--- 1/draft-ietf-tsvwg-behave-requirements-update-01.txt 2015-08-12 08:15:04.991412933 -0700 +++ 2/draft-ietf-tsvwg-behave-requirements-update-02.txt 2015-08-12 08:15:05.019413614 -0700 @@ -1,596 +1,521 @@ TSVWG R. Penno Internet-Draft Cisco Intended status: Best Current Practice S. Perreault -Expires: August 22, 2015 Viagenie +Expires: February 13, 2016 Jive Communications S. Kamiset Insieme Networks M. Boucadair France Telecom K. Naito NTT - February 18, 2015 + August 12, 2015 Network Address Translation (NAT) Behavioral Requirements Updates - draft-ietf-tsvwg-behave-requirements-update-01 + draft-ietf-tsvwg-behave-requirements-update-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. - -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]. + The focus of this document is NAT44. 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 August 22, 2015. + This Internet-Draft will expire on February 13, 2016. Copyright Notice Copyright (c) 2015 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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 - 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 + 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. TCP Session Tracking . . . . . . . . . . . . . . . . . . . . 3 2.1. TCP Transitory Connection Idle-Timeout . . . . . . . . . 4 - 2.2. TIME_WAIT State . . . . . . . . . . . . . . . . . . . . . 5 - 2.2.1. Proposal: Apply RFC6191 and PAWS to NAT . . . . . . 5 - 2.3. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . 8 - 3. Port Overlapping behavior . . . . . . . . . . . . . . . . . . 8 - 4. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . 8 - 5. EIF Security . . . . . . . . . . . . . . . . . . . . . . . . 9 - 6. EIF Protocol Independence . . . . . . . . . . . . . . . . . . 9 - 7. EIF Mapping Refresh . . . . . . . . . . . . . . . . . . . . . 9 - 7.1. Outbound Mapping Refresh and Error Packets . . . . . . . 10 - 8. EIM Protocol Independence . . . . . . . . . . . . . . . . . . 10 - 9. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 10. Port Randomization . . . . . . . . . . . . . . . . . . . . . 10 - 11. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . 11 - 12. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . 11 - 13. Hairpinning Support for ICMP Packets . . . . . . . . . . . . 11 - 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 - 15. Security Considerations . . . . . . . . . . . . . . . . . . . 11 - 16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 - 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 17.1. Normative References . . . . . . . . . . . . . . . . . . 12 - 17.2. Informative References . . . . . . . . . . . . . . . . . 13 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 + 2.2. TCP RST . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 3. Port Overlapping Behavior . . . . . . . . . . . . . . . . . . 5 + 4. Address Pooling Paired (APP) . . . . . . . . . . . . . . . . 6 + 5. EIF Protocol Independence . . . . . . . . . . . . . . . . . . 6 + 6. EIF Mapping Refresh . . . . . . . . . . . . . . . . . . . . . 7 + 6.1. Outbound Mapping Refresh and Error Packets . . . . . . . 7 + 7. EIM Protocol Independence . . . . . . . . . . . . . . . . . . 7 + 8. Port Parity . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 9. Port Randomization . . . . . . . . . . . . . . . . . . . . . 8 + 10. IP Identification (IP ID) . . . . . . . . . . . . . . . . . . 8 + 11. ICMP Query Mappings Timeout . . . . . . . . . . . . . . . . . 8 + 12. Hairpinning Support for ICMP Packets . . . . . . . . . . . . 9 + 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 + 14. Security Considerations . . . . . . . . . . . . . . . . . . . 9 + 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 + 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 16.1. Normative References . . . . . . . . . . . . . . . . . . 10 + 16.2. Informative References . . . . . . . . . . . . . . . . . 10 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. 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 document provides such clarifications - and updates. + evolution of Network Address Translation (NAT) more development and + operational experience was acquired some areas of the original + documents need further clarification or updates. This document + provides such clarifications and updates. 1.1. Scope - This document focuses solely on NAPT44 and its goal is to clarify, - fill gaps or update requirements of [RFC4787], [RFC5382] and - [RFC5508]. + The goal of this document is to clarify and update the set of + requirements listed in [RFC4787], [RFC5382] and [RFC5508]. The + document focuses exclusively on NAT44. - 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]. + The scope of this document has been set so that it does not create + new requirements beyond those specified in the documents cited above. + Carrier-Grade NAT (CGN) related requirements are defined in + [RFC6888]. 1.2. Terminology - The reader should be familiar with the terms defined in - [RFC2663],[RFC4787],[RFC5382],and [RFC5508] + 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]. + + The reader is assumed to be familiar withe terminology defined in: + [RFC2663],[RFC4787],[RFC5382], and [RFC5508]. + + 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]). 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. + states but does not specify the TCP state machine a NAT44 should + follow as a basis to apply such timers. - +-----------------------------+ + Update: The TCP state machine depicted in Figure 1, adapted from + [RFC6146], SHOULD be implemented by a NAT for TCP session tracking + purposes. + + +----------------------------+ | | V | - +------+ CV4 | + +------+ Client | |CLOSED|-----SYN------+ | +------+ | | ^ | | |TCP_TRANS T.O. | | | V | +-------+ +-------+ | - | TRANS | |V4 INIT| | + | TRANS | | INIT | | +-------+ +-------+ | | ^ | | data pkt | | | - | V4 or V4 RST | | + | Server/Client RST | | | TCP_EST T.O. | | - V | SV4 SYN | + V | Server SYN | +--------------+ | | | ESTABLISHED |<---------+ | +--------------+ | | | | - CV4 FIN SV4 FIN | + Client FIN Server FIN | | | | V V | +---------+ +----------+ | - |CV4 FIN | | SV4 FIN | | + | C FIN | | S FIN | | | RCV | | RCV | | +---------+ +----------+ | | | | - SV4 FIN CV4 FIN TCP_TRANS + Server FIN Client FIN TCP_TRANS | | T.O. V V | +----------------------+ | - | CV4 FIN + SV4 FIN RCV|--------------------+ + | C FIN + S 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 - 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 - 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- - between network, and delivered to the end relatively later, we - should prevent the packets from being transferred and interpreted - as a packet that belongs to a new session. - - 2: If the remote TCP has not received the acknowledgment of its - connection termination request, it will re-send the FIN packet - several times. - - These points are important for the TCP to work without problems. - - [RFC5382] leaves the handling of TCP connections in TIME_WAIT state - unspecified and mentions that TIME_WAIT state is not part of the - transitory connection idle-timeout. If the NAT device honors the - TIME_WAIT state, each TCP connection and its associated resources is - kept for a certain period, typically for four minutes, which consumes - port resources. - - [RFC6191] explains that in certain situation it is necessary to - 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 - 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 - - This section proposes to apply [RFC6191] mechanism at NAT. This - mechanism MAY be adopted for both clients' and remote hosts' TCP - active close. - - client NAT remote host - | | | - | FIN | FIN | - |------------------------>|------------------------>| - | | | - | 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 - 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 - 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 + Legend: + * Messages sent to (resp. received from) the server + are prefixed with "Server". + * Messages sent to (resp. received from) the client + are prefixed with "Client". + * "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]. - Rewrite timestamp and sequence number values of outgoings packets at - NAT to be monotonically increasing. This can be done by adopting - following mechanisms at NAT. + Figure 1: State Machine - A: Store the newest rewritten value of timestamp and sequence number - as the "max value at the time". +2.1. TCP Transitory Connection Idle-Timeout - B: NAT rewrite timestamp and sequence number values of incoming - packets to be monotonically increasing. + 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. - When packets come back as replies from remote hosts, NAT rewrite - again the timestamp and sequence number values to be the original - values. This can be done by adopting following mechanisms at NAT. + Clarification: This document clarifies that a NAT SHOULD provide + different configurable parameters for configuring the open and + closing idle timeouts. - C: Store the values of original timestamp and sequence number of - packets, and rewritten values of those. + To accommodate deployments that consider a partially open timeout + of 4 minutes as being excessive from a security standpoint, a NAT + 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. -2.2.1.2. Split an assignable number of port space to each client +2.2. TCP RST - Adopt following mechanisms at NAT. + [RFC5382] leaves the handling of TCP RST packets unspecified. - A: Choose clients that can be assigned ports. + 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. - B: Split assignable port numbers between clients. + Admittedly, the NAT has to verify whether received TCP RST packets + belong to a connection. These verification checks are required to + avoid off-path attacks. - Packets from other clients which are not chosen by these mechanisms - are rejected at NAT, unless there is unassigned port left. + If the NAT removes immediately the NAT mapping upon receipt of a + TCP RST message, stale connections may be maintained by endpoints + if the first RST message is lost between the NAT and the + recipient. -2.2.1.3. Resend the last ACK to the retransmisstted FIN +3. Port Overlapping Behavior - We need to solve another scenario to make [RFC6191] work with NAT. - In the case the remote TCP could not receive the acknowledgment of - its connection termination request, the NAT device, on behalf of - clients, resends the last ACK packet when it receives a FIN packet of - the previous connection, and when the state of the previous - connection has been deleted from the NAT. This mechanism MAY be used - when clients starts closing process, and the remote host could not - receive the last ACK. + REQ-1 from [RFC4787] and REQ-1 from [RFC5382] specify a specific port + overlapping behavior; that is the external IP address and port can be + 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). -2.2.1.4. Remote host behavior of several implementations + Update: This document clarifies that this port overlapping behavior + may be extended to connections originating from different internal + source IP addresses and ports as long as their destinations are + different. - To solve the port shortage problem on the client side, the behavior - 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. + The following mechanism MAY be implemented by a NAT: -2.3. TCP RST + 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). - [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. + 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])). -3. Port Overlapping behavior +4. Address Pooling Paired (APP) - [RFC4787] [RFC5382]: REQ-1 Current RFCs specifiy a specific port - 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. + The Address Pooling Paired (APP) behavior for a NAT was recommended + in REQ-2 from [RFC4787], but the behavior when a public IPv4 runs out + of ports was left undefined. - If destination addresses and ports are different for outgoing - connections started by local clients, 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) . - 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. + 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. - Discussions: + The administrator MAY provide a configurable parameter that allows + a NAT to starting using ports from another external IP address + when the one that anchored the APP mapping ran out of ports. This + is a trade-off between service continuity and APP strict + enforcement. (Note, this behavior is sometimes referred as 'soft- + APP'.) - [RFC4787] and [RFC5382] requires "endpoint-independent mapping" at - 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. + Update: This behavior SHOULD apply also for TCP. -4. Address Pooling Paired (APP) +5. EIF Protocol Independence - [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. - (Note, it is sometimes referred as 'soft-APP') + 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. -5. EIF Security + Update: 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 address and port + through the NAT and also maintain compatibility with stateful + NAT64 . The administrator MAY provide a configuration parameter to + make it protocol-dependent. The default value of this + configuration parameter is to allow for protocol-independent EIF. - [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. This is specially - important in the case of Mobile networks where such attacks can - consume radio resources and count against the user quota. + 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. -6. EIF Protocol Independence +6. EIF Mapping Refresh - [RFC4787]:REQ-8 and[RFC5382]: REQ-3 Current RFCs 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. - 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. + The NAT mapping Refresh direction may have a "NAT Inbound refresh + behavior" of "True" according to REQ-6 from [RFC4787], but [RFC4787] + does not clarify how this behavior 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. -7. EIF Mapping Refresh + 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]: 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, such packets SHOULD NOT refresh the - mapping. Otherwise a simple attack of a packet every 2 minutes can - keep the mapping indefinitely. + Update: This behavior SHOULD apply also for TCP. -7.1. Outbound Mapping Refresh and Error Packets +6.1. Outbound Mapping Refresh and Error Packets - In the case of NAT outbound refresh behavior there are certain types - of packets that should not refresh the mapping even if their - direction is outbound. For example, if the mapping is kept alive by - ICMP Errors or TCP RST outbound packets sent as response to inbound - packets, these SHOULD NOT refresh the mapping. + Update: In the case of NAT outbound refresh behavior there are + certain types of packets that should not refresh the mapping even + if their direction is outbound. For example, if the mapping is + kept alive by ICMP Errors or TCP RST outbound packets sent as + response to inbound packets, these SHOULD NOT refresh the mapping. -8. EIM Protocol Independence +7. EIM Protocol Independence - [RFC4787] [RFC5382]: REQ-1 Current RFCs do not specify whether EIM - are protocol independent. In other words, if a outbound TCP SYN + REQ-1 from [RFC4787] and REQ-1 from [RFC5382] 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 + 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. + UDP, ICMP). -9. Port Parity + 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. - A NAT devices MAY disable port parity preservation for dynamic +8. Port Parity + + 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]). -10. Port Randomization + Note: According to [RFC6887], dynamic mappings are said to be + dynamic in the sense that they are created on demand, either + implicitly or explicitly: - A NAT SHOULD follow the recommendations specified in Section 4 of - [RFC6056] especially: + 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. + + 2. Explicit dynamic mappings refer to mappings that are created + as a result, for example, of explicit PCP MAP and PEER + requests. Explicit dynamic mappings have a finite lifetime, + and this lifetime is communicated to the client. + +9. Port Randomization + + Update: 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)." + 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) +10. IP Identification (IP ID) - A NAT SHOULD handle the Identification field of translated IPv4 - packets as specified in Section 9 of [RFC6864]. + Update: A NAT SHOULD handle the Identification field of translated + IPv4 packets as specified in Section 5.3.1 of [RFC6864]. -12. ICMP Query Mappings Timeout + Discussion: This recommendation may have undesired effects on the + performance of the NAT in environments in which fragmentation is + massively experienced. Such issue can be used as an attack vector + against NATs. - 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. +11. ICMP Query Mappings Timeout - ICMP Query Mappings MAY be deleted once the last the session using - the mapping is deleted. + 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. -13. Hairpinning Support for ICMP Packets + Update: ICMP Query Mappings MAY be deleted once the last the session + using the mapping is deleted. - [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 (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. +12. Hairpinning Support for ICMP Packets -14. IANA Considerations + REQ-7 from [RFC5508] specifies that a NAT enforcing 'Basic NAT' must + support traversal of hairpinned ICMP Query sessions. - This document does not require any IANA action. + Clarification: 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, a NAT can then translate to an internal IP. -15. Security Considerations + REQ-7 from [RFC5508] specifies that all NATs must support the + traversal of hairpinned ICMP Error messages. - 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. + Clarification: This behavior requires a NAT 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 + [RFC5508]. - [I-D.ietf-tcpm-tcp-security] contains a detailed discussion of the - security implications of TCP Timestamps and of different timestamp - generation algorithms. +13. IANA Considerations -16. Acknowledgements + This document does not require any IANA action. - Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan and - Senthil Sivamular for review and discussions +14. Security Considerations -17. References + NAT behavioral considerations are discussed in [RFC4787]. -17.1. Normative References + Security considerations discussed in Section 5 of [RFC6146] apply + also fro NAT44. - [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC - 793, September 1981. + 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. - [RFC1122] Braden, R., "Requirements for Internet Hosts - - Communication Layers", STD 3, RFC 1122, October 1989. +15. Acknowledgements - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, March 1997. + Thanks to Dan Wing, Suresh Kumar, Mayuresh Bakshi, Rajesh Mohan, + Senthil Sivamular, Lars Eggert, and Gorry Fairhurst for review and + discussions. - [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address - Translator (NAT) Terminology and Considerations", RFC - 2663, August 1999. +16. References +16.1. Normative References - [RFC4787] Audet, F. and C. Jennings, "Network Address Translation - (NAT) Behavioral Requirements for Unicast UDP", BCP 127, - RFC 4787, January 2007. + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, + DOI 10.17487/RFC2119, March 1997, + . - [RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. + [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address + Translation (NAT) Behavioral Requirements for Unicast + UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January + 2007, . + + [RFC5382] Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, - RFC 5382, October 2008. + RFC 5382, DOI 10.17487/RFC5382, October 2008, + . [RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT Behavioral Requirements for ICMP", BCP 148, RFC 5508, - April 2009. + DOI 10.17487/RFC5508, April 2009, + . [RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport- - Protocol Port Randomization", BCP 156, RFC 6056, January - 2011. + Protocol Port Randomization", BCP 156, RFC 6056, + DOI 10.17487/RFC6056, 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. - - [RFC6191] Gont, F., "Reducing the TIME-WAIT State Using TCP - Timestamps", BCP 159, RFC 6191, April 2011. + Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, + 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., - and H. Ashida, "Common Requirements for Carrier-Grade NATs - (CGNs)", BCP 127, RFC 6888, April 2013. + RFC 6864, DOI 10.17487/RFC6864, February 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, . - [FLOWRATE] - Zhang, Y., Breslau, L., Paxson, V., and S. Shenker, "On - the Characteristics and Origins of Internet Flow Rates", . +16.2. Informative References [I-D.ietf-pcp-port-set] Qiong, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, T., and S. Perreault, "Port Control Protocol (PCP) 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] - Gont, F., "Survey of Security Hardening Methods for - Transmission Control Protocol (TCP) Implementations", - draft-ietf-tcpm-tcp-security-03 (work in progress), March - 2012. + [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address + Translator (NAT) Terminology and Considerations", + RFC 2663, DOI 10.17487/RFC2663, August 1999, + . - [TCPWILD] Qian, F., Subhabrata, S., Spatscheck, O., Morley Mao, Z., - and W. Willinger, "TCP Revisited: A Fresh Look at TCP in - the Wild", . + [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network + Address Translator (Traditional NAT)", RFC 3022, + DOI 10.17487/RFC3022, January 2001, + . + + [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, + . + + [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, + . Authors' Addresses Reinaldo Penno Cisco Systems, Inc. 170 West Tasman Drive San Jose, California 95134 USA Email: repenno@cisco.com Simon Perreault - Viagenie - 2875 boul. Laurier, suite D2-630 - Quebec, QC G1V 2M2 + Jive Communications Canada - Email: simon.perreault@viagenie.ca + Email: sperreault@jive.com + Sarat Kamiset Insieme Networks California - Mohamed Boucadair France Telecom Rennes 35000 France Email: mohamed.boucadair@orange.com Kengo Naito NTT Tokyo