draft-ietf-tsvwg-behave-requirements-update-08.txt		rfc7857.txt
	TSVWG R. Penno		Internet Engineering Task Force (IETF) R. Penno
	Internet-Draft Cisco		Request for Comments: 7857 Cisco
	Updates: 4787, 5382, 5508 (if approved) S. Perreault		BCP: 127 S. Perreault
	Intended status: Best Current Practice Jive Communications		Updates: 4787, 5382, 5508 Jive Communications
	Expires: September 3, 2016 M. Boucadair, Ed.		Category: Best Current Practice M. Boucadair, Ed.
	Orange		ISSN: 2070-1721 Orange
	S. Sivakumar		S. Sivakumar
	Cisco		Cisco
	K. Naito		K. Naito
	NTT		NTT
	March 2, 2016		April 2016
	Network Address Translation (NAT) Behavioral Requirements Updates		Updates to Network Address Translation (NAT) Behavioral Requirements
	draft-ietf-tsvwg-behave-requirements-update-08
	Abstract		Abstract
	This document clarifies and updates several requirements of RFC4787,		This document clarifies and updates several requirements of RFCs
	RFC5382, and RFC5508 based on operational and development experience.		4787, 5382, and 5508 based on operational and development experience.
	The focus of this document is NAT44.		The focus of this document is Network Address Translation from IPv4
			to IPv4 (NAT44).
	This document updates RFCs 4787, 5382, and 5508.		This document updates RFCs 4787, 5382, and 5508.
	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 September 3, 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/rfc7857.
	Copyright Notice		Copyright Notice
	Copyright (c) 2016 IETF Trust and the persons identified as the		Copyright (c) 2016 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
	skipping to change at page 2, line 28 ¶		skipping to change at page 3, line 9 ¶
	the copyright in such materials, this document may not be modified		the copyright in such materials, this document may not be modified
	outside the IETF Standards Process, and derivative works of it may		outside the IETF Standards Process, and derivative works of it may
	not be created outside the IETF Standards Process, except to format		not be created outside the IETF Standards Process, except to format
	it for publication as an RFC or to translate it into languages other		it for publication as an RFC or to translate it into languages other
	than English.		than English.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3		1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3		1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
	2. TCP Session Tracking . . . . . . . . . . . . . . . . . . . . 3		2. TCP Session Tracking . . . . . . . . . . . . . . . . . . . . 4
	2.1. TCP Transitory Connection Idle-Timeout . . . . . . . . . 5		2.1. TCP Transitory Connection Idle-Timeout . . . . . . . . . 6
	2.2. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . . 5		2.2. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . . 6
	3. Port Overlapping Behavior . . . . . . . . . . . . . . . . . . 5		3. Port Overlapping Behavior . . . . . . . . . . . . . . . . . . 6
	4. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . 6		4. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . 7
	5. Endpoint-Independent Mapping (EIM) Protocol Independence . . 7		5. Endpoint-Independent Mapping (EIM) Protocol Independence . . 8
	6. Endpoint-Independent Filtering (EIF) Protocol Independence . 7		6. Endpoint-Independent Filtering (EIF) Protocol Independence . 8
	7. Endpoint-Independent Filtering (EIF) Mapping Refresh . . . . 7		7. Endpoint-Independent Filtering (EIF) Mapping Refresh . . . . 8
	7.1. Outbound Mapping Refresh and Error Packets . . . . . . . 8		7.1. Outbound Mapping Refresh and Error Packets . . . . . . . 9
	8. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . 8		8. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . 9
	9. Port Randomization . . . . . . . . . . . . . . . . . . . . . 8		9. Port Randomization . . . . . . . . . . . . . . . . . . . . . 9
	10. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . 9		10. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . 10
	11. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . 9		11. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . 10
	12. Hairpinning Support for ICMP Packets . . . . . . . . . . . . 9		12. Hairpinning Support for ICMP Packets . . . . . . . . . . . . 10
	13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9		13. Security Considerations . . . . . . . . . . . . . . . . . . . 11
	14. Security Considerations . . . . . . . . . . . . . . . . . . . 10		14. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
	15. References . . . . . . . . . . . . . . . . . . . . . . . . . 11		14.1. Normative References . . . . . . . . . . . . . . . . . . 12
	15.1. Normative References . . . . . . . . . . . . . . . . . . 11		14.2. Informative References . . . . . . . . . . . . . . . . . 12
	15.2. Informative References . . . . . . . . . . . . . . . . . 11		Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 13
	Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12		Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 14
	Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 13		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
	1. Introduction		1. Introduction
	[RFC4787], [RFC5382], and [RFC5508] contributed to enhance Network		[RFC4787], [RFC5382], and [RFC5508] contributed to enhance Network
	Address Translation (NAT) interoperability and conformance.		Address Translation (NAT) interoperability and conformance.
	Operational experience gained through widespread deployment and		Operational experience gained through widespread deployment and
	evolution of NAT indicates that some areas of the original documents		evolution of NAT indicates that some areas of the original documents
	need further clarification or updates. This document provides such		need further clarification or updates. This document provides such
	clarifications and updates.		clarifications and updates.
	1.1. Scope		1.1. Scope
	The goal of this document is to clarify and update the set of		The goal of this document is to clarify and update the set of
	requirements listed in [RFC4787], [RFC5382], and [RFC5508]. The		requirements listed in [RFC4787], [RFC5382], and [RFC5508]. The
	document focuses exclusively on NAT44.		document focuses exclusively on NAT44.
	The scope of this document has been set so that it does not create		The scope of this document has been set so that it does not create
	new requirements beyond those specified in the documents cited above.		new requirements beyond those specified in the documents cited above.
	Carrier-Grade NAT (CGN) related requirements are defined in		Requirements related to Carrier-Grade NAT (CGN) are defined in
	[RFC6888].		[RFC6888].
	1.2. Terminology		1.2. Terminology
	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 [RFC2119].		document are to be interpreted as described in [RFC2119].
	The reader is assumed to be familiar with the terminology defined in:		The reader is assumed to be familiar with the terminology defined in
	[RFC2663],[RFC4787],[RFC5382], and [RFC5508].		[RFC2663], [RFC4787], [RFC5382], and [RFC5508].
	In this document, the term "NAT" refers to both "Basic NAT" and		In this document, the term "NAT" refers to both "Basic NAT" and
	"Network Address/Port Translator (NAPT)" (see Section 3 of		"Network Address/Port Translator (NAPT)" (see Section 3 of
	[RFC4787]). As a reminder, Basic NAT and NAPT are two variations of		[RFC4787]). As a reminder, Basic NAT and NAPT are two variations of
	traditional NAT, in that translation in Basic NAT is limited to IP		traditional NAT in that translation in Basic NAT is limited to IP
	addresses alone, whereas translation in NAPT is extended to include		addresses alone, whereas translation in NAPT is extended to include
	IP address and Transport identifier (such as TCP/UDP port or ICMP		IP addresses and transport identifiers (such as a TCP/UDP port or
	query ID) (refer to Section 2 of [RFC3022]).		ICMP query ID); refer to Section 2 of [RFC3022].
	2. TCP Session Tracking		2. TCP Session Tracking
	[RFC5382] specifies TCP timers associated with various connection		[RFC5382] specifies TCP timers associated with various connection
	states but does not specify the TCP state machine a NAT44 should		states but does not specify the TCP state machine a NAT44 should
	follow as a basis to apply such timers.		follow as a basis to apply such timers.
	Update: The TCP state machine depicted in Figure 1, adapted from		Update: The TCP state machine depicted in Figure 1, adapted from
	[RFC6146], SHOULD be implemented by a NAT for TCP session tracking		[RFC6146], SHOULD be implemented by a NAT for TCP session tracking
	purposes.		purposes.
	skipping to change at page 4, line 45 ¶		skipping to change at page 5, line 45 ¶
	| | T.O.		| | T.O.
	V V |		V V |
	+----------------------+ |		+----------------------+ |
	| C FIN + S FIN RCV |-----------------+		| C FIN + S FIN RCV |-----------------+
	+----------------------+		+----------------------+
	Legend:		Legend:
	* Messages sent or received from the server are		* Messages sent or received from the server are
	prefixed with "Server".		prefixed with "Server".
	* Messages sent or received from the client are		* Messages sent or received from the client are
	prefixed with "Client".		prefixed with "Client".
	* "C" means "Client-side"		* "C" means "Client-side".
	* "S" means "Server-side".		* "S" means "Server-side".
	* TCP_EST T.O: refers to the established connection		* TCP_EST T.O. refers to the established connection
	idle timeout as defined in [RFC5382].		idle-timeout as defined in [RFC5382].
	* TCP_TRANS T.O: refers to the transitory connection		* TCP_TRANS T.O. refers to the transitory connection
	idle timeout as defined in [RFC5382].		idle-timeout as defined in [RFC5382].
	Figure 1: Simplified version of the TCP State Machine		Figure 1: Simplified Version of the TCP State Machine
	2.1. TCP Transitory Connection Idle-Timeout		2.1. TCP Transitory Connection Idle-Timeout
	The transitory connection idle-timeout is defined as the minimum time		The transitory connection idle-timeout is defined as the minimum time
	a TCP connection in the partially open or closing phases must remain		a TCP connection in the partially open or closing phases must remain
	idle before the NAT considers the associated session a candidate for		idle before the NAT considers the associated session a candidate for
	removal (REQ-5 of [RFC5382]). But [RFC5382] does not clearly state		removal (REQ-5 of [RFC5382]). However, [RFC5382] does not clearly
	whether these can be configured separately.		state whether these can be configured separately.
	Clarification: This document clarifies that a NAT SHOULD provide		Clarification: This document clarifies that a NAT SHOULD provide
	different configurable parameters for configuring the open and		different configurable parameters for configuring the open and
	closing idle timeouts.		closing idle timeouts.
	To accommodate deployments that consider a partially open timeout		To accommodate deployments that consider a partially open timeout
	of 4 minutes as being excessive from a security standpoint, a NAT		of 4 minutes as being excessive from a security standpoint, a NAT
	MAY allow the configured timeout to be less than 4 minutes.		MAY allow the configured timeout to be less than 4 minutes.
	However, a minimum default transitory connection idle-timeout of 4		However, a minimum default transitory connection idle-timeout of 4
	minutes is RECOMMENDED.		minutes is RECOMMENDED.
	2.2. TCP RST		2.2. TCP RST
	[RFC5382] leaves the handling of TCP RST packets unspecified.		[RFC5382] leaves the handling of TCP RST packets unspecified.
	Update: This document adopts a similar default behavior as in		Update: This document adopts a similar default behavior as in
	[RFC6146]. Concretely, when the NAT receives a TCP RST matching		[RFC6146]. Concretely, when the NAT receives a TCP RST matching
	an existing mapping, it MUST translate the packet according to the		an existing mapping, it MUST translate the packet according to the
	NAT mapping entry. Moreover, the NAT SHOULD wait for 4 minutes		NAT mapping entry. Moreover, the NAT SHOULD wait for 4 minutes
	before deleting the session and removing any state associated with		before deleting the session and removing any state associated with
	it if no packets are received during that 4 minutes timeout.		it if no packets are received during that 4-minute timeout.
	Notes:		Notes:
	* Admittedly, the NAT has to verify whether received TCP RST		* Admittedly, the NAT has to verify whether received TCP RST
	packets belong to a connection. This verification check is		packets belong to a connection. This verification check is
	required to avoid off-path attacks.		required to avoid off-path attacks.
	* If the NAT removes immediately the NAT mapping upon receipt of		* If the NAT immediately removes the NAT mapping upon receipt of
	a TCP RST message, stale connections may be maintained by		a TCP RST message, stale connections may be maintained by
	endpoints if the first RST message is lost between the NAT and		endpoints if the first RST message is lost between the NAT and
	the recipient.		the recipient.
	3. Port Overlapping Behavior		3. Port Overlapping Behavior
	REQ-1 from [RFC4787] and REQ-1 from [RFC5382] specify a specific port		REQ-1 from [RFC4787] and REQ-1 from [RFC5382] specify a specific port
	overlapping behavior; that is the external IP address and port can be		overlapping behavior; that is, the external IP address and port can
	reused for connections originating from the same internal source IP		be reused for connections originating from the same internal source
	address and port irrespective of the destination. This is known as		IP address and port irrespective of the destination. This is known
	endpoint-independent mapping (EIM).		as Endpoint-Independent Mapping (EIM).
	Update: This document clarifies that this port overlapping behavior		Update: This document clarifies that this port overlapping behavior
	may be extended to connections originating from different internal		may be extended to connections originating from different internal
	source IP addresses and ports as long as their destinations are		source IP addresses and ports as long as their destinations are
	different.		different.
	The following mechanism MAY be implemented by a NAT:		The following mechanism MAY be implemented by a NAT:
	If destination addresses and ports are different for outgoing		If destination addresses and ports are different for outgoing
	connections started by local clients, a NAT MAY assign the same		connections started by local clients, a NAT MAY assign the same
	external port as the source ports for the connections. The		external port as the source ports for the connections. The
	port overlapping mechanism manages mappings between external		port overlapping mechanism manages mappings between external
	packets and internal packets by looking at and storing their		packets and internal packets by looking at and storing their
	5-tuple (protocol, source address, source port, destination		5-tuple (protocol, source address, source port, destination
	address, destination port).		address, and destination port).
	This enables concurrent use of a single NAT external port for		This enables concurrent use of a single NAT external port for
	multiple transport sessions, which allows a NAT to successfully		multiple transport sessions, which allows a NAT to successfully
	process packets in an IP address resource limited network (e.g.,		process packets in a network that has a limited number of IP
	deployment with high address space multiplicative factor (refer to		addresses (e.g., deployment with a high address space
	Appendix B. of [RFC6269])).		multiplicative factor (refer to Appendix B of [RFC6269])).
	4. Address Pooling Paired (APP)		4. Address Pooling Paired (APP)
	The "IP address pooling" behavior of "Paired" (APP) was recommended		The "IP address pooling" behavior of "Paired" (APP) was recommended
	in REQ-2 from [RFC4787], but the behavior when an external IPv4 runs		in REQ-2 from [RFC4787], but the behavior when an external IPv4 runs
	out of ports was left undefined.		out of ports was left undefined.
	Clarification: This document clarifies that if APP is enabled, new		Clarification: This document clarifies that if APP is enabled, new
	sessions from a host that already has a mapping associated with an		sessions from a host that already has a mapping associated with an
	external IP that ran out of ports SHOULD be dropped. A		external IP that ran out of ports SHOULD be dropped. A
	configuration parameter MAY be provided to allow a NAT to starting		configuration parameter MAY be provided to allow a NAT to start
	using ports from another external IP address when the one that		using ports from another external IP address when the one that
	anchored the APP mapping ran out of ports. Tweaking this		anchored the APP mapping ran out of ports. Tweaking this
	configuration parameter is a trade-off between service continuity		configuration parameter is a trade-off between service continuity
	and APP strict enforcement. Note, this behavior is sometimes		and APP strict enforcement. Note, this behavior is sometimes
	referred as 'soft-APP'.		referred to as "soft-APP".
	As a reminder, the recommendation for the particular case of a CGN		As a reminder, the recommendation for the particular case of a CGN
	is that an implementation must use the same external IP address		is that an implementation must use the same external IP address
	mapping for all sessions associated with the same internal IP		mapping for all sessions associated with the same internal IP
	address, be they TCP, UDP, ICMP, something else, or a mix of		address, be they TCP, UDP, ICMP, something else, or a mix of
	different protocols [RFC6888].		different protocols [RFC6888].
	Update: This behavior SHOULD apply also for TCP.		Update: This behavior SHOULD apply also for TCP.
	5. Endpoint-Independent Mapping (EIM) Protocol Independence		5. Endpoint-Independent Mapping (EIM) Protocol Independence
	REQ-1 from [RFC4787] and REQ-1 from [RFC5382] do not specify whether		REQ-1 from [RFC4787] and REQ-1 from [RFC5382] do not specify whether
	EIM are protocol-dependent or protocol-independent. For example, if		EIM are protocol dependent or protocol independent. For example, if
	an outbound TCP SYN creates a mapping, it is left undefined whether		an outbound TCP SYN creates a mapping, it is left undefined whether
	outbound UDP packets can reuse such mapping.		outbound UDP packets can reuse such mapping.
	Update: EIM mappings SHOULD be protocol-dependent. A configuration		Update: EIM mappings SHOULD be protocol dependent. A configuration
	parameter MAY be provided to allow protocols that multiplex TCP		parameter MAY be provided to allow protocols that multiplex TCP
	and UDP over the same source IP address and port number to use a		and UDP over the same source IP address and port number to use a
	single mapping. The default value of this configuration parameter		single mapping. The default value of this configuration parameter
	MUST be protocol-dependent EIM.		MUST be protocol-dependent EIM.
	This update is consistent with the stateful NAT64 [RFC6146] that		This update is consistent with the stateful Network Address and
	clearly specifies three binding information bases (TCP, UDP,		Protocol Translation from IPv6 Clients to IPv4 Servers (NAT64)
	ICMP).		[RFC6146] that clearly specifies three binding information bases
			(TCP, UDP, and ICMP).
	6. Endpoint-Independent Filtering (EIF) Protocol Independence		6. Endpoint-Independent Filtering (EIF) Protocol Independence
	REQ-8 from [RFC4787] and REQ-3 from [RFC5382] do not specify whether		REQ-8 from [RFC4787] and REQ-3 from [RFC5382] do not specify whether
	mappings with endpoint-independent filtering (EIF) are protocol-		mappings with Endpoint-Independent Filtering (EIF) are protocol
	independent or protocol-dependent. For example, if an outbound TCP		independent or protocol dependent. For example, if an outbound TCP
	SYN creates a mapping, it is left undefined whether inbound UDP		SYN creates a mapping, it is left undefined whether inbound UDP
	packets matching that mapping should be accepted or rejected.		packets matching that mapping should be accepted or rejected.
	Update: EIF filtering SHOULD be protocol-dependent. A configuration		Update: EIF filtering SHOULD be protocol dependent. A configuration
	parameter MAY be provided to make it protocol-independent. The		parameter MAY be provided to make it protocol independent. The
	default value of this configuration parameter MUST be protocol-		default value of this configuration parameter MUST be protocol-
	dependent EIF.		dependent EIF.
	This behavior is aligned with the update in Section 5.		This behavior is aligned with the update in Section 5.
	Applications that can be transported over a variety of transport		Applications that can be transported over a variety of transport
	protocols and/or support transport fall back schemes won't		protocols and/or support transport fallback schemes won't
	experience connectivity failures if the NAT is configured with		experience connectivity failures if the NAT is configured with
	protocol-independent EIM and protocol-independent EIF.		protocol-independent EIM and protocol-independent EIF.
	7. Endpoint-Independent Filtering (EIF) Mapping Refresh		7. Endpoint-Independent Filtering (EIF) Mapping Refresh
	The NAT mapping Refresh direction may have a "NAT Inbound refresh		The NAT mapping Refresh direction may have a "NAT Inbound refresh
	behavior" of "True" according to REQ-6 from [RFC4787], but [RFC4787]		behavior" of "True" according to REQ-6 from [RFC4787], but [RFC4787]
	does not clarify how this behavior applies to EIF mappings. The		does not clarify how this behavior applies to EIF mappings. The
	issue in question is whether inbound packets that match an EIF		issue in question is whether inbound packets that match an EIF
	mapping but do not create a new session due to a security policy		mapping but do not create a new session due to a security policy
	should refresh the mapping timer.		should refresh the mapping timer.
	Clarification: This document clarifies that even when a NAT has an		Clarification: This document clarifies that even when a NAT has an
	inbound refresh behavior set to 'TRUE', such packets SHOULD NOT		inbound refresh behavior set to "TRUE", such packets SHOULD NOT
	refresh the mapping. Otherwise a simple attack of a packet every		refresh the mapping. Otherwise, a simple attack of a packet every
	2 minutes can keep the mapping indefinitely.		two minutes can keep the mapping indefinitely.
	Update: This behavior SHOULD apply also for TCP.		Update: This behavior SHOULD apply also for TCP.
	7.1. Outbound Mapping Refresh and Error Packets		7.1. Outbound Mapping Refresh and Error Packets
	Update: In the case of NAT outbound refresh behavior, ICMP Errors or		Update: In the case of NAT outbound refresh behavior, ICMP Errors or
	TCP RST outbound packets, sent as response to inbound packets,		TCP RST outbound packets sent as a response to inbound packets
	SHOULD NOT refresh the mapping. Other packets which indicate the		SHOULD NOT refresh the mapping. Other packets that indicate the
	host is not interested in receiving packets MAY be configurable to		host is not interested in receiving packets MAY be configurable to
	also not refresh state, such as STUN error response [RFC5389] or		also not refresh state, such as a Session Traversal Utilities for
	IKE INVALID_SYNTAX [RFC7296].		NAT (STUN) error response [RFC5389] or IKE INVALID_SYNTAX
			[RFC7296].
	8. Port Parity		8. Port Parity
	Update: A NAT MAY disable port parity preservation for all dynamic		Update: A NAT MAY disable port parity preservation for all dynamic
	mappings. Nevertheless, A NAT SHOULD support means to explicitly		mappings. Nevertheless, A NAT SHOULD support means to explicitly
	request to preserve port parity (e.g., [RFC7753]).		request to preserve port parity (e.g., [RFC7753]).
	Note: According to [RFC6887], dynamic mappings are said to be		Note: According to [RFC6887], dynamic mappings are said to be
	dynamic in the sense that they are created on demand, either		dynamic in the sense that they are created on demand, either
	implicitly or explicitly:		implicitly or explicitly:
	skipping to change at page 8, line 45 ¶		skipping to change at page 9, line 49 ¶
	as a result, for example, of explicit Port Control Protocol		as a result, for example, of explicit Port Control Protocol
	(PCP) MAP and PEER requests. Explicit dynamic mappings have a		(PCP) MAP and PEER requests. Explicit dynamic mappings have a
	finite lifetime, and this lifetime is communicated to the		finite lifetime, and this lifetime is communicated to the
	client.		client.
	9. Port Randomization		9. Port Randomization
	Update: A NAT SHOULD follow the recommendations specified in		Update: A NAT SHOULD follow the recommendations specified in
	Section 4 of [RFC6056], especially:		Section 4 of [RFC6056], especially:
	"A NAPT that does not implement port preservation [RFC4787]		A NAPT that does not implement port preservation [RFC4787]
	[RFC5382] SHOULD obfuscate selection of the ephemeral port of a		[RFC5382] SHOULD obfuscate selection of the ephemeral port of a
	packet when it is changed during translation of that packet. A		packet when it is changed during translation of that packet.
	NAPT that does implement port preservation SHOULD obfuscate the
	ephemeral port of a packet only if the port must be changed as		A NAPT that does implement port preservation SHOULD obfuscate
	a result of the port being already in use for some other		the ephemeral port of a packet only if the port must be changed
	session. A NAPT that performs parity preservation and that		as a result of the port being already in use for some other
	must change the ephemeral port during translation of a packet		session.
	SHOULD obfuscate the ephemeral ports. The algorithms described
	in this document could be easily adapted such that the parity		A NAPT that performs parity preservation and that must change
	is preserved (i.e., force the lowest order bit of the resulting		the ephemeral port during translation of a packet SHOULD
			obfuscate the ephemeral ports. The algorithms described in
			this document could be easily adapted such that the parity is
			preserved (i.e., force the lowest order bit of the resulting
	port number to 0 or 1 according to whether even or odd parity		port number to 0 or 1 according to whether even or odd parity
	is desired)."		is desired).
	10. IP Identification (IP ID)		10. IP Identification (IP ID)
	Update: A NAT SHOULD handle the Identification field of translated		Update: A NAT SHOULD handle the Identification field of translated
	IPv4 packets as specified in Section 5.3.1 of [RFC6864].		IPv4 packets as specified in Section 5.3.1 of [RFC6864].
	11. ICMP Query Mappings Timeout		11. ICMP Query Mappings Timeout
	Section 3.1 of [RFC5508] specifies that ICMP Query Mappings are to be		Section 3.1 of [RFC5508] specifies that ICMP Query mappings are to be
	maintained by a NAT. However, the specification doesn't discuss		maintained by a NAT. However, the specification doesn't discuss
	Query Mapping timeout values. Section 3.2 of [RFC5508] only		Query mapping timeout values. Section 3.2 of [RFC5508] only
	discusses ICMP Query Session Timeouts.		discusses ICMP Query session timeouts.
	Update: ICMP Query Mappings MAY be deleted once the last session		Update: ICMP Query mappings MAY be deleted once the last session
	using the mapping is deleted.		using the mapping is deleted.
	12. Hairpinning Support for ICMP Packets		12. Hairpinning Support for ICMP Packets
	REQ-7 from [RFC5508] specifies that a NAT enforcing 'Basic NAT' must		REQ-7 from [RFC5508] specifies that a NAT enforcing Basic NAT must
	support traversal of hairpinned ICMP Query sessions.		support traversal of hairpinned ICMP Query sessions.
	Clarification: This implicitly means that address mappings from		Clarification: This implicitly means that address mappings from
	external address to internal address (similar to Endpoint		external address to internal address (similar to Endpoint-
	Independent Filters) must be maintained to allow inbound ICMP		Independent Filters) must be maintained to allow inbound ICMP
	Query sessions. If an ICMP Query is received on an external		Query sessions. If an ICMP Query is received on an external
	address, a NAT can then translate to an internal IP.		address, a NAT can then translate to an internal IP.
	REQ-7 from [RFC5508] specifies that all NATs must support the		REQ-7 from [RFC5508] specifies that all NATs must support the
	traversal of hairpinned ICMP Error messages.		traversal of hairpinned ICMP Error messages.
	Clarification: This behavior requires a NAT to maintain address		Clarification: This behavior requires a NAT to maintain address
	mappings from external IP address to internal IP address in		mappings from external IP address to internal IP address in
	addition to the ICMP Query Mappings described in Section 3.1 of		addition to the ICMP Query mappings described in Section 3.1 of
	[RFC5508].		[RFC5508].
	13. IANA Considerations		13. Security Considerations
	This document does not require any IANA action.
	14. Security Considerations
	NAT behavioral considerations are discussed in [RFC4787], [RFC5382],		NAT behavioral considerations are discussed in [RFC4787], [RFC5382],
	and [RFC5508].		and [RFC5508].
	Because some of the clarifications and updates (e.g., Section 2) are		Because some of the clarifications and updates (e.g., Section 2) are
	inspired from NAT64, the security considerations discussed in		inspired from NAT64, the security considerations discussed in
	Section 5 of [RFC6146] apply also for this specification.		Section 5 of [RFC6146] apply also for this specification.
	The update in Section 3 allows for an optimized NAT resource usage.		The update in Section 3 allows for an optimized NAT resource usage.
	In order to avoid service disruption, the NAT must not invoke this		In order to avoid service disruption, the NAT must not invoke this
	functionality unless the packets are to be sent to distinct		functionality unless the packets are to be sent to distinct
	destination addresses.		destination addresses.
	Some of the updates (e.g., Section 7, Section 9, and Section 11)		Some of the updates (e.g., Sections 7, 9, and 11) allow for increased
	allow for an increased security compared to [RFC4787], [RFC5382], and		security compared to [RFC4787], [RFC5382], and [RFC5508].
	[RFC5508]. Particularly:		Particularly,
	o The updates in Section 7 and Section 11 prevent an illegitimate		o the updates in Sections 7 and 11 prevent an illegitimate node to
	node to maintain mappings activated in the NAT while these		maintain mappings activated in the NAT while these mappings should
	mappings should be cleared.		be cleared, and
	o Port randomization (Section 9) complicates tracking hosts located		o port randomization (Section 9) complicates tracking hosts located
	behind a NAT.		behind a NAT.
	Section 4 and Section 12 propose updates that increase the		Sections 4 and 12 propose updates that increase the serviceability of
	serviceability of a host located behind a NAT. These updates do not		a host located behind a NAT. These updates do not introduce any
	introduce any additional security concerns to [RFC4787], [RFC5382],		additional security concerns to [RFC4787], [RFC5382], and [RFC5508].
	and [RFC5508].
	The updates in Section 5 and Section 6 allow for a better NAT		The updates in Sections 5 and 6 allow for a better NAT transparency
	transparency from an application standpoint. Hosts that require a		from an application standpoint. Hosts that require a restricted
	restricted filtering behavior should enable specific policies (e.g.,		filtering behavior should enable specific policies (e.g., Access
	access control list (ACL)) either locally or by soliciting a		Control List (ACL)) either locally or by soliciting a dedicated
	dedicated security device (e.g., firewall). How a host updates its		security device (e.g., firewall). How a host updates its filtering
	filtering policies is out of scope of this document.		policies is out of scope of this document.
	The update in Section 8 induces security concerns that are specific		The update in Section 8 induces security concerns that are specific
	to the protocol used to interact with the NAT. For example, if PCP		to the protocol used to interact with the NAT. For example, if PCP
	is used to explicitly request parity preservation for a given		is used to explicitly request parity preservation for a given
	mapping, the security considerations discussed in [RFC6887] should be		mapping, the security considerations discussed in [RFC6887] should be
	taken into account.		taken into account.
	The update in Section 10 may have undesired effects on the		The update in Section 10 may have undesired effects on the
	performance of the NAT in environments in which fragmentation is		performance of the NAT in environments in which fragmentation is
	massively experienced. Such issue may be used as an attack vector		massively experienced. Such an issue may be used as an attack vector
	against NATs.		against NATs.
	15. References		14. References
	15.1. Normative References		14.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<http://www.rfc-editor.org/info/rfc2119>.		<http://www.rfc-editor.org/info/rfc2119>.
	[RFC4787] Audet, F., Ed. and C. Jennings, "Network Address		[RFC4787] Audet, F., Ed. and C. Jennings, "Network Address
	Translation (NAT) Behavioral Requirements for Unicast		Translation (NAT) Behavioral Requirements for Unicast
	UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January		UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
	2007, <http://www.rfc-editor.org/info/rfc4787>.		2007, <http://www.rfc-editor.org/info/rfc4787>.
	skipping to change at page 11, line 43 ¶		skipping to change at page 12, line 43 ¶
	[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful		[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
	NAT64: Network Address and Protocol Translation from IPv6		NAT64: Network Address and Protocol Translation from IPv6
	Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,		Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
	April 2011, <http://www.rfc-editor.org/info/rfc6146>.		April 2011, <http://www.rfc-editor.org/info/rfc6146>.
	[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",		[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
	RFC 6864, DOI 10.17487/RFC6864, February 2013,		RFC 6864, DOI 10.17487/RFC6864, February 2013,
	<http://www.rfc-editor.org/info/rfc6864>.		<http://www.rfc-editor.org/info/rfc6864>.
	15.2. Informative References		14.2. Informative References
	[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address		[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
	Translator (NAT) Terminology and Considerations",		Translator (NAT) Terminology and Considerations",
	RFC 2663, DOI 10.17487/RFC2663, August 1999,		RFC 2663, DOI 10.17487/RFC2663, August 1999,
	<http://www.rfc-editor.org/info/rfc2663>.		<http://www.rfc-editor.org/info/rfc2663>.
	[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network		[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
	Address Translator (Traditional NAT)", RFC 3022,		Address Translator (Traditional NAT)", RFC 3022,
	DOI 10.17487/RFC3022, January 2001,		DOI 10.17487/RFC3022, January 2001,
	<http://www.rfc-editor.org/info/rfc3022>.		<http://www.rfc-editor.org/info/rfc3022>.
	skipping to change at page 12, line 46 ¶		skipping to change at page 13, line 46 ¶
	and S. Perreault, "Port Control Protocol (PCP) Extension		and S. Perreault, "Port Control Protocol (PCP) Extension
	for Port-Set Allocation", RFC 7753, DOI 10.17487/RFC7753,		for Port-Set Allocation", RFC 7753, DOI 10.17487/RFC7753,
	February 2016, <http://www.rfc-editor.org/info/rfc7753>.		February 2016, <http://www.rfc-editor.org/info/rfc7753>.
	Acknowledgements		Acknowledgements
	Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan, Lars		Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan, Lars
	Eggert, Gorry Fairhurst, Brandon Williams, and David Black for their		Eggert, Gorry Fairhurst, Brandon Williams, and David Black for their
	review and discussion.		review and discussion.
	Many thanks to Ben Laurie for the secdir review, and Dan Romascanu		Many thanks to Ben Laurie for the SecDir review and Dan Romascanu for
	for the Gen-ART review.		the Gen-ART review.
	Dan Wing proposed some text for the configurable errors in		Dan Wing proposed some text for the configurable errors in
	Section 7.1.		Section 7.1.
	Contributors		Contributors
	The following individual contributed text to the document:		The following individual contributed text to the document:
	Sarat Kamiset, Insieme Networks, United States		Sarat Kamiset
			Insieme Networks
			United States
	Authors' Addresses		Authors' Addresses
	Reinaldo Penno		Reinaldo Penno
	Cisco Systems, Inc.		Cisco Systems, Inc.
	170 West Tasman Drive		170 West Tasman Drive
	San Jose, California 95134		San Jose, California 95134
	USA		United States
	Email: repenno@cisco.com		Email: repenno@cisco.com
	Simon Perreault		Simon Perreault
	Jive Communications		Jive Communications
	Canada		Canada
	Email: sperreault@jive.com		Email: sperreault@jive.com
	Mohamed Boucadair (editor)		Mohamed Boucadair (editor)
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