draft-ietf-tsvwg-behave-requirements-update-00.txt   draft-ietf-tsvwg-behave-requirements-update-01.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: May 23, 2014 Viagenie Expires: August 22, 2015 Viagenie
S. Kamiset S. Kamiset
Insieme Networks Insieme Networks
M. Boucadair M. Boucadair
France Telecom France Telecom
K. Naito K. Naito
NTT NTT
November 19, 2013 February 18, 2015
Network Address Translation (NAT) Behavioral Requirements Updates Network Address Translation (NAT) Behavioral Requirements Updates
draft-ietf-tsvwg-behave-requirements-update-00 draft-ietf-tsvwg-behave-requirements-update-01
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 NAPT44.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
skipping to change at page 1, line 45 skipping to change at page 1, line 45
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 May 23, 2014. This Internet-Draft will expire on August 22, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2013 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
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. TCP Session Tracking . . . . . . . . . . . . . . . . . . . . 3 2. TCP Session Tracking . . . . . . . . . . . . . . . . . . . . 3
3.1. TCP Transitory Connection Idle-Timeout . . . . . . . . . 4 2.1. TCP Transitory Connection Idle-Timeout . . . . . . . . . 4
3.2. TIME_WAIT State . . . . . . . . . . . . . . . . . . . . . 4 2.2. TIME_WAIT State . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. Proposal: Apply RFC6191 and PAWS to NAT . . . . . . 5 2.2.1. Proposal: Apply RFC6191 and PAWS to NAT . . . . . . 5
3.3. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Port Overlapping behavior . . . . . . . . . . . . . . . . . . 8 3. Port Overlapping behavior . . . . . . . . . . . . . . . . . . 8
5. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . 8 4. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . 8
6. EIF Security . . . . . . . . . . . . . . . . . . . . . . . . 8 5. EIF Security . . . . . . . . . . . . . . . . . . . . . . . . 9
7. EIF Protocol Independence . . . . . . . . . . . . . . . . . . 9 6. EIF Protocol Independence . . . . . . . . . . . . . . . . . . 9
8. EIF Mapping Refresh . . . . . . . . . . . . . . . . . . . . . 9 7. EIF Mapping Refresh . . . . . . . . . . . . . . . . . . . . . 9
8.1. Outbound Mapping Refresh and Error Packets . . . . . . . 9 7.1. Outbound Mapping Refresh and Error Packets . . . . . . . 10
9. EIM Protocol Independence . . . . . . . . . . . . . . . . . . 9 8. EIM Protocol Independence . . . . . . . . . . . . . . . . . . 10
10. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . 10 9. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . 10
11. Port Randomization . . . . . . . . . . . . . . . . . . . . . 10 10. Port Randomization . . . . . . . . . . . . . . . . . . . . . 10
12. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . 10 11. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . 11
13. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . 10 12. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . 11
14. Hairpinning Support for ICMP Packets . . . . . . . . . . . . 10 13. Hairpinning Support for ICMP Packets . . . . . . . . . . . . 11
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
16. Security Considerations . . . . . . . . . . . . . . . . . . . 11 15. Security Considerations . . . . . . . . . . . . . . . . . . . 11
17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
18.1. Normative References . . . . . . . . . . . . . . . . . . 11 17.1. Normative References . . . . . . . . . . . . . . . . . . 12
18.2. Informative References . . . . . . . . . . . . . . . . . 12 17.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Terminology 1. Introduction
The reader should be familiar with all terms defined in RFC2663
[RFC2663],RFC4787 [RFC4787],RFC5382 [RFC5382],RFC5508 [RFC5508]
2. 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 NAT more development and operational experience was
acquired some areas of the original documents need further acquired some areas of the original documents need further
clarification or updates. This documents provides such clarification or updates. This document provides such clarifications
clarifications and updates. and updates.
2.1. Scope 1.1. Scope
This document focuses solely on NAPT44 and its goal is to clarify, This document focuses solely on NAPT44 and its goal is to clarify,
fill gaps or update requirements of [RFC4787], [RFC5382] and fill gaps or update requirements of [RFC4787], [RFC5382] and
[RFC5508]. It is out of the scope of this document the creation of [RFC5508].
completely new requirements not associated with the documents cited
above. New requirements would be better served elsewhere and if they
are CGN specific in an update to [RFC6888].
3. TCP Session Tracking It is out of the scope of this document the creation of completely
new requirements not associated with the documents cited above. New
requirements would be better served elsewhere and if they are CGN
specific in an update to [RFC6888].
1.2. Terminology
The reader should be familiar with the terms defined in
[RFC2663],[RFC4787],[RFC5382],and [RFC5508]
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 NAPT44 should use states but does not specify the TCP state machine a NAPT44 should use
as a basis to apply such timers. The TCP state machine below, as a basis to apply such timers. The TCP state machine depicted in
adapted from [RFC6146], provides guidance on how TCP session tracking Figure 1, adapted from [RFC6146], provides guidance on how TCP
could be implemented - it is non-normative. session tracking could be implemented - it is non-normative.
+-----------------------------+ +-----------------------------+
| | | |
V | V |
+------+ CV4 | +------+ CV4 |
|CLOSED|-----SYN------+ | |CLOSED|-----SYN------+ |
+------+ | | +------+ | |
^ | | ^ | |
|TCP_TRANS T.O. | | |TCP_TRANS T.O. | |
| V | | V |
skipping to change at page 4, line 24 skipping to change at page 4, line 41
| RCV | | RCV | | | RCV | | RCV | |
+---------+ +----------+ | +---------+ +----------+ |
| | | | | |
SV4 FIN CV4 FIN TCP_TRANS SV4 FIN CV4 FIN TCP_TRANS
| | T.O. | | T.O.
V V | V V |
+----------------------+ | +----------------------+ |
| CV4 FIN + SV4 FIN RCV|--------------------+ | CV4 FIN + SV4 FIN RCV|--------------------+
+----------------------+ +----------------------+
3.1. TCP Transitory Connection Idle-Timeout Figure 1
2.1. TCP Transitory Connection Idle-Timeout
[RFC5382]:REQ-5 The transitory connection idle-timeout is defined as [RFC5382]:REQ-5 The transitory connection idle-timeout is defined as
the minimum time a TCP connection in the partially open or closing the minimum time a TCP connection in the partially open or closing
phases must remain idle before the NAT considers the associated phases must remain idle before the NAT considers the associated
session a candidate for removal. But the document does not clearly session a candidate for removal. But the document does not clearly
states if these can be configured separately. This document states if these can be configured separately.
clarifies that a NAT device SHOULD provide different knobs for
configuring the open and closing idle timeouts. This 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.
3.2. TIME_WAIT State This document clarifies that a NAT device SHOULD provide different
knobs for configuring the open and closing idle timeouts. This
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
The TCP TIME_WAIT state is described in [RFC0793]. The TCP TIME_WAIT The TCP TIME_WAIT state is described in [RFC0793]. The TCP TIME_WAIT
state needs to be kept for 2MSL before a connection is CLOSED, for state needs to be kept for 2MSL before a connection is CLOSED, for
the reasons below. the reasons listed below:
1: In the event that packets from a session are delayed in the in- 1: In the event that packets from a session are delayed in the in-
between network, and delivered to the end relatively later, we between network, and delivered to the end relatively later, we
should prevent the packets from being transferred and interpreted should prevent the packets from being transferred and interpreted
as a packet that belongs to a new session. as a packet that belongs to a new session.
2: If the remote TCP has not received the acknowledgment of its 2: If the remote TCP has not received the acknowledgment of its
connection termination request, it will re-send the FIN packet connection termination request, it will re-send the FIN packet
several times. several times.
These points are important for the TCP to work without problems. These points are important for the TCP to work without problems.
[RFC5283] leaves the handling of TCP connections in TIME_WAIT state [RFC5382] leaves the handling of TCP connections in TIME_WAIT state
unspecified and mentions that TIME_WAIT state is not part of the unspecified and mentions that TIME_WAIT state is not part of the
transitory connection idle-timeout. If the NAT device honors the transitory connection idle-timeout. If the NAT device honors the
TIME_WAIT state, each TCP connection and its associated resources is TIME_WAIT state, each TCP connection and its associated resources is
kept for a certain period, typically for four minutes, which consumes kept for a certain period, typically for four minutes, which consumes
port resources. port resources.
[RFC6191] explains that in certain situation it is necessary to [RFC6191] explains that in certain situation it is necessary to
reduce the TIME_WAIT state and defines such a mechanism using TCP reduce the TIME_WAIT state and defines such a mechanism using TCP
timestamps and sequence numbers. When a connection request is timestamps and sequence numbers. When a connection request is
received with a four-tuple that is in the TIME-WAIT state, the received with a four-tuple that is in the TIME-WAIT state, the
connection request may be accepted if the sequence number or the connection request may be accepted if the sequence number or the
timestamp of the incoming SYN segment is greater than the last timestamp of the incoming SYN segment is greater than the last
sequence number seen on the previous incarnation of the connection. sequence number seen on the previous incarnation of the connection.
[N.E] This document specifies that a NAT device should keep TCP This document specifies that a NAT device should keep TCP connections
connections in TIME_WAIT state unless it implements the proposal in TIME_WAIT state unless it implements the proposal described in the
below? following sub-section.
3.2.1. Proposal: Apply RFC6191 and PAWS to NAT 2.2.1. Proposal: Apply RFC6191 and PAWS to NAT
This section proposes to apply [RFC6191] mechanism at NAT. This This section proposes to apply [RFC6191] mechanism at NAT. This
mechanism MAY be adopted for both clients' and remote hosts' TCP mechanism MAY be adopted for both clients' and remote hosts' TCP
active close. active close.
client NAT remote host client NAT remote host
| | | | | |
| FIN | FIN | | FIN | FIN |
|------------------------>|------------------------>| |------------------------>|------------------------>|
| | | | | |
skipping to change at page 6, line 17 skipping to change at page 6, line 34
| | | | | | | |
| | | | | | | |
| SYN(TSval>A) | x SYN | | SYN(TSval>A) | x SYN |
|------------------------>|------------------------>| |------------------------>|------------------------>|
| | - | | | - |
| | | | | | | |
| | | SYN_SENT | | | | SYN_SENT |
| | | | | | | |
| | | | | | | |
(postamble)
Also, PAWS works to discard old duplicate packets at NAT. A packet Also, PAWS works to discard old duplicate packets at NAT. A packet
can be discarded as an old duplicate if it is received with a can be discarded as an old duplicate if it is received with a
timestamp or sequence number value less than a value recently timestamp or sequence number value less than a value recently
received on the connection. received on the connection.
To make these mechanisms work, we should concern the case that there To make these mechanisms work, we should concern the case that there
are several clients with nonsuccessive timestamp or sequence number are several clients with nonsuccessive timestamp or sequence number
values are connected to a NAT device (i.e. not monotonically values are connected to a NAT device (i.e., not monotonically
increasing among clients). Two mechanisms to solve this mechanism increasing among clients). Two mechanisms to solve this mechanism
and applying [RFC6191] and PAWS to NAT are described below. These and applying [RFC6191] and PAWS to NAT are described below. These
mechanisms are optional. mechanisms are optional.
3.2.1.1. Rewrite timestamp and sequence number values at NAT 2.2.1.1. Rewrite timestamp and sequence number values at NAT
Rewrite timestamp and sequence number values of outgoings packets at Rewrite timestamp and sequence number values of outgoings packets at
NAT to be monotonically increasing. This can be done by adopting NAT to be monotonically increasing. This can be done by adopting
following mechanisms at NAT. following mechanisms at NAT.
A: Store the newest rewritten value of timestamp and sequence number A: Store the newest rewritten value of timestamp and sequence number
as the "max value at the time". as the "max value at the time".
B: NAT rewrite timestamp and sequence number values of incoming B: NAT rewrite timestamp and sequence number values of incoming
packets to be monotonically increasing. packets to be monotonically increasing.
When packets come back as replies from remote hosts, NAT rewrite When packets come back as replies from remote hosts, NAT rewrite
again the timestamp and sequence number values to be the original again the timestamp and sequence number values to be the original
values. This can be done by adopting following mechanisms at NAT. values. This can be done by adopting following mechanisms at NAT.
C: Store the values of original timestamp and sequence number of C: Store the values of original timestamp and sequence number of
packets, and rewritten values of those. packets, and rewritten values of those.
3.2.1.2. Split an assignable number of port space to each client 2.2.1.2. Split an assignable number of port space to each client
Adopt following mechanisms at NAT. Adopt following mechanisms at NAT.
A: Choose clients that can be assigned ports. A: Choose clients that can be assigned ports.
B: Split assignable port numbers between clients. B: Split assignable port numbers between clients.
Packets from other clients which are not chosen by these mechanisms Packets from other clients which are not chosen by these mechanisms
are rejected at NAT, unless there is unassigned port left. are rejected at NAT, unless there is unassigned port left.
3.2.1.3. Resend the last ACK to the retransmisstted FIN 2.2.1.3. Resend the last ACK to the retransmisstted FIN
We need to solve another scenario to make RFC6191 work with NAT. In We need to solve another scenario to make [RFC6191] work with NAT.
the case the remote TCP could not receive the acknowledgment of its In the case the remote TCP could not receive the acknowledgment of
connection termination request, the NAT device, on behalf of clients, its connection termination request, the NAT device, on behalf of
resends the last ACK packet when it receives a FIN packet of the clients, resends the last ACK packet when it receives a FIN packet of
previous connection, and when the state of the previous connection the previous connection, and when the state of the previous
has been deleted from the NAT. This mechanism MAY be used when connection has been deleted from the NAT. This mechanism MAY be used
clients starts closing process, and the remote host could not receive when clients starts closing process, and the remote host could not
the last ACK. receive the last ACK.
3.2.1.4. Remote host behavior of several implementations 2.2.1.4. Remote host behavior of several implementations
To solve the port shortage problem on the client side, the behavior To solve the port shortage problem on the client side, the behavior
of remote host should be compliant to [RFC6191] or the mechanism of remote host should be compliant to [RFC6191] or the mechanism
written in 4.2.2.13 of [RFC1122], since NAT may reuse the same 5 written in Section 4.2.2.13 of [RFC1122], since NAT may reuse the
tuple for a new connection. We have investigated behaviors of OSes same 5 tuple for a new connection. We have investigated behaviors of
(e.g., Linux, FreeBSD, Windows, MacOS), and found that they OSes (e.g., Linux, FreeBSD, Windows, MacOS), and found that they
implemented the server side behavior of the above two. implemented the server side behavior of the above two.
3.3. TCP RST 2.3. TCP RST
[RFC5382] leaves the handling of TCP RST packets unspecified. This [RFC5382] leaves the handling of TCP RST packets unspecified. This
document does not try standardize such behavior but clarifies based document does not try standardize such behavior but clarifies based
on operational experience that a NAT that receives a TCP RST for an on operational experience that a NAT that receives a TCP RST for an
active mapping and performs session tracking MAY immediately delete active mapping and performs session tracking MAY immediately delete
the sessions and remove any state associated with it. If the NAT the sessions and remove any state associated with it. If the NAT
device that performs TCP session tracking receives a TCP RST for the device that performs TCP session tracking receives a TCP RST for the
first session that created a mapping, it MAY remove the session and first session that created a mapping, it MAY remove the session and
the mapping immediately. the mapping immediately.
4. Port Overlapping behavior 3. Port Overlapping behavior
[RFC4787] [RFC5382]: REQ-1 Current RFCs specifiy a specific port [RFC4787] [RFC5382]: REQ-1 Current RFCs specifiy a specific port
overlapping behavior, i.e., that the external IP:port can be reused overlapping behavior, i.e., that the external IP:port can be reused
for connections originating from the same internal source IP:port for connections originating from the same internal source IP:port
irrespective of the destination. This is known as endpoint- irrespective of the destination. This is known as endpoint-
independent mapping. This document clarifies that this port independent mapping. This document clarifies that this port
overlapping behavior can be extended to connections originating from overlapping behavior can be extended to connections originating from
different internal source IP:ports as long as their destinations are different internal source IP:ports as long as their destinations are
different. This known as EDM (Endpoint Dependent Mapping). The different. This known as EDM (Endpoint Dependent Mapping). The
mechanism below MAY be one optional implement to NAT. mechanism below MAY be one optional implement to NAT.
skipping to change at page 8, line 37 skipping to change at page 8, line 48
Discussions: Discussions:
[RFC4787] and [RFC5382] requires "endpoint-independent mapping" at [RFC4787] and [RFC5382] requires "endpoint-independent mapping" at
NAT, and port overlapping NAT cannot meet the requirement. This NAT, and port overlapping NAT cannot meet the requirement. This
mechanism can degrade the transparency of NAT in that its mapping mechanism can degrade the transparency of NAT in that its mapping
mechanism is endpoint-dependent and makes NAT traversal harder. mechanism is endpoint-dependent and makes NAT traversal harder.
However, if a NAT adopts endpoint-independent mapping together with However, if a NAT adopts endpoint-independent mapping together with
endpoint-dependent filtering, then the actual behavior of the NAT endpoint-dependent filtering, then the actual behavior of the NAT
will be the same as port overlapping NAT. will be the same as port overlapping NAT.
5. Address Pooling Paired (APP) 4. Address Pooling Paired (APP)
[RFC4787]: REQ-2 [RFC5382]:ND Address Pooling Paired behavior for NAT [RFC4787]: REQ-2 [RFC5382]:ND Address Pooling Paired behavior for NAT
is recommended in previous documents but behavior when a public IPv4 is recommended in previous documents but behavior when a public IPv4
run out of ports is left undefined. This document clarifies that if run out of ports is left undefined. This document clarifies that if
APP is enabled new sessions from a subscriber that already has a APP is enabled new sessions from a subscriber that already has a
mapping associated with a public IP that ran out of ports SHOULD be mapping associated with a public IP that ran out of ports SHOULD be
dropped. The administrator MAY provide a knob that allows a NAT dropped. The administrator MAY provide a knob that allows a NAT
device to starting using ports from another public IP when the one 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 that anchored the APP mapping ran out of ports. This is trade-off
between subscriber service continuity and APP strict enforcement. between subscriber service continuity and APP strict enforcement.
(NE: It is sometimes referred as 'soft-APP') (Note, it is sometimes referred as 'soft-APP')
6. EIF Security 5. EIF Security
[RFC4787]:REQ-8 and [RFC5382]:REQ-3 End-point independent filtering [RFC4787]:REQ-8 and [RFC5382]:REQ-3 End-point independent filtering
could potentially result in security attacks from the public realm. could potentially result in security attacks from the public realm.
In order to handle this, when possible there MUST be strict filtering In order to handle this, when possible there MUST be strict filtering
checks in the inbound direction. A knob SHOULD be provided to limit checks in the inbound direction. A knob SHOULD be provided to limit
the number of inbound sessions and a knob SHOULD be provided to the number of inbound sessions and a knob SHOULD be provided to
enable or disable EIF on a per application basis. This is specially enable or disable EIF on a per application basis. This is specially
important in the case of Mobile networks where such attacks can important in the case of Mobile networks where such attacks can
consume radio resources and count against the user quota. consume radio resources and count against the user quota.
7. EIF Protocol Independence 6. EIF Protocol Independence
[RFC4787]:REQ-8 and[RFC5382]: REQ-3 Current RFCs do not specify [RFC4787]:REQ-8 and[RFC5382]: REQ-3 Current RFCs do not specify
whether EIF mappings are protocol independent. In other words, if an whether EIF mappings are protocol independent. In other words, if an
outbound TCP SYN creates a mapping, it is left undefined whether outbound TCP SYN creates a mapping, it is left undefined whether
inbound UDP packets destined to that mapping should be forwarded. inbound UDP packets destined to that mapping should be forwarded.
This document specifies that EIF mappings SHOULD be protocol This document specifies that EIF mappings SHOULD be protocol
independent in order allow inbound packets for protocols that independent in order allow inbound packets for protocols that
multiplex TCP and UDP over the same IP: port through the NAT and also multiplex TCP and UDP over the same IP: port through the NAT and also
maintain compatibility with stateful NAT64 RFC6146 [RFC6146]. But maintain compatibility with stateful NAT64 RFC6146 [RFC6146]. But,
the administrator MAY provide a configuration knob to make it the administrator MAY provide a configuration knob to make it
protocol dependent. protocol dependent.
8. EIF Mapping Refresh 7. EIF Mapping Refresh
[RFC4787]: REQ-6 [RFC5382]: ND The NAT mapping Refresh direction MAY [RFC4787]: REQ-6 [RFC5382]: ND The NAT mapping Refresh direction MAY
have a "NAT Inbound refresh behavior" of "True" but it does not have a "NAT Inbound refresh behavior" of "True" but it does not
clarifies how this applies to EIF mappings. The issue in question is clarifies how this applies to EIF mappings. The issue in question is
whether inbound packets that match an EIF mapping but do not create a whether inbound packets that match an EIF mapping but do not create a
new session due to a security policy should refresh the mapping new session due to a security policy should refresh the mapping
timer. This document clarifies that even when a NAT device has a timer. This document clarifies that even when a NAT device has a
inbound refresh behavior of TRUE, such packets SHOULD NOT refresh the inbound refresh behavior of TRUE, such packets SHOULD NOT refresh the
mapping. Otherwise a simple attack of a packet every 2 minutes can mapping. Otherwise a simple attack of a packet every 2 minutes can
keep the mapping indefinitely. keep the mapping indefinitely.
8.1. Outbound Mapping Refresh and Error Packets 7.1. Outbound Mapping Refresh and Error Packets
In the case of NAT outbound refresh behavior there are certain types In the case of NAT outbound refresh behavior there are certain types
of packets that should not refresh the mapping even if their of packets that should not refresh the mapping even if their
direction is outbound. For example, if the mapping is kept alive by direction is outbound. For example, if the mapping is kept alive by
ICMP Errors or TCP RST outbound packets sent as response to inbound ICMP Errors or TCP RST outbound packets sent as response to inbound
packets, these SHOULD NOT refresh the mapping. packets, these SHOULD NOT refresh the mapping.
9. EIM Protocol Independence 8. EIM Protocol Independence
[RFC4787] [RFC5382]: REQ-1 Current RFCs do not specify whether EIM [RFC4787] [RFC5382]: REQ-1 Current RFCs do not specify whether EIM
are protocol independent. In other words, if a outbound TCP SYN are protocol independent. In other words, if a outbound TCP SYN
creates a mapping it is left undefined whether outbound UDP can reuse creates a mapping it is left undefined whether outbound UDP can reuse
such mapping and create session. On the other hand, Stateful NAT64 such mapping and create session. On the other hand, Stateful NAT64
[RFC6146] clearly specifies three binding information bases (TCP, [RFC6146] clearly specifies three binding information bases (TCP,
UDP, ICMP). This document clarifies that EIM mappings SHOULD be UDP, ICMP). This document clarifies that EIM mappings SHOULD be
protocol dependent . A knob MAY be provided in order allow protocols 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 that multiplex TCP and UDP over the same source IP and port to use a
single mapping. single mapping.
10. Port Parity 9. Port Parity
A NAT devices MAY disable port parity preservation for dynamic A NAT devices MAY disable port parity preservation for 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., [I-D.pcp-port-set]). request to preserve port parity (e.g., [I-D.ietf-pcp-port-set]).
11. Port Randomization 10. Port Randomization
A NAT SHOULD follow the recommendations specified in Section 4 of A NAT SHOULD follow the recommendations specified in Section 4 of
[RFC6056] especially: "A NAPT that does not implement port [RFC6056] especially:
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)."
12. IP Identification (IP ID) "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)."
11. IP Identification (IP ID)
A NAT SHOULD handle the Identification field of translated IPv4 A NAT SHOULD handle the Identification field of translated IPv4
packets as specified in Section 9 of [I-D.ietf-intarea-ipv4-id- packets as specified in Section 9 of [RFC6864].
update].
13. ICMP Query Mappings Timeout 12. ICMP Query Mappings Timeout
Section 3.1 of [RFC5508] says that ICMP Query Mappings are to be Section 3.1 of [RFC5508] says that ICMP Query Mappings are to be
maintained by NAT device. However, RFC doesn't discuss about the maintained by NAT device. However, RFC doesn't discuss about the
Query Mapping timeout values. Section 3.2 of that RFC only discusses Query Mapping timeout values. Section 3.2 of that RFC only discusses
about ICMP Query Session Timeouts. ICMP Query Mappings MAY be about ICMP Query Session Timeouts.
deleted once the last the session using the mapping is deleted.
14. Hairpinning Support for ICMP Packets ICMP Query Mappings MAY be deleted once the last the session using
the mapping is deleted.
13. Hairpinning Support for ICMP Packets
[RFC5508]:REQ-7 This requirement specifies that NAT devices enforcing [RFC5508]:REQ-7 This requirement specifies that NAT devices enforcing
Basic NAT MUST support traversal of hairpinned ICMP Query sessions. Basic NAT MUST support traversal of hairpinned ICMP Query sessions.
This implicitly means that address mappings from external address to This implicitly means that address mappings from external address to
internal address (similar to Endpoint Independent Filters) MUST be internal address (similar to Endpoint Independent Filters) MUST be
maintained to allow inbound ICMP Query sessions. If an ICMP Query is maintained to allow inbound ICMP Query sessions. If an ICMP Query is
received on an external address, NAT device can then translate to an received on an external address, NAT device can then translate to an
internal IP. [RFC5508]:REQ-7 This requirement specifies that all NAT internal IP. [RFC5508]:REQ-7 This requirement specifies that all NAT
devices (i.e., Basic NAT as well as NAPT devices) MUST support the devices (i.e., Basic NAT as well as NAPT devices) MUST support the
traversal of hairpinned ICMP Error messages. This too requires NAT traversal of hairpinned ICMP Error messages. This requires NAT
devices to maintain address mappings from external IP address to devices to maintain address mappings from external IP address to
internal IP address in addition to the ICMP Query Mappings described internal IP address in addition to the ICMP Query Mappings described
in section 3.1 of that RFC. in section 3.1 of that RFC.
15. IANA Considerations 14. IANA Considerations
TBD This document does not require any IANA action.
16. Security Considerations 15. Security Considerations
In the case of EIF mappings due to high risk of resource crunch, a 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 NAT device MAY provide a knob to limit the number of inbound sessions
spawned from a EIF mapping. spawned from a EIF mapping.
[TCP-Security] contains a detailed discussion of the security [I-D.ietf-tcpm-tcp-security] contains a detailed discussion of the
implications of TCP Timestamps and of different timestamp generation security implications of TCP Timestamps and of different timestamp
algorithms. generation algorithms.
17. Acknowledgements 16. Acknowledgements
Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan and Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan and
Senthil Sivamular for review and discussions Senthil Sivamular for review and discussions
18. References 17. References
18.1. Normative References 17.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981. 793, September 1981.
[RFC1122] Braden, R., "Requirements for Internet Hosts - [RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989. Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions
for High Performance", RFC 1323, May 1992.
[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, March 1997.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC Translator (NAT) Terminology and Considerations", RFC
2663, August 1999. 2663, August 1999.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute
in Session Description Protocol (SDP)", RFC 3605, October
2003.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation [RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127, (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007. RFC 4787, January 2007.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. [RFC5382] Guha, S., 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, October 2008.
[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,
skipping to change at page 12, line 32 skipping to change at page 12, line 50
Protocol Port Randomization", BCP 156, RFC 6056, January Protocol Port Randomization", BCP 156, RFC 6056, January
2011. 2011.
[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, April 2011.
[RFC6191] Gont, F., "Reducing the TIME-WAIT State Using TCP [RFC6191] Gont, F., "Reducing the TIME-WAIT State Using TCP
Timestamps", BCP 159, RFC 6191, April 2011. Timestamps", BCP 159, RFC 6191, April 2011.
[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
RFC 6864, February 2013.
[RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A., [RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
and H. Ashida, "Common Requirements for Carrier-Grade NATs and H. Ashida, "Common Requirements for Carrier-Grade NATs
(CGNs)", BCP 127, RFC 6888, April 2013. (CGNs)", BCP 127, RFC 6888, April 2013.
18.2. Informative References 17.2. Informative References
[FLOWRATE] [FLOWRATE]
Zhang, Y., Breslau, L., Paxson, V., and S. Shenker, "On Zhang, Y., Breslau, L., Paxson, V., and S. Shenker, "On
the Characteristics and Origins of Internet Flow Rates", . 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-03 (work in progress), October 2013. set-07 (work in progress), November 2014.
[I-D.naito-nat-resource-optimizing-extension] [I-D.ietf-tcpm-tcp-security]
Kengo, K. and A. Matsumoto, "NAT TIME_WAIT reduction", Gont, F., "Survey of Security Hardening Methods for
draft-naito-nat-resource-optimizing-extension-02 (work in Transmission Control Protocol (TCP) Implementations",
progress), July 2012. draft-ietf-tcpm-tcp-security-03 (work in progress), March
2012.
[TCPWILD] Qian, F., Subhabrata, S., Spatscheck, O., Morley Mao, Z., [TCPWILD] Qian, F., Subhabrata, S., Spatscheck, O., Morley Mao, Z.,
and W. Willinger, "TCP Revisited: A Fresh Look at TCP in and W. Willinger, "TCP Revisited: A Fresh Look at TCP in
the Wild", . the Wild", .
Authors' Addresses Authors' Addresses
Reinaldo Penno Reinaldo Penno
Cisco Systems, Inc. Cisco Systems, Inc.
170 West Tasman Drive 170 West Tasman Drive
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