draft-ietf-tsvwg-behave-requirements-update-01.txt   draft-ietf-tsvwg-behave-requirements-update-02.txt 
TSVWG R. Penno TSVWG R. Penno
Internet-Draft Cisco Internet-Draft Cisco
Intended status: Best Current Practice S. Perreault Intended status: Best Current Practice S. Perreault
Expires: August 22, 2015 Viagenie Expires: February 13, 2016 Jive Communications
S. Kamiset S. Kamiset
Insieme Networks Insieme Networks
M. Boucadair M. Boucadair
France Telecom France Telecom
K. Naito K. Naito
NTT NTT
February 18, 2015 August 12, 2015
Network Address Translation (NAT) Behavioral Requirements Updates Network Address Translation (NAT) Behavioral Requirements Updates
draft-ietf-tsvwg-behave-requirements-update-01 draft-ietf-tsvwg-behave-requirements-update-02
Abstract Abstract
This document clarifies and updates several requirements of RFC4787, This document clarifies and updates several requirements of RFC4787,
RFC5382 and RFC5508 based on operational and development experience. RFC5382 and RFC5508 based on operational and development experience.
The focus of this document is NAPT44. The focus of this document is NAT44.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 August 22, 2015. This Internet-Draft will expire on February 13, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. TCP Session Tracking . . . . . . . . . . . . . . . . . . . . 3 2. TCP Session Tracking . . . . . . . . . . . . . . . . . . . . 3
2.1. TCP Transitory Connection Idle-Timeout . . . . . . . . . 4 2.1. TCP Transitory Connection Idle-Timeout . . . . . . . . . 4
2.2. TIME_WAIT State . . . . . . . . . . . . . . . . . . . . . 5 2.2. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1. Proposal: Apply RFC6191 and PAWS to NAT . . . . . . 5 3. Port Overlapping Behavior . . . . . . . . . . . . . . . . . . 5
2.3. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . 6
3. Port Overlapping behavior . . . . . . . . . . . . . . . . . . 8 5. EIF Protocol Independence . . . . . . . . . . . . . . . . . . 6
4. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . 8 6. EIF Mapping Refresh . . . . . . . . . . . . . . . . . . . . . 7
5. EIF Security . . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Outbound Mapping Refresh and Error Packets . . . . . . . 7
6. EIF Protocol Independence . . . . . . . . . . . . . . . . . . 9 7. EIM Protocol Independence . . . . . . . . . . . . . . . . . . 7
7. EIF Mapping Refresh . . . . . . . . . . . . . . . . . . . . . 9 8. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Outbound Mapping Refresh and Error Packets . . . . . . . 10 9. Port Randomization . . . . . . . . . . . . . . . . . . . . . 8
8. EIM Protocol Independence . . . . . . . . . . . . . . . . . . 10 10. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . 8
9. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . 10 11. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . 8
10. Port Randomization . . . . . . . . . . . . . . . . . . . . . 10 12. Hairpinning Support for ICMP Packets . . . . . . . . . . . . 9
11. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . 11 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
12. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . 11 14. Security Considerations . . . . . . . . . . . . . . . . . . . 9
13. Hairpinning Support for ICMP Packets . . . . . . . . . . . . 11 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
15. Security Considerations . . . . . . . . . . . . . . . . . . . 11 16.1. Normative References . . . . . . . . . . . . . . . . . . 10
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 16.2. Informative References . . . . . . . . . . . . . . . . . 10
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
17.1. Normative References . . . . . . . . . . . . . . . . . . 12
17.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
[RFC4787], [RFC5382] and [RFC5508] greatly advanced NAT [RFC4787], [RFC5382] and [RFC5508] greatly advanced NAT
interoperability and conformance. But with widespread deployment and interoperability and conformance. But with widespread deployment and
evolution of NAT more development and operational experience was evolution of Network Address Translation (NAT) more development and
acquired some areas of the original documents need further operational experience was acquired some areas of the original
clarification or updates. This document provides such clarifications documents need further clarification or updates. This document
and updates. provides such clarifications and updates.
1.1. Scope 1.1. Scope
This document focuses solely on NAPT44 and its goal is to clarify, The goal of this document is to clarify and update the set of
fill gaps or update requirements of [RFC4787], [RFC5382] and requirements listed in [RFC4787], [RFC5382] and [RFC5508]. The
[RFC5508]. document focuses exclusively on NAT44.
It is out of the scope of this document the creation of completely The scope of this document has been set so that it does not create
new requirements not associated with the documents cited above. New new requirements beyond those specified in the documents cited above.
requirements would be better served elsewhere and if they are CGN Carrier-Grade NAT (CGN) related requirements are defined in
specific in an update to [RFC6888]. [RFC6888].
1.2. Terminology 1.2. Terminology
The reader should be familiar with the terms defined in The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
[RFC2663],[RFC4787],[RFC5382],and [RFC5508] "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. TCP Session Tracking
[RFC5382] specifies TCP timers associated with various connection
states but does not specify the TCP state machine a NAPT44 should use
as a basis to apply such timers. The TCP state machine depicted in
Figure 1, adapted from [RFC6146], provides guidance on how TCP
session tracking could be implemented - it is non-normative.
+-----------------------------+
| |
V |
+------+ CV4 |
|CLOSED|-----SYN------+ |
+------+ | |
^ | |
|TCP_TRANS T.O. | |
| V |
+-------+ +-------+ |
| TRANS | |V4 INIT| |
+-------+ +-------+ |
| ^ | |
data pkt | | |
| V4 or V4 RST | |
| TCP_EST T.O. | |
V | SV4 SYN |
+--------------+ | |
| ESTABLISHED |<---------+ |
+--------------+ |
| | |
CV4 FIN SV4 FIN |
| | |
V V |
+---------+ +----------+ |
|CV4 FIN | | SV4 FIN | |
| RCV | | RCV | |
+---------+ +----------+ |
| | |
SV4 FIN CV4 FIN TCP_TRANS
| | T.O.
V V |
+----------------------+ |
| CV4 FIN + SV4 FIN RCV|--------------------+
+----------------------+
Figure 1
2.1. TCP Transitory Connection Idle-Timeout
[RFC5382]:REQ-5 The transitory connection idle-timeout is defined as
the minimum time a TCP connection in the partially open or closing
phases must remain idle before the NAT considers the associated
session a candidate for removal. But the document does not clearly
states if these can be configured separately.
This document clarifies that a NAT device SHOULD provide different The reader is assumed to be familiar withe terminology defined in:
knobs for configuring the open and closing idle timeouts. This [RFC2663],[RFC4787],[RFC5382], and [RFC5508].
document further acknowledges that most TCP flows are very short
(less than 10 seconds) [FLOWRATE][TCPWILD] and therefore a partially
open timeout of 4 minutes might be excessive if security is a
concern. Therefore, it MAY be configured to be less than 4 minutes
in such cases. There also may be cases that a timeout of 4 minutes
might be excessive. The case and the solution are written below.
2.2. TIME_WAIT State In this document, the term "NAT" refers to both "Basic NAT" and
"Network Address/Port Translator (NAPT)" (see Section 3 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
addresses alone, whereas translation in NAPT is extended to include
IP address and Transport identifier (such as TCP/UDP port or ICMP
query ID) (refer to Section 2 of [RFC3022]).
The TCP TIME_WAIT state is described in [RFC0793]. The TCP TIME_WAIT 2. TCP Session Tracking
state needs to be kept for 2MSL before a connection is CLOSED, for
the reasons listed below:
1: In the event that packets from a session are delayed in the in- [RFC5382] specifies TCP timers associated with various connection
between network, and delivered to the end relatively later, we states but does not specify the TCP state machine a NAT44 should
should prevent the packets from being transferred and interpreted follow as a basis to apply such timers.
as a packet that belongs to a new session.
2: If the remote TCP has not received the acknowledgment of its Update: The TCP state machine depicted in Figure 1, adapted from
connection termination request, it will re-send the FIN packet [RFC6146], SHOULD be implemented by a NAT for TCP session tracking
several times. purposes.
These points are important for the TCP to work without problems. +----------------------------+
| |
V |
+------+ Client |
|CLOSED|-----SYN------+ |
+------+ | |
^ | |
|TCP_TRANS T.O. | |
| V |
+-------+ +-------+ |
| TRANS | | INIT | |
+-------+ +-------+ |
| ^ | |
data pkt | | |
| Server/Client RST | |
| TCP_EST T.O. | |
V | Server SYN |
+--------------+ | |
| ESTABLISHED |<---------+ |
+--------------+ |
| | |
Client FIN Server FIN |
| | |
V V |
+---------+ +----------+ |
| C FIN | | S FIN | |
| RCV | | RCV | |
+---------+ +----------+ |
| | |
Server FIN Client FIN TCP_TRANS
| | T.O.
V V |
+----------------------+ |
| C FIN + S FIN RCV |-----------------+
+----------------------+
[RFC5382] leaves the handling of TCP connections in TIME_WAIT state Legend:
unspecified and mentions that TIME_WAIT state is not part of the * Messages sent to (resp. received from) the server
transitory connection idle-timeout. If the NAT device honors the are prefixed with "Server".
TIME_WAIT state, each TCP connection and its associated resources is * Messages sent to (resp. received from) the client
kept for a certain period, typically for four minutes, which consumes are prefixed with "Client".
port resources. * "C" means "Client-side"
* "S" means "Server-side".
* TCP_EST T.O: refers to the established connection
idle timeout as defined in [RFC5382].
* TCP_TRANS T.O: refers to the transitory connection
idle timeout as defined in [RFC5382].
[RFC6191] explains that in certain situation it is necessary to Figure 1: State Machine
reduce the TIME_WAIT state and defines such a mechanism using TCP
timestamps and sequence numbers. When a connection request is
received with a four-tuple that is in the TIME-WAIT state, the
connection request may be accepted if the sequence number or the
timestamp of the incoming SYN segment is greater than the last
sequence number seen on the previous incarnation of the connection.
This document specifies that a NAT device should keep TCP connections 2.1. TCP Transitory Connection Idle-Timeout
in TIME_WAIT state unless it implements the proposal described in the
following sub-section.
2.2.1. Proposal: Apply RFC6191 and PAWS to NAT The transitory connection idle-timeout is defined as the minimum time
a TCP connection in the partially open or closing phases must remain
idle before the NAT considers the associated session a candidate for
removal (REQ-5 of [RFC5382]). But [RFC5382] does not clearly state
whether these can be configured separately.
This section proposes to apply [RFC6191] mechanism at NAT. This Clarification: This document clarifies that a NAT SHOULD provide
mechanism MAY be adopted for both clients' and remote hosts' TCP different configurable parameters for configuring the open and
active close. closing idle timeouts.
client NAT remote host To accommodate deployments that consider a partially open timeout
| | | of 4 minutes as being excessive from a security standpoint, a NAT
| FIN | FIN | MAY allow to configure the timeout to be less than 4 minutes.
|------------------------>|------------------------>| Still, this specification recommends the default "transitory
| | | connection idle-timeout" minimum value to be set to 4 minutes.
| ACK | ACK |
|<------------------------|<------------------------|
| FIN | FIN |
|<------------------------|<------------------------|
| | |
| ACK(TSval=A) | ACK |
|------------------------>|------------------------>|
| | - |
| | | |
| | | |
| | | |
| | | TIME_WAIT |
| | | ->assassinated at x |
| | | |
| | | |
| | | |
| SYN(TSval>A) | x SYN |
|------------------------>|------------------------>|
| | - |
| | | |
| | | SYN_SENT |
| | | |
| | | |
Also, PAWS works to discard old duplicate packets at NAT. A packet 2.2. TCP RST
can be discarded as an old duplicate if it is received with a
timestamp or sequence number value less than a value recently
received on the connection.
To make these mechanisms work, we should concern the case that there [RFC5382] leaves the handling of TCP RST packets unspecified.
are several clients with nonsuccessive timestamp or sequence number
values are connected to a NAT device (i.e., not monotonically
increasing among clients). Two mechanisms to solve this mechanism
and applying [RFC6191] and PAWS to NAT are described below. These
mechanisms are optional.
2.2.1.1. Rewrite timestamp and sequence number values at NAT Update: This document adopts a similar default behavior as in
[RFC6146]. Concretely, when the NAT receives a TCP RST matching
an existing mapping, it MUST translate the packet according the
NAT mapping entry. Moreover, the NAT SHOULD wait for 4 minutes
before deleting the session and removing any state associate with
it if no packets are received during that 4 minutes timeout.
Rewrite timestamp and sequence number values of outgoings packets at Admittedly, the NAT has to verify whether received TCP RST packets
NAT to be monotonically increasing. This can be done by adopting belong to a connection. These verification checks are required to
following mechanisms at NAT. avoid off-path attacks.
A: Store the newest rewritten value of timestamp and sequence number If the NAT removes immediately the NAT mapping upon receipt of a
as the "max value at the time". TCP RST message, stale connections may be maintained by endpoints
if the first RST message is lost between the NAT and the
recipient.
B: NAT rewrite timestamp and sequence number values of incoming 3. Port Overlapping Behavior
packets to be monotonically increasing.
When packets come back as replies from remote hosts, NAT rewrite REQ-1 from [RFC4787] and REQ-1 from [RFC5382] specify a specific port
again the timestamp and sequence number values to be the original overlapping behavior; that is the external IP address and port can be
values. This can be done by adopting following mechanisms at NAT. reused for connections originating from the same internal source IP
address and port irrespective of the destination. This is known as
endpoint-independent mapping (EIM).
C: Store the values of original timestamp and sequence number of Update: This document clarifies that this port overlapping behavior
packets, and rewritten values of those. may be extended to connections originating from different internal
source IP addresses and ports as long as their destinations are
different.
2.2.1.2. Split an assignable number of port space to each client The following mechanism MAY be implemented by a NAT:
Adopt following mechanisms at NAT. If destination addresses and ports are different for outgoing
connections started by local clients, a NAT MAY assign the same
external port as the source ports for the connections. The
port overlapping mechanism manages mappings between external
packets and internal packets by looking at and storing their
5-tuple (protocol, source address, source port, destination
address, destination port).
A: Choose clients that can be assigned ports. This enables concurrent use of a single NAT external port for
multiple transport sessions, which allows a NAT to successfully
process packets in an IP address resource limited network (e.g.,
deployment with high address space multiplicative factor (refer to
Appendix B. of [RFC6269])).
B: Split assignable port numbers between clients. 4. Address Pooling Paired (APP)
Packets from other clients which are not chosen by these mechanisms The Address Pooling Paired (APP) behavior for a NAT was recommended
are rejected at NAT, unless there is unassigned port left. in REQ-2 from [RFC4787], but the behavior when a public IPv4 runs out
of ports was left undefined.
2.2.1.3. Resend the last ACK to the retransmisstted FIN Clarification: This document clarifies that if APP is enabled, new
sessions from a host that already has a mapping associated with an
external IP that ran out of ports SHOULD be dropped.
We need to solve another scenario to make [RFC6191] work with NAT. The administrator MAY provide a configurable parameter that allows
In the case the remote TCP could not receive the acknowledgment of a NAT to starting using ports from another external IP address
its connection termination request, the NAT device, on behalf of when the one that anchored the APP mapping ran out of ports. This
clients, resends the last ACK packet when it receives a FIN packet of is a trade-off between service continuity and APP strict
the previous connection, and when the state of the previous enforcement. (Note, this behavior is sometimes referred as 'soft-
connection has been deleted from the NAT. This mechanism MAY be used APP'.)
when clients starts closing process, and the remote host could not
receive the last ACK.
2.2.1.4. Remote host behavior of several implementations Update: This behavior SHOULD apply also for TCP.
To solve the port shortage problem on the client side, the behavior 5. EIF Protocol Independence
of remote host should be compliant to [RFC6191] or the mechanism
written in Section 4.2.2.13 of [RFC1122], since NAT may reuse the
same 5 tuple for a new connection. We have investigated behaviors of
OSes (e.g., Linux, FreeBSD, Windows, MacOS), and found that they
implemented the server side behavior of the above two.
2.3. TCP RST REQ-8 from [RFC4787] and REQ-3 from [RFC5382] do not specify whether
EIF mappings are protocol-independent. In other words, if an
outbound TCP SYN creates a mapping, it is left undefined whether
inbound UDP packets destined to that mapping should be forwarded.
[RFC5382] leaves the handling of TCP RST packets unspecified. This Update: This document specifies that EIF mappings SHOULD be
document does not try standardize such behavior but clarifies based protocol-independent in order allow inbound packets for protocols
on operational experience that a NAT that receives a TCP RST for an that multiplex TCP and UDP over the same IP address and port
active mapping and performs session tracking MAY immediately delete through the NAT and also maintain compatibility with stateful
the sessions and remove any state associated with it. If the NAT NAT64 . The administrator MAY provide a configuration parameter to
device that performs TCP session tracking receives a TCP RST for the make it protocol-dependent. The default value of this
first session that created a mapping, it MAY remove the session and configuration parameter is to allow for protocol-independent EIF.
the mapping immediately.
3. Port Overlapping behavior Applications that can be transported over a variety of transport
protocols and/or support transport fall back schemes won't
experience connectivity failures as a function of the underlying
transport protocol or the filtering mode enabled at the NAT.
[RFC4787] [RFC5382]: REQ-1 Current RFCs specifiy a specific port 6. EIF Mapping Refresh
overlapping behavior, i.e., that the external IP:port can be reused
for connections originating from the same internal source IP:port
irrespective of the destination. This is known as endpoint-
independent mapping. This document clarifies that this port
overlapping behavior can be extended to connections originating from
different internal source IP:ports as long as their destinations are
different. This known as EDM (Endpoint Dependent Mapping). The
mechanism below MAY be one optional implement to NAT.
If destination addresses and ports are different for outgoing The NAT mapping Refresh direction may have a "NAT Inbound refresh
connections started by local clients, NAT MAY assign the same behavior" of "True" according to REQ-6 from [RFC4787], but [RFC4787]
external port as the source ports for the connections. The port does not clarify how this behavior applies to EIF mappings. The
overlapping mechanism manages mappings between external packets and issue in question is whether inbound packets that match an EIF
internal packets by looking at and storing their 5-tuple (protocol, mapping but do not create a new session due to a security policy
source address, source port, destination address, destination port) . should refresh the mapping timer.
This enables concurrent use of a single NAT external port for
multiple transport sessions, which enables NAT to work correctly in
IP address resource limited network.
Discussions: Clarification: This document clarifies that even when a NAT has an
inbound refresh behavior set to 'TRUE', such packets SHOULD NOT
refresh the mapping. Otherwise a simple attack of a packet every
2 minutes can keep the mapping indefinitely.
[RFC4787] and [RFC5382] requires "endpoint-independent mapping" at Update: This behavior SHOULD apply also for TCP.
NAT, and port overlapping NAT cannot meet the requirement. This
mechanism can degrade the transparency of NAT in that its mapping
mechanism is endpoint-dependent and makes NAT traversal harder.
However, if a NAT adopts endpoint-independent mapping together with
endpoint-dependent filtering, then the actual behavior of the NAT
will be the same as port overlapping NAT.
4. Address Pooling Paired (APP) 6.1. Outbound Mapping Refresh and Error Packets
[RFC4787]: REQ-2 [RFC5382]:ND Address Pooling Paired behavior for NAT Update: In the case of NAT outbound refresh behavior there are
is recommended in previous documents but behavior when a public IPv4 certain types of packets that should not refresh the mapping even
run out of ports is left undefined. This document clarifies that if if their direction is outbound. For example, if the mapping is
APP is enabled new sessions from a subscriber that already has a kept alive by ICMP Errors or TCP RST outbound packets sent as
mapping associated with a public IP that ran out of ports SHOULD be response to inbound packets, these SHOULD NOT refresh the mapping.
dropped. The administrator MAY provide a knob that allows a NAT
device to starting using ports from another public IP when the one
that anchored the APP mapping ran out of ports. This is trade-off
between subscriber service continuity and APP strict enforcement.
(Note, it is sometimes referred as 'soft-APP')
5. EIF Security 7. EIM Protocol Independence
[RFC4787]:REQ-8 and [RFC5382]:REQ-3 End-point independent filtering REQ-1 from [RFC4787] and REQ-1 from [RFC5382] do not specify whether
could potentially result in security attacks from the public realm. EIM are protocol-independent. In other words, if a outbound TCP SYN
In order to handle this, when possible there MUST be strict filtering creates a mapping it is left undefined whether outbound UDP can reuse
checks in the inbound direction. A knob SHOULD be provided to limit such mapping and create session. On the other hand, stateful NAT64
the number of inbound sessions and a knob SHOULD be provided to [RFC6146] clearly specifies three binding information bases (TCP,
enable or disable EIF on a per application basis. This is specially UDP, ICMP).
important in the case of Mobile networks where such attacks can
consume radio resources and count against the user quota.
6. EIF Protocol Independence Update: EIM mappings SHOULD be protocol-dependent. A configuration
parameter MAY be provided in order allow protocols that multiplex
TCP and UDP over the same source IP address and port number to use
a single mapping.
[RFC4787]:REQ-8 and[RFC5382]: REQ-3 Current RFCs do not specify 8. Port Parity
whether EIF mappings are protocol independent. In other words, if an
outbound TCP SYN creates a mapping, it is left undefined whether
inbound UDP packets destined to that mapping should be forwarded.
This document specifies that EIF mappings SHOULD be protocol
independent in order allow inbound packets for protocols that
multiplex TCP and UDP over the same IP: port through the NAT and also
maintain compatibility with stateful NAT64 RFC6146 [RFC6146]. But,
the administrator MAY provide a configuration knob to make it
protocol dependent.
7. EIF Mapping Refresh Update: A NAT MAY disable port parity preservation for all dynamic
mappings. Nevertheless, A NAT SHOULD support means to explicitly
request to preserve port parity (e.g., [I-D.ietf-pcp-port-set]).
[RFC4787]: REQ-6 [RFC5382]: ND The NAT mapping Refresh direction MAY Note: According to [RFC6887], dynamic mappings are said to be
have a "NAT Inbound refresh behavior" of "True" but it does not dynamic in the sense that they are created on demand, either
clarifies how this applies to EIF mappings. The issue in question is implicitly or explicitly:
whether inbound packets that match an EIF mapping but do not create a
new session due to a security policy should refresh the mapping
timer. This document clarifies that even when a NAT device has a
inbound refresh behavior of TRUE, such packets SHOULD NOT refresh the
mapping. Otherwise a simple attack of a packet every 2 minutes can
keep the mapping indefinitely.
7.1. Outbound Mapping Refresh and Error Packets 1. Implicit dynamic mappings refer to mappings that are created
as a side effect of traffic such as an outgoing TCP SYN or
outgoing UDP packet. Implicit dynamic mappings usually have a
finite lifetime, though this lifetime is generally not known
to the client using them.
In the case of NAT outbound refresh behavior there are certain types 2. Explicit dynamic mappings refer to mappings that are created
of packets that should not refresh the mapping even if their as a result, for example, of explicit PCP MAP and PEER
direction is outbound. For example, if the mapping is kept alive by requests. Explicit dynamic mappings have a finite lifetime,
ICMP Errors or TCP RST outbound packets sent as response to inbound and this lifetime is communicated to the client.
packets, these SHOULD NOT refresh the mapping.
8. EIM Protocol Independence 9. Port Randomization
[RFC4787] [RFC5382]: REQ-1 Current RFCs do not specify whether EIM Update: A NAT SHOULD follow the recommendations specified in
are protocol independent. In other words, if a outbound TCP SYN Section 4 of [RFC6056], especially:
creates a mapping it is left undefined whether outbound UDP can reuse
such mapping and create session. On the other hand, Stateful NAT64
[RFC6146] clearly specifies three binding information bases (TCP,
UDP, ICMP). This document clarifies that EIM mappings SHOULD be
protocol dependent . A knob MAY be provided in order allow protocols
that multiplex TCP and UDP over the same source IP and port to use a
single mapping.
9. Port Parity "A NAPT that does not implement port preservation [RFC4787]
[RFC5382] SHOULD obfuscate selection of the ephemeral port of a
packet when it is changed during translation of that packet. A
NAPT that does implement port preservation SHOULD obfuscate the
ephemeral port of a packet only if the port must be changed as
a result of the port being already in use for some other
session. A NAPT that performs parity preservation and that
must change 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
is desired)."
A NAT devices MAY disable port parity preservation for dynamic 10. IP Identification (IP ID)
mappings. Nevertheless, A NAT SHOULD support means to explicitly
request to preserve port parity (e.g., [I-D.ietf-pcp-port-set]).
10. Port Randomization Update: A NAT SHOULD handle the Identification field of translated
IPv4 packets as specified in Section 5.3.1 of [RFC6864].
A NAT SHOULD follow the recommendations specified in Section 4 of Discussion: This recommendation may have undesired effects on the
[RFC6056] especially: performance of the NAT in environments in which fragmentation is
massively experienced. Such issue can be used as an attack vector
against NATs.
"A NAPT that does not implement port preservation [RFC4787] 11. ICMP Query Mappings Timeout
[RFC5382] SHOULD obfuscate selection of the ephemeral port of a
packet when it is changed during translation of that packet. A
NAPT that does implement port preservation SHOULD obfuscate the
ephemeral port of a packet only if the port must be changed as a
result of the port being already in use for some other session. A
NAPT that performs parity preservation and that must change 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 is desired)."
11. IP Identification (IP ID) Section 3.1 of [RFC5508] precises that ICMP Query Mappings are to be
maintained by a NAT. However, the specification doesn't discuss
Query Mapping timeout values. Section 3.2 of [RFC5508] only
discusses ICMP Query Session Timeouts.
A NAT SHOULD handle the Identification field of translated IPv4 Update: ICMP Query Mappings MAY be deleted once the last the session
packets as specified in Section 9 of [RFC6864]. using the mapping is deleted.
12. ICMP Query Mappings Timeout 12. Hairpinning Support for ICMP Packets
Section 3.1 of [RFC5508] says that ICMP Query Mappings are to be REQ-7 from [RFC5508] specifies that a NAT enforcing 'Basic NAT' must
maintained by NAT device. However, RFC doesn't discuss about the support traversal of hairpinned ICMP Query sessions.
Query Mapping timeout values. Section 3.2 of that RFC only discusses
about ICMP Query Session Timeouts.
ICMP Query Mappings MAY be deleted once the last the session using Clarification: This implicitly means that address mappings from
the mapping is deleted. external address to internal address (similar to Endpoint
Independent Filters) must be maintained to allow inbound ICMP
Query sessions. If an ICMP Query is received on an external
address, a NAT can then translate to an internal IP.
13. Hairpinning Support for ICMP Packets REQ-7 from [RFC5508] specifies that all NATs must support the
traversal of hairpinned ICMP Error messages.
[RFC5508]:REQ-7 This requirement specifies that NAT devices enforcing Clarification: This behavior requires a NAT to maintain address
Basic NAT MUST support traversal of hairpinned ICMP Query sessions. mappings from external IP address to internal IP address in
This implicitly means that address mappings from external address to addition to the ICMP Query Mappings described in Section 3.1 of
internal address (similar to Endpoint Independent Filters) MUST be [RFC5508].
maintained to allow inbound ICMP Query sessions. If an ICMP Query is
received on an external address, NAT device can then translate to an
internal IP. [RFC5508]:REQ-7 This requirement specifies that all NAT
devices (i.e., Basic NAT as well as NAPT devices) MUST support the
traversal of hairpinned ICMP Error messages. This requires NAT
devices to maintain address mappings from external IP address to
internal IP address in addition to the ICMP Query Mappings described
in section 3.1 of that RFC.
14. IANA Considerations 13. IANA Considerations
This document does not require any IANA action. This document does not require any IANA action.
15. Security Considerations 14. Security Considerations
In the case of EIF mappings due to high risk of resource crunch, a
NAT device MAY provide a knob to limit the number of inbound sessions
spawned from a EIF mapping.
[I-D.ietf-tcpm-tcp-security] contains a detailed discussion of the
security implications of TCP Timestamps and of different timestamp
generation algorithms.
16. Acknowledgements NAT behavioral considerations are discussed in [RFC4787].
Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan and Security considerations discussed in Section 5 of [RFC6146] apply
Senthil Sivamular for review and discussions also fro NAT44.
17. References In the case of EIF mappings due to high risk of resource crunch, a
NAT MAY provide a configurable parameter to limit the number of
inbound sessions spawned from a EIF mapping.
17.1. Normative References 15. Acknowledgements
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan,
793, September 1981. Senthil Sivamular, Lars Eggert, and Gorry Fairhurst for review and
discussions.
[RFC1122] Braden, R., "Requirements for Internet Hosts - 16. References
Communication Layers", STD 3, RFC 1122, October 1989. 16.1. 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, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address <http://www.rfc-editor.org/info/rfc2119>.
Translator (NAT) Terminology and Considerations", RFC
2663, August 1999.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address
(NAT) Behavioral Requirements for Unicast UDP", BCP 127, Translation (NAT) Behavioral Requirements for Unicast
RFC 4787, January 2007. UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
2007, <http://www.rfc-editor.org/info/rfc4787>.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. [RFC5382] Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008. RFC 5382, DOI 10.17487/RFC5382, October 2008,
<http://www.rfc-editor.org/info/rfc5382>.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT [RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508, Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009. DOI 10.17487/RFC5508, April 2009,
<http://www.rfc-editor.org/info/rfc5508>.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport- [RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056, January Protocol Port Randomization", BCP 156, RFC 6056,
2011. DOI 10.17487/RFC6056, January 2011,
<http://www.rfc-editor.org/info/rfc6056>.
[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, April 2011. Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <http://www.rfc-editor.org/info/rfc6146>.
[RFC6191] Gont, F., "Reducing the TIME-WAIT State Using TCP
Timestamps", BCP 159, RFC 6191, April 2011.
[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
RFC 6864, February 2013. RFC 6864, DOI 10.17487/RFC6864, February 2013,
<http://www.rfc-editor.org/info/rfc6864>.
[RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
and H. Ashida, "Common Requirements for Carrier-Grade NATs
(CGNs)", BCP 127, RFC 6888, April 2013.
17.2. Informative References [RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
A., and H. Ashida, "Common Requirements for Carrier-Grade
NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
April 2013, <http://www.rfc-editor.org/info/rfc6888>.
[FLOWRATE] 16.2. Informative References
Zhang, Y., Breslau, L., Paxson, V., and S. Shenker, "On
the Characteristics and Origins of Internet Flow Rates", .
[I-D.ietf-pcp-port-set] [I-D.ietf-pcp-port-set]
Qiong, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, Qiong, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou,
T., and S. Perreault, "Port Control Protocol (PCP) T., and S. Perreault, "Port Control Protocol (PCP)
Extension for Port Set Allocation", draft-ietf-pcp-port- Extension for Port Set Allocation", draft-ietf-pcp-port-
set-07 (work in progress), November 2014. set-09 (work in progress), May 2015.
[I-D.ietf-tcpm-tcp-security] [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Gont, F., "Survey of Security Hardening Methods for Translator (NAT) Terminology and Considerations",
Transmission Control Protocol (TCP) Implementations", RFC 2663, DOI 10.17487/RFC2663, August 1999,
draft-ietf-tcpm-tcp-security-03 (work in progress), March <http://www.rfc-editor.org/info/rfc2663>.
2012.
[TCPWILD] Qian, F., Subhabrata, S., Spatscheck, O., Morley Mao, Z., [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
and W. Willinger, "TCP Revisited: A Fresh Look at TCP in Address Translator (Traditional NAT)", RFC 3022,
the Wild", . DOI 10.17487/RFC3022, January 2001,
<http://www.rfc-editor.org/info/rfc3022>.
[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
P. Roberts, "Issues with IP Address Sharing", RFC 6269,
DOI 10.17487/RFC6269, June 2011,
<http://www.rfc-editor.org/info/rfc6269>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<http://www.rfc-editor.org/info/rfc6887>.
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 USA
Email: repenno@cisco.com Email: repenno@cisco.com
Simon Perreault Simon Perreault
Viagenie Jive Communications
2875 boul. Laurier, suite D2-630
Quebec, QC G1V 2M2
Canada Canada
Email: simon.perreault@viagenie.ca Email: sperreault@jive.com
Sarat Kamiset Sarat Kamiset
Insieme Networks Insieme Networks
California California
Mohamed Boucadair Mohamed Boucadair
France Telecom France Telecom
Rennes 35000 Rennes 35000
France France
Email: mohamed.boucadair@orange.com Email: mohamed.boucadair@orange.com
Kengo Naito Kengo Naito
NTT NTT
Tokyo Tokyo
 End of changes. 95 change blocks. 
409 lines changed or deleted 334 lines changed or added

This html diff was produced by rfcdiff 1.42. The latest version is available from http://tools.ietf.org/tools/rfcdiff/