draft-ietf-opsec-dhcpv6-shield-08.txt   rfc7610.txt 
opsec F. Gont Internet Engineering Task Force (IETF) F. Gont
Internet-Draft SI6 Networks / UTN-FRH Request for Comments: 7610 SI6 Networks / UTN-FRH
Intended status: Best Current Practice W. Liu BCP: 199 W. Liu
Expires: January 7, 2016 Huawei Technologies Category: Best Current Practice Huawei Technologies
G. Van de Velde ISSN: 2070-1721 G. Van de Velde
Alcatel-Lucent Alcatel-Lucent
July 6, 2015 August 2015
DHCPv6-Shield: Protecting Against Rogue DHCPv6 Servers DHCPv6-Shield: Protecting against Rogue DHCPv6 Servers
draft-ietf-opsec-dhcpv6-shield-08
Abstract Abstract
This document specifies a mechanism for protecting hosts connected to This document specifies a mechanism for protecting hosts connected to
a switched network against rogue DHCPv6 servers. It is based on a switched network against rogue DHCPv6 servers. It is based on
DHCPv6 packet-filtering at the layer-2 device at which the packets DHCPv6 packet filtering at the layer 2 device at which the packets
are received. A similar mechanism has been widely deployed in IPv4 are received. A similar mechanism has been widely deployed in IPv4
networks ('DHCP snooping'), and hence it is desirable that similar networks ('DHCP snooping'); hence, it is desirable that similar
functionality be provided for IPv6 networks. This document specifies functionality be provided for IPv6 networks. This document specifies
a Best Current Practice for the implementation of DHCPv6 Shield. a Best Current Practice for the implementation of DHCPv6-Shield.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This memo documents an Internet Best Current Practice.
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 This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
This Internet-Draft will expire on January 7, 2016. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7610.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction ....................................................3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language ...........................................3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology .....................................................3
4. DHCPv6-Shield Configuration . . . . . . . . . . . . . . . . . 4 4. DHCPv6-Shield Configuration .....................................5
5. DHCPv6-Shield Implementation Requirements . . . . . . . . . . 4 5. DHCPv6-Shield Implementation Requirements .......................5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations .........................................7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. References ......................................................9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 7.1. Normative References .......................................9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.2. Informative References ....................................10
9.1. Normative References . . . . . . . . . . . . . . . . . . 9 Acknowledgements ..................................................11
9.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses ................................................12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
This document specifies DHCPv6-Shield: a mechanism for protecting This document specifies DHCPv6-Shield, a mechanism for protecting
hosts connected to a switched network against rogue DHCPv6 servers hosts connected to a switched network against rogue DHCPv6 servers
[RFC3315]. The basic concept behind DHCPv6-Shield is that a layer-2 [RFC3315]. The basic concept behind DHCPv6-Shield is that a layer 2
device filters DHCPv6 messages intended for DHCPv6 clients device filters DHCPv6 messages intended for DHCPv6 clients
(henceforth "DHCPv6-server messages"), according to a number of (henceforth, "DHCPv6-server messages"), according to a number of
different criteria. The most basic filtering criterion is that different criteria. The most basic filtering criterion is that
DHCPv6-server messages are discarded by the layer-2 device unless DHCPv6-server messages are discarded by the layer 2 device unless
they are received on specific ports of the layer-2 device. they are received on specific ports of the layer 2 device.
Before the DHCPv6-Shield device is deployed, the administrator Before the DHCPv6-Shield device is deployed, the administrator
specifies the layer-2 port(s) on which DHCPv6-server messages are to specifies the layer 2 port(s) on which DHCPv6-server messages are to
be allowed. Only those ports to which a DHCPv6 server or relay is to be allowed. Only those ports to which a DHCPv6 server or relay is to
be connected should be specified as such. Once deployed, the be connected should be specified as such. Once deployed, the
DHCPv6-Shield device inspects received packets, and allows (i.e. DHCPv6-Shield device inspects received packets and allows (i.e.,
passes) DHCPv6-server messages only if they are received on layer-2 passes) DHCPv6-server messages only if they are received on layer 2
ports that have been explicitly configured for such purpose. ports that have been explicitly configured for such purpose.
DHCPv6-Shield is analogous to the RA-Guard mechanism [RFC6104] DHCPv6-Shield is analogous to the Router Advertisement Guard
[RFC6105] [RFC7113], intended for protection against rogue Router (RA-Guard) mechanism [RFC6104] [RFC6105] [RFC7113], intended for
Advertisement [RFC4861] messages. protection against rogue Router Advertisement [RFC4861] messages.
We note that DHCPv6-Shield mitigates only DHCPv6-based attacks We note that DHCPv6-Shield mitigates only DHCPv6-based attacks
against hosts. Attack vectors based on other messages meant for against hosts. Attack vectors based on other messages meant for
network configuration (such as ICMPv6 Router Advertisements) are not network configuration (such as ICMPv6 Router Advertisements) are not
addressed by DHCPv6-Shield itself. In a similar vein, addressed by DHCPv6-Shield itself. In a similar vein, DHCPv6-Shield
DHCPv6-Shielddoes not mitigate attacks against DHCPv6 servers (e.g., does not mitigate attacks against DHCPv6 servers (e.g., Denial of
Denial of Service). Service).
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. Terminology 3. Terminology
DHCPv6-Shield: DHCPv6-Shield:
the set of filtering rules specified in this document, meant to The set of filtering rules specified in this document, meant to
mitigate attacks that employ DHCPv6-server packets. mitigate attacks that employ DHCPv6-server packets.
DHCPv6-Shield device: DHCPv6-Shield device:
A layer-2 device (typically a layer-2 switch) that enforces the A layer 2 device (typically a layer 2 switch) that enforces the
filtering policy specified in this document. filtering policy specified in this document.
For the purposes of this document, the terms Extension Header, Header For the purposes of this document, the terms "IPv6 Extension Header",
Chain, First Fragment, and Upper-layer Header are used as specified "First Fragment", "IPv6 Header Chain", and "Upper-Layer Header" are
in [RFC7112]: used as specified in [RFC7112]:
IPv6 Extension Header: IPv6 Extension Header:
Extension Headers are defined in Section 4 of [RFC2460]. As a IPv6 Extension Headers are defined in Section 4 of [RFC2460]. As
result of [RFC7045], [IANA-PROTO] provides a list of assigned a result of [RFC7045], [IANA-PROTO] provides a list of assigned
Internet Protocol Numbers and designates which of those protocol Internet Protocol Numbers and designates which of those protocol
numbers also represent extension headers. numbers also represent IPv6 Extension Headers.
First Fragment: First Fragment:
An IPv6 fragment with fragment offset equal to 0. An IPv6 fragment with a Fragment Offset equal to 0.
IPv6 Header Chain: IPv6 Header Chain:
The header chain contains an initial IPv6 header, zero or more The IPv6 Header Chain contains an initial IPv6 header, zero or
IPv6 extension headers, and optionally, a single upper-layer more IPv6 Extension Headers, and optionally, a single Upper-Layer
header. If an upper-layer header is present, it terminates the Header. If an Upper-Layer Header is present, it terminates the
header chain; otherwise the "No Next Header" value (Next Header = IPv6 Header Chain; otherwise, the "No Next Header" value (Next
59) terminates it. Header = 59) terminates it.
The first member of the header chain is always an IPv6 header. The first member of the IPv6 Header Chain is always an IPv6
For a subsequent header to qualify as a member of the header header. For a subsequent header to qualify as a member of the
chain, it must be referenced by the "Next Header" field of the IPv6 Header Chain, it must be referenced by the "Next Header"
previous member of the header chain. However, if a second IPv6 field of the previous member of the IPv6 Header Chain. However,
header appears in the header chain, as is the case when IPv6 is if a second IPv6 header appears in the IPv6 Header Chain, as is
tunneled over IPv6, the second IPv6 header is considered to be an the case when IPv6 is tunneled over IPv6, the second IPv6 header
upper-layer header and terminates the header chain. Likewise, if is considered to be an Upper-Layer Header and terminates the IPv6
an Encapsulating Security Payload (ESP) header appears in the Header Chain. Likewise, if an Encapsulating Security Payload
header chain it is considered to be an upper-layer header and it (ESP) header appears in the IPv6 Header Chain, it is considered to
terminates the header chain. be an Upper-Layer Header, and it terminates the IPv6 Header Chain.
Upper-layer Header: Upper-Layer Header:
In the general case, the upper-layer header is the first member of In the general case, the Upper-Layer Header is the first member of
the header chain that is neither an IPv6 header nor an IPv6 the Header Chain that is neither an IPv6 header nor an IPv6
extension header. However, if either an ESP header, or a second Extension Header. However, if either an ESP header or a second
IPv6 header occur in the header chain, they are considered to be IPv6 header occurs in the IPv6 Header Chain, it is considered to
upper layer headers and they terminate the header chain. be an Upper-Layer Header, and it terminates the IPv6 Header Chain.
Neither the upper-layer payload, nor any protocol data following Neither the upper-layer payload nor any protocol data following
the upper-layer payload, is considered to be part of the header the upper-layer payload is considered to be part of the IPv6
chain. In a simple example, if the upper-layer header is a TCP Header Chain. In a simple example, if the Upper-Layer Header is a
header, the TCP payload is not part of the header chain. In a TCP header, the TCP payload is not part of the IPv6 Header Chain.
more complex example, if the upper-layer header is an ESP header, In a more complex example, if the Upper-Layer Header is an ESP
neither the payload data, nor any of the fields that follow the header, neither the payload data nor any of the fields that follow
payload data in the ESP header are part of the header chain. the payload data in the ESP header are part of the IPv6 Header
Chain.
4. DHCPv6-Shield Configuration 4. DHCPv6-Shield Configuration
Before being deployed for production, the DHCPv6-Shield device is Before being deployed for production, the DHCPv6-Shield device is
explicitly configured with respect to which layer-2 ports are allowed explicitly configured with respect to which layer 2 ports are allowed
to receive DHCPv6 packets destined to DHCPv6 clients (i.e. to receive DHCPv6 packets destined to DHCPv6 clients (i.e.,
DHCPv6-server messages). Only those layer-2 ports explicitly DHCPv6-server messages). Only those layer 2 ports explicitly
configured for such purpose will be allowed to receive DHCPv6 packets configured for such purpose are allowed to receive DHCPv6 packets to
to DHCPv6 clients. pass to DHCPv6 clients.
5. DHCPv6-Shield Implementation Requirements 5. DHCPv6-Shield Implementation Requirements
The following are the filtering rules that are enforced as part of a Following are the filtering rules that are enforced as part of a
DHCPv6-Shield implementation on those ports that are not allowed to DHCPv6-Shield implementation on those ports that are not allowed to
receive DHCPv6 packets to DHCPv6 clients: receive DHCPv6 packets to DHCPv6 clients:
1. DHCPv6-Shield implementations MUST parse the entire IPv6 header 1. DHCPv6-Shield implementations MUST parse the entire IPv6 Header
chain present in the packet, to identify whether it is a DHCPv6 Chain present in the packet to identify whether or not it is a
packet meant for a DHCPv6 client (i.e., a DHCPv6-server message). DHCPv6 packet meant for a DHCPv6 client (i.e., a DHCPv6-server
message).
RATIONALE: DHCPv6-Shield implementations MUST NOT enforce a RATIONALE: DHCPv6-Shield implementations MUST NOT enforce a
limit on the number of bytes they can inspect (starting from limit on the number of bytes they can inspect (starting from
the beginning of the IPv6 packet), since this could introduce the beginning of the IPv6 packet), since this could introduce
false-negatives: DHCP6-server packets received on ports not false negatives: DHCP6-server packets received on ports not
allowed to receive such packets could be allowed simply allowed to receive such packets could be allowed simply
because the DHCPv6-Shield device does not parse the entire because the DHCPv6-Shield device does not parse the entire
IPv6 header chain present in the packet. IPv6 Header Chain present in the packet.
2. When parsing the IPv6 header chain, if the packet is a first- 2. When parsing the IPv6 Header Chain, if the packet is a First
fragment (i.e., a packet containing a Fragment Header with the Fragment (i.e., a packet containing a Fragment Header with the
Fragment Offset set to 0) and it fails to contain the entire IPv6 Fragment Offset set to 0) and it fails to contain the entire IPv6
header chain (i.e., all the headers starting from the IPv6 header Header Chain (i.e., all the headers starting from the IPv6 header
up to, and including, the upper-layer header), DHCPv6-Shield MUST up to, and including, the Upper-Layer Header), DHCPv6-Shield MUST
drop the packet, and ought to log the packet drop event in an drop the packet and ought to log the packet drop event in an
implementation-specific manner as a security fault. implementation-specific manner as a security fault.
RATIONALE: Packets that fail to contain the entire IPv6 header RATIONALE: Packets that fail to contain the entire IPv6 Header
chain could otherwise be leveraged for circumventing Chain could otherwise be leveraged for circumventing
DHCPv6-Shield. [RFC7112] requires that the first-fragment DHCPv6-Shield. [RFC7112] requires that the First Fragment
(i.e., the fragment with the Fragment Offset set to 0) (i.e., the fragment with the Fragment Offset set to 0) contain
contains the entire IPv6 header chain, and allows intermediate the entire IPv6 Header Chain. [RFC7112] also allows
systems such as routers to drop those packets that fail to intermediate systems such as routers to drop packets that fail
comply with this requirement. to comply with this requirement.
NOTE: This rule should only be applied to IPv6 fragments with NOTE: This rule should only be applied to IPv6 fragments with
a Fragment Offset of 0 (non-first fragments can be safely a Fragment Offset of 0 (non-First Fragments can be safely
passed, since they will never reassemble into a complete passed, since they will never reassemble into a complete
datagram if they are part of a DHCPv6 packet meant for a datagram if they are part of a DHCPv6 packet meant for a
DHCPv6 client received on a port where such packets are not DHCPv6 client received on a port where such packets are not
allowed). allowed).
3. DHCPv6-Shield MUST provide a configuration knob that controls 3. DHCPv6-Shield MUST provide a configuration knob that controls
whether packets with unrecognized Next Header values are dropped; whether or not packets with unrecognized Next Header values are
this configuration knob MUST default to "drop". When parsing the dropped; this configuration knob MUST default to "drop". When
IPv6 header chain, if the packet contains an unrecognized Next parsing the IPv6 Header Chain, if the packet contains an
Header value and the configuration knob is configured to "drop", unrecognized Next Header value and the configuration knob is
DHCPv6-Shield MUST drop the packet, and ought to log the packet configured to "drop", DHCPv6-Shield MUST drop the packet and
drop event in an implementation-specific manner as a security ought to log the packet drop event in an implementation-specific
fault. manner as a security fault.
RATIONALE: An unrecognized Next Header value could possibly RATIONALE: An unrecognized Next Header value could possibly
identify an IPv6 Extension Header, and thus be leveraged to identify an IPv6 Extension Header and thus be leveraged to
conceal a DHCPv6-server packet (since there is no way for conceal a DHCPv6-server packet (since there is no way for
DHCPv6-Shield to parse past unrecognized Next Header values DHCPv6-Shield to parse past unrecognized Next Header values
[I-D.gont-6man-rfc6564bis]). [RFC7045] requires that nodes be [IPV6-UEH]). [RFC7045] requires that nodes be configurable
configurable with respect to whether packets with unrecognized with respect to whether or not packets with unrecognized
headers are forwarded, and allows the default behavior to be headers are forwarded and allows the default behavior to be
that such packets be dropped. that such packets be dropped.
4. When parsing the IPv6 header chain, if the packet is identified 4. When parsing the IPv6 Header Chain, if the packet is identified
to be a DHCPv6 packet meant for a DHCPv6 client, DHCPv6-Shield to be a DHCPv6 packet meant for a DHCPv6 client, DHCPv6-Shield
MUST drop the packet, and SHOULD log the packet drop event in an MUST drop the packet and SHOULD log the packet drop event in an
implementation-specific manner as a security alert. implementation-specific manner as a security alert.
RATIONALE: Ultimately, the goal of DHCPv6-Shield is drop RATIONALE: Ultimately, the goal of DHCPv6-Shield is to drop
DHCPv6 packets destined to DHCPv6 clients (i.e. DHCPv6-server DHCPv6 packets destined to DHCPv6 clients (i.e., DHCPv6-server
messages) that are received on ports that have not been messages) that are received on ports that have not been
explicitly configured to allow the receipt of such packets. explicitly configured to allow the receipt of such packets.
5. In all other cases, DHCPv6-Shield MUST pass the packet as usual. 5. In all other cases, DHCPv6-Shield MUST pass the packet as usual.
NOTE: For the purpose of enforcing the DHCPv6-Shield filtering NOTE: For the purpose of enforcing the DHCPv6-Shield filtering
policy, an ESP header [RFC4303] should be considered to be an policy, an ESP header [RFC4303] should be considered to be an
"upper-layer protocol" (that is, it should be considered the last "upper-layer protocol" (that is, it should be considered the last
header in the IPv6 header chain). This means that packets header in the IPv6 Header Chain). This means that packets
employing ESP would be passed by the DHCPv6-Shield device to the employing ESP would be passed by the DHCPv6-Shield device to the
intended destination. If the destination host does not have a intended destination. If the destination host does not have a
security association with the sender of the aforementioned IPv6 security association with the sender of the aforementioned IPv6
packet, the packet would be dropped. Otherwise, if the packet is packet, the packet would be dropped. Otherwise, if the packet is
considered valid by the IPsec implementation at the receiving host considered valid by the IPsec implementation at the receiving host
and encapsulates a DHCPv6 message, it is up to the receiving host and encapsulates a DHCPv6 message, what to do with such a packet
what to do with such packet. is up to the receiving host.
The above indicates that if a packet is dropped due to this filtering The rules above indicate that if a packet is dropped due to this
policy, the packet drop event be logged in an implementation-specific filtering policy, the packet drop event should be logged in an
manner as a security fault. It is useful for the logging mechanism implementation-specific manner as a security fault. It is useful for
to include a per-port drop counter dedicated to DHCPv6-Shield packet the logging mechanism to include a per-port drop counter dedicated to
drops. DHCPv6-Shield packet drops.
In order to protect current end-node IPv6 implementations, Rule #2 In order to protect current end-node IPv6 implementations, Rule #2
has been defined as a default rule to drop packets that cannot be has been defined such that the default is for packets that cannot be
positively identified as not being DHCPv6-server packets (because the positively identified as not being DHCPv6-server packets (because the
packet is a fragment that fails to include the entire IPv6 header packet is a fragment that fails to include the entire IPv6 Header
chain). This means that, at least in theory, DHCPv6-Shield could Chain) to be dropped. This means that, at least in theory,
result in false-positive blocking of some legitimate (non DHCPv6-Shield could result in false-positive blocking of some
DHCPv6-server) packets. However, as noted in [RFC7112], IPv6 packets legitimate (non-DHCPv6-server) packets. However, as noted in
that fail to include the entire IPv6 header chain are virtually [RFC7112], IPv6 packets that fail to include the entire IPv6 Header
impossible to police with state-less filters and firewalls, and hence Chain are virtually impossible to police with stateless filters and
are unlikely to survive in real networks. [RFC7112] requires that firewalls; hence, they are unlikely to survive in real networks.
hosts employing fragmentation include the entire IPv6 header chain in [RFC7112] requires that hosts employing fragmentation include the
the first fragment (the fragment with the Fragment Offset set to 0), entire IPv6 Header Chain in the First Fragment (the fragment with the
thus eliminating the aforementioned false positives. Fragment Offset set to 0), thus eliminating the aforementioned false
positives.
The aforementioned filtering rules implicitly handle the case of The aforementioned filtering rules implicitly handle the case of
fragmented packets: if the DHCPv6-Shield device fails to identify the fragmented packets: if the DHCPv6-Shield device fails to identify the
upper-layer protocol as a result of the use of fragmentation, the upper-layer protocol as a result of the use of fragmentation, the
corresponding packets would be dropped. corresponding packets would be dropped.
Finally, we note that IPv6 implementations that allow overlapping Finally, we note that IPv6 implementations that allow overlapping
fragments (i.e. that do not comply with [RFC5722]) might still be fragments (i.e., that do not comply with [RFC5722]) might still be
subject of DHCPv6-based attacks. However, a recent assessment of subject of DHCPv6-based attacks. However, a recent assessment of
IPv6 implementations [SI6-FRAG] with respect to their fragment IPv6 implementations [SI6-FRAG] with respect to their fragment
reassembly policy seems to indicate that most current implementations reassembly policy seems to indicate that most current implementations
comply with [RFC5722]. comply with [RFC5722].
6. IANA Considerations 6. Security Considerations
This document has no actions for IANA.
7. Security Considerations
The recommendations in this document represent the ideal behavior of The recommendations in this document represent the ideal behavior of
a DHCPv6 shield device. However, in order to implement DHCPv6 shield a DHCPv6-Shield device. However, in order to implement DHCPv6-Shield
on the fast path, it may be necessary to limit the depth into the on the fast path, it may be necessary to limit the depth into the
packet that can be scanned before giving up. In circumstances where packet that can be scanned before giving up. In circumstances where
there is such a limitation, it is recommended that implementations there is such a limitation, it is recommended that implementations
drop packets after attempting to find a protocol header up to that drop packets after attempting to find a protocol header up to that
limit, whatever it is. Ideally, such devices should be configurable limit, whatever it is. Ideally, such devices should be configurable
with a list of protocol header identifiers so that if new transport with a list of protocol header identifiers so that if new transport
protocols are standardized after the device is released, they can be protocols are standardized after the device is released, they can be
added to the list of protocol header types that the device added to the list of protocol header types that the device
recognizes. Since any protocol header that is not a UDP header would recognizes. Since any protocol header that is not a UDP header would
be passed by the DHCPv6 shield algorithm, this would allow such be passed by the DHCPv6-Shield algorithm, this would allow such
devices to avoid blocking the use of new transport protocols. When devices to avoid blocking the use of new transport protocols. When
an implementation must stop searching for recognizable header types an implementation must stop searching for recognizable header types
in a packet due to such limitations, whether the device passes or in a packet due to such limitations, the device SHOULD be
drop that packet SHOULD be configurable. configurable to either pass or drop that packet.
The mechanism specified in this document can be used to mitigate The mechanism specified in this document can be used to mitigate
DHCPv6-based attacks against hosts. Attack vectors based on other DHCPv6-based attacks against hosts. Attack vectors based on other
messages meant for network configuration (such as ICMPv6 Router messages meant for network configuration (such as ICMPv6 Router
Advertisements) are out of the scope of this document. Additionally, Advertisements) are out of the scope of this document. Additionally,
the mechanism specified in this document does not mitigate attacks the mechanism specified in this document does not mitigate attacks
against DHCPv6 servers (e.g., Denial of Service). against DHCPv6 servers (e.g., Denial of Service).
If deployed in layer-2 domain with several cascading switches, there If deployed in a layer 2 domain with several cascading switches,
will be an ingress port on the host's local switch which will need to there will be an ingress port on the host's local switch that will
be enabled for receiving DHCPv6-server messages. However, this local need to be enabled for receiving DHCPv6-server messages. However,
switch will be reliant on the upstream devices to have filtered out this local switch will be reliant on the upstream devices filtering
rogue DHCPv6-server messages, as the local switch has no way of out rogue DHCPv6-server messages, as the local switch has no way of
determining which upstream DHCP-server messages are valid. determining which upstream DHCP-server messages are valid.
Therefore, in order to be effective DHCPv6 Shield should be deployed Therefore, in order to be effective, DHCPv6-Shield should be deployed
and enabled on all layer-2 switches of a given layer-2 domain. and enabled on all layer 2 switches of a given layer 2 domain.
As noted in Section 5, IPv6 implementations that allow overlapping As noted in Section 5, IPv6 implementations that allow overlapping
fragments (i.e. that do not comply with [RFC5722]) might still be fragments (i.e., that do not comply with [RFC5722]) might still be
subject of DHCPv6-based attacks. However, most current subject to DHCPv6-based attacks. However, most current
implementations seem to comply with [RFC5722], and hence forbid IPv6 implementations seem to comply with [RFC5722] and hence forbid IPv6
overlapping fragments. overlapping fragments.
We note that if an attacker sends a fragmented DHCPv6 packet on a We note that if an attacker sends a fragmented DHCPv6 packet on a
port not allowed to receive such packets, the first-fragment would be port not allowed to receive such packets, the First Fragment would be
dropped, and the rest of the fragments would be passed. This means dropped, and the rest of the fragments would be passed. This means
that the victim node would tie memory buffers for the aforementioned that the victim node would tie memory buffers for the aforementioned
fragments, which would never reassemble into a complete datagram. If fragments, which would never reassemble into a complete datagram. If
a large number of such packets were sent by an attacker, and the a large number of such packets were sent by an attacker, and the
victim node failed to implement proper resource management for the victim node failed to implement proper resource management for the
fragment reassembly buffer, this could lead to a Denial of Service fragment reassembly buffer, this could lead to a Denial of Service
(DoS). However, this does not really introduce a new attack vector, (DoS). However, this does not really introduce a new attack vector,
since an attacker could always perform the same attack by sending since an attacker could always perform the same attack by sending a
forged fragmented datagram in which at least one of the fragments is forged fragmented datagram in which at least one of the fragments is
missing. [CPNI-IPv6] discusses some resource management strategies missing. [CPNI-IPv6] discusses some resource management strategies
that could be implemented for the fragment reassembly buffer. that could be implemented for the fragment reassembly buffer.
Additionally, we note that the security of a site employing DHCPv6 Additionally, we note that the security of a site employing
Shield could be further improved by deploying [I-D.ietf-savi-dhcp], DHCPv6-Shield could be further improved by deploying [RFC7513] to
to mitigate IPv6 address spoofing attacks. mitigate IPv6 address spoofing attacks.
Finally, we note that other mechanisms for mitigating attacks based Finally, we note that other mechanisms for mitigating attacks based
on DHCPv6-server messages are available that have different on DHCPv6-server messages are available that have different
deployment considerations. For example, [I-D.ietf-dhc-secure-dhcpv6] deployment considerations. For example, [SECURE-DHCPV6] allows for
allows for authentication of DHCPv6-server packets if the IPv6 authentication of DHCPv6-server packets if the IPv6 addresses of the
addresses of the DHCPv6 servers can be pre-configured at the client DHCPv6 servers can be pre-configured at the client nodes.
nodes.
8. Acknowledgements 7. References
The authors would like to thank Mike Heard, who provided detailed 7.1. Normative References
feedback on earlier versions of this document and helped a lot in
producing a technically-sound document throughout the whole
publication process.
The authors would like to thank (in alphabetical order) Ben Campbell, [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Jean-Michel Combes, Sheng Jiang, Ted Lemon, Pete Resnick, Juergen Requirement Levels", BCP 14, RFC 2119,
Schoenwaelder, Carsten Schmoll, Robert Sleigh, Donald Smith, Mark DOI 10.17487/RFC2119, March 1997,
Smith, Hannes Tschofenig, Eric Vyncke, and Qin Wu, for providing <http://www.rfc-editor.org/info/rfc2119>.
valuable comments on earlier versions of this document.
Part of Section 3 of this document was borrowed from [RFC7112], [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
authored by Fernando Gont, Vishwas Manral, and Ron Bonica. (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
This document is heavily based on the document [RFC7113] authored by [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
Fernando Gont. Thus, the authors would like to thank Ran Atkinson, C., and M. Carney, "Dynamic Host Configuration Protocol
Karl Auer, Robert Downie, Washam Fan, David Farmer, Mike Heard, Marc for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
Heuse, Nick Hilliard, Ray Hunter, Joel Jaeggli, Simon Perreault, 2003, <http://www.rfc-editor.org/info/rfc3315>.
Arturo Servin, Gunter van de Velde, James Woodyatt, and Bjoern A.
Zeeb, for providing valuable comments on [RFC7113], on which this
document is based.
The authors would like to thank Joel Jaeggli for his advice and [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
guidance throughout the IETF process. 4303, DOI 10.17487/RFC4303, December 2005,
<http://www.rfc-editor.org/info/rfc4303>.
9. References [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<http://www.rfc-editor.org/info/rfc4861>.
9.1. Normative References [RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",
RFC 5722, DOI 10.17487/RFC5722, December 2009,
<http://www.rfc-editor.org/info/rfc5722>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
Requirement Levels", BCP 14, RFC 2119, March 1997. of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<http://www.rfc-editor.org/info/rfc7045>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of
(IPv6) Specification", RFC 2460, December 1998. Oversized IPv6 Header Chains", RFC 7112,
DOI 10.17487/RFC7112, January 2014,
<http://www.rfc-editor.org/info/rfc7112>.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 7.2. Informative References
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC [CPNI-IPv6] Gont, F., "Security Assessment of the Internet Protocol
4303, December 2005. version 6 (IPv6)", UK Centre for the Protection of
National Infrastructure, (available on request).
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, [IANA-PROTO] IANA, "Protocol Numbers",
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, <http://www.iana.org/assignments/protocol-numbers>.
September 2007.
[RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments", [IPV6-UEH] Gont, F., Liu, W., Krishnan, S., and H. Pfeifer, "IPv6
RFC 5722, December 2009. Universal Extension Header", Work in Progress,
draft-gont-6man-rfc6564bis-00, April 2014.
[RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of [RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router
Oversized IPv6 Header Chains", RFC 7112, January 2014. Advertisement Problem Statement", RFC 6104,
DOI 10.17487/RFC6104, February 2011,
<http://www.rfc-editor.org/info/rfc6104>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and
of IPv6 Extension Headers", RFC 7045, December 2013. J. Mohacsi, "IPv6 Router Advertisement Guard", RFC
6105, DOI 10.17487/RFC6105, February 2011,
<http://www.rfc-editor.org/info/rfc6105>.
9.2. Informative References [RFC7113] Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113,
DOI 10.17487/RFC7113, February 2014,
<http://www.rfc-editor.org/info/rfc7113>.
[I-D.ietf-dhc-secure-dhcpv6] [RFC7513] Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address
Jiang, S. and S. Shen, "Secure DHCPv6 Using CGAs", draft- Validation Improvement (SAVI) Solution for DHCP", RFC
ietf-dhc-secure-dhcpv6-07 (work in progress), September 7513, DOI 10.17487/RFC7513, May 2015,
2012. <http://www.rfc-editor.org/info/rfc7513>.
[I-D.gont-6man-rfc6564bis] [SECURE-DHCPV6]
Gont, F., Will, W., Krishnan, S., and H. Pfeifer, "IPv6 Jiang, S. and S. Shen, "Secure DHCPv6 Using CGAs", Work
Universal Extension Header", draft-gont-6man-rfc6564bis-00 in Progress, draft-ietf-dhc-secure-dhcpv6-07, September
(work in progress), April 2014. 2012.
[RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement [SI6-FRAG] SI6 Networks, "IPv6 NIDS evasion and improvements in
Problem Statement", RFC 6104, February 2011. IPv6 fragmentation/reassembly", 2012,
<http://blog.si6networks.com/2012/02/
ipv6-nids-evasion-and-improvements-in.html>.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. Acknowledgements
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
February 2011.
[RFC7113] Gont, F., "Implementation Advice for IPv6 Router The authors would like to thank Mike Heard, who provided detailed
Advertisement Guard (RA-Guard)", RFC 7113, February 2014. feedback on earlier draft versions of this document and helped a lot
in producing a technically sound document throughout the whole
publication process.
[IANA-PROTO] The authors would like to thank (in alphabetical order) Ben Campbell,
Internet Assigned Numbers Authority, "Protocol Numbers", Jean-Michel Combes, Sheng Jiang, Ted Lemon, Pete Resnick, Carsten
February 2013, <http://www.iana.org/assignments/protocol- Schmoll, Juergen Schoenwaelder, Robert Sleigh, Donald Smith, Mark
numbers/protocol-numbers.txt>. Smith, Hannes Tschofenig, Eric Vyncke, and Qin Wu for providing
valuable comments on earlier draft versions of this document.
[SI6-FRAG] Part of Section 3 of this document was borrowed from [RFC7112],
SI6 Networks, "IPv6 NIDS evasion and improvements in IPv6 authored by Fernando Gont, Vishwas Manral, and Ron Bonica.
fragmentation/reassembly", 2012,
<http://blog.si6networks.com/2012/02/
ipv6-nids-evasion-and-improvements-in.html>.
[I-D.ietf-savi-dhcp] This document is heavily based on [RFC7113], authored by Fernando
Bi, J., Wu, J., Yao, G., and F. Baker, "SAVI Solution for Gont. Thus, the authors would like to thank the following
DHCP", draft-ietf-savi-dhcp-34 (work in progress), individuals for providing valuable comments on [RFC7113]: Ran
February 2015. Atkinson, Karl Auer, Robert Downie, Washam Fan, David Farmer, Mike
Heard, Marc Heuse, Nick Hilliard, Ray Hunter, Joel Jaeggli, Simon
Perreault, Arturo Servin, Gunter Van de Velde, James Woodyatt, and
Bjoern A. Zeeb.
[CPNI-IPv6] The authors would like to thank Joel Jaeggli for his advice and
Gont, F., "Security Assessment of the Internet Protocol guidance throughout the IETF process.
version 6 (IPv6)", UK Centre for the Protection of
National Infrastructure, (available on request). Fernando Gont would like to thank Diego Armando Maradona for his
magic and inspiration.
Authors' Addresses Authors' Addresses
Fernando Gont Fernando Gont
SI6 Networks / UTN-FRH SI6 Networks / UTN-FRH
Evaristo Carriego 2644 Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706 Haedo, Provincia de Buenos Aires 1706
Argentina Argentina
Phone: +54 11 4650 8472 Phone: +54 11 4650 8472
Email: fgont@si6networks.com Email: fgont@si6networks.com
URI: http://www.si6networks.com URI: http://www.si6networks.com
Will Liu Will (Shucheng) Liu
Huawei Technologies Huawei Technologies
Bantian, Longgang District Bantian, Longgang District
Shenzhen 518129 Shenzhen 518129
P.R. China China
Email: liushucheng@huawei.com Email: liushucheng@huawei.com
Gunter Van de Velde Gunter Van de Velde
Alcatel-Lucent Alcatel-Lucent
Copernicuslaan 50 Copernicuslaan 50
Antwerp, Antwerp 2018 Antwerp, Antwerp 2018
Belgium Belgium
Phone: +32 476 476 022 Phone: +32 476 476 022
Email: gunter.van_de_velde@alcatel-lucent.com Email: gunter.van_de_velde@alcatel-lucent.com
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