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 This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 12, 2012. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Penno, et al. Expires April 12, 2012 [Page 1] Internet-Draft NAT behavioral updates October 2011 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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 Penno, et al. Expires April 12, 2012 [Page 2] Internet-Draft NAT behavioral updates October 2011 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. Penno, et al. Expires April 12, 2012 [Page 3] Internet-Draft NAT behavioral updates October 2011 +-----------------------------+ | | 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 Penno, et al. Expires April 12, 2012 [Page 4] Internet-Draft NAT behavioral updates October 2011 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 Penno, et al. Expires April 12, 2012 [Page 5] Internet-Draft NAT behavioral updates October 2011 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]). Penno, et al. Expires April 12, 2012 [Page 6] Internet-Draft NAT behavioral updates October 2011 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 Penno, et al. Expires April 12, 2012 [Page 7] Internet-Draft NAT behavioral updates October 2011 (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. Penno, et al. Expires April 12, 2012 [Page 8] Internet-Draft NAT behavioral updates October 2011 [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". Penno, et al. Expires April 12, 2012 [Page 9] Internet-Draft NAT behavioral updates October 2011 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: Penno, et al. Expires April 12, 2012 [Page 10]