open for
   DNS traffic, port 123 for NTP, port 443 for QUIC, port 500 for IKE,
   port 3478 for STUN, i.e., filter judiciously).

   Teredo is now hardly never used and no longer enabled by default in
   most environments, so, it is less of a threat, however, special
   consideration must be taken in case of devices with older or non-
   updated operating systems may be present and by default were running
   Teredo.

2.7.3.  Translation Mechanisms

   Translation mechanisms between IPv4 and IPv6 networks are alternate
   coexistence strategies while networks transition to IPv6.  While a
   framework is described in [RFC6144], the specific security
   considerations are documented with each individual mechanism.  For
   the most part, they specifically mention interference with IPsec or
   DNSSEC deployments, how to mitigate spoofed traffic, and what some
   effective filtering strategies may be.

   While not really a transition mechanism to IPv6, this section also
   includes the discussion about the use of heavy IPv4-to-IPv4 network
   address and port translation to prolong the life of IPv4-only
   networks.



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2.7.3.1.  Carrier-Grade NAT (CGN)

   Carrier-Grade NAT (CGN), also called NAT444 CGN or Large Scale NAT
   (LSN) or SP NAT is described in [RFC6264] and is utilized as an
   interim measure to extend the use of IPv4 in a large service provider
   network until the provider can deploy an effective IPv6 solution.
   [RFC6598] requested a specific IANA allocated /10 IPv4 address block
   to be used as address space shared by all access networks using CGN.
   This has been allocated as 100.64.0.0/10.

   Section 13 of [RFC6269] lists some specific security-related issues
   caused by large scale address sharing.  The Security Considerations
   section of [RFC6598] also lists some specific mitigation techniques
   for potential misuse of shared address space.  Some Law Enforcement
   Agencies have identified CGN as impeding their cyber-crime
   investigations (for example Europol press release on CGN
   [europol-cgn]).  Many translation techniques (NAT64, DS-lite, ...)
   have the same security issues as CGN when one part of the connection
   is IPv4-only.

   [RFC6302] has recommendations for Internet-facing servers to also log
   the source TCP or UDP ports of incoming connections in an attempt to
   help identify the users behind such a CGN.

   [RFC7422] suggests the use of deterministic address mapping in order
   to reduce logging requirements for CGN.  The idea is to have a known
   algorithm for mapping the internal subscriber to/from public TCP and
   UDP ports.

   [RFC6888] lists common requirements for CGNs.  [RFC6967] analyzes
   some solutions to enforce policies on misbehaving nodes when address
   sharing is used.  [RFC7857] also updates the NAT behavioral
   requirements.

2.7.3.2.  NAT64/DNS64 and 464XLAT

   Stateful NAT64 translation [RFC6146] allows IPv6-only clients to
   contact IPv4 servers using unicast UDP, TCP, or ICMP.  It can be used
   in conjunction with DNS64 [RFC6147], a mechanism which synthesizes
   AAAA records from existing A records.  There is also a stateless
   NAT64 [RFC7915], which has similar security aspects but with the
   added benefit of being stateless, so, less prone to a state
   exhaustion attack.

   The Security Consideration sections of [RFC6146] and [RFC6147] list
   the comprehensive issues.  A specific issue with the use of NAT64 is
   that it will interfere with most IPsec deployments unless UDP




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   encapsulation is used.  DNSSEC and DNS64 negatively interact, see
   section 3.1 of [RFC7050].

   Another translation mechanism relying on a combination of stateful
   and stateless translation, 464XLAT [RFC6877], can be used to do host
   local translation from IPv4 to IPv6 and a network provider
   translation from IPv6 to IPv4, i.e., giving IPv4-only application
   access to an IPv4-only server over an IPv6-only network. 464XLAT
   shares the same security considerations as NAT64 and DNS64, however
   it can be used without DNS64, avoiding the DNSSEC implications.

2.7.3.3.  DS-Lite

   Dual-Stack Lite (DS-Lite) [RFC6333] is a transition technique that
   enables a service provider to share IPv4 addresses among customers by
   combining two well-known technologies: IP in IP (IPv4-in-IPv6) and
   IPv4 NAPT.

   Security considerations with respect to DS-Lite mainly revolve around
   logging data, preventing DoS attacks from rogue devices (as the
   Address Family Translation Router (AFTR) [RFC6333] function is
   stateful) and restricting service offered by the AFTR only to
   registered customers.

   Section 11 of [RFC6333] and section 2 of [RFC7785] describe important
   security issues associated with this technology.

2.8.  General Device Hardening

   With almost all devices being IPv6 enabled by default and with many
   end points having IPv6 connectivity to the Internet, it is critical
   to also harden those devices against attacks over IPv6.

   The following guidelines should be used to ensure appropriate
   hardening of the device, be it an individual host, router, firewall,
   load-balancer, server, etc. device.

   o  Restrict device access to authorized individuals

   o  Monitor and audit access to the device

   o  Turn off any unused services on the end node

   o  Understand which IPv6 addresses are being used to source traffic
      and change defaults if necessary

   o  Use cryptographically protected protocols for device management if
      possible (SCP, SNMPv3, SSH, TLS, etc.)



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   o  Use host firewall capabilities to control traffic that gets
      processed by upper-layer protocols

   o  Use virus scanners to detect malicious programs

3.  Enterprises Specific Security Considerations

   Enterprises [RFC7381] generally have robust network security policies
   in place to protect existing IPv4 networks.  These policies have been
   distilled from years of experiential knowledge of securing IPv4
   networks.  At the very least, it is recommended that enterprise
   networks have parity between their security policies for both
   protocol versions.  This section also applies to the enterprise part
   of all SP networks, i.e., the part of the network where the SP
   employees are connected.

   Security considerations in the enterprise can be broadly categorized
   into two groups: External and Internal.

3.1.  External Security Considerations

   The external aspect deals with providing security at the edge or
   perimeter of the enterprise network where it meets the service
   provider's network.  This is commonly achieved by enforcing a
   security policy either by implementing dedicated firewalls with
   stateful packet inspection or a router with ACLs.  A common default
   IPv4 policy on firewalls that could easily be ported to IPv6 is to
   allow all traffic outbound while only allowing specific traffic, such
   as established sessions, inbound (see also [RFC6092]).  Section 3.2
   of [RFC7381] also provides similar recommendations.

   Here are a few more things that could enhance the default policy:

   o  Filter internal-use IPv6 addresses at the perimeter this will also
      mitigate the vulnerabilities listed in [RFC7359]

   o  Discard packets from and to bogon and reserved space, see also
      [CYMRU] and [RFC8190]

   o  Accept certain ICMPv6 messages to allow proper operation of ND and
      PMTUD, see also [RFC4890] or [REY_PF] for hosts

   o  Filter specific extension headers by accepting only the required
      ones (permit list approach) such as ESP, AH (not forgetting the
      required transport layers: ICMP, TCP, UDP, ...), where possible at
      the edge and possibly inside the perimeter; see also
      [I-D.ietf-opsec-ipv6-eh-filtering]




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   o  Filter packets having an illegal IPv6 headers chain at the
      perimeter (and if possible, inside the network as well), see
      Section 2.2

   o  Filter unneeded services at the perimeter

   o  Implement ingress and egress anti-spoofing in the forwarding and
      control planes, see [RFC2827] and [RFC3704]

   o  Implement appropriate rate-limiters and control-plane policers

   Having global IPv6 address on all the enterprises sites is different
   than in IPv4 where [RFC1918] addresses are often used internally and
   not routed over the Internet.  [RFC7359] and [WEBER_VPN] explain that
   without careful design, there could be IPv6 leakages from layer-3
   VPNs.

3.2.  Internal Security Considerations

   The internal aspect deals with providing security inside the
   perimeter of the network, including end hosts.  Internal networks of
   enterprises are often different: University campus, wireless guest
   access, ... so there is no "one size fits all" recommendation.

   The most significant concerns here are related to Neighbor Discovery.
   At the network level, it is recommended that all security
   considerations discussed in Section 2.3 be reviewed carefully and the
   recommendations be considered in-depth as well.  Section 4.1 of
   [RFC7381] also provides some recommendations.

   As mentioned in Section 2.7.2, care must be taken when running
   automated IPv6-in-IPv4 tunnels.

   When site-to-site VPNs are used it should be kept in mind that, given
   the global scope of IPv6 global addresses as opposed to the common
   use of IPv4 private address space [RFC1918], sites might be able to
   communicate with each other over the Internet even when the VPN
   mechanism is not available and hence no traffic encryption is
   performed and traffic could be injected from the Internet into the
   site, see [WEBER_VPN].  It is recommended to filter at Internet
   connection(s) packets having a source or destination address
   belonging to the site internal prefix(es); this should be done for
   ingress and egress traffic.

   Hosts need to be hardened directly through security policy to protect
   against security threats.  The host firewall default capabilities
   have to be clearly understood.  In some cases, 3rd party firewalls
   have no IPv6 support whereas the native firewall installed by default



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   has IPv6 support.  General device hardening guidelines are provided
   in Section 2.8.

   It should also be noted that many hosts still use IPv4 for
   transporting logs for RADIUS, DIAMETER, TACACS+, SYSLOG, etc.
   Operators cannot rely on an IPv6-only security policy to secure such
   protocols that are still using IPv4.

4.  Service Providers Security Considerations

4.1.  BGP

   The threats and mitigation techniques are identical between IPv4 and
   IPv6.  Broadly speaking they are:

   o  Authenticating the TCP session;

   o  TTL security (which becomes hop-limit security in IPv6) as
      [RFC5082];

   o  bogon AS filtering, see [CYMRU];

   o  Prefix filtering.

   These are explained in more detail in Section 2.5.  Also, the
   recommendations of [RFC7454] should be considered.

4.1.1.  Remote Triggered Black Hole Filtering (RTBH)

   RTBH [RFC5635] works identically in IPv4 and IPv6.  IANA has
   allocated the 100::/64 prefix to be used as the discard prefix
   [RFC6666].

4.2.  Transition/Coexistence Mechanism

   SPs will typically use transition mechanisms such as 6rd, 6PE, MAP,
   and NAT64 which have been analyzed in the transition and coexistence
   Section 2.7 section.

4.3.  Lawful Intercept

   The Lawful Intercept requirements are similar for IPv6 and IPv4
   architectures and will be subject to the laws enforced in different
   geographic regions.  The local issues with each jurisdiction can make
   this challenging and both corporate legal and privacy personnel
   should be involved in discussions pertaining to what information gets
   logged and with regard to the respective log retention policies for
   this information.



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   The target of interception will usually be a residential subscriber
   (e.g., his/her PPP session, physical line, or CPE MAC address).  With
   the absence of IPv6 NAT on the CPE, IPv6 has the possibility to allow
   for intercepting the traffic from a single host (i.e., a /128 target)
   rather than the whole set of hosts of a subscriber (which could be a
   /48, /60, or /64).

   In contrast, in mobile environments, since the 3GPP specifications
   allocate a /64 per device, it may be sufficient to intercept traffic
   from the /64 rather than specific /128's (since each time the device
   establishes a data connection it gets a new IID).

   A sample architecture which was written for informational purposes is
   found in [RFC3924].

5.  Residential Users Security Considerations

   The IETF Homenet working group is working on standards and guidelines
   for IPv6 residential networks; this obviously includes operational
   security considerations; but this is still work in progress.
   [RFC8520] is an interesting approach on how firewalls could retrieve
   and apply specific security policies to some residential devices.

   Some residential users have less experience and knowledge about
   security or networking.  As most of the recent hosts (e.g.,
   smartphones, tablets) have IPv6 enabled by default, IPv6 security is
   important for those users.  Even with an IPv4-only ISP, those users
   can get IPv6 Internet access with the help of Teredo
   (Section 2.7.2.8) tunnels.  Several peer-to-peer programs support
   IPv6 and those programs can initiate a Teredo tunnel through an IPv4
   residential gateway, with the consequence of making the internal host
   reachable from any IPv6 host on the Internet.  It is therefore
   recommended that all host security products (including personal
   firewalls) are configured with a dual-stack security policy.

   If the residential CPE has IPv6 connectivity, [RFC7084] defines the
   requirements of an IPv6 CPE and does not take a position on the
   debate of default IPv6 security policy as defined in [RFC6092]:

   o  outbound only: allowing all internally initiated connections and
      block all externally initiated ones, which is a common default
      security policy enforced by IPv4 Residential Gateway doing NAPT
      but it also breaks the end-to-end reachability promise of IPv6.
      [RFC6092] lists several recommendations to design such a CPE;

   o  open/transparent: allowing all internally and externally initiated
      connections, therefore restoring the end-to-end nature of the




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      Internet for IPv6 traffic but having a different security policy
      for IPv6 than for IPv4.

   [RFC6092] REC-49 states that a choice must be given to the user to
   select one of those two policies.

6.  Further Reading

   There are several documents that describe in more detail the security
   of an IPv6 network; these documents are not written by the IETF and
   some of them are dated but are listed here for the reader's
   convenience:

   1.  Guidelines for the Secure Deployment of IPv6 [NIST]

   2.  North American IPv6 Task Force Technology Report - IPv6 Security
       Technology Paper [NAv6TF_Security]

   3.  IPv6 Security [IPv6_Security_Book]

7.  Acknowledgements

   The authors would like to thank the following people for their useful
   comments: Mikael Abrahamsson, Fred Baker, Mustafa Suha Botsali,
   Mohamed Boucadair, Brian Carpenter, Tim Chown, Lorenzo Colitti,
   Markus de Bruen, Tobias Fiebig, Fernando Gont, Jeffry Handal, Lee
   Howard, Panos Kampanakis, Erik Kline, Jouni Korhonen, Warren Kumari,
   Ted Lemon, Mark Lentczner, Acee Lindem (and his detailed nits), Jen
   Linkova (and her detailed review), Gyan S.  Mishra, Jordi Palet, Bob
   Sleigh, Donald Smith, Tarko Tikan, Ole Troan, Bernie Volz (by
   alphabetical order).

8.  Security Considerations

   This memo attempts to give an overview of security considerations of
   operating an IPv6 network both for an IPv6-only network and for
   networks utilizing the most widely deployed IPv4/IPv6 coexistence
   strategies.

9.  References

9.1.  Normative References

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.




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9.2.  Informative References

   [CYMRU]    Team, C., "The Bogon Reference", Existing in 2021,
              <https://team-cymru.com/community-services/bogon-
              reference/>.

   [europol-cgn]
              Europol, "ARE YOU SHARING THE SAME IP ADDRESS AS A
              CRIMINAL? LAW ENFORCEMENT CALL FOR THE END OF CARRIER
              GRADE NAT (CGN) TO INCREASE ACCOUNTABILITY ONLINE",
              October 2017,
              <https://www.europol.europa.eu/newsroom/news/are-you-
              sharing-same-ip-address-criminal-law-enforcement-call-for-
              end-of-carrier-grade-nat-cgn-to-increase-accountability-
              online>.

   [GDPR]     Union, O. J. O. T. E., "Regulation (EU) 2016/679 of the
              European Parliament and of the Council of 27 April 2016 on
              the protection of natural persons with regard to the
              processing of personal data and on the free movement of
              such data, and repealing Directive 95/46/EC (General Data
              Protection Regulation)", April 2016,
              <https://eur-lex.europa.eu/eli/reg/2016/679/oj>.

   [I-D.ietf-opsec-ipv6-eh-filtering]
              Gont, F. and W. LIU, "Recommendations on the Filtering of
              IPv6 Packets Containing IPv6 Extension Headers at Transit
              Routers", draft-ietf-opsec-ipv6-eh-filtering-07 (work in
              progress), January 2021.

   [I-D.kampanakis-6man-ipv6-eh-parsing]
              Kampanakis, P., "Implementation Guidelines for parsing
              IPv6 Extension Headers", draft-kampanakis-6man-ipv6-eh-
              parsing-01 (work in progress), August 2014.

   [IANA-IPFIX]
              IANA, "IP Flow Information Export (IPFIX) Entities",
              <http://www.iana.org/assignments/ipfix>.

   [IEEE-802.1X]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks - Port-Based Network Access Control", IEEE Std
              802.1X-2010, February 2010.

   [IPv6_Security_Book]
              Hogg, S. and E. Vyncke, "IPv6 Security",
              ISBN 1-58705-594-5, Publisher CiscoPress, December 2008.




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   [NAv6TF_Security]
              Kaeo, M., Green, D., Bound, J., and Y. Pouffary, "North
              American IPv6 Task Force Technology Report - IPv6 Security
              Technology Paper", 2006,
              <http://www.ipv6forum.com/dl/white/
              NAv6TF_Security_Report.pdf>.

   [NIST]     Frankel, S., Graveman, R., Pearce, J., and M. Rooks,
              "Guidelines for the Secure Deployment of IPv6", 2010,
              <http://csrc.nist.gov/publications/nistpubs/800-119/
              sp800-119.pdf>.

   [RADB]     INC., M. N., "RADb The Internet Routing Registry",
              Existing in 2021, <https://www.radb.net/>.

   [REY_PF]   Rey, E., "Local Packet Filtering with IPv6", July 2017,
              <https://labs.ripe.net/Members/enno_rey/local-packet-
              filtering-with-ipv6>.

   [RFC0826]  Plummer, D., "An Ethernet Address Resolution Protocol: Or
              Converting Network Protocol Addresses to 48.bit Ethernet
              Address for Transmission on Ethernet Hardware", STD 37,
              RFC 826, DOI 10.17487/RFC0826, November 1982,
              <https://www.rfc-editor.org/info/rfc826>.

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <https://www.rfc-editor.org/info/rfc1918>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <https://www.rfc-editor.org/info/rfc2460>.

   [RFC2529]  Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
              Domains without Explicit Tunnels", RFC 2529,
              DOI 10.17487/RFC2529, March 1999,
              <https://www.rfc-editor.org/info/rfc2529>.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, DOI 10.17487/RFC2663, August 1999,
              <https://www.rfc-editor.org/info/rfc2663>.




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   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              DOI 10.17487/RFC2784, March 2000,
              <https://www.rfc-editor.org/info/rfc2784>.

   [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>.

   [RFC2866]  Rigney, C., "RADIUS Accounting", RFC 2866,
              DOI 10.17487/RFC2866, June 2000,
              <https://www.rfc-editor.org/info/rfc2866>.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February
              2001, <https://www.rfc-editor.org/info/rfc3056>.

   [RFC3068]  Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
              RFC 3068, DOI 10.17487/RFC3068, June 2001,
              <https://www.rfc-editor.org/info/rfc3068>.

   [RFC3627]  Savola, P., "Use of /127 Prefix Length Between Routers
              Considered Harmful", RFC 3627, DOI 10.17487/RFC3627,
              September 2003, <https://www.rfc-editor.org/info/rfc3627>.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
              2004, <https://www.rfc-editor.org/info/rfc3704>.

   [RFC3756]  Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
              Neighbor Discovery (ND) Trust Models and Threats",
              RFC 3756, DOI 10.17487/RFC3756, May 2004,
              <https://www.rfc-editor.org/info/rfc3756>.

   [RFC3924]  Baker, F., Foster, B., and C. Sharp, "Cisco Architecture
              for Lawful Intercept in IP Networks", RFC 3924,
              DOI 10.17487/RFC3924, October 2004,
              <https://www.rfc-editor.org/info/rfc3924>.

   [RFC3964]  Savola, P. and C. Patel, "Security Considerations for
              6to4", RFC 3964, DOI 10.17487/RFC3964, December 2004,
              <https://www.rfc-editor.org/info/rfc3964>.

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <https://www.rfc-editor.org/info/rfc3971>.



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   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, DOI 10.17487/RFC3972, March 2005,
              <https://www.rfc-editor.org/info/rfc3972>.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [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>.

   [RFC4293]  Routhier, S., Ed., "Management Information Base for the
              Internet Protocol (IP)", RFC 4293, DOI 10.17487/RFC4293,
              April 2006, <https://www.rfc-editor.org/info/rfc4293>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <https://www.rfc-editor.org/info/rfc4301>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,
              <https://www.rfc-editor.org/info/rfc4302>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

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

   [RFC4381]  Behringer, M., "Analysis of the Security of BGP/MPLS IP
              Virtual Private Networks (VPNs)", RFC 4381,
              DOI 10.17487/RFC4381, February 2006,
              <https://www.rfc-editor.org/info/rfc4381>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.



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   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

   [RFC4649]  Volz, B., "Dynamic Host Configuration Protocol for IPv6
              (DHCPv6) Relay Agent Remote-ID Option", RFC 4649,
              DOI 10.17487/RFC4649, August 2006,
              <https://www.rfc-editor.org/info/rfc4649>.

   [RFC4659]  De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
              "BGP-MPLS IP Virtual Private Network (VPN) Extension for
              IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006,
              <https://www.rfc-editor.org/info/rfc4659>.

   [RFC4798]  De Clercq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
              "Connecting IPv6 Islands over IPv4 MPLS Using IPv6
              Provider Edge Routers (6PE)", RFC 4798,
              DOI 10.17487/RFC4798, February 2007,
              <https://www.rfc-editor.org/info/rfc4798>.

   [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>.

   [RFC4864]  Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
              E. Klein, "Local Network Protection for IPv6", RFC 4864,
              DOI 10.17487/RFC4864, May 2007,
              <https://www.rfc-editor.org/info/rfc4864>.

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

   [RFC4942]  Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
              Co-existence Security Considerations", RFC 4942,
              DOI 10.17487/RFC4942, September 2007,
              <https://www.rfc-editor.org/info/rfc4942>.

   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
              Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
              <https://www.rfc-editor.org/info/rfc5082>.







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   [RFC5214]  Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
              Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
              DOI 10.17487/RFC5214, March 2008,
              <https://www.rfc-editor.org/info/rfc5214>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC5635]  Kumari, W. and D. McPherson, "Remote Triggered Black Hole
              Filtering with Unicast Reverse Path Forwarding (uRPF)",
              RFC 5635, DOI 10.17487/RFC5635, August 2009,
              <https://www.rfc-editor.org/info/rfc5635>.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952,
              DOI 10.17487/RFC5952, August 2010,
              <https://www.rfc-editor.org/info/rfc5952>.

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification",
              RFC 5969, DOI 10.17487/RFC5969, August 2010,
              <https://www.rfc-editor.org/info/rfc5969>.

   [RFC6092]  Woodyatt, J., Ed., "Recommended Simple Security
              Capabilities in Customer Premises Equipment (CPE) for
              Providing Residential IPv6 Internet Service", RFC 6092,
              DOI 10.17487/RFC6092, January 2011,
              <https://www.rfc-editor.org/info/rfc6092>.

   [RFC6104]  Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement
              Problem Statement", RFC 6104, DOI 10.17487/RFC6104,
              February 2011, <https://www.rfc-editor.org/info/rfc6104>.

   [RFC6105]  Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
              Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
              DOI 10.17487/RFC6105, February 2011,
              <https://www.rfc-editor.org/info/rfc6105>.

   [RFC6144]  Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation", RFC 6144, DOI 10.17487/RFC6144,
              April 2011, <https://www.rfc-editor.org/info/rfc6144>.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <https://www.rfc-editor.org/info/rfc6146>.




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   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              DOI 10.17487/RFC6147, April 2011,
              <https://www.rfc-editor.org/info/rfc6147>.

   [RFC6164]  Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,
              L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-
              Router Links", RFC 6164, DOI 10.17487/RFC6164, April 2011,
              <https://www.rfc-editor.org/info/rfc6164>.

   [RFC6169]  Krishnan, S., Thaler, D., and J. Hoagland, "Security
              Concerns with IP Tunneling", RFC 6169,
              DOI 10.17487/RFC6169, April 2011,
              <https://www.rfc-editor.org/info/rfc6169>.

   [RFC6177]  Narten, T., Huston, G., and L. Roberts, "IPv6 Address
              Assignment to End Sites", BCP 157, RFC 6177,
              DOI 10.17487/RFC6177, March 2011,
              <https://www.rfc-editor.org/info/rfc6177>.

   [RFC6192]  Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
              Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
              March 2011, <https://www.rfc-editor.org/info/rfc6192>.

   [RFC6221]  Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.
              Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221,
              DOI 10.17487/RFC6221, May 2011,
              <https://www.rfc-editor.org/info/rfc6221>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6264]  Jiang, S., Guo, D., and B. Carpenter, "An Incremental
              Carrier-Grade NAT (CGN) for IPv6 Transition", RFC 6264,
              DOI 10.17487/RFC6264, June 2011,
              <https://www.rfc-editor.org/info/rfc6264>.

   [RFC6269]  Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
              P. Roberts, "Issues with IP Address Sharing", RFC 6269,
              DOI 10.17487/RFC6269, June 2011,
              <https://www.rfc-editor.org/info/rfc6269>.

   [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>.



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   [RFC6302]  Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
              "Logging Recommendations for Internet-Facing Servers",
              BCP 162, RFC 6302, DOI 10.17487/RFC6302, June 2011,
              <https://www.rfc-editor.org/info/rfc6302>.

   [RFC6324]  Nakibly, G. and F. Templin, "Routing Loop Attack Using
              IPv6 Automatic Tunnels: Problem Statement and Proposed
              Mitigations", RFC 6324, DOI 10.17487/RFC6324, August 2011,
              <https://www.rfc-editor.org/info/rfc6324>.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
              <https://www.rfc-editor.org/info/rfc6333>.

   [RFC6343]  Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
              RFC 6343, DOI 10.17487/RFC6343, August 2011,
              <https://www.rfc-editor.org/info/rfc6343>.

   [RFC6459]  Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
              T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
              Partnership Project (3GPP) Evolved Packet System (EPS)",
              RFC 6459, DOI 10.17487/RFC6459, January 2012,
              <https://www.rfc-editor.org/info/rfc6459>.

   [RFC6547]  George, W., "RFC 3627 to Historic Status", RFC 6547,
              DOI 10.17487/RFC6547, February 2012,
              <https://www.rfc-editor.org/info/rfc6547>.

   [RFC6564]  Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
              M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
              RFC 6564, DOI 10.17487/RFC6564, April 2012,
              <https://www.rfc-editor.org/info/rfc6564>.

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

   [RFC6598]  Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
              M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
              Space", BCP 153, RFC 6598, DOI 10.17487/RFC6598, April
              2012, <https://www.rfc-editor.org/info/rfc6598>.








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   [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,
              <https://www.rfc-editor.org/info/rfc6620>.

   [RFC6666]  Hilliard, N. and D. Freedman, "A Discard Prefix for IPv6",
              RFC 6666, DOI 10.17487/RFC6666, August 2012,
              <https://www.rfc-editor.org/info/rfc6666>.

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

   [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>.

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <https://www.rfc-editor.org/info/rfc6775>.

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,
              <https://www.rfc-editor.org/info/rfc6877>.

   [RFC6888]  Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
              A., and H. Ashida, "Common Requirements for Carrier-Grade
              NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
              April 2013, <https://www.rfc-editor.org/info/rfc6888>.

   [RFC6939]  Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer
              Address Option in DHCPv6", RFC 6939, DOI 10.17487/RFC6939,
              May 2013, <https://www.rfc-editor.org/info/rfc6939>.

   [RFC6964]  Templin, F., "Operational Guidance for IPv6 Deployment in
              IPv4 Sites Using the Intra-Site Automatic Tunnel
              Addressing Protocol (ISATAP)", RFC 6964,
              DOI 10.17487/RFC6964, May 2013,
              <https://www.rfc-editor.org/info/rfc6964>.








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   [RFC6967]  Boucadair, M., Touch, J., Levis, P., and R. Penno,
              "Analysis of Potential Solutions for Revealing a Host
              Identifier (HOST_ID) in Shared Address Deployments",
              RFC 6967, DOI 10.17487/RFC6967, June 2013,
              <https://www.rfc-editor.org/info/rfc6967>.

   [RFC6980]  Gont, F., "Security Implications of IPv6 Fragmentation
              with IPv6 Neighbor Discovery", RFC 6980,
              DOI 10.17487/RFC6980, August 2013,
              <https://www.rfc-editor.org/info/rfc6980>.

   [RFC7010]  Liu, B., Jiang, S., Carpenter, B., Venaas, S., and W.
              George, "IPv6 Site Renumbering Gap Analysis", RFC 7010,
              DOI 10.17487/RFC7010, September 2013,
              <https://www.rfc-editor.org/info/rfc7010>.

   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
              "Specification of the IP Flow Information Export (IPFIX)
              Protocol for the Exchange of Flow Information", STD 77,
              RFC 7011, DOI 10.17487/RFC7011, September 2013,
              <https://www.rfc-editor.org/info/rfc7011>.

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

   [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>.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045,
              DOI 10.17487/RFC7045, December 2013,
              <https://www.rfc-editor.org/info/rfc7045>.

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis",
              RFC 7050, DOI 10.17487/RFC7050, November 2013,
              <https://www.rfc-editor.org/info/rfc7050>.

   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              DOI 10.17487/RFC7084, November 2013,
              <https://www.rfc-editor.org/info/rfc7084>.





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   [RFC7112]  Gont, F., Manral, V., and R. Bonica, "Implications of
              Oversized IPv6 Header Chains", RFC 7112,
              DOI 10.17487/RFC7112, January 2014,
              <https://www.rfc-editor.org/info/rfc7112>.

   [RFC7113]  Gont, F., "Implementation Advice for IPv6 Router
              Advertisement Guard (RA-Guard)", RFC 7113,
              DOI 10.17487/RFC7113, February 2014,
              <https://www.rfc-editor.org/info/rfc7113>.

   [RFC7123]  Gont, F. and W. Liu, "Security Implications of IPv6 on
              IPv4 Networks", RFC 7123, DOI 10.17487/RFC7123, February
              2014, <https://www.rfc-editor.org/info/rfc7123>.

   [RFC7166]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
              Authentication Trailer for OSPFv3", RFC 7166,
              DOI 10.17487/RFC7166, March 2014,
              <https://www.rfc-editor.org/info/rfc7166>.

   [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>.

   [RFC7359]  Gont, F., "Layer 3 Virtual Private Network (VPN) Tunnel
              Traffic Leakages in Dual-Stack Hosts/Networks", RFC 7359,
              DOI 10.17487/RFC7359, August 2014,
              <https://www.rfc-editor.org/info/rfc7359>.

   [RFC7381]  Chittimaneni, K., Chown, T., Howard, L., Kuarsingh, V.,
              Pouffary, Y., and E. Vyncke, "Enterprise IPv6 Deployment
              Guidelines", RFC 7381, DOI 10.17487/RFC7381, October 2014,
              <https://www.rfc-editor.org/info/rfc7381>.

   [RFC7404]  Behringer, M. and E. Vyncke, "Using Only Link-Local
              Addressing inside an IPv6 Network", RFC 7404,
              DOI 10.17487/RFC7404, November 2014,
              <https://www.rfc-editor.org/info/rfc7404>.

   [RFC7422]  Donley, C., Grundemann, C., Sarawat, V., Sundaresan, K.,
              and O. Vautrin, "Deterministic Address Mapping to Reduce
              Logging in Carrier-Grade NAT Deployments", RFC 7422,
              DOI 10.17487/RFC7422, December 2014,
              <https://www.rfc-editor.org/info/rfc7422>.






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   [RFC7454]  Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
              and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
              February 2015, <https://www.rfc-editor.org/info/rfc7454>.

   [RFC7513]  Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address
              Validation Improvement (SAVI) Solution for DHCP",
              RFC 7513, DOI 10.17487/RFC7513, May 2015,
              <https://www.rfc-editor.org/info/rfc7513>.

   [RFC7526]  Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast
              Prefix for 6to4 Relay Routers", BCP 196, RFC 7526,
              DOI 10.17487/RFC7526, May 2015,
              <https://www.rfc-editor.org/info/rfc7526>.

   [RFC7552]  Asati, R., Pignataro, C., Raza, K., Manral, V., and R.
              Papneja, "Updates to LDP for IPv6", RFC 7552,
              DOI 10.17487/RFC7552, June 2015,
              <https://www.rfc-editor.org/info/rfc7552>.

   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
              Port with Encapsulation (MAP-E)", RFC 7597,
              DOI 10.17487/RFC7597, July 2015,
              <https://www.rfc-editor.org/info/rfc7597>.

   [RFC7599]  Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S.,
              and T. Murakami, "Mapping of Address and Port using
              Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599, July
              2015, <https://www.rfc-editor.org/info/rfc7599>.

   [RFC7610]  Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-Shield:
              Protecting against Rogue DHCPv6 Servers", BCP 199,
              RFC 7610, DOI 10.17487/RFC7610, August 2015,
              <https://www.rfc-editor.org/info/rfc7610>.

   [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>.

   [RFC7772]  Yourtchenko, A. and L. Colitti, "Reducing Energy
              Consumption of Router Advertisements", BCP 202, RFC 7772,
              DOI 10.17487/RFC7772, February 2016,
              <https://www.rfc-editor.org/info/rfc7772>.



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   [RFC7785]  Vinapamula, S. and M. Boucadair, "Recommendations for
              Prefix Binding in the Context of Softwire Dual-Stack
              Lite", RFC 7785, DOI 10.17487/RFC7785, February 2016,
              <https://www.rfc-editor.org/info/rfc7785>.

   [RFC7824]  Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy
              Considerations for DHCPv6", RFC 7824,
              DOI 10.17487/RFC7824, May 2016,
              <https://www.rfc-editor.org/info/rfc7824>.

   [RFC7844]  Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
              Profiles for DHCP Clients", RFC 7844,
              DOI 10.17487/RFC7844, May 2016,
              <https://www.rfc-editor.org/info/rfc7844>.

   [RFC7857]  Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar,
              S., and K. Naito, "Updates to Network Address Translation
              (NAT) Behavioral Requirements", BCP 127, RFC 7857,
              DOI 10.17487/RFC7857, April 2016,
              <https://www.rfc-editor.org/info/rfc7857>.

   [RFC7872]  Gont, F., Linkova, J., Chown, T., and W. Liu,
              "Observations on the Dropping of Packets with IPv6
              Extension Headers in the Real World", RFC 7872,
              DOI 10.17487/RFC7872, June 2016,
              <https://www.rfc-editor.org/info/rfc7872>.

   [RFC7915]  Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,
              "IP/ICMP Translation Algorithm", RFC 7915,
              DOI 10.17487/RFC7915, June 2016,
              <https://www.rfc-editor.org/info/rfc7915>.

   [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>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [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>.






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   [RFC8177]  Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
              Zhang, "YANG Data Model for Key Chains", RFC 8177,
              DOI 10.17487/RFC8177, June 2017,
              <https://www.rfc-editor.org/info/rfc8177>.

   [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>.

   [RFC8210]  Bush, R. and R. Austein, "The Resource Public Key
              Infrastructure (RPKI) to Router Protocol, Version 1",
              RFC 8210, DOI 10.17487/RFC8210, September 2017,
              <https://www.rfc-editor.org/info/rfc8210>.

   [RFC8273]  Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
              per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,
              <https://www.rfc-editor.org/info/rfc8273>.

   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
              <https://www.rfc-editor.org/info/rfc8343>.

   [RFC8344]  Bjorklund, M., "A YANG Data Model for IP Management",
              RFC 8344, DOI 10.17487/RFC8344, March 2018,
              <https://www.rfc-editor.org/info/rfc8344>.

   [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>.

   [RFC8520]  Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
              Description Specification", RFC 8520,
              DOI 10.17487/RFC8520, March 2019,
              <https://www.rfc-editor.org/info/rfc8520>.

   [RFC8541]  Litkowski, S., Decraene, B., and M. Horneffer, "Impact of
              Shortest Path First (SPF) Trigger and Delay Strategies on
              IGP Micro-loops", RFC 8541, DOI 10.17487/RFC8541, March
              2019, <https://www.rfc-editor.org/info/rfc8541>.





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   [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>.

   [SCANNING]
              Barnes, R., Altmann, R., and D. Kerr, "Mapping the Great
              Void - Smarter scanning for IPv6", February 2012,
              <http://www.caida.org/workshops/isma/1202/slides/
              aims1202_rbarnes.pdf>.

   [WEBER_VPN]
              Weber, J., "Dynamic IPv6 Prefix - Problems and VPNs",
              March 2018, <https://blog.webernetz.net/wp-
              content/uploads/2018/03/TR18-Johannes-Weber-Dynamic-IPv6-
              Prefix-Problems-and-VPNs.pdf>.

Authors' Addresses

   Eric Vyncke
   Cisco
   De Kleetlaan 6a
   Diegem  1831
   Belgium

   Phone: +32 2 778 4677
   Email: evyncke@cisco.com


   Kiran Kumar
   WeWork
   415 Mission St.
   San Francisco  94105
   United States of America

   Email: kk.chittimaneni@gmail.com


   Merike Kaeo
   Double Shot Security
   3518 Fremont Ave N 363
   Seattle  98103
   United States of America

   Phone: +12066696394
   Email: merike@doubleshotsecurity.com




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   Enno Rey
   ERNW
   Carl-Bosch-Str. 4
   Heidelberg, Baden-Wuertemberg  69115
   Germany

   Phone: +49 6221 480390
   Email: erey@ernw.de











































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