Behave R. Penno
Internet-Draft S. Kamiset
Updates: 4787 5382 5508 Juniper Networks
(if approved) S. Perreault
Intended status: BCP Viagenie
Expires: April 12, 2012 M. Boucadair
France Telecom
November 16, 2011
Network Address Translation (NAT) Behavioral Requirements Updates
draft-penno-behave-rfc4787-5382-5508-bis-02
Abstract
This document clarifies and updates several requirements of RFC4787,
RFC5382 and RFC5508 based on operational and development experience.
The focus of this document is NAPT44.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 12, 2012.
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. TCP Session Tracking . . . . . . . . . . . . . . . . . . . . . 3
3.1. TCP Transitory Connection Idle-Timeout . . . . . . . . . . 4
3.2. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . . 5
5. EIF Security . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. EIF Protocol Independent . . . . . . . . . . . . . . . . . . . 5
7. EIF Mapping Refresh . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Outbound Mapping Refresh and Error Packets . . . . . . . . 6
8. EIM Protocol Independent . . . . . . . . . . . . . . . . . . . 6
9. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10. Port Randomization . . . . . . . . . . . . . . . . . . . . . . 7
11. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . . 7
12. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . . 7
13. Hairpinning Support for ICMP Packets . . . . . . . . . . . . . 7
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
16. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
17.1. Normative References . . . . . . . . . . . . . . . . . . . 8
17.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Terminology
The reader should be familiar with all terms defined in [RFC2663] ,
[RFC4787] , [RFC5382] and [RFC5508]
2. Introduction
[RFC4787], [RFC5382] and [RFC5508] greatly advanced NAT
interoperability and conformance. But with widespread deployment and
evolution of NAT more development and operational experience was
acquired some areas of the original documents need further
clarification or updates. This documents provides such
clarifications and updates.
2.1. 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 [RFC2119].
2.2. Scope
This document focuses solely on NAPT44 and its goal is to clarify,
fill gaps or update requirements of [RFC4787], [RFC5382] and
[RFC5508]. 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 [I-D.ietf-behave-lsn-requirements]
3. 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 below,
adapted from [RFC6146], provides guidance on how TCP session tracking
could be implemented - it is non-normative.
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+-----------------------------+
| |
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|--------------------+
+----------------------+
3.1. 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 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
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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.
3.2. TCP RST
[RFC5382] leaves the handling of TCP RST packets unspecified. This
document does not try standardize such behavior but clarifies based
on operational experience that a NAT that receives a TCP RST for an
active mapping and performs session tracking MAY immediately delete
the sessions and remove any state associated with it.
If the NAT device that performs TCP session tracking receives a TCP
RST for the first session that created a mapping, it MAY remove the
session and the mapping immediately.
4. Address Pooling Paired (APP)
[RFC4787]: REQ-2 [RFC5382]:ND Address Pooling Paired behavior for NAT
is recommended in previous documents but behavior when a public IPv4
run out of ports is left undefined. This document clarifies that if
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
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.
(NE: It is sometimes referred as 'soft-APP')
5. EIF Security
[RFC4787]:REQ-8 and [RFC5382]:REQ-3 End-point independent filtering
could potentially result in security attacks from the public realm.
In order to handle this, when possible there MUST be strict filtering
checks in the inbound direction. A knob SHOULD be provided to limit
the number of inbound sessions and a knob SHOULD be provided to
enable or disable EIF on a per application basis.
6. EIF Protocol Independent
[RFC4787]:REQ-8 and[RFC5382]: REQ-3 Current RFCs do not specify
whether EIF mappings are protocol independent. In other words, if a
outbound TCP SYN creates a mapping it is left undefined whether
inbound UDP can create sessions and packets are forwarded. EIF
mappings SHOULD be protocol independent in order allow inbound
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packets for protocols that multiplex TCP and UDP over the same IP:
port through the NAT and maintain compatibility with stateful NAT64
[RFC6146]. But the administrator MAY provide a configuration knob to
make it protocol dependent.
7. EIF Mapping Refresh
[RFC4787]: REQ-6 [RFC5382]: ND The NAT mapping Refresh direction MAY
have a "NAT Inbound refresh behavior" of "True" but it does not
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
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, that 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
In the case of NAT outbound refresh behavior there might be certain
types of packets that should not refresh the mapping. For example,
if the mapping is kept alive by ICMP Error or TCP RST outbound
packets sent as response to inbound packets, these SHOULD NOT refresh
the mapping.
8. EIM Protocol Independent
[RFC4787] [RFC5382]: REQ-1 Current RFCs do not specify whether EIM
are protocol independent. In other words, if a outbound TCP SYN
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 NAT devices MAY disable port parity preservation for dynamic
mappings. Nevertheless, A NAT SHOULD support means to explicitly
request to preserve port parity (e.g., [I-D.boucadair-pcp-rtp-rtcp]).
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10. Port Randomization
A NAT SHOULD follow the recommendations specified in Section 4 of
[RFC6056] especially:
"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
packets as specified in Section 9 of
[I-D.ietf-intarea-ipv4-id-update].
12. ICMP Query Mappings Timeout
Section 3.1 of [RFC5508] says that ICMP Query Mappings are to be
maintained by NAT device. However, RFC doesn't discuss about the
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 the mapping is deleted.
13. Hairpinning Support for ICMP Packets
[RFC5508]:REQ-7 This requirement specifies that NAT devices enforcing
Basic NAT MUST support traversal of hairpinned ICMP Query sessions.
This implicitly means that address mappings from 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, NAT device can then translate to an
internal IP.
[RFC5508]:REQ-7 This requirement specifies that all NAT devices
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(i.e., Basic NAT as well as NAPT devices) MUST support the traversal
of hairpinned ICMP Error messages. This too 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. Acknowledgements
Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan and
Senthil Sivamular for review and discussions.
15. IANA Considerations
None.
16. 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.
17. References
17.1. Normative References
[I-D.ietf-intarea-ipv4-id-update]
Touch, J., "Updated Specification of the IPv4 ID Field",
draft-ietf-intarea-ipv4-id-update-04 (work in progress),
September 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 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
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
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[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056,
January 2011.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
17.2. Informative References
[FLOWRATE]
Zhang, Y., Breslau, L., Paxson, V., and S. Shenker, "On
the Characteristics and Origins of Internet Flow Rates",
2002.
[I-D.boucadair-pcp-rtp-rtcp]
Boucadair, M. and S. Sivakumar, "Reserving N and N+1 Ports
with PCP", draft-boucadair-pcp-rtp-rtcp-03 (work in
progress), October 2011.
[I-D.ietf-behave-lsn-requirements]
Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
and H. Ashida, "Common requirements for Carrier Grade NAT
(CGN)", draft-ietf-behave-lsn-requirements-04 (work in
progress), October 2011.
[TCPWILD] Qian, F., Subhabrata, S., Gerber, A., Spatscheck, O.,
Morley Mao, Z., and W. Willinger, "TCP Revisited: A Fresh
Look at TCP in the Wild".
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Authors' Addresses
Renaldo Penno
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, California 94089
USA
Phone:
Email: rpenno@juniper.net
Sarat Kamiset
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, California 94089
USA
Email: skamiset@juniper.net
URI:
Simon Perreault
Viagenie
2875 boul. Laurier, suite D2-630
Quebec, QC G1V 2M2
Canada
Email: simon.perreault@viagenie.ca
URI:
Mohamed Boucadair
France Telecom
Rennes, 35000
France
Email: mohamed.boucadair@orange-ftgroup.com
URI:
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