OPSEC K. Chittimaneni
Internet-Draft Google
Intended status: Informational M. Kaeo
Expires: January 16, 2014 Double Shot Security
E. Vyncke
Cisco Systems
July 15, 2013
Operational Security Considerations for IPv6 Networks
draft-ietf-opsec-v6-03
Abstract
Knowledge and experience on how to operate IPv4 securely is
available: whether it is the Internet or an enterprise internal
network. However, IPv6 presents some new security challenges. RFC
4942 describes the security issues in the protocol but network
managers also need a more practical, operations-minded best common
practices.
This document analyzes the operational security issues in all places
of a network (service providers, enterprises and residential users)
and proposes technical and procedural mitigations techniques.
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 http://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 January 16, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Generic Security Considerations . . . . . . . . . . . . . . . 3
2.1. Addressing Architecture . . . . . . . . . . . . . . . . . 3
2.1.1. Overall Structure . . . . . . . . . . . . . . . . . . 4
2.1.2. Use of ULAs . . . . . . . . . . . . . . . . . . . . . 4
2.1.3. Point-to-Point Links . . . . . . . . . . . . . . . . 5
2.1.4. Temporary Addresses - Privacy Extensions for SLAAC . 6
2.1.5. DHCP/DNS Considerations . . . . . . . . . . . . . . . 7
2.2. Link-Layer Security . . . . . . . . . . . . . . . . . . . 7
2.2.1. SeND and CGA . . . . . . . . . . . . . . . . . . . . 7
2.2.2. DHCP Snooping . . . . . . . . . . . . . . . . . . . . 8
2.2.3. ND/RA Rate Limiting . . . . . . . . . . . . . . . . . 9
2.2.4. ND/RA Filtering . . . . . . . . . . . . . . . . . . . 10
2.2.5. 3GPP Link-Layer Security . . . . . . . . . . . . . . 11
2.3. Control Plane Security . . . . . . . . . . . . . . . . . 12
2.3.1. Control Protocols . . . . . . . . . . . . . . . . . . 13
2.3.2. Management Protocols . . . . . . . . . . . . . . . . 13
2.3.3. Packet Exceptions . . . . . . . . . . . . . . . . . . 13
2.4. Routing Security . . . . . . . . . . . . . . . . . . . . 14
2.4.1. Authenticating Neighbors/Peers . . . . . . . . . . . 14
2.4.2. Securing Routing Updates Between Peers . . . . . . . 15
2.4.3. Route Filtering . . . . . . . . . . . . . . . . . . . 16
2.5. Logging/Monitoring . . . . . . . . . . . . . . . . . . . 16
2.5.1. Data Sources . . . . . . . . . . . . . . . . . . . . 17
2.5.2. Use of Collected Data . . . . . . . . . . . . . . . . 20
2.5.3. Summary . . . . . . . . . . . . . . . . . . . . . . . 22
2.6. Transition/Coexistence Technologies . . . . . . . . . . . 22
2.6.1. Dual Stack . . . . . . . . . . . . . . . . . . . . . 22
2.6.2. Transition Mechanisms . . . . . . . . . . . . . . . . 23
2.6.3. Translation Mechanisms . . . . . . . . . . . . . . . 27
2.7. General Device Hardening . . . . . . . . . . . . . . . . 28
3. Enterprises Specific Security Considerations . . . . . . . . 28
3.1. External Security Considerations: . . . . . . . . . . . . 29
3.2. Internal Security Considerations: . . . . . . . . . . . . 29
4. Service Providers Security Considerations . . . . . . . . . . 30
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4.1. BGP . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1.1. Remote Triggered Black Hole Filtering . . . . . . . . 30
4.2. Transition Mechanism . . . . . . . . . . . . . . . . . . 30
4.3. Lawful Intercept . . . . . . . . . . . . . . . . . . . . 30
5. Residential Users Security Considerations . . . . . . . . . . 31
6. Further Reading . . . . . . . . . . . . . . . . . . . . . . . 32
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
9. Security Considerations . . . . . . . . . . . . . . . . . . . 32
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.1. Normative References . . . . . . . . . . . . . . . . . . 32
10.2. Informative References . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40
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 differences between IPv4 and IPv6 especially with
respect to security. For example, all layer-2 interactions are now
done by Neighbor Discovery Protocol [RFC4861] rather than by Address
Resolution Protocol [RFC0826]. Also, there are subtle differences
between NAT44 and NPTv6 [RFC6296] which are explicitly pointed out in
the latter's security considerations section.
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 utilizing varying transition technologies
and updating with ones that have been standardized since 2007. It
also provides more recent operational deployment experiences where
warranted.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] when they
appear in ALL CAPS. These words may also appear in this document in
lower case as plain English words, absent their normative meanings.
2. Generic Security Considerations
2.1. Addressing Architecture
IPv6 address allocations and overall architecture are an important
part of securing IPv6.
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2.1.1. Overall Structure
Once an address allocation has been assigned, there should be some
thought given to an overall address allocation plan. A structured
address allocation plan can lead to more concise and simpler firewall
filtering rules. With the abundance of address space available, an
address allocation may be structured around services along with
geographic locations, which then can be a basis for more structured
network filters to permit or deny services between geographic
regions.
There still exists a debate whether companies should use PI vs PA
space [I-D.ietf-v6ops-enterprise-incremental-ipv6] but from a
security perspective there is little difference. However, one aspect
to keep in mind is who has ownership of the address space and who is
responsible if/when Law Enforcement may need to enforce restrictions
on routability of the space due to malicious criminal activity.
When considering how to assign manually configured addresses it is
necessary to take into consideration the effectiveness of perimeter
security in a given environment. There is a trade-off between ease
of operational deployment where some portions of the IPv6 address
could be easily recognizable for operational debugging and
troubleshooting versus the risk of scanning; [SCANNING] shows that
there are scientifically based mechanisms that make scanning for IPv6
reachable nodes more realizable than expected. The use of common
multicast groups which are defined for important networked devices
and the use of commonly repeated addresses could make it easy to
figure out which devices are name servers, routers or other critical
devices. While in some environments the perimeter security is so
poor that obfuscating addresses is considered a benefit; it is a much
better practice to ensure that perimeter rules are actively checked
and enforced and that manually configured addresses follow some
logical allocation scheme for ease of operation.
2.1.2. Use of ULAs
ULAs are intended for scenarios where IP addresses will not have
global scope. The implicit expectation from the RFC is that all ULAs
will be randomly created as /48s. However, in practice some
environments have chosen to create ULAs as a /32 by removing the
random part of the address. The use of a /32 violates [RFC4193] and
greatly reduces the probability of non-collision. ULAs are also
useful for infrastructure hiding as described in [RFC4864]. Although
ULAs are supposed to be used in conjunction with global addresses for
hosts that desire external connectivity, a few operators chose to use
ULAs in conjunction with some sort of address translation at the
border in order to maintain a perception of parity between their IPv4
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and IPv6 setup. Additionally, there have been some issues with
source address selection, although these should be considered bugs to
be fixed rather than worked around using NAT. Some operators believe
that stateful IPv6 Network Address and Port Translation (NAPT)
provides some security not provided by NPTv6 (the authors of this
document do not share this point of view). The latter would be
problematic in trying to track specific machines that may source
malware although this is less of an issue if appropriate logging is
done which includes utilizing accurate timestamps and logging a
node's source ports [RFC6302].
The use of ULA does not isolate 'by magic' the part of the network
using ULA from other parts of the network (including the Internet).
Although section 4.1 of [RFC4193] explicitly states "If BGP is being
used at the site border with an ISP, the default BGP configuration
must filter out any Local IPv6 address prefixes, both incoming and
outgoing.", the operational reality is that this guideline is not
always followed. As written, RFC4193 makes no changes to default
routing behavior of exterior protocols. Therefore, routers will
happily forward packets whose source or destination address is ULA as
long as they have a route to the destination and there is no ACL
blocking those packets. This means that using ULA does not prevent
route and packet filters to be implemented and monitored. This also
means that all transit networks should consider ULA as source or
destination as bogons packets and drop them.
It is important to carefully weigh the benefits of using ULAs versus
utilizing a section of the global allocation and creating a more
effective filtering strategy. A typical argument is that there are
too many mistakes made with filters and ULAs make things easier to
hide machines.
2.1.3. Point-to-Point Links
[RFC6164] recommends the use of /127 for inter-router point-to-point
links. /127 prevents the ping-pong attack between routers non
enforced RFC4443. However, it should be noted that at the time of
this writing, there are still many networks out there that follow the
advice provided by [RFC3627] (Obsoleted and marked Historic by
[RFC6547]) and therefore continue to use /64's and/or /112's. We
recommend that the guidance provided by RFC6164 be followed.
Some environments are also using link-local addressing for point-to-
point links. While this practice could further reduce the attack
surface against infrastructure devices, the operational disadvantages
need also to be carefully considered [I-D.ietf-opsec-lla-only].
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2.1.4. Temporary Addresses - Privacy Extensions for SLAAC
Normal stateless address autoconfiguration (SLAAC) relies on the
automatically generated EUI-64 address, which together with the /64
prefix makes up the global unique IPv6 address. The EUI-64 address
is generated from the MAC address. Randomly generating an interface
ID, as described in [RFC4941], is part of SLAAC with so-called
temporary addresses and used to address some privacy concerns.
Temporary addresses a.k.a. privacy extensions may help to mitigate
the correlation of activities of a node within the same network, and
may also reduce the attack exposure window.
As temporary address could also be used to obfuscate some illegal
activities (whether on purpose or not), it is advised in scenarios
where attribution is important to disable SLAAC and rely only on
DHCPv6. However, in scenarios where anonymity is a strong desire
since protecting user privacy is more important than attribution,
temporary addresses should be used
Some people also feel that SLAAC means that the operator may not know
addresses operating in the networks ahead of time in order to to
build host specific access control lists (ACLs) of authorized users.
While privacy addresses are truly generated randomly to protect
against user tracking, but assuming that nodes use the EUI-64 format
for global addressing, a list of expected pre-authorized host
addresses can be generated. It must be noted that recent versions of
Windows do not use the MAC address anymore to build the stable
address but use a mechanism similar to the one described in
[I-D.ietf-6man-stable-privacy-addresses], this also means that such
an ACL cannot be configured based solely on the MAC address of the
nodes, diminushing the value of such ACL. On the other hand,
different VLANs are often used to seggregate users, then ACL can rely
on a /64 prefix per VLAN rather than a per host ACL entry.
The decision to utilize temporary addresses can come down to whether
the network is managed versus unmanaged. In some environments full
visibility into the network is required at all times which requires
that all traffic be attributable to where it is sourced or where it
is destined to within a specific network. This situation is
dependent on what level of logging is performed. If logging
considerations include utilizing accurate timestamps and logging a
node's source ports [RFC6302] then there should always exist
appropriate attribution needed to get to the source of any malware
originator or source of criminal activity.
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However, there are several privacy issues still present with
[RFC4941] such as host tracking, and address scanning attacks are
still possible. More details are provided in Appendix A. of
[I-D.ietf-6man-stable-privacy-addresses].
Disabling SLAAC and temporary addresses can be done by sending Router
Advertisement with a hint to use DHCPv6 by setting the M-bit but also
disabling SLAAC by resetting all A-bits in all prefixes sent in the
Router Advertisement message.
2.1.5. DHCP/DNS Considerations
Many environments use DHCPv6 in their environments to ensure
audibility and traceability (but see Section 2.5.1.5). A main
security concern is the ability to detect and mitigate against rogue
DHCP servers (Section 2.2.2).
DNS is often used for malware activities and while there are no
fundamental differences with IPv4 and IPv6 security concerns, there
are specific consideration in DNS64 [RFC6147] environments that need
to be understood. Specifically the interactions and potential to
interference with DNSsec implementation need to be understood - these
are pointed out in detail in Section 2.6.3.2.
2.2. Link-Layer Security
IPv6 relies heavily on the Neighbor Discovery protocol (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].
2.2.1. SeND and CGA
The original NDP specification called for using IPsec to protect
Neighbor Discovery messages. However, manually configuring security
associations among multiple hosts on a large network can be very
challenging. In many environments the tradeoff between using
technologies that require an effective key management lifecycle
process creates more of an operational burden than the protection
offered by a given technology. IPsec protection for NDP typically
falls under this category.
SEcure Neighbor Discovery (SeND), as described in [RFC3971], is a
mechanism that was designed to secure ND messages without having to
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rely on manual IPsec configuration. 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, CGA and SeND do not have wide support from
generic operating systems; hence, their usefulness is limited.
2.2.2. DHCP Snooping
Dynamic Host Configuration Protocol for IPv6 (DHCPv6), as detailed in
[RFC3315], enables DHCP servers to pass configuration parameters such
as IPv6 network addresses and other configuration information to IPv6
nodes. DHCP plays an important role in any large network by
providing robust stateful autoconfiguration and autoregistration of
DNS Host Names.
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The two most common threats to DHCP clients come from malicious or
misconfigured DHCP servers. A malicious DHCP server is one that is
established with the intent of providing incorrect configuration
information to the client. The motivation for doing so may be to
mount a "man in the middle" attack instead of a valid server for
services such as DNS or to cause a denial of service attack through
misconfiguration of the client that causes all network communication
from the client to fail. A misconfigured, or sometimes referred to
as rogue, DHCP server is one that has unintentionally been configured
to answer DHCP client requests with incorrect configuration
parameters. Some additional threats against DHCP are discussed in
the security considerations section of [RFC3315]
[I-D.ietf-opsec-dhcpv6-shield] specifies a mechanism for protecting
hosts connected to a broadcast network against rogue DHCPv6 servers.
This mechanism is based on DHCPv6 packet-filtering at the layer-2
device on which the packets are received. Before the DCHPv6-Shield
device is deployed, the administrator specifies the layer-2 port(s)
on which DHCPv6 packets meant for DHCPv6 clients are allowed. Only
those ports to which a DHCPv6 server is to be connected should be
specified as such. Once deployed, the DHCPv6-Shield device inspects
received packets, and allows DHCPv6 messages meant for DHCPv6 clients
only if they are received on layer-2 ports that have been explicitly
configured for such purpose.
Additionally, the Source Address Validation Improvements (SAVI)
working group is currently working on other ways to mitigate the
effects of such attacks. [I-D.ietf-savi-dhcp] would help in creating
bindings between a DHCPv4 [RFC2131] /DHCPv6 [RFC3315] assigned source
IP address and a binding anchor [I-D.ietf-savi-framework] 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 address.
2.2.3. ND/RA Rate Limiting
Neighbor Discovery (ND) can be vulnerable to denial of service (DoS)
attacks in which a router is forced to perform address resolution for
a large number of unassigned addresses. Possible side effects of
this attack preclude new devices from joining the network or even
worse rendering 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 DOS in detail and suggests
implementation improvements and operational mitigation techniques
that may be used to mitigate or alleviate the impact of such attacks.
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Here are some feasible mitigation options that can be employed by
network operators today:
o Ingress filtering of unused addresses by ACL, route filtering,
longer than /64 prefix; These require static configuration of the
addresses.
o Tuning of NDP process (where supported).
Additionally, IPv6 ND uses multicast extensively for signaling
messages on the local link to avoid broadcast messages for on-the-
wire efficiency. However, this has some side effects on wifi
networks, especially a negative impact on battery life of smartphones
and other battery operated devices that are connected to such
networks. The following drafts are actively discussing methods to
rate limit RAs and other ND messages on wifi networks in order to
address this issue:
o [I-D.thubert-savi-ra-throttler]
o [I-D.chakrabarti-nordmark-6man-efficient-nd]
2.2.4. ND/RA Filtering
Router Advertisement spoofing is a well-known attack vector and has
been extensively documented. The presence of rogue RAs, either
intentional or malicious, can cause partial or complete failure of
operation of hosts on an IPv6 link. For example, a host can select
an incorrect router address which can be used as a man-in-the-middle
(MITM) attack or can assume wrong prefixes to be used for stateless
address configuration (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.
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. An
attacker can conceal the attack by fragmenting his 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 in the same packet.
[I-D.ietf-v6ops-ra-guard-implementation] describes such evasion
techniques, and provides advice to RA-Guard implementers such that
the aforementioned evasion vectors can be eliminated.
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Given that the IPv6 Fragmentation Header can be leveraged to
circumvent current implementations of RA-Guard,
[I-D.ietf-6man-nd-extension-headers] aims to update [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 Neighbor Discovery attacks.
It is still recommended that RA-Guard be be employed as a first line
of defense against common attack vectors including misconfigured
hosts.
2.2.5. 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 and the first-
hop router i.e., a GGSN or a PGW on that link. The GGSN/PGW never
configures a non link-local address on the link using the prefix
advertised on it and the advertised prefix must not be used for on-
link determination. There is no need for an 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 built
by the cellular 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 cellular
host's).
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 cellular host that fall under the prefix
assigned to it. This implies the GGSN/PGW may implement a minimal
neighbor discovery protocol subset; since, due the point-to-point
link model and the absence of link-layer addressing the address
resolution can be entirely statically configured per each 3GPP link,
and there is no need to defend any other address than the link-local
address for very unlikely duplicates.
See Section 5 of [RFC6459] for a more detailed discussion on the 3GPP
link model, NDP on it and the address configuration detail.
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2.3. Control Plane Security
[RFC6192] defines the router control plane and this definition is
repeated here for the reader's convenience.
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 determine the best outgoing
interface towards the destination, and forwarding the packet out
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
(named router 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.
The mitigation technique is:
o To drop non-legit control packet 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
the Dijkstra algorithm, therefore the number of Dijsktra execution
should be also rate limited).
This section will consider several classes of control packets:
o Control protocols: routing protocols: such as OSPFv3, BGP and by
extension Neighbor Discovery and ICMP
o Management protocols: SSH, SNMP, IPfix, etc
o Packet exceptions: which are normal data packets which requires a
specific processing such as generating a packet-too-big ICMP
message or having the hop-by-hop extension header.
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2.3.1. Control Protocols
This class includes OSPFv3, BGP, NDP, ICMP.
An ingress ACL to be applied on all the router interfaces SHOULD be
configured such as:
o drop OSPFv3 (identified by Next-Header being 89) and RIPng
(identified by UDP port 521) packets from a non link-local address
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 whose ACL are unable to parse the IPsec
ESP or AH extension headers.
Rate limiting of the valid packets SHOULD be done. The exact
configuration obviously depends on the power of the Route Processor.
2.3.2. Management Protocols
This class includes: SSH, SNMP, syslog, NTP, etc
An ingress ACL to be applied on all the router interfaces SHOULD be
configured such as:
o Drop packets destined to the routers except those belonging to
protocols which are used (for example, permit TCP 22 and drop all
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
NOC, then the ACL should permit TCP port 22 packets only from the
NOC prefix.
Rate limiting of the valid packets SHOULD be done. The exact
configuration obviously depends on the power of the Route Processor.
2.3.3. 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;
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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;
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 extension header.
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. [I-D.ietf-6man-oversized-header-chain] highlights the
security implications of oversized header chains on routers and aims
to update RFC2460 such that the first fragment of a packet is
required to contain the entire IPv6 header chain.
An ingress ACL cannot help to mitigate a control plane attack using
those packet exceptions. The only protection for the RP is to limit
the rate of those packet exceptions forwarded to the RP, this means
that some data plane packets will be dropped without any ICMP
messages back to the source which will cause Path MTU holes. But,
there is no other solution.
In addition to limiting the rate of data plane packets queued to the
RP, it is also important to limit the generation rate of ICMP
messages both the save the RP but also to prevent an amplification
attack using the router as a reflector.
2.4. Routing Security
Routing security in general can be broadly divided into three
sections:
1. Authenticating neighbors/peers
2. Securing routing updates between peers
3. Route filtering
[I-D.ietf-opsec-bgp-security] covers these sections specifically for
BGP in detail.
2.4.1. Authenticating Neighbors/Peers
A basic element of routing is the process of forming adjacencies,
neighbor, or peering relationships with other routers. From a
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security perspective, it is very important to establish such
relationships only with routers and/or administrative domains that
one trusts. A traditional approach has been to use MD5 HMAC, which
allows routers to authenticate each other prior to establishing a
routing relationship.
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
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 [RFC2740] and the
updated [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 wordings. OSPFv3 can
also use normal ESP to encrypt the OSPFv3 payload to hide the routing
information.
[RFC6506] changes OSPFv3's reliance on IPsec by appending an
authentication trailer to the end of the OSPFv3 packets. This
document does not specifically provide for a mechanism that will
authenticate the specific originator of a packet. Rather, it will
allow a router to confirm that the packet has indeed 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 cause outages
and therefore the tradeoff between utilizing this functionality needs
to be weighed against the protection it provides.
2.4.2. Securing Routing Updates Between Peers
IPv6 initially mandated the provisioning of IPsec capability in all
nodes. However, in the updated IPv6 Nodes Requirement standard
[RFC6434] is now a SHOULD and not MUST implement. Theoretically it
is possible, and recommended, that communication between two IPv6
nodes, including routers exchanging routing information be encrypted
using IPsec. In practice however, deploying IPsec is not always
feasible given hardware and software limitations of various platforms
deployed, as described in the earlier section. Additionally, in a
protocol such as OSPFv3 where adjacencies are formed on a one-to-many
basis, IPsec key management becomes difficult to maintain and is not
often utilized.
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2.4.3. 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.,
o Filter internal-use, non-globally routable IPv6 addresses at the
perimeter
o Discard packets from and to bogon and reserved space
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 [RFC6810]
Some good recommendations for filtering can be found from Team CYMRU
at [CYMRU].
2.5. Logging/Monitoring
In order to perform forensic research in case of any security
incident or to detect abnormal behaviors, network operator should log
multiple pieces of information.
This includes:
o logs of all applications when available (for example web servers);
o use of IP Flow Information Export [RFC5101] also known as IPfix;
o use of SNMP MIB [RFC4293];
o use of the Neighbor cache;
o use of stateful DHCPv6 [RFC3315] lease cache.
Please note that there are privacy issues related to how those logs
are collected, kept and safely discarded. Operators are urged to
check their country legislation.
All those pieces of information will be used for:
o forensic (Section 2.5.2.1) research to answer questions such as
who did what and when?
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o correlation (Section 2.5.2.3): which IP addresses were used by a
specific node (assuming the use of privacy extensions addresses
[RFC4941])
o inventory (Section 2.5.2.2): which IPv6 nodes are on my network?
o abnormal behavior detection (Section 2.5.2.4): unusual traffic
patterns are often the symptoms of a abnormal behavior which is in
turn a potential attack (denial of services, network scan, a node
being part of a botnet, ...)
2.5.1. Data Sources
This section lists the most important sources of data that are useful
for operational security.
2.5.1.1. Logs of Applications
Those logs are usually text files where the remote IPv6 address is
stored in all characters (not binary). This can complicate the
processing since one IPv6 address, 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.
RFC 5952 [RFC5952] explains this problem in detail and recommends the
use of a single canonical format (in short use lower case and
suppress leading 0). This memo recommends the use of canonical
format [RFC5952] for IPv6 addresses in all possible cases. If the
existing application cannot log under the canonical format, then this
memo recommends the use an external program (or filter) in order to
canonicalize all IPv6 addresses.
For example, this perl script can be used:
#!/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
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while (my $line = <STDIN>) {
chomp $line;
foreach my $word (split /[ \n]/, $line) {
$binary_address = inet_pton AF_INET6, $word ;
if ($binary_address) {
print inet_ntop AF_INET6, $binary_address ;
} else {
print $word ;
}
print " " ;
}
print "\n" ;
}
2.5.1.2. IP Flow Information Export by IPv6 Routers
IPfix [RFC5102] 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.
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.
2.5.1.3. SNMP MIB 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.
2.5.1.4. Neighbor Cache of IPv6 Routers
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The neighbor cache of routers contains all mappings between IPv6
addresses and data-link layer addresses. It is usually available by
two means:
o the SNMP MIB (Section 2.5.1.3) as explained above;
o also by connecting over a secure management channel (such as SSH
or HTTPS) and explicitely requesting a neighbor cache dump.
The neighbor cache is highly dynamic as mappings are added when a new
IPv6 address appears on the network (could be quite often with
privacy extension addresses [RFC4941] 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 typical host such as Windows 7). This means that
the content of the neighbor cache must periodically be fetched every
30 seconds (to be on the safe side) and stored for later use.
This is an important source of information because it is trivial (on
a switch not using the SAVI [I-D.ietf-savi-framework] 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
forensic and audit trail.
2.5.1.5. Stateful DHCPv6 Lease
In some networks, IPv6 addresses are managed by stateful DHCPv6
server [RFC3315] that leases IPv6 addresses 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 and data-
link layer addresses as it was usually done in the IPv4 era.
It is not so easy in the IPv6 era 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 operation
security. Moreover, when the DUID is based on the data-link address,
this address can be of any interface of the client (such as the
wireless interface while the client actually uses its wired interface
to connect to the network).
In short, the DHCPv6 lease file is less interesting than in the IPv4
era. DHCPv6 servers that keeps the relayed data-link layer address
in addition to the DUID in the lease file do not suffer from this
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limitation. On a managed network where all hosts support DHCPv6,
special care must be taken to prevent stateless autoconfiguration
anyway (and if applicable) by sending RA with all announced prefixes
without the A-bit set.
The mapping between data-link layer address and the IPv6 address can
be secured by using switches implementing the SAVI
[I-D.ietf-savi-dhcp] algorithms.
2.5.1.6. Other Data Sources
There are other data sources that must be kept exactly as in the IPv4
network:
o historical mapping of MAC address to RADIUS user authentication in
a IEEE 802.1X network or an IPsec-based remote access VPN;
o historical mapping of MAC address to switch interface in a wired
network.
2.5.2. Use of Collected Data
This section leverages the data collected as described before
(Section 2.5.1) in order to achieve several security benefits.
2.5.2.1. Forensic
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
still currently in the network.
The source of information can be, in decreasing order, neighbor
cache, DHCP lease file. Then, the procedure is:
1. based on the IPv6 prefix of the IPv6 address find the router(s)
which are used to reach this prefix;
2. based on this limited set of routers, on the incident time and on
IPv6 address to retrieve the data-link address from live neighbor
cache, from the historical data of the neighbor cache, or from
the DHCP lease file;
3. based on the data-link layer address, look-up on which switch
interface was this data-link layer address. In the case of
wireless LAN, the RADIUS log should have the mapping between user
identification and the MAC address.
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At the end of the process, the interface where the malicious user was
connected or the username that was used by the malicious user is
found.
2.5.2.2. Inventory
RFC 5157 [RFC5157] is about the difficulties to scan an IPv6 network
due to the vast number of IPv6 addresses per link. This has the side
effect of making 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 operation of a network.
There are two ways to do an inventory of an IPv6 network.
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 node that never transmitted such packets... 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 2.5.1.4.
Another way works only for local network, it consists in sending a
ICMP ECHO_REQUEST to the link-local multicast address ff02::1 which
is all IPv6 nodes on the network. All nodes should reply to this
ECHO_REQUEST per [RFC4443].
2.5.2.3. 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 was 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 with canonical IPv6 addresses. 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
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historical neighbor cache data sets must be searched for all IPv6
addresses associated to this data-link layer address: this is 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.
2.5.2.4. Abnormal Behavior Detection
Abnormal behaviors (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 [RFC5102];
o change of traffic pattern (number of connection per second, number
of connection per host...) with the use of IPfix [RFC5102]
2.5.3. 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 in a character
string the same IPv6 address renders the use of filters mandatory
when correlation must be done.
2.6. Transition/Coexistence Technologies
Some text
2.6.1. Dual Stack
Dual stack has established itself as the preferred deployment choice
for most network operators without a MPLS core where 6PE [RFC4798] is
quite common. Dual stacking the network offers many advantages over
other transition mechanisms. Firstly, it is easy to turn on without
impacting normal IPv4 operations. Secondly, perhaps more
importantly, it is easier to troubleshoot when things break. Dual
stack allows you to gradually turn IPv4 operations down when your
IPv6 network is ready for prime time.
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From an operational security perspective, this now means that you
have twice the exposure. One needs to think about protecting both
protocols now. At a minimum, the IPv6 portion of a dual stacked
network should maintain parity with IPv4 from a security policy point
of view. Typically, the following methods are employed to protect
IPv4 networks at the edge:
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. Also, given the end-to-
end connectivity that IPv6 provides, it is also recommended that
hosts be fortified against threats. General device hardening
guidelines are provided in Section 2.7
2.6.2. Transition 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 (most of them being described in RFC 6169 [RFC6169]);
o tunnel injection: a malevolent person knowing a few pieces of
information (for example the tunnel endpoints and the used
protocol) can forge a packet which looks like a legit and valid
encapsulated packet that will gladly be accepted by the
destination tunnel endpoint, this is a specific case of spoofing;
o traffic interception: no confidentiality is provided by the tunnel
protocols (without the use of IPsec), therefore anybody on the
tunnel path can intercept the traffic and have access to the
clear-text IPv6 packet;
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 one 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 will probably neither inspect not detect an
malevolent IPv6 traffic contained in the tunnel.
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To mitigate the bypassing of security policies, it could be helpful
to block all default configuration tunnels by denying all IPv4
traffic matching:
o IP protocol 41: this will block ISATAP (Section 2.6.2.2), 6to4
(Section 2.6.2.4), 6rd (Section 2.6.2.5) as well as 6in4
(Section 2.6.2.1) tunnels;
o IP protocol 47: this will block GRE (Section 2.6.2.1) tunnels;
o UDP protocol 3544: this will block the default encapsulation of
Teredo (Section 2.6.2.3) 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 embeb 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.
2.6.2.1. 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
service theft is mostly impossible) but traffic interception ad
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.
2.6.2.2. ISATAP
ISATAP tunnels [RFC5214] are mainly used within a single
administrative domain and to connect a single IPv6 host to the IPv6
network. This means that endpoints and and the tunnel endpoint 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 looping attack by implementing
the measures of RFC 6324 [RFC6324] and of [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.
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2.6.2.3. Teredo
Teredo tunnels [RFC4380] are mainly used in a residential environment
because that can easily traverse an IPv4 NAT-PT device thanks to its
UDP encapsulation and they 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 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
accept 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
more efficient 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).
2.6.2.4. 6to4
6to4 tunnels [RFC3056] require a public routable IPv4 address in
order to work correctly. They can be used to provide either one IPv6
host connectivity to the IPv6 Internet or multiple IPv6 networks
connectivity to the IPV6 Internet. The 6to4 relay is usually the
anycast address defined in [RFC3068]. 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
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
2.6.2.5. 6rd
While 6rd tunnels share the same encapsulation as 6to4 tunnels
(Section 2.6.2.4), 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 little security issues except
lack of confidentiality. The security considerations (Section 12) of
[RFC5969] describes how to secure the 6rd tunnels.
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IPsec [RFC4301] for the transported IPv6 traffic can be used if
confidentiality is important.
2.6.2.6. 6PE and 6VPE
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 VPN described in [RFC4364], the
security of these networks is also similar to the one described in
[RFC4381]. It relies on:
o Address space, routing and traffic seperation with the help of VRF
(only applicable to 6VPE);
o Hiding the IPv4 core, hence removing all attacks against
P-routers;
o Securing the routing protocol between CE and PE, in the case of
6PE and 6VPE, link-local addresses (see [I-D.ietf-opsec-lla-only])
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 the
IPv4 BGP/MPLS IP VPN.
2.6.2.7. DS-Lite
DS-lite is more a translation mechanism and is therefore analyzed
further (Section 2.6.3.3) in this document.
2.6.2.8. Mapping of Address and Port
With the tunnel and encapsulation versions of Mapping of Address and
Port (MAP [I-D.ietf-softwire-map]), the access network is purely an
IPv6 network and MAP protocols are used to give 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 2.6.3.3
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 MUST implement all the security considerations
of [I-D.ietf-softwire-map]; notably, ensuring that the mapping of the
IPv4 address and port are consistent with the configuration.
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2.6.3. Translation Mechanisms
Translation mechanisms between IPv4 and IPv6 networks are alternative
coexistence strategies while networks transition to IPv6. While a
framework is described in [RFC6144] the specific security
considerations are documented in 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.
2.6.3.1. 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 prolong the use of IPv4 in a large service
provider network until the provider can deploy and 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.
[From Panos K: could mention the log size concern and draft-donley-
behave-deterministic-cgn that alleviates it]
2.6.3.2. NAT64/DNS64
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.
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
encapsulation is used. DNS64 has an incidence on DNSSEC see section
3.1 of [I-D.ietf-behave-nat64-discovery-heuristic].
2.6.3.3. 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
Network Address and Port Translation (NAPT)
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Security considerations with respect to DS-Lite mainly revolve around
logging data, preventing DoS attacks from rogue devices and
restricting service offered by the AFTR only to registered customers.
Section 11 of [RFC6333] describes important security issues
associated with this technology.
2.7. General Device Hardening
There are many environments which rely too much on the network
infrastructure to disallow malicious traffic to get access to
critical hosts. In new IPv6 deployments it has been common to see
IPv6 traffic enabled but none of the typical access control
mechanisms enabled for IPv6 device access. With the possibility of
network device configuration mistakes and the growth of IPv6 in the
overall Internet it is important to ensure that all individual
devices are hardened agains miscreant behavior.
The following guidelines should be used to ensure appropriate
hardening of the host, be it an individual computer or router,
firewall, load-balancer,server, etc device.
o Restrict access to the device to authenticated and 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)
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 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.
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Security considerations in the enterprise can be broadly categorized
into two sections - 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
providers network. This is commonly achieved by filtering traffic
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. Here are a few more things that could enhance the
default policy:
o Filter internal-use IPv6 addresses at the perimeter
o Discard packets from and to bogon and reserved space
o Accept certain ICMPv6 messages to allow proper operation of ND and
PMTUD, see also [RFC4890]
o Filter specific extension headers, where possible
o Filter unneeded services at the perimeter
o Implement anti-spoofing filtering or other anti-spoof protections
o Implement appropriate rate-limiters and control-plane policers
3.2. Internal Security Considerations:
The internal aspect deals with providing security inside the
perimeter of the network, including the end host. The most
significant concerns here are related to Neighbor Discovery. At the
network level, it is recommended that all security considerations
discussed in Section 2.2 be reviewed carefully and the
recommendations be considered in-depth as well.
As mentioned in Section 2.6.2, care must be taken when running
automated IPv6-in-IP4 tunnels.
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Hosts need to be hardened directly through security policy to protect
against security threats. The host firewall default capabilities
have to be clearly understood, especially 3rd party ones which can
have different settings for IPv4 or IPv6 default permit/deny
behavior. In some cases, 3rd party firewalls have no IPv6 support
whereas the native firewall installed by default has it. General
device hardening guidelines are provided in Section 2.7
It should also be noted that many hosts still use IPv4 for transport
for things like RADIUS, TACACS+, SYSLOG, etc. This will require some
extra level of due diligence on the part of the operator.
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);
o Prefix Filtering.
These are explained in more detail in section Section 2.4.
4.1.1. Remote Triggered Black Hole Filtering
RTBH [RFC5635] works identically in IPv4 and IPv6. IANA has
allocated 100::/64 as discard prefix [RFC6666].
4.2. Transition Mechanism
SP will typically use transition mechanisms such as 6rd, 6PE, MAP,
DS-LITE which have been analyzed in the transition Section 2.6.2
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 varying
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 what the logging retention policies will be.
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The target of interception will usually be a residential subscriber
(e.g. his/her PPP session or physical line or CPE MAC address). With
the absence of NAT on the CPE, IPv6 has the provision to allow for
intercepting the traffic from a single host (a /128 target) rather
than the whole set of hosts of a subscriber (which could be a /48, a
/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
powers up 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 how IPv6 residential
network should be done; this obviously includes operational security
considerations; but, this is still work in progress.
Residential users have usually less experience and knowledge about
security or networking. As most of the recent hosts, smartphones,
tablets have all 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 tunnels. Several peer-
to-peer programs (notably Bittorrent) support IPv6 and those programs
can initiate a Teredo tunnel through the 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 (personal firewall, ...) are configured with a
dual-stack security policy.
If the Residential Gateway has IPv6 connectivity, [RFC6204] defines
the requirements of an IPv6 CPE and does not take position on the
debate of default IPv6 security policy:
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 NAT-PT
but it also breaks the end-to-end reachability promise of IPv6.
[RFC6092] lists several recommendations to design such a CPE;
o open: allowing all internally and externally initiated
connections, therefore restoring the end-to-end nature of the
Internet for the IPv6 traffic but having a different security
policy for IPv6 than for IPv4.
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[RFC6204] states that a clear choice must be given to the user to
select one of those two policies.
There is also an alternate solution which has been deployed notably
by Swisscom ([I-D.v6ops-vyncke-balanced-ipv6-security]: open to all
outbound and inbound connections at the exception of an handful of
TCP and UDP ports known as vulnerable.
6. Further Reading
There are several documents that describe in more details the
security of an IPv6 network; these documents are not written by the
IETF but are listed here for your 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, Brian Carpenter, Tim Chown, Fernando
Gont, Panos Kampanakis, Jouni Korhonen, Mark Lentczner, Tarko Tikan
(by alphabetical order).
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
This memo attempts to give an overview of security considerations of
operating an IPv6 network both in an IPv6-only network and in
utilizing the most widely deployed IPv4/IPv6 coexistence strategies.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement
Problem Statement", RFC 6104, February 2011.
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[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
February 2011.
10.2. Informative References
[CYMRU] , "Packet Filter and Route Filter Recommendation for IPv6
at xSP routers", , <http://www.team-cymru.org/ReadingRoom/
Templates/IPv6Routers/xsp-recommendations.html>.
[I-D.chakrabarti-nordmark-6man-efficient-nd]
Chakrabarti, S., Nordmark, E., and M. Wasserman,
"Efficiency aware IPv6 Neighbor Discovery Optimizations",
draft-chakrabarti-nordmark-6man-efficient-nd-01 (work in
progress), November 2012.
[]
Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", draft-ietf-6man-nd-
extension-headers-05 (work in progress), June 2013.
[]
Gont, F. and V. Manral, "Security and Interoperability
Implications of Oversized IPv6 Header Chains", draft-ietf-
6man-oversized-header-chain-02 (work in progress),
November 2012.
[I-D.ietf-6man-stable-privacy-addresses]
Gont, F., "A method for Generating Stable Privacy-Enhanced
Addresses with IPv6 Stateless Address Autoconfiguration
(SLAAC)", draft-ietf-6man-stable-privacy-addresses-10
(work in progress), June 2013.
[I-D.ietf-behave-nat64-discovery-heuristic]
Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis", draft-
ietf-behave-nat64-discovery-heuristic-17 (work in
progress), April 2013.
[I-D.ietf-opsec-bgp-security]
Durand, J., Pepelnjak, I., and G. Doering, "BGP operations
and security", draft-ietf-opsec-bgp-security-01 (work in
progress), July 2013.
[I-D.ietf-opsec-dhcpv6-shield]
Gont, F., Liu, W., and G. Velde, "DHCPv6-Shield:
Protecting Against Rogue DHCPv6 Servers", draft-ietf-
opsec-dhcpv6-shield-00 (work in progress), December 2012.
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[I-D.ietf-opsec-lla-only]
Behringer, M. and E. Vyncke, "Using Only Link-Local
Addressing Inside an IPv6 Network", draft-ietf-opsec-lla-
only-03 (work in progress), February 2013.
[I-D.ietf-savi-dhcp]
Bi, J., Wu, J., Yao, G., and F. Baker, "SAVI Solution for
DHCP", draft-ietf-savi-dhcp-18 (work in progress), June
2013.
[I-D.ietf-savi-framework]
Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt,
"Source Address Validation Improvement Framework", draft-
ietf-savi-framework-06 (work in progress), January 2012.
[I-D.ietf-softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, "Mapping of Address and Port
with Encapsulation (MAP)", draft-ietf-softwire-map-07
(work in progress), May 2013.
[I-D.ietf-v6ops-enterprise-incremental-ipv6]
Chittimaneni, K., Chown, T., Howard, L., Kuarsingh, V.,
Pouffary, Y., and E. Vyncke, "Enterprise IPv6 Deployment
Guidelines", draft-ietf-v6ops-enterprise-incremental-
ipv6-03 (work in progress), July 2013.
[I-D.ietf-v6ops-ra-guard-implementation]
Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", draft-ietf-v6ops-ra-
guard-implementation-07 (work in progress), November 2012.
[I-D.thubert-savi-ra-throttler]
Thubert, P., "Throttling RAs on constrained interfaces",
draft-thubert-savi-ra-throttler-01 (work in progress),
June 2012.
[I-D.v6ops-vyncke-balanced-ipv6-security]
Gysi, M., Leclanche, G., Vyncke, E., and R. Anfinsen,
"Balanced Security for IPv6 CPE", draft-v6ops-vyncke-
balanced-ipv6-security-01 (work in progress), July 2013.
[IPv6_Security_Book]
Hogg, . and . Vyncke, "IPv6 Security", ISBN 1-58705-594-5,
Publisher CiscoPress, December 2008.
[NAv6TF_Security]
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Kaeo, ., Green, ., Bound, ., and . 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, ., Graveman, ., Pearce, ., and . Rooks,
"Guidelines for the Secure Deployment of IPv6", 2010,
<http://csrc.nist.gov/publications/nistpubs/800-119/
sp800-119.pdf>.
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC2740] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6", RFC
2740, December 1999.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, June 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3627] Savola, P., "Use of /127 Prefix Length Between Routers
Considered Harmful", RFC 3627, September 2003.
[RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756, May
2004.
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[RFC3924] Baker, F., Foster, B., and C. Sharp, "Cisco Architecture
for Lawful Intercept in IP Networks", RFC 3924, October
2004.
[RFC3964] Savola, P. and C. Patel, "Security Considerations for
6to4", RFC 3964, December 2004.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4293] Routhier, S., "Management Information Base for the
Internet Protocol (IP)", RFC 4293, April 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380, February
2006.
[RFC4381] Behringer, M., "Analysis of the Security of BGP/MPLS IP
Virtual Private Networks (VPNs)", RFC 4381, February 2006.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, June 2006.
[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, September 2006.
[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, February 2007.
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[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4864] Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
E. Klein, "Local Network Protection for IPv6", RFC 4864,
May 2007.
[RFC4890] Davies, E. and J. Mohacsi, "Recommendations for Filtering
ICMPv6 Messages in Firewalls", RFC 4890, May 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC4942] Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
Co-existence Security Considerations", RFC 4942, September
2007.
[RFC5101] Claise, B., "Specification of the IP Flow Information
Export (IPFIX) Protocol for the Exchange of IP Traffic
Flow Information", RFC 5101, January 2008.
[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
Meyer, "Information Model for IP Flow Information Export",
RFC 5102, January 2008.
[RFC5157] Chown, T., "IPv6 Implications for Network Scanning", RFC
5157, March 2008.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
[RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole
Filtering with Unicast Reverse Path Forwarding (uRPF)",
RFC 5635, August 2009.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, August 2010.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification", RFC
5969, August 2010.
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[RFC6092] Woodyatt, J., "Recommended Simple Security Capabilities in
Customer Premises Equipment (CPE) for Providing
Residential IPv6 Internet Service", RFC 6092, January
2011.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, April 2011.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[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,
April 2011.
[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, April 2011.
[RFC6169] Krishnan, S., Thaler, D., and J. Hoagland, "Security
Concerns with IP Tunneling", RFC 6169, April 2011.
[RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
Router Control Plane", RFC 6192, March 2011.
[RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O.
Troan, "Basic Requirements for IPv6 Customer Edge
Routers", RFC 6204, April 2011.
[RFC6264] Jiang, S., Guo, D., and B. Carpenter, "An Incremental
Carrier-Grade NAT (CGN) for IPv6 Transition", RFC 6264,
June 2011.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, June
2011.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011.
[RFC6302] Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
"Logging Recommendations for Internet-Facing Servers", BCP
162, RFC 6302, June 2011.
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[RFC6324] Nakibly, G. and F. Templin, "Routing Loop Attack Using
IPv6 Automatic Tunnels: Problem Statement and Proposed
Mitigations", RFC 6324, August 2011.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
[RFC6343] Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
RFC 6343, August 2011.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
Requirements", RFC 6434, December 2011.
[RFC6459] Korhonen, J., Soininen, J., Patil, B., Savolainen, T.,
Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, January 2012.
[RFC6506] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 6506, February
2012.
[RFC6547] George, W., "RFC 3627 to Historic Status", RFC 6547,
February 2012.
[RFC6583] Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
Neighbor Discovery Problems", RFC 6583, March 2012.
[RFC6598] Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
Space", BCP 153, RFC 6598, April 2012.
[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, May 2012.
[RFC6666] Hilliard, N. and D. Freedman, "A Discard Prefix for IPv6",
RFC 6666, August 2012.
[RFC6810] Bush, R. and R. Austein, "The Resource Public Key
Infrastructure (RPKI) to Router Protocol", RFC 6810,
January 2013.
[RFC6964] Templin, F., "Operational Guidance for IPv6 Deployment in
IPv4 Sites Using the Intra-Site Automatic Tunnel
Addressing Protocol (ISATAP)", RFC 6964, May 2013.
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[SCANNING]
, "Mapping the Great Void - Smarter scanning for IPv6", ,
<http://www.caida.org/workshops/isma/1202/slides/
aims1202_rbarnes.pdf>.
Authors' Addresses
Kiran Kumar Chittimaneni
Google
1600 Amphitheater Pkwy
Mountain View 94043
USA
Phone: +16502249772
Email: kk@google.com
Merike Kaeo
Double Shot Security
3518 Fremont Ave N 363
Seattle 98103
USA
Phone: +12066696394
Email: merike@doubleshotsecurity.com
Eric Vyncke
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Phone: +32 2 778 4677
Email: evyncke@cisco.com
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