draft-ietf-v6ops-cpe-simple-security-14.txt   draft-ietf-v6ops-cpe-simple-security-15.txt 
IPv6 Operations j. woodyatt, Ed. IPv6 Operations j. woodyatt, Ed.
Internet-Draft Apple Internet-Draft Apple
Intended status: Informational September 29, 2010 Intended status: Informational October 12, 2010
Expires: April 2, 2011 Expires: April 15, 2011
Recommended Simple Security Capabilities in Customer Premises Equipment Recommended Simple Security Capabilities in Customer Premises Equipment
for Providing Residential IPv6 Internet Service for Providing Residential IPv6 Internet Service
draft-ietf-v6ops-cpe-simple-security-14 draft-ietf-v6ops-cpe-simple-security-15
Abstract Abstract
This document identifies a set of recommendations for the makers of This document identifies a set of recommendations for the makers of
devices describing how to provide for "simple security" capabilities devices describing how to provide for "simple security" capabilities
at the perimeter of local-area IPv6 networks in Internet-enabled at the perimeter of local-area IPv6 networks in Internet-enabled
homes and small offices. homes and small offices.
Status of this Memo Status of this Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 2, 2011. This Internet-Draft will expire on April 15, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Basic Sanitation . . . . . . . . . . . . . . . . . . . . . 5 2.1. Basic Sanitation . . . . . . . . . . . . . . . . . . . . . 5
2.2. Internet Layer Protocols . . . . . . . . . . . . . . . . . 5 2.2. Internet Layer Protocols . . . . . . . . . . . . . . . . . 5
2.3. Transport Layer Protocols . . . . . . . . . . . . . . . . 6 2.3. Transport Layer Protocols . . . . . . . . . . . . . . . . 6
3. Detailed Recommendations . . . . . . . . . . . . . . . . . . . 6 3. Detailed Recommendations . . . . . . . . . . . . . . . . . . . 6
3.1. Stateless Filters . . . . . . . . . . . . . . . . . . . . 6 3.1. Stateless Filters . . . . . . . . . . . . . . . . . . . . 6
3.2. Connection-free Filters . . . . . . . . . . . . . . . . . 8 3.2. Connection-free Filters . . . . . . . . . . . . . . . . . 8
3.2.1. Internet Control and Management . . . . . . . . . . . 8 3.2.1. Internet Control and Management . . . . . . . . . . . 8
3.2.2. Upper-layer Transport Protocols . . . . . . . . . . . 8 3.2.2. Upper-layer Transport Protocols . . . . . . . . . . . 8
3.2.3. UDP Filters . . . . . . . . . . . . . . . . . . . . . 9 3.2.3. UDP Filters . . . . . . . . . . . . . . . . . . . . . 9
3.2.4. IPsec and Internet Key Exchange (IKE) . . . . . . . . 10 3.2.4. IPsec and Internet Key Exchange (IKE) . . . . . . . . 11
3.2.5. Mobility Support in IPv6 . . . . . . . . . . . . . . . 11 3.2.5. Mobility Support in IPv6 . . . . . . . . . . . . . . . 12
3.3. Connection-oriented Filters . . . . . . . . . . . . . . . 12 3.3. Connection-oriented Filters . . . . . . . . . . . . . . . 13
3.3.1. TCP Filters . . . . . . . . . . . . . . . . . . . . . 13 3.3.1. TCP Filters . . . . . . . . . . . . . . . . . . . . . 13
3.3.2. SCTP Filters . . . . . . . . . . . . . . . . . . . . . 16 3.3.2. SCTP Filters . . . . . . . . . . . . . . . . . . . . . 16
3.3.3. DCCP Filters . . . . . . . . . . . . . . . . . . . . . 19 3.3.3. DCCP Filters . . . . . . . . . . . . . . . . . . . . . 20
3.3.4. Level 3 Multihoming Shim Protocol for IPv6 (SHIM6) . . 21 3.3.4. Level 3 Multihoming Shim Protocol for IPv6 (SHIM6) . . 22
3.4. Passive Listeners . . . . . . . . . . . . . . . . . . . . 22 3.4. Passive Listeners . . . . . . . . . . . . . . . . . . . . 22
3.5. Management Applications . . . . . . . . . . . . . . . . . 23 3.5. Management Applications . . . . . . . . . . . . . . . . . 23
4. Summary of Recommendations . . . . . . . . . . . . . . . . . . 23 4. Summary of Recommendations . . . . . . . . . . . . . . . . . . 24
5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 29 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 30
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
7. Security Considerations . . . . . . . . . . . . . . . . . . . 30 7. Security Considerations . . . . . . . . . . . . . . . . . . . 31
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.1. Normative References . . . . . . . . . . . . . . . . . . . 31 8.1. Normative References . . . . . . . . . . . . . . . . . . . 32
8.2. Informative References . . . . . . . . . . . . . . . . . . 32 8.2. Informative References . . . . . . . . . . . . . . . . . . 33
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 34 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction 1. Introduction
Some IPv6 gateway devices that enable delivery of Internet services Some IPv6 gateway devices that enable delivery of Internet services
in residential and small office settings may be augmented with in residential and small office settings may be augmented with
'simple security' capabilities as described in "Local Network 'simple security' capabilities as described in "Local Network
Protection for IPv6" [RFC4864]. In general, these capabilities cause Protection for IPv6" [RFC4864]. In general, these capabilities cause
packets to be discarded in an attempt to make local networks and the packets to be discarded in an attempt to make local networks and the
Internet more secure. However, it is worth noting that some packets Internet more secure. However, it is worth noting that some packets
sent by legitimate applications may also be discarded in this sent by legitimate applications may also be discarded in this
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document as pertaining to a configuration as applied by a vendor, document as pertaining to a configuration as applied by a vendor,
prior to the administrator changing it for its initial activation. prior to the administrator changing it for its initial activation.
1.2. Use of Normative Keywords 1.2. Use of Normative Keywords
NOTE WELL: This document is not a standard, and conformance with it NOTE WELL: This document is not a standard, and conformance with it
is not required in order to claim conformance with IETF standards for is not required in order to claim conformance with IETF standards for
IPv6. It uses the normative keywords defined in the previous section IPv6. It uses the normative keywords defined in the previous section
only for precision. only for precision.
Particular attention is drawn to recommendation REC-47, which calls Particular attention is drawn to recommendation REC-49, which calls
for an easy way to set a gateway to a transparent mode of operation. for an easy way to set a gateway to a transparent mode of operation.
2. Overview 2. Overview
For the purposes of this document, residential Internet gateways are For the purposes of this document, residential Internet gateways are
assumed to be fairly simple devices with a limited subset of the full assumed to be fairly simple devices with a limited subset of the full
range of possible features. They function as default routers range of possible features. They function as default routers
[RFC4294] for a single local-area network, e.g. an Ethernet, a Wi-Fi [RFC4294] for a single local-area network, e.g. an Ethernet, a Wi-Fi
network, a bridge between two or more such segments. They have only network, a bridge between two or more such segments. They have only
one interface by which they can access the Internet service at any one interface by which they can access the Internet service at any
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As virtual private networking tunnels are regarded as an unacceptably As virtual private networking tunnels are regarded as an unacceptably
wide attack surface, this document recommends the DEFAULT operating wide attack surface, this document recommends the DEFAULT operating
mode for residential IPv6 simple security is to treat Generic Packet mode for residential IPv6 simple security is to treat Generic Packet
Tunneling [RFC2473] and similar protocols as opaque transport layers, Tunneling [RFC2473] and similar protocols as opaque transport layers,
i.e. inbound tunnel initiations are denied and outbound tunnel i.e. inbound tunnel initiations are denied and outbound tunnel
initiations are accepted. initiations are accepted.
IPsec transport and tunnel modes are explicitly secured by IPsec transport and tunnel modes are explicitly secured by
definition, so this document recommends the DEFAULT operating mode definition, so this document recommends the DEFAULT operating mode
permit IPsec. To facilitate the use of IPsec in support of IPv6 permit IPsec. To facilitate the use of IPsec in support of IPv6
Mobility, Internet Key Exchange (IKE) protocol [RFC4306] and "Host Mobility, Internet Key Exchange (IKE) protocol [RFC5996] and "Host
Identity Protocol (HIP)" [RFC5201] should also be permitted in the Identity Protocol (HIP)" [RFC5201] should also be permitted in the
DEFAULT operating mode. DEFAULT operating mode.
2.3. Transport Layer Protocols 2.3. Transport Layer Protocols
IPv6 simple security functions are principally concerned with the IPv6 simple security functions are principally concerned with the
stateful filtering of Internet Control Message Protocol (ICMPv6) stateful filtering of Internet Control Message Protocol (ICMPv6)
[RFC4443] and transport layers like User Datagram Protocol (UDP) [RFC4443] and transport layers like User Datagram Protocol (UDP)
[RFC0768], Lightweight User Datagram Protocol (UDP-Lite) [RFC3828], [RFC0768], Lightweight User Datagram Protocol (UDP-Lite) [RFC3828],
Transport Control Protocol (TCP) [RFC0793], the Stream Control Transport Control Protocol (TCP) [RFC0793], the Stream Control
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REC-7: By DEFAULT, packets with unique local source and/or REC-7: By DEFAULT, packets with unique local source and/or
destination addresses [RFC4193] SHOULD NOT be forwarded to or from destination addresses [RFC4193] SHOULD NOT be forwarded to or from
the exterior network. the exterior network.
REC-8: By DEFAULT, inbound DNS queries received on exterior REC-8: By DEFAULT, inbound DNS queries received on exterior
interfaces MUST NOT be processed by any integrated DNS resolving interfaces MUST NOT be processed by any integrated DNS resolving
server. server.
REC-9: Inbound DHCPv6 discovery packets [RFC3315] received on REC-9: Inbound DHCPv6 discovery packets [RFC3315] received on
exterior interfaces MUST NOT be processed by any integrated DHCPv6 exterior interfaces MUST NOT be processed by any integrated DHCPv6
server. server or relay agent.
NOTE WELL: nothing in this document relieves residential Internet
gateways, when processing headers to identify valid sequences of
upper-layer transport packets, from any of the requirements of the
Internet Protocol, Version 6 (IPv6) Specification [RFC2460],
including any and all future updates and revisions.
3.2. Connection-free Filters 3.2. Connection-free Filters
Some Internet applications use connection-free transport protocols Some Internet applications use connection-free transport protocols
with no release semantics, e.g. UDP. These protocols pose a special with no release semantics, e.g. UDP. These protocols pose a special
difficulty for stateful packet filters because most of the difficulty for stateful packet filters because most of the
application state is not carried at the transport level. State application state is not carried at the transport level. State
records are created when communication is initiated and abandoned records are created when communication is initiated and abandoned
when no further communication is detected after some period of time. when no further communication is detected after some period of time.
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discussed in subsequent sections of this document are expected to be discussed in subsequent sections of this document are expected to be
treated consistently, i.e. as having connection-free semantics and no treated consistently, i.e. as having connection-free semantics and no
special requirements to inspect the transport headers. special requirements to inspect the transport headers.
In general, upper-layer transport filter state records are expected In general, upper-layer transport filter state records are expected
to be created when an interior endpoint sends a packet to an exterior to be created when an interior endpoint sends a packet to an exterior
address. The filter allocates (or reuses) a record for the duration address. The filter allocates (or reuses) a record for the duration
of communications, with an idle timer to delete the state record when of communications, with an idle timer to delete the state record when
no further communications are detected. no further communications are detected.
One key aspect of how a packet filter behaves is the way it evaluates
the exterior address of an enpoint when applying a filtering rule. A
gateway is said to have "endpoint independent filtering" behavior
when the exterior address is not evaluated when matching a packet
with a flow. A gateway is said to have "address dependent filtering"
behavior when the exterior address of a packet is required to match
the exterior address for its flow.
REC-11: If application transparency is most important, then a REC-11: If application transparency is most important, then a
stateful packet filter SHOULD have "Endpoint independent filter" stateful packet filter SHOULD have "endpoint independent filter"
behavior for generic upper-layer transport protocols. If a more behavior for generic upper-layer transport protocols. If a more
stringent filtering behavior is most important, then a filter SHOULD stringent filtering behavior is most important, then a filter SHOULD
have "Address dependent filtering" behavior. The filtering behavior have "address dependent filtering" behavior. The filtering behavior
MAY be an option configurable by the network administrator, and it MAY be an option configurable by the network administrator, and it
MAY be independent of the filtering behavior for other protocols. MAY be independent of the filtering behavior for other protocols.
Filtering behavior SHOULD be endpoint independent by DEFAULT in Filtering behavior SHOULD be endpoint independent by DEFAULT in
gateways intended for provisioning without service-provider gateways intended for provisioning without service-provider
management. management.
REC-12: Filter state records for generic upper-layer transport REC-12: Filter state records for generic upper-layer transport
protocols MUST NOT be deleted or recycled until an idle timer not protocols MUST NOT be deleted or recycled until an idle timer not
less than two minutes has expired without having forwarded a packet less than two minutes has expired without having forwarded a packet
matching the state in some configurable amount of time. By DEFAULT, matching the state in some configurable amount of time. By DEFAULT,
the idle timer for such state records is five minutes. the idle timer for such state records is five minutes.
The Internet security community never is never completely at rest.
New attack surfaces, and vulnerabilities in them, are typically
discovered faster than they can be patched by normal equipment
upgrade cycles. It's therefore important for vendors of residential
gateway equipment to provide automatic softare updates to patch
vulnerabilties as they are discovered.
REC-13: By DEFAULT, Internet gateways SHOULD, automatically download
and install software updates for extending IPv6 simple security for
support of future standard upper layer transports and extension
headers.
3.2.3. UDP Filters 3.2.3. UDP Filters
"Network Address Translation (NAT) Behavioral Requirements for "Network Address Translation (NAT) Behavioral Requirements for
Unicast UDP" [RFC4787] defines the terminology and best current Unicast UDP" [RFC4787] defines the terminology and best current
practice for stateful filtering of UDP applications in IPv4 with NAT, practice for stateful filtering of UDP applications in IPv4 with NAT,
which serves as the model for behavioral requirements for simple UDP which serves as the model for behavioral requirements for simple UDP
security in IPv6 gateways, notwithstanding the requirements related security in IPv6 gateways, notwithstanding the requirements related
specifically to network address translation. specifically to network address translation.
An interior endpoint initiates a UDP flow through a stateful packet An interior endpoint initiates a UDP flow through a stateful packet
filter by sending a packet to an exterior address. The filter filter by sending a packet to an exterior address. The filter
allocates (or reuses) a filter state record for the duration of the allocates (or reuses) a filter state record for the duration of the
flow. The state record defines the interior and exterior IP flow. The state record defines the interior and exterior IP
addresses and ports used between all packets in the flow. addresses and ports used between all packets in the flow.
State records for UDP flows remain active while they are in use and State records for UDP flows remain active while they are in use and
only abandoned after an idle period of some time. only abandoned after an idle period of some time.
REC-13: A state record for a UDP flow where both source and REC-14: A state record for a UDP flow where both source and
destination ports are outside the well-known port range (ports destination ports are outside the well-known port range (ports
0-1023) MUST NOT expire in less than two minutes of idle time. The 0-1023) MUST NOT expire in less than two minutes of idle time. The
value of the UDP state record idle timer MAY be configurable. The value of the UDP state record idle timer MAY be configurable. The
DEFAULT is five minutes. DEFAULT is five minutes.
REC-14: A state record for a UDP flow where one or both of the source REC-15: A state record for a UDP flow where one or both of the source
and destination ports are in the well-known port range (ports 0-1023) and destination ports are in the well-known port range (ports 0-1023)
MAY expire after a period of idle time shorter than two minutes to MAY expire after a period of idle time shorter than two minutes to
facilitate the operation of the IANA-registered service assigned to facilitate the operation of the IANA-registered service assigned to
the port in question. the port in question.
As [RFC4787] notes, outbound refresh is necessary for allowing the As [RFC4787] notes, outbound refresh is necessary for allowing the
interior endpoint to keep the state record alive. Inbound refresh interior endpoint to keep the state record alive. Inbound refresh
may be useful for applications with no outbound UDP traffic. may be useful for applications with no outbound UDP traffic.
However, allowing inbound refresh can allow an attacker in the However, allowing inbound refresh can allow an attacker in the
exterior or a misbehaving application to keep a state record alive exterior or a misbehaving application to keep a state record alive
indefinitely. This could be a security risk. Also, if the process indefinitely. This could be a security risk. Also, if the process
is repeated with different ports, over time, it could use up all the is repeated with different ports, over time, it could use up all the
state record memory and resources in the filter. state record memory and resources in the filter.
REC-15: A state record for a UDP flow MUST be refreshed when a packet REC-16: A state record for a UDP flow MUST be refreshed when a packet
is forwarded from the interior to the exterior, and it MAY be is forwarded from the interior to the exterior, and it MAY be
refreshed when a packet is forwarded in the reverse direction. refreshed when a packet is forwarded in the reverse direction.
As described in Section 5.5 of [RFC4787], the connection-free As described in Section 5.5 of [RFC4787], the connection-free
semantics of UDP pose a difficulty for packet filters in trying to semantics of UDP pose a difficulty for packet filters in trying to
recognize which packets comprise an application flow and which are recognize which packets comprise an application flow and which are
unsolicited. Various strategies have been used in IPv4/NAT gateways unsolicited. Various strategies have been used in IPv4/NAT gateways
with differing effects. with differing effects.
REC-16: If application transparency is most important, then a REC-17: If application transparency is most important, then a
stateful packet filter SHOULD have "Endpoint independent filter" stateful packet filter SHOULD have "endpoint independent filter"
behavior for UDP. If a more stringent filtering behavior is most behavior for UDP. If a more stringent filtering behavior is most
important, then a filter SHOULD have "Address dependent filtering" important, then a filter SHOULD have "address dependent filtering"
behavior. The filtering behavior MAY be an option configurable by behavior. The filtering behavior MAY be an option configurable by
the network administrator, and it MAY be independent of the filtering the network administrator, and it MAY be independent of the filtering
behavior for TCP and other protocols. Filtering behavior SHOULD be behavior for TCP and other protocols. Filtering behavior SHOULD be
endpoint independent by DEFAULT in gateways intended for provisioning endpoint independent by DEFAULT in gateways intended for provisioning
without service-provider management. without service-provider management.
Applications mechanisms may depend on the reception of ICMPv6 error Applications mechanisms may depend on the reception of ICMPv6 error
messages triggered by the transmission of UDP messages. One such messages triggered by the transmission of UDP messages. One such
mechanism is path MTU discovery. mechanism is path MTU discovery.
REC-17: If a gateway forwards a UDP flow, it MUST also forward ICMPv6 REC-18: If a gateway forwards a UDP flow, it MUST also forward ICMPv6
"Destination Unreachable" and "Packet Too Big" messages containing "Destination Unreachable" and "Packet Too Big" messages containing
UDP headers that match the flow state record. UDP headers that match the flow state record.
REC-18: Receipt of any sort of ICMPv6 message MUST NOT terminate the REC-19: Receipt of any sort of ICMPv6 message MUST NOT terminate the
state record for a UDP flow. state record for a UDP flow.
REC-19: UDP-Lite flows [RFC3828] SHOULD be handled in the same way as REC-20: UDP-Lite flows [RFC3828] SHOULD be handled in the same way as
UDP flows, except that the upper-layer transport protocol identifier UDP flows, except that the upper-layer transport protocol identifier
for UDP-Lite is not the same as UDP, and therefore UDP packets MUST for UDP-Lite is not the same as UDP, and therefore UDP packets MUST
NOT match UDP-Lite state records, and vice versa. NOT match UDP-Lite state records, and vice versa.
3.2.4. IPsec and Internet Key Exchange (IKE) 3.2.4. IPsec and Internet Key Exchange (IKE)
The Internet protocol security suite (IPsec) offers greater The Internet protocol security suite (IPsec) offers greater
flexibility and better overall security than the simple security of flexibility and better overall security than the simple security of
stateful packet filtering at network perimeters. Therefore, stateful packet filtering at network perimeters. Therefore,
residential IPv6 gateways need not prohibit IPsec traffic flows. residential IPv6 gateways need not prohibit IPsec traffic flows.
REC-20: In their DEFAULT operating mode, IPv6 gateways MUST NOT REC-21: In their DEFAULT operating mode, IPv6 gateways MUST NOT
prohibit the forwarding of packets, to and from legitimate node prohibit the forwarding of packets, to and from legitimate node
addresses, with destination extension headers of type "Authenticated addresses, with destination extension headers of type "Authenticated
Header (AH)" [RFC4302] in their outer IP extension header chain. Header (AH)" [RFC4302] in their outer IP extension header chain.
REC-21: In their DEFAULT operating mode, IPv6 gateways MUST NOT REC-22: In their DEFAULT operating mode, IPv6 gateways MUST NOT
prohibit the forwarding of packets, to and from legitimate node prohibit the forwarding of packets, to and from legitimate node
addresses, with an upper layer protocol of type "Encapsulating addresses, with an upper layer protocol of type "Encapsulating
Security Payload (ESP)" [RFC4303] in their outer IP extension header Security Payload (ESP)" [RFC4303] in their outer IP extension header
chain. chain.
REC-22: If a gateway forwards an ESP flow, it MUST also forward (in REC-23: If a gateway forwards an ESP flow, it MUST also forward (in
the reverse direction) ICMPv6 "Destination Unreachable" and "Packet the reverse direction) ICMPv6 "Destination Unreachable" and "Packet
Too Big" messages containing ESP headers that match the flow state Too Big" messages containing ESP headers that match the flow state
record. record.
Internet Key Exchange (IKE) is a secure mechanism for performing Internet Key Exchange (IKE) is a secure mechanism for performing
mutual authentication, exchanging cryptographic material and mutual authentication, exchanging cryptographic material and
establishing IPsec Security Associations between peers. Residential establishing IPsec Security Associations between peers. Residential
IPv6 gateways are expected to facilitate the use of IPsec security IPv6 gateways are expected to facilitate the use of IPsec security
policies by allowing inbound IKE flows. policies by allowing inbound IKE flows.
REC-23: In their DEFAULT operating mode, IPv6 gateways MUST NOT REC-24: In their DEFAULT operating mode, IPv6 gateways MUST NOT
prohibit the forwarding of any UDP packets, to and from legitimate prohibit the forwarding of any UDP packets, to and from legitimate
node addresses, with a destination port of 500, i.e. the port node addresses, with a destination port of 500, i.e. the port
reserved by IANA for the Internet Key Exchange (IKE) protocol reserved by IANA for the Internet Key Exchange (IKE) protocol
[RFC4306]. [RFC5996].
REC-24: In all operating modes, IPv6 gateways SHOULD use filter state REC-25: In all operating modes, IPv6 gateways SHOULD use filter state
records for Encapsulating Security Payload (ESP) [RFC4303] that are records for Encapsulating Security Payload (ESP) [RFC4303] that are
indexable by a 3-tuple comprising the interior node address, the indexable by a 3-tuple comprising the interior node address, the
exterior node address and the ESP protocol identifier. In exterior node address and the ESP protocol identifier. In
particular, the IPv4/NAT method of indexing state records also by particular, the IPv4/NAT method of indexing state records also by
security parameters index (SPI) SHOULD NOT be used. Likewise, any security parameters index (SPI) SHOULD NOT be used. Likewise, any
mechanism that depends on detection of Internet Key Exchange (IKE) mechanism that depends on detection of Internet Key Exchange (IKE)
[RFC4306] initiations SHOULD NOT be used. [RFC5996] initiations SHOULD NOT be used.
"Host Identity Protocol (HIP)" is a secure mechanism for establishing "Host Identity Protocol (HIP)" is a secure mechanism for establishing
host identity and secure communications between authenticated hosts. host identity and secure communications between authenticated hosts.
Residential IPv6 gateways need not prohibit inbound HIP flows. Residential IPv6 gateways need not prohibit inbound HIP flows.
REC-25: In their DEFAULT operating mode, IPv6 gateways MUST NOT REC-26: In their DEFAULT operating mode, IPv6 gateways MUST NOT
prohibit the forwarding of packets, to and from legitimate node prohibit the forwarding of packets, to and from legitimate node
addresses, with destination extension headers of type "Host Identity addresses, with destination extension headers of type "Host Identity
Protocol (HIP)" [RFC5201] in their outer IP extension header chain. Protocol (HIP)" [RFC5201] in their outer IP extension header chain.
3.2.5. Mobility Support in IPv6 3.2.5. Mobility Support in IPv6
Mobility support in IPv6 [RFC3775] relies on the use of an Mobility support in IPv6 [RFC3775] relies on the use of an
encapsulation mechanism in flows between mobile nodes and their encapsulation mechanism in flows between mobile nodes and their
correspondent nodes, involving the use of the type 2 IPv6 routing correspondent nodes, involving the use of the type 2 IPv6 routing
header, the Home Address destination header option and the Mobility header, the Home Address destination header option and the Mobility
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to be gained by denying communications with either interior or to be gained by denying communications with either interior or
exterior mobile nodes. exterior mobile nodes.
Not all usage scenarios of Mobility support in IPv6 are expected to Not all usage scenarios of Mobility support in IPv6 are expected to
compatible with IPv6 simple security. In particular, exterior mobile compatible with IPv6 simple security. In particular, exterior mobile
nodes are expected to be prohibited from establishing bindings with nodes are expected to be prohibited from establishing bindings with
interior correspondent nodes by the filtering of unsolicited inbound interior correspondent nodes by the filtering of unsolicited inbound
Mobility Header messages unless they are the subject of an IPsec Mobility Header messages unless they are the subject of an IPsec
security policy. security policy.
REC-26: The state records for flows initiated by outbound packets REC-27: The state records for flows initiated by outbound packets
that bear a Home Address destination option [RFC3775] are that bear a Home Address destination option [RFC3775] are
distinguished by the addition of the home address of the flow as well distinguished by the addition of the home address of the flow as well
as the interior care-of address. IPv6 gateways MUST NOT prohibit the as the interior care-of address. IPv6 gateways MUST NOT prohibit the
forwarding of any inbound packets bearing type 2 routing headers, forwarding of any inbound packets bearing type 2 routing headers,
which otherwise match a flow state record, and where A) the address which otherwise match a flow state record, and where A) the address
in the destination field of the IPv6 header matches the interior in the destination field of the IPv6 header matches the interior
care-of address of the flow, and B) the Home Address field in the care-of address of the flow, and B) the Home Address field in the
Type 2 Routing Header matches the home address of the flow. Type 2 Routing Header matches the home address of the flow.
REC-27: Valid sequences of Mobility Header [RFC3775] packets MUST be REC-28: Valid sequences of Mobility Header [RFC3775] packets MUST be
forwarded for all outbound and explicitly permitted inbound Mobility forwarded for all outbound and explicitly permitted inbound Mobility
Header flows. Header flows.
REC-28: If a gateway forwards a Mobility Header [RFC3775] flow, then REC-29: If a gateway forwards a Mobility Header [RFC3775] flow, then
it MUST also forward, in both directions, the IPv4 and IPv6 packets it MUST also forward, in both directions, the IPv4 and IPv6 packets
that are encapsulated in IPv6 associated with the tunnel between the that are encapsulated in IPv6 associated with the tunnel between the
home agent and the correspondent node. home agent and the correspondent node.
REC-29: If a gateway forwards a Mobility Header [RFC3775] flow, then REC-30: If a gateway forwards a Mobility Header [RFC3775] flow, then
it MUST also forward (in the reverse direction) ICMPv6 "Destination it MUST also forward (in the reverse direction) ICMPv6 "Destination
Unreachable" and "Packet Too Big" messages containing any headers Unreachable" and "Packet Too Big" messages containing any headers
that match the associated flow state records. that match the associated flow state records.
3.3. Connection-oriented Filters 3.3. Connection-oriented Filters
Most Internet applications use connection-oriented transport Most Internet applications use connection-oriented transport
protocols with orderly release semantics. These protocols include protocols with orderly release semantics. These protocols include
TCP, SCTP, DCCP, and potentially any future IETF standards-track TCP, SCTP, DCCP, and potentially any future IETF standards-track
transport protocols that use such semantics. Stateful packet filters transport protocols that use such semantics. Stateful packet filters
skipping to change at page 13, line 27 skipping to change at page 13, line 52
in the network. Upon receiving the other end's SYN packet, each end in the network. Upon receiving the other end's SYN packet, each end
responds with a SYN-ACK packet, which also cross in the network. The responds with a SYN-ACK packet, which also cross in the network. The
connection is established at each endpoint once the SYN-ACK packets connection is established at each endpoint once the SYN-ACK packets
are received. are received.
To provide stateful packet filtering service for TCP, it is necessary To provide stateful packet filtering service for TCP, it is necessary
for a filter to receive, process and forward all packets for a flow for a filter to receive, process and forward all packets for a flow
that conform to valid transitions of the TCP state machine (Fig. 6, that conform to valid transitions of the TCP state machine (Fig. 6,
[RFC0793]). [RFC0793]).
REC-30: All valid sequences of TCP packets (defined in [RFC0793]) REC-31: All valid sequences of TCP packets (defined in [RFC0793])
MUST be forwarded for outbound flows and explicitly permitted inbound MUST be forwarded for outbound flows and explicitly permitted inbound
flows. In particular, both the normal TCP 3-way handshake mode of flows. In particular, both the normal TCP 3-way handshake mode of
operation and the simultaneous-open modes of operation MUST be operation and the simultaneous-open modes of operation MUST be
supported. supported.
It is possible to reconstruct enough of the state of a TCP flow to It is possible to reconstruct enough of the state of a TCP flow to
allow forwarding between an interior and exterior node even when the allow forwarding between an interior and exterior node even when the
filter starts operating after TCP enters the established state. In filter starts operating after TCP enters the established state. In
this case, because the filter has not seen the TCP window-scale this case, because the filter has not seen the TCP window-scale
option, it is not possible for the filter to enforce the TCP window option, it is not possible for the filter to enforce the TCP window
invariant by dropping out-of-window segments. invariant by dropping out-of-window segments.
REC-31: The TCP window invariant MUST NOT be enforced on flows for REC-32: The TCP window invariant MUST NOT be enforced on flows for
which the filter did not detect whether the window-scale option (see which the filter did not detect whether the window-scale option (see
[RFC1323]) was sent in the 3-way handshake or simultaneous open. [RFC1323]) was sent in the 3-way handshake or simultaneous open.
A stateful filter can allow an existing state record to be reused by A stateful filter can allow an existing state record to be reused by
an externally initiated flow if its security policy permits. Several an externally initiated flow if its security policy permits. Several
different policies are possible as described in [RFC4787] and different policies are possible as described in [RFC4787] and
extended in [RFC5382]. extended in [RFC5382].
REC-32: If application transparency is most important, then a REC-33: If application transparency is most important, then a
stateful packet filter SHOULD have "Endpoint independent filter" stateful packet filter SHOULD have "endpoint independent filter"
behavior for TCP. If a more stringent filtering behavior is most behavior for TCP. If a more stringent filtering behavior is most
important, then a filter SHOULD have "Address dependent filtering" important, then a filter SHOULD have "address dependent filtering"
behavior. The filtering behavior MAY be an option configurable by behavior. The filtering behavior MAY be an option configurable by
the network administrator, and it MAY be independent of the filtering the network administrator, and it MAY be independent of the filtering
behavior for UDP and other protocols. Filtering behavior SHOULD be behavior for UDP and other protocols. Filtering behavior SHOULD be
endpoint independent by DEFAULT in gateways intended for provisioning endpoint independent by DEFAULT in gateways intended for provisioning
without service-provider management. without service-provider management.
If an inbound SYN packet is filtered, either because a corresponding If an inbound SYN packet is filtered, either because a corresponding
state record does not exist or because of the filter's normal state record does not exist or because of the filter's normal
behavior, a filter has two basic choices: to discard the packet behavior, a filter has two basic choices: to discard the packet
silently, or to signal an error to the sender. Signaling an error silently, or to signal an error to the sender. Signaling an error
through ICMPv6 messages allows the sender to detect that the SYN did through ICMPv6 messages allows the sender to detect that the SYN did
not reach the intended destination. Discarding the packet, on the not reach the intended destination. Discarding the packet, on the
other hand, allows applications to perform simultaneous-open more other hand, allows applications to perform simultaneous-open more
reliably. A more detailed discussion of this issue can be found in reliably. A more detailed discussion of this issue can be found in
[RFC5382], but the basic outcome of it is that filters need to wait [RFC5382], but the basic outcome of it is that filters need to wait
on signaling errors until simultaneous-open will not be impaired. on signaling errors until simultaneous-open will not be impaired.
REC-33: By DEFAULT, a gateway MUST respond with an ICMPv6 REC-34: By DEFAULT, a gateway MUST respond with an ICMPv6
"Destination Unreachable" error code 1 (administratively prohibited) "Destination Unreachable" error code 1 (administratively prohibited)
to any unsolicited inbound SYN packet after waiting at least 6 to any unsolicited inbound SYN packet after waiting at least 6
seconds without first forwarding the associated outbound SYN or SYN/ seconds without first forwarding the associated outbound SYN or SYN/
ACK from the interior peer. ACK from the interior peer.
A TCP filter maintains state associated with in-progress connections A TCP filter maintains state associated with in-progress connections
and established flows. Because of this, a filter is susceptible to a and established flows. Because of this, a filter is susceptible to a
resource-exhaustion attack whereby an attacker (or virus) on the resource-exhaustion attack whereby an attacker (or virus) on the
interior attempts to cause the filter to exhaust its capacity for interior attempts to cause the filter to exhaust its capacity for
creating state records. To defend against such attacks, a filter creating state records. To defend against such attacks, a filter
skipping to change at page 15, line 21 skipping to change at page 15, line 47
The "established flow idle-timeout" for a stateful packet filter is The "established flow idle-timeout" for a stateful packet filter is
defined as the minimum time a TCP flow in the established phase must defined as the minimum time a TCP flow in the established phase must
remain idle before the filter considers the associated state record a remain idle before the filter considers the associated state record a
candidate for collection. The "transitory flow idle-timeout" for a candidate for collection. The "transitory flow idle-timeout" for a
filter is defined as the minimum time a TCP flow in the partially- filter is defined as the minimum time a TCP flow in the partially-
open or closing phases must remain idle before the filter considers open or closing phases must remain idle before the filter considers
the associated state record a candidate for collection. TCP flows in the associated state record a candidate for collection. TCP flows in
the TIME_WAIT state are not affected by the "transitory flow idle- the TIME_WAIT state are not affected by the "transitory flow idle-
timeout" parameter. timeout" parameter.
REC-34: If a gateway cannot determine whether the endpoints of a TCP REC-35: If a gateway cannot determine whether the endpoints of a TCP
flow are active, then it MAY abandon the state record if it has been flow are active, then it MAY abandon the state record if it has been
idle for some time. In such cases, the value of the "established idle for some time. In such cases, the value of the "established
flow idle-timeout" MUST NOT be less than two hours four minutes, as flow idle-timeout" MUST NOT be less than two hours four minutes, as
discussed in [RFC5382]. The value of the "transitory flow idle- discussed in [RFC5382]. The value of the "transitory flow idle-
timeout" MUST NOT be less than four minutes. The value of the idle- timeout" MUST NOT be less than four minutes. The value of the idle-
timeouts MAY be configurable by the network administrator. timeouts MAY be configurable by the network administrator.
Behavior for handing RST packets, or TCP flows in the TIME_WAIT state Behavior for handing RST packets, or TCP flows in the TIME_WAIT state
is left unspecified. A gateway MAY hold state for a flow in is left unspecified. A gateway MAY hold state for a flow in
TIME_WAIT state to accommodate retransmissions of the last ACK. TIME_WAIT state to accommodate retransmissions of the last ACK.
skipping to change at page 16, line 11 skipping to change at page 16, line 36
endpoint on behalf of the other. Sending a RST notification allows endpoint on behalf of the other. Sending a RST notification allows
endpoint applications to recover more quickly, however, notifying endpoint applications to recover more quickly, however, notifying
endpoints might not always be possible if, for example, state records endpoints might not always be possible if, for example, state records
are lost due to power interruption. are lost due to power interruption.
Several TCP mechanisms depend on the reception of ICMPv6 error Several TCP mechanisms depend on the reception of ICMPv6 error
messages triggered by the transmission of TCP segments. One such messages triggered by the transmission of TCP segments. One such
mechanism is path MTU discovery, which is required for correct mechanism is path MTU discovery, which is required for correct
operation of TCP. operation of TCP.
REC-35: If a gateway forwards a TCP flow, it MUST also forward ICMPv6 REC-36: If a gateway forwards a TCP flow, it MUST also forward ICMPv6
"Destination Unreachable" and "Packet Too Big" messages containing "Destination Unreachable" and "Packet Too Big" messages containing
TCP headers that match the flow state record. TCP headers that match the flow state record.
REC-36: Receipt of any sort of ICMPv6 message MUST NOT terminate the REC-37: Receipt of any sort of ICMPv6 message MUST NOT terminate the
state record for a TCP flow. state record for a TCP flow.
3.3.2. SCTP Filters 3.3.2. SCTP Filters
Because Stream Control Transmission Protocol (SCTP) [RFC4960] flows Because Stream Control Transmission Protocol (SCTP) [RFC4960] flows
can be terminated at multiple network addresses, IPv6 simple security can be terminated at multiple network addresses, IPv6 simple security
functions cannot achieve full transparency for SCTP applications. In functions cannot achieve full transparency for SCTP applications. In
multipath traversal scenarios, full transparency requires multipath traversal scenarios, full transparency requires
coordination between all the packet filter processes in the various coordination between all the packet filter processes in the various
paths between the endpoint network addresses. Such coordination is paths between the endpoint network addresses. Such coordination is
skipping to change at page 17, line 13 skipping to change at page 17, line 38
of the peers in simultaneous-open mode of operation will send an of the peers in simultaneous-open mode of operation will send an
ERROR or ABORT chunk along with the INIT-ACK chunk. The association ERROR or ABORT chunk along with the INIT-ACK chunk. The association
is established at each endpoint once an INIT-ACK chunks is received is established at each endpoint once an INIT-ACK chunks is received
at one end without an ERROR or ABORT chunk. at one end without an ERROR or ABORT chunk.
To provide stateful packet filtering service for SCTP, it is To provide stateful packet filtering service for SCTP, it is
necessary for a filter to receive, process and forward all packets necessary for a filter to receive, process and forward all packets
for an association that conform to valid transitions of the SCTP for an association that conform to valid transitions of the SCTP
state machine (Fig. 3, [RFC4960]). state machine (Fig. 3, [RFC4960]).
REC-37: All valid sequences of SCTP packets (defined in [RFC4960]) REC-38: All valid sequences of SCTP packets (defined in [RFC4960])
MUST be forwarded for outbound associations and explicitly permitted MUST be forwarded for outbound associations and explicitly permitted
inbound associations. In particular, both the normal SCTP inbound associations. In particular, both the normal SCTP
association establishment and simultaneous-open modes of operation association establishment and simultaneous-open modes of operation
MUST be supported. MUST be supported.
If an inbound INIT packet is filtered, either because a corresponding If an inbound INIT packet is filtered, either because a corresponding
state record does not exist or because of the filter's normal state record does not exist or because of the filter's normal
behavior, a filter has two basic choices: to discard the packet behavior, a filter has two basic choices: to discard the packet
silently, or to signal an error to the sender. Signaling an error silently, or to signal an error to the sender. Signaling an error
through ICMPv6 messages allows the sender to detect that the INIT through ICMPv6 messages allows the sender to detect that the INIT
packet did not reach the intended destination. Discarding the packet did not reach the intended destination. Discarding the
packet, on the other hand, allows applications to perform packet, on the other hand, allows applications to perform
simultaneous-open more reliably. Delays in signaling errors can simultaneous-open more reliably. Delays in signaling errors can
prevent the impairment of simultaneous-open mode of operation. prevent the impairment of simultaneous-open mode of operation.
REC-38: By DEFAULT, a gateway MUST respond with an ICMPv6 REC-39: By DEFAULT, a gateway MUST respond with an ICMPv6
"Destination Unreachable" error code 1 (administratively prohibited), "Destination Unreachable" error code 1 (administratively prohibited),
to any unsolicited inbound INIT packet after waiting at least 6 to any unsolicited inbound INIT packet after waiting at least 6
seconds without first forwarding the associated outbound INIT from seconds without first forwarding the associated outbound INIT from
the interior peer. the interior peer.
An SCTP filter maintains state associated with in-progress and An SCTP filter maintains state associated with in-progress and
established associations. Because of this, a filter is susceptible established associations. Because of this, a filter is susceptible
to a resource-exhaustion attack whereby an attacker (or virus) on the to a resource-exhaustion attack whereby an attacker (or virus) on the
interior attempts to cause the filter to exhaust its capacity for interior attempts to cause the filter to exhaust its capacity for
creating state records. To defend against such attacks, a filter creating state records. To defend against such attacks, a filter
skipping to change at page 18, line 30 skipping to change at page 19, line 7
The "established association idle-timeout" for a stateful packet The "established association idle-timeout" for a stateful packet
filter is defined as the minimum time an SCTP association in the filter is defined as the minimum time an SCTP association in the
established phase must remain idle before the filter considers the established phase must remain idle before the filter considers the
corresponding state record a candidate for collection. The corresponding state record a candidate for collection. The
"transitory association idle-timeout" for a filter is defined as the "transitory association idle-timeout" for a filter is defined as the
minimum time an SCTP association in the partially-open or closing minimum time an SCTP association in the partially-open or closing
phases must remain idle before the filter considers the corresponding phases must remain idle before the filter considers the corresponding
state record a candidate for collection. state record a candidate for collection.
REC-39: If a gateway cannot determine whether the endpoints of an REC-40: If a gateway cannot determine whether the endpoints of an
SCTP association are active, then it MAY abandon the state record if SCTP association are active, then it MAY abandon the state record if
it has been idle for some time. In such cases, the value of the it has been idle for some time. In such cases, the value of the
"established association idle-timeout" MUST NOT be less than two "established association idle-timeout" MUST NOT be less than two
hours four minutes. The value of the "transitory association idle- hours four minutes. The value of the "transitory association idle-
timeout" MUST NOT be less than four minutes. The value of the idle- timeout" MUST NOT be less than four minutes. The value of the idle-
timeouts MAY be configurable by the network administrator. timeouts MAY be configurable by the network administrator.
Behavior for handling ERROR and ABORT packets is left unspecified. A Behavior for handling ERROR and ABORT packets is left unspecified. A
gateway MAY hold state for an association after its closing phases gateway MAY hold state for an association after its closing phases
have completed to accommodate retransmissions of its final SHUTDOWN have completed to accommodate retransmissions of its final SHUTDOWN
skipping to change at page 19, line 17 skipping to change at page 19, line 42
left unspecified. When a gateway abandons a live association, for left unspecified. When a gateway abandons a live association, for
example due to a timeout expiring, the filter MAY send an ABORT example due to a timeout expiring, the filter MAY send an ABORT
packet to each endpoint on behalf of the other. Sending an ABORT packet to each endpoint on behalf of the other. Sending an ABORT
notification allows endpoint applications to recover more quickly, notification allows endpoint applications to recover more quickly,
however, notifying endpoints might not always be possible if, for however, notifying endpoints might not always be possible if, for
example, state records are lost due to power interruption. example, state records are lost due to power interruption.
Several SCTP mechanisms depend on the reception of ICMPv6 error Several SCTP mechanisms depend on the reception of ICMPv6 error
messages triggered by the transmission of SCTP packets. messages triggered by the transmission of SCTP packets.
REC-40: If a gateway forwards an SCTP association, it MUST also REC-41: If a gateway forwards an SCTP association, it MUST also
forward ICMPv6 "Destination Unreachable" and "Packet Too Big" forward ICMPv6 "Destination Unreachable" and "Packet Too Big"
messages containing SCTP headers that match the association state messages containing SCTP headers that match the association state
record. record.
REC-41: Receipt of any sort of ICMPv6 message MUST NOT terminate the REC-42: Receipt of any sort of ICMPv6 message MUST NOT terminate the
state record for an SCTP association. state record for an SCTP association.
3.3.3. DCCP Filters 3.3.3. DCCP Filters
The connection semantics described in Datagram Congestion Control The connection semantics described in Datagram Congestion Control
Protocol (DCCP) [RFC4340] are very similar to those of TCP. An Protocol (DCCP) [RFC4340] are very similar to those of TCP. An
interior endpoint initiates a DCCP flow through a stateful packet interior endpoint initiates a DCCP flow through a stateful packet
filter by sending a DCCP-Request packet. Simultaneous open is not filter by sending a DCCP-Request packet. Simultaneous open is not
defined for DCCP. defined for DCCP.
In order to provide stateful packet filtering service for DCCP, it is In order to provide stateful packet filtering service for DCCP, it is
necessary for a filter to receive, process and forward all packets necessary for a filter to receive, process and forward all packets
for a flow that conform to valid transitions of the DCCP state for a flow that conform to valid transitions of the DCCP state
machine (Section 8, [RFC4340]). machine (Section 8, [RFC4340]).
REC-42: All valid sequences of DCCP packets (defined in [RFC4340]) REC-43: All valid sequences of DCCP packets (defined in [RFC4340])
MUST be forwarded for all flows to exterior servers and those flows MUST be forwarded for all flows to exterior servers and those flows
to interior servers with explicitly permitted service codes. to interior servers with explicitly permitted service codes.
It is possible to reconstruct enough of the state of a DCCP flow to It is possible to reconstruct enough of the state of a DCCP flow to
allow forwarding between an interior and exterior node even when the allow forwarding between an interior and exterior node even when the
filter starts operating after DCCP enters the OPEN state. Also, a filter starts operating after DCCP enters the OPEN state. Also, a
filter can allow an existing state record to be reused by an filter can allow an existing state record to be reused by an
externally initiated flow if its security policy permits. As with externally initiated flow if its security policy permits. As with
TCP, several different policies are possible, with a good discussion TCP, several different policies are possible, with a good discussion
of the issue involved presented in [RFC4787] and extended in of the issue involved presented in [RFC4787] and extended in
skipping to change at page 20, line 44 skipping to change at page 21, line 23
The "open flow idle-timeout" for a stateful packet filter is defined The "open flow idle-timeout" for a stateful packet filter is defined
as the minimum time a DCCP flow in the open state must remain idle as the minimum time a DCCP flow in the open state must remain idle
before the filter considers the associated state record a candidate before the filter considers the associated state record a candidate
for collection. The "transitory flow idle-timeout" for a filter is for collection. The "transitory flow idle-timeout" for a filter is
defined as the minimum time a DCCP flow in the partially-open or defined as the minimum time a DCCP flow in the partially-open or
closing phases must remain idle before the filter considers the closing phases must remain idle before the filter considers the
associated state record a candidate for collection. DCCP flows in associated state record a candidate for collection. DCCP flows in
the TIMEWAIT state are not affected by the "transitory flow idle- the TIMEWAIT state are not affected by the "transitory flow idle-
timeout" parameter. timeout" parameter.
REC-43: A gateway MAY abandon a DCCP state record if it has been idle REC-44: A gateway MAY abandon a DCCP state record if it has been idle
for some time. In such cases, the value of the "established flow for some time. In such cases, the value of the "established flow
idle-timeout" MUST NOT be less than two hours four minutes. The idle-timeout" MUST NOT be less than two hours four minutes. The
value of the "transitory flow idle-timeout" MUST NOT be less than value of the "transitory flow idle-timeout" MUST NOT be less than
eight minutes. The value of the idle-timeouts MAY be configurable by eight minutes. The value of the idle-timeouts MAY be configurable by
the network administrator. the network administrator.
Behavior for handing DCCP-Reset packets, or flows in the TIMEWAIT Behavior for handing DCCP-Reset packets, or flows in the TIMEWAIT
state is left unspecified. A gateway MAY hold state for a flow in state is left unspecified. A gateway MAY hold state for a flow in
TIMEWAIT state to accommodate retransmissions of the last DCCP-Reset. TIMEWAIT state to accommodate retransmissions of the last DCCP-Reset.
However, since the TIMEWAIT state is commonly encountered by interior However, since the TIMEWAIT state is commonly encountered by interior
skipping to change at page 21, line 33 skipping to change at page 22, line 12
endpoint on behalf of the other. Sending a DCCP-Reset notification endpoint on behalf of the other. Sending a DCCP-Reset notification
allows endpoint applications to recover more quickly, however, allows endpoint applications to recover more quickly, however,
notifying endpoints might not always be possible if, for example, notifying endpoints might not always be possible if, for example,
state records are lost due to power interruption. state records are lost due to power interruption.
Several DCCP mechanisms depend on the reception of ICMPv6 error Several DCCP mechanisms depend on the reception of ICMPv6 error
messages triggered by the transmission of DCCP packets. One such messages triggered by the transmission of DCCP packets. One such
mechanism is path MTU discovery, which is required for correct mechanism is path MTU discovery, which is required for correct
operation. operation.
REC-44: If an Internet gateway forwards a DCCP flow, it MUST also REC-45: If an Internet gateway forwards a DCCP flow, it MUST also
forward ICMPv6 "Destination Unreachable" and "Packet Too Big" forward ICMPv6 "Destination Unreachable" and "Packet Too Big"
messages containing DCCP headers that match the flow state record. messages containing DCCP headers that match the flow state record.
REC-45: Receipt of any sort of ICMPv6 message MUST NOT terminate the REC-46: Receipt of any sort of ICMPv6 message MUST NOT terminate the
state record for a DCCP flow. state record for a DCCP flow.
3.3.4. Level 3 Multihoming Shim Protocol for IPv6 (SHIM6) 3.3.4. Level 3 Multihoming Shim Protocol for IPv6 (SHIM6)
IPv6 simple security is applicable to residential networks with only While IPv6 simple security is applicable to residential networks with
one Internet service provider at a time. The use of Level 3 only one Internet service provider at a time, the use of Level 3
Multihoming Shim Protocol for IPv6 (SHIM6) [RFC5533] as a site multi- Multihoming Shim Protocol for IPv6 (SHIM6) [RFC5533] is necessary for
homing solution is not generally compatible with IPv6 simple communications with some multihomed exterior destinations. No
security. No special recommendations with regard to SHIM6 are made special recommendations are made in this document for processing the
in this document. SHIM6 message format (protocol 140) beyond the recommendations in
Section 3.2.2. The content of the SHIM6 payload extension header may
be ignored.
REC-47: Valid sequences of packets bearing SHIM6 payload extension
headers in their outer IP extension header chains MUST be forwarded
for all outbound and explicitly permitted flows. The content of the
SHIM6 payload extension header MAY be ignored for the purpose of
state tracking.
3.4. Passive Listeners 3.4. Passive Listeners
Some applications expect to solicit traffic from exterior nodes Some applications expect to solicit traffic from exterior nodes
without advance knowledge of the exterior addresses of their peers. without advance knowledge of the exterior addresses of their peers.
This requirement is met by IPv4/NAT gateways typically by the use of This requirement is met by IPv4/NAT gateways typically by the use of
either [I-D.cheshire-nat-pmp] or [UPnP-IGD]. On IPv4/NAT networks either [I-D.cheshire-nat-pmp] or [UPnP-IGD]. On IPv4/NAT networks
connected by gateways without such services, applications must use connected by gateways without such services, applications must use
techniques like Session Traversal Utilities for NAT (STUN) [RFC5389] techniques like Session Traversal Utilities for NAT (STUN) [RFC5389]
to obtain and maintain connectivity, despite the translation and to obtain and maintain connectivity, despite the translation and
skipping to change at page 22, line 37 skipping to change at page 23, line 20
One proposal that has been offered as an Internet Draft is the One proposal that has been offered as an Internet Draft is the
Application Listener Discovery Protocol [I-D.woodyatt-ald]. It Application Listener Discovery Protocol [I-D.woodyatt-ald]. It
remains to be seen whether the Internet Gateway Device profile of the remains to be seen whether the Internet Gateway Device profile of the
Universal Plug And Play protocol will be extended for IPv6. Other Universal Plug And Play protocol will be extended for IPv6. Other
proposals of note include the Middlebox Communication Protocol proposals of note include the Middlebox Communication Protocol
[RFC5189] and the Next Steps in Signaling framework [RFC4080]. Until [RFC5189] and the Next Steps in Signaling framework [RFC4080]. Until
a consensus emerges around a specific method, the following a consensus emerges around a specific method, the following
recommendations are the best guidance available. recommendations are the best guidance available.
REC-46: Internet gateways with IPv6 simple security capabilities REC-48: Internet gateways with IPv6 simple security capabilities
SHOULD implement a protocol to permit applications to solicit inbound SHOULD implement a protocol to permit applications to solicit inbound
traffic without advance knowledge of the addresses of exterior nodes traffic without advance knowledge of the addresses of exterior nodes
with which they expect to communicate. with which they expect to communicate.
REC-47: Internet gateways with IPv6 simple security capabilities MUST REC-49: Internet gateways with IPv6 simple security capabilities MUST
provide an easily selected configuration option that permits a provide an easily selected configuration option that permits a
"transparent mode" of operation that forwards all unsolicited flows "transparent mode" of operation that forwards all unsolicited flows
regardless of forwarding direction, i.e. not to use the IPv6 simple regardless of forwarding direction, i.e. not to use the IPv6 simple
security capabilities of the gateway. The transparent mode of security capabilities of the gateway. The transparent mode of
operation MAY be the default configuration. operation MAY be the default configuration.
In general, "transparent mode" will enable more flexibility and In general, "transparent mode" will enable more flexibility and
reliability for applications which require devices to be contacted reliability for applications which require devices to be contacted
inside the home directly, particularly in absence of a protocol as inside the home directly, particularly in absence of a protocol as
described in REC-46. Operating in transparent mode may come at the described in REC-48. Operating in transparent mode may come at the
expense of security if there are IPv6 nodes in the home that do not expense of security if there are IPv6 nodes in the home that do not
have their own host-based firewall capability and require a firewall have their own host-based firewall capability and require a firewall
in the gateway in order not to be compromised. in the gateway in order not to be compromised.
3.5. Management Applications 3.5. Management Applications
Subscriber managed residential gateways are unlikely ever to be Subscriber managed residential gateways are unlikely ever to be
completely zero-configuration, but their administrators will very completely zero-configuration, but their administrators will very
often possess no particular expertise in Internet engineering. In often possess no particular expertise in Internet engineering. In
general, the specification of management interfaces for residential general, the specification of management interfaces for residential
gateways is out of scope for this document, but security of gateways is out of scope for this document, but security of
subscriber managed gateways merit special attention here. subscriber managed gateways merit special attention here.
REC-48: By DEFAULT, subscriber managed residential gateways MUST NOT REC-50: By DEFAULT, subscriber managed residential gateways MUST NOT
offer management application services to the exterior network. offer management application services to the exterior network.
4. Summary of Recommendations 4. Summary of Recommendations
This section collects all of the recommendations made in this This section collects all of the recommendations made in this
document into a convenient list. document into a convenient list.
REC-1 Packets bearing in their outer IPv6 headers multicast source REC-1 Packets bearing in their outer IPv6 headers multicast source
addresses MUST NOT be forwarded or transmitted on any addresses MUST NOT be forwarded or transmitted on any
interface. interface.
skipping to change at page 24, line 25 skipping to change at page 25, line 11
REC-7 By DEFAULT, packets with unique local source and/or REC-7 By DEFAULT, packets with unique local source and/or
destination addresses [RFC4193] SHOULD NOT be forwarded to or destination addresses [RFC4193] SHOULD NOT be forwarded to or
from the exterior network. from the exterior network.
REC-8 By DEFAULT, inbound DNS queries received on exterior REC-8 By DEFAULT, inbound DNS queries received on exterior
interfaces MUST NOT be processed by any integrated DNS interfaces MUST NOT be processed by any integrated DNS
resolving server. resolving server.
REC-9 Inbound DHCPv6 discovery packets [RFC3315] received on REC-9 Inbound DHCPv6 discovery packets [RFC3315] received on
exterior interfaces MUST NOT be processed by any integrated exterior interfaces MUST NOT be processed by any integrated
DHCPv6 server. DHCPv6 server or relay agent.
REC-10 IPv6 gateways MUST forward ICMPv6 "Destination Unreachable" REC-10 IPv6 gateways MUST forward ICMPv6 "Destination Unreachable"
and "Packet Too Big" messages containing IP headers that and "Packet Too Big" messages containing IP headers that
match generic upper-layer transport state records. match generic upper-layer transport state records.
REC-11 If application transparency is most important, then a REC-11 If application transparency is most important, then a
stateful packet filter SHOULD have "Endpoint independent stateful packet filter SHOULD have "endpoint independent
filter" behavior for generic upper-layer transport protocols. filter" behavior for generic upper-layer transport protocols.
If a more stringent filtering behavior is most important, If a more stringent filtering behavior is most important,
then a filter SHOULD have "Address dependent filtering" then a filter SHOULD have "address dependent filtering"
behavior. The filtering behavior MAY be an option behavior. The filtering behavior MAY be an option
configurable by the network administrator, and it MAY be configurable by the network administrator, and it MAY be
independent of the filtering behavior for other protocols. independent of the filtering behavior for other protocols.
Filtering behavior SHOULD be endpoint independent by DEFAULT Filtering behavior SHOULD be endpoint independent by DEFAULT
in gateways intended for provisioning without service- in gateways intended for provisioning without service-
provider management. provider management.
REC-12 Filter state records for generic upper-layer transport REC-12 Filter state records for generic upper-layer transport
protocols MUST NOT be deleted or recycled until an idle timer protocols MUST NOT be deleted or recycled until an idle timer
not less than two minutes has expired without having not less than two minutes has expired without having
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0-1023) MAY expire after a period of idle time shorter than 0-1023) MAY expire after a period of idle time shorter than
two minutes to facilitate the operation of the IANA- two minutes to facilitate the operation of the IANA-
registered service assigned to the port in question. registered service assigned to the port in question.
REC-15 A state record for a UDP flow MUST be refreshed when a packet REC-15 A state record for a UDP flow MUST be refreshed when a packet
is forwarded from the interior to the exterior, and it MAY be is forwarded from the interior to the exterior, and it MAY be
refreshed when a packet is forwarded in the reverse refreshed when a packet is forwarded in the reverse
direction. direction.
REC-16 If application transparency is most important, then a REC-16 If application transparency is most important, then a
stateful packet filter SHOULD have "Endpoint independent stateful packet filter SHOULD have "endpoint independent
filter" behavior for UDP. If a more stringent filtering filter" behavior for UDP. If a more stringent filtering
behavior is most important, then a filter SHOULD have behavior is most important, then a filter SHOULD have
"Address dependent filtering" behavior. The filtering "address dependent filtering" behavior. The filtering
behavior MAY be an option configurable by the network behavior MAY be an option configurable by the network
administrator, and it MAY be independent of the filtering administrator, and it MAY be independent of the filtering
behavior for TCP and other protocols. Filtering behavior behavior for TCP and other protocols. Filtering behavior
SHOULD be endpoint independent by DEFAULT in gateways SHOULD be endpoint independent by DEFAULT in gateways
intended for provisioning without service-provider intended for provisioning without service-provider
management. management.
REC-17 If a gateway forwards a UDP flow, it MUST also forward ICMPv6 REC-17 If a gateway forwards a UDP flow, it MUST also forward ICMPv6
"Destination Unreachable" and "Packet Too Big" messages "Destination Unreachable" and "Packet Too Big" messages
containing UDP headers that match the flow state record. containing UDP headers that match the flow state record.
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REC-22 If a gateway forwards an ESP flow, it MUST also forward (in REC-22 If a gateway forwards an ESP flow, it MUST also forward (in
the reverse direction) ICMPv6 "Destination Unreachable" and the reverse direction) ICMPv6 "Destination Unreachable" and
"Packet Too Big" messages containing ESP headers that match "Packet Too Big" messages containing ESP headers that match
the flow state record. the flow state record.
REC-23 In their DEFAULT operating mode, IPv6 gateways MUST NOT REC-23 In their DEFAULT operating mode, IPv6 gateways MUST NOT
prohibit the forwarding of any UDP packets, to and from prohibit the forwarding of any UDP packets, to and from
legitimate node addresses, with a destination port of 500, legitimate node addresses, with a destination port of 500,
i.e. the port reserved by IANA for the Internet Key Exchange i.e. the port reserved by IANA for the Internet Key Exchange
Protocol [RFC4306]. Protocol [RFC5996].
REC-24 In all operating modes, IPv6 gateways SHOULD use filter state REC-24 In all operating modes, IPv6 gateways SHOULD use filter state
records for Encapsulating Security Payload (ESP) [RFC4303] records for Encapsulating Security Payload (ESP) [RFC4303]
that are indexable by a 3-tuple comprising the interior node that are indexable by a 3-tuple comprising the interior node
address, the exterior node address and the ESP protocol address, the exterior node address and the ESP protocol
identifier. In particular, the IPv4/NAT method of indexing identifier. In particular, the IPv4/NAT method of indexing
state records also by security parameters index (SPI) SHOULD state records also by security parameters index (SPI) SHOULD
NOT be used. Likewise, any mechanism that depends on NOT be used. Likewise, any mechanism that depends on
detection of Internet Key Exchange (IKE) [RFC4306] detection of Internet Key Exchange (IKE) [RFC5996]
initiations SHOULD NOT be used. initiations SHOULD NOT be used.
REC-25 In their DEFAULT operating mode, IPv6 gateways MUST NOT REC-25 In their DEFAULT operating mode, IPv6 gateways MUST NOT
prohibit the forwarding of packets, to and from legitimate prohibit the forwarding of packets, to and from legitimate
node addresses, with destination extension headers of type node addresses, with destination extension headers of type
"Host Identity Protocol (HIP)" [RFC5201] in their outer IP "Host Identity Protocol (HIP)" [RFC5201] in their outer IP
extension header chain. extension header chain.
REC-26 The state records for flows initiated by outbound packets REC-26 The state records for flows initiated by outbound packets
that bear a Home Address destination option [RFC3775] are that bear a Home Address destination option [RFC3775] are
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inbound flows. In particular, both the normal TCP 3-way inbound flows. In particular, both the normal TCP 3-way
handshake mode of operation and the simultaneous-open modes handshake mode of operation and the simultaneous-open modes
of operation MUST be supported. of operation MUST be supported.
REC-31 The TCP window invariant MUST NOT be enforced on flows for REC-31 The TCP window invariant MUST NOT be enforced on flows for
which the filter did not detect whether the window-scale which the filter did not detect whether the window-scale
option (see [RFC1323]) was sent in the 3-way handshake or option (see [RFC1323]) was sent in the 3-way handshake or
simultaneous open. simultaneous open.
REC-32 If application transparency is most important, then a REC-32 If application transparency is most important, then a
stateful packet filter SHOULD have "Endpoint independent stateful packet filter SHOULD have "endpoint independent
filter" behavior for TCP. If a more stringent filtering filter" behavior for TCP. If a more stringent filtering
behavior is most important, then a filter SHOULD have behavior is most important, then a filter SHOULD have
"Address dependent filtering" behavior. The filtering "address dependent filtering" behavior. The filtering
behavior MAY be an option configurable by the network behavior MAY be an option configurable by the network
administrator, and it MAY be independent of the filtering administrator, and it MAY be independent of the filtering
behavior for UDP and other protocols. Filtering behavior behavior for UDP and other protocols. Filtering behavior
SHOULD be endpoint independent by DEFAULT in gateways SHOULD be endpoint independent by DEFAULT in gateways
intended for provisioning without service-provider intended for provisioning without service-provider
management. management.
REC-33 By DEFAULT, a gateway MUST respond with an ICMPv6 REC-33 By DEFAULT, a gateway MUST respond with an ICMPv6
"Destination Unreachable" error code 1 (administratively "Destination Unreachable" error code 1 (administratively
prohibited) to any unsolicited inbound SYN packet after prohibited) to any unsolicited inbound SYN packet after
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REC-48 By DEFAULT, subscriber managed residential gateways MUST NOT REC-48 By DEFAULT, subscriber managed residential gateways MUST NOT
offer management application services to the exterior offer management application services to the exterior
network. network.
5. Contributors 5. Contributors
Comments and criticisms during the development of this document were Comments and criticisms during the development of this document were
received from the following IETF participants: received from the following IETF participants:
+-------------------+----------------------------+ +-------------------+----------------------------+
| Jari Arkko | Ran Atkinson |
| Fred Baker | Norbert Bollow | | Fred Baker | Norbert Bollow |
| Cameron Byrne | Brian Carpenter | | Cameron Byrne | Brian Carpenter |
| Remi Despres | Arnaud Ebalard | | Remi Despres | Arnaud Ebalard |
| Fabrice Fontaine | Jun-ichiro "itojun" Hagino | | Fabrice Fontaine | Jun-ichiro "itojun" Hagino |
| Thomas Herbst | Christian Huitema | | Thomas Herbst | Christian Huitema |
| Joel Jaeggli | Cullen Jennings | | Joel Jaeggli | Cullen Jennings |
| Suresh Krishnan | Erik Kline | | Suresh Krishnan | Erik Kline |
| Julien Laganier | Kurt Erik Lindqvist | | Julien Laganier | Kurt Erik Lindqvist |
| Boucadair Mohamed | Keith Moore | | Boucadair Mohamed | Keith Moore |
| Robert Moskowitz | Teemu Savolainen | | Robert Moskowitz | Teemu Savolainen |
skipping to change at page 32, line 16 skipping to change at page 33, line 5
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005. Addresses", RFC 4193, October 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, [RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005. December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005. RFC 4303, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram [RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340, March 2006. Congestion Control Protocol (DCCP)", RFC 4340, March 2006.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006. Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation [RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127, (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007. RFC 4787, January 2007.
skipping to change at page 32, line 46 skipping to change at page 33, line 32
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095, of Type 0 Routing Headers in IPv6", RFC 5095,
December 2007. December 2007.
[RFC5156] Blanchet, M., "Special-Use IPv6 Addresses", RFC 5156, [RFC5156] Blanchet, M., "Special-Use IPv6 Addresses", RFC 5156,
April 2008. April 2008.
[RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson, [RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
"Host Identity Protocol", RFC 5201, April 2008. "Host Identity Protocol", RFC 5201, April 2008.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
8.2. Informative References 8.2. Informative References
[I-D.cheshire-nat-pmp] [I-D.cheshire-nat-pmp]
Cheshire, S., "NAT Port Mapping Protocol (NAT-PMP)", Cheshire, S., "NAT Port Mapping Protocol (NAT-PMP)",
draft-cheshire-nat-pmp-03 (work in progress), April 2008. draft-cheshire-nat-pmp-03 (work in progress), April 2008.
[I-D.woodyatt-ald] [I-D.woodyatt-ald]
Woodyatt, J., "Application Listener Discovery (ALD) for Woodyatt, J., "Application Listener Discovery (ALD) for
IPv6", draft-woodyatt-ald-03 (work in progress), IPv6", draft-woodyatt-ald-03 (work in progress),
July 2008. July 2008.
 End of changes. 68 change blocks. 
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