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
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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.
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| | 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:
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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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