Network Working Group M. Boucadair Internet-Draft France Telecom Intended status: Informational J. Touch Expires: September 15, 2011 USC/ISI P. Levis France Telecom March 14, 2011 Analysis of Solution Candidates to Reveal the Origin IP Address in Shared Address Deployments draft-boucadair-intarea-nat-reveal-analysis-01 Abstract This document analyzes a set of solution candidates which have been proposed to mitigate some of the issues encountered when address sharing is used. In particular, this document focuses on means to reveal the origin of an IP packet when a Carrier Grade NAT is involved in the path. The ultimate goal is to assess the viability of proposed solutions and hopefully to make a recommendation on the more suitable solution(s). Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Status of this Memo 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 September 15, 2011. Copyright Notice Boucadair, et al. Expires September 15, 2011 [Page 1] Internet-Draft Revealing the origin IP address March 2011 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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Problem to Be Solved . . . . . . . . . . . . . . . . . . . 4 2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Preserve Source Port Number . . . . . . . . . . . . . . . 7 3. Solutions Analysis . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Define an IP Option . . . . . . . . . . . . . . . . . . . 7 3.1.1. Description . . . . . . . . . . . . . . . . . . . . . 7 3.1.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Define a TCP Option . . . . . . . . . . . . . . . . . . . 8 3.2.1. Description . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 8 3.3. Use the Identification Field of IP Header (IP-ID) . . . . 9 3.3.1. Description . . . . . . . . . . . . . . . . . . . . . 9 3.3.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Inject Application Headers . . . . . . . . . . . . . . . . 10 3.4.1. Description . . . . . . . . . . . . . . . . . . . . . 10 3.4.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 10 3.5. PROXY Protocol . . . . . . . . . . . . . . . . . . . . . . 11 3.5.1. Description . . . . . . . . . . . . . . . . . . . . . 11 3.5.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 11 3.6. Enforce a Source-based Selection Algorithm at the Server Side . . . . . . . . . . . . . . . . . . . . . . . 11 3.6.1. Description . . . . . . . . . . . . . . . . . . . . . 11 3.6.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 12 3.7. Host Identity Protocol (HIP) . . . . . . . . . . . . . . . 12 3.7.1. Description . . . . . . . . . . . . . . . . . . . . . 12 3.7.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . 12 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 5. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . . 13 Boucadair, et al. Expires September 15, 2011 [Page 2] Internet-Draft Revealing the origin IP address March 2011 7.2. Informative References . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Boucadair, et al. Expires September 15, 2011 [Page 3] Internet-Draft Revealing the origin IP address March 2011 1. Introduction As reported in [I-D.ietf-intarea-shared-addressing-issues], several issues are encountered when an IP address is shared among several subscribers. Examples of such issues are listed below: o Implicit authentication o SPAM o Blacklisting a mis-behaving user o Redirect users with infected machines to a dedicated portal The sole use of the IPv4 address is not sufficient to uniquely distinguish a user. As a mitigation, it is tempting to investigate means which would help in disclosing an information to be used by the remote server as a means to uniquely disambiguate packets of subscribers using the same IPv4 address. The purpose of this document is to analyze the solutions that have been proposed so far and to assess to what extent they solve the problem. Not need to remind that IPv6 is the only perennial solution. Only IPv4-based solutions are analyzed in the following sections: define a new IP option (Section 3.1), define a new TCP option (Section 3.2), use the Identification field of IP header (denoted as IP-ID, Section 3.3), inject application headers (Section 3.4), enable Proxy Protocol Section 3.5, use of port set (Section 3.6) and activate HIP (Section 3.7). 1.1. Problem to Be Solved Observation: Today, servers use the source IPv4 address as an identifier to treat some incoming connections differently. Tomorrow, due to the introduction of CGNs (e.g., NAT44, NAT64), that address will be shared. In particular, when a server receives packets from the same source address. Because this address is shared, the server does not know which host is the sending host. Objective: The server should be able to sort out the packets by sending host. Requirement: The server must have extra information than the source IP address to differentiate the sending host. We call USER_HINT this information. Boucadair, et al. Expires September 15, 2011 [Page 4] Internet-Draft Revealing the origin IP address March 2011 For all solutions analyzed, we provide answers to the following questions: o What is the USER_HINT? It must be unique to each user under the same address. It does not need to be globally unique. Of course, the combination of the (public) IPv4 source address and the identifier ends up being relatively unique. As unique as today's 32-bit IPv4 addresses which, today, can change when a user re- connects. o Where is the USER_HINT? (which protocol, which field): If the USER_HINT is put at the IP level, all packets will have to bear the identifier. If it is put at a higher connection-oriented level, the identifier is only needed once in the session establishment phase (for instance TCP three-way-handshake), then, all packets received in this session will be attributed to the host id designated during the session opening. o Who puts the USER_HINT?: For almost all the analyzed solutions, the address sharing function injects the USER_HINT. When there are several address sharing functions in the data path, we describe to what extent the proposed solution is efficient. o What are the security considerations?: Security consideration are common to all analyzed solutions (see Section 5). 2. Recommendations The following Table 1 summarizes the approaches analyzed in this document. o "Success ratio" indicates the ratio of successful communications when the option is used. Provided figures are inspired from the results documented in [Options]. o "Deployable today" column indicates if the solution can be generalized without any constraint on current architectures and practices. Boucadair, et al. Expires September 15, 2011 [Page 5] Internet-Draft Revealing the origin IP address March 2011 +---+---+----+---------+-------+----------+----- |UDP|TCP|HTTP|Encrypted|Success|Deployable|Notes | | | | traffic | ratio | today? | -----------+---+---+----+---------+-------+----------+----- IP option |Yes|Yes|Yes | Yes | 30% | Yes | -----------+---+---+----+---------+-------+----------+----- TCP option |No |Yes|Yes | Yes | 99% | Yes | -----------+---+---+----+---------+-------+----------+----- IP-ID |Yes|Yes|Yes | Yes | 100% | Yes | (1) -----------+---+---+----+---------+-------+----------+----- HTTP header|No |No |Yes | No | 100% | Yes | (2) -----------+---+---+----+---------+-------+----------+----- Proxy Proto| No|Yes|Yes | Yes | Low | No | -----------+---+---+----+---------+-------+----------+----- Port set |Yes|Yes|Yes | Yes | 100% | Yes |(1)(3) -----------+---+---+----+---------+-------+----------+----- HIP |-- |-- |-- | -- | Low | No |(4)(5) -----------+---+---+----+---------+-------+----------+------ Table 1: Summary of analyzed solutions. Notes for the above table: (1) requires mechanism to advertise NAT is participating in this scheme (e.g., DNS PTR record) (2) this solution is widely deployed (3) when the port set is not advertised, the solution is less efficient. (4) requires the client and the server to be HIP-compliant and HIP infrastructure to be deployed. (5) if the client and the server are HIP-enabled, the address sharing function does not need to insert a user-hint. If the client is not HIP-enabled, designing the device that performs address sharing to act as a UDP/TCP-HIP relay is not viable. According to the above table and the analysis elaborated in Section 3: o IP Option, IP-ID and Proxy Protocol proposals are broken; o HIP is not largely deployed; Boucadair, et al. Expires September 15, 2011 [Page 6] Internet-Draft Revealing the origin IP address March 2011 o The use of Port Set may contradict the port randomization [RFC6056] requirement identified in [I-D.ietf-intarea-shared-addressing-issues]; o XFF is de facto standard deployed and supported in operational networks (e.g., HTTP Severs, Load-Balancers, etc.). o From an application standpoint, the TCP Option is superior to XFF since it is not restricted to HTTP. Nevertheless XFF is compatible with the presence of address sharing and load-balancers in the communication path. To provide a similar functionality, the TCP Option may be extended to allow conveying a list of IP addresses to not loose the source IP address in the presence of load-balancers. 2.1. Preserve Source Port Number In order to implement the recommendation documented in [I-D.ietf-intarea-server-logging-recommendations], extensions are required to preserve the source port number and to avoid this information to be lost when load-balancers are involved in the path. Examples of mitigation solutions are provided below: 1. Extend XFF to convey the port in addition to the IP address 2. Define a header similar to XFF to convey the source port 3. Extend the TCP Option to convey the source port 4. Enable the Proxy Protocol [Proxy]. [[Note: Is there an interest to consider this issue or this should be left out of scope of this I-D?]]. 3. Solutions Analysis 3.1. Define an IP Option 3.1.1. Description This proposal aims to define an IP option [RFC0791] to convey a "user identifier". This identifier can be inserted by the address sharing function to uniquely distinguish a user among those sharing the same IP address. The option can convey an IPv4 address, the prefix part of an IPv6 address, etc. Another way for using IP option has been described in Section 4.6 of Boucadair, et al. Expires September 15, 2011 [Page 7] Internet-Draft Revealing the origin IP address March 2011 [RFC3022]. 3.1.2. Analysis Unlike the solution presented in Section 3.2, this proposal can apply for any transport protocol. Nevertheless, it is widely known that routers (and other middle boxes) filter IP options. IP packets with IP options can be dropped by some IP nodes. Previous studies demonstrated that "IP Options are not an option" (Refer to [Not_An_Option], [Options]). As a conclusion, using an IP option to convey a user-hint is not viable. 3.2. Define a TCP Option 3.2.1. Description This proposal [I-D.wing-nat-reveal-option] defines a new TCP option called CX-ID. This option encloses the client's identifier (e.g., an IPv4 address, a subscriber ID, or 64 bits of an IPv6 address). The address sharing device inserts this TCP option to the TCP SYN packet or in the initial ACK. 3.2.2. Analysis The risk related to handling a new TCP option is low as measured in [Options]. Using a new TCP option to convey the user-hint does not require any modification to the applications but it is applicable only for TCP-based applications. Applications relying on other transport protocols are therefore left unsolved. Some downsides have been raised against defining a TCP option to reveal a user identity: o Conveying an IP address in a TCP option may be seen as a violation of OSI layers but since IP addresses are already used for the checksum computation, this is not seen as a blocking point. o TCP option space is limited, and might be consumed by the TCP client. o TCP options are not reliably transmitted. If the first segment is lost and the payload bytes it contained are retransmitted, the retransmitted segment is not required to contain the same options as the lost segment. [I-D.wing-nat-reveal-option] discusses two approaches to sending the USER_HINT: sending the USER_HINT in the TCP SYN (which consumes more bytes in the TCP header of the TCP Boucadair, et al. Expires September 15, 2011 [Page 8] Internet-Draft Revealing the origin IP address March 2011 SYN) and sending the USER_HINT in a TCP ACK (which consumes only two bytes in the TCP SYN). Content providers may find it more desirable to receive the USER_HINT in the TCP SYN, as that more closely preserves the user hint received in the source IP address as per current practices. It is more complicated to implement sending the USER_HINT in a TCP ACK, as it can introduce MTU issues if the ACK packet also contains TCP data, or a TCP segment is lost. o When there are several NATs in the path, the original USER_HINT may be lost. In such case, the procedure may not be efficient. o Interference with current usages such as X-Forwarded-For (see Section 3.4) should be elaborated to specify the behavior of servers when both options are used; in particular specify which information to use: the content of the TCP option or what is conveyed in the application headers. 3.3. Use the Identification Field of IP Header (IP-ID) 3.3.1. Description IP-ID (Identification field of IP header) can be used to insert an information which uniquely distinguishes a user among those sharing the same IPv4 address. An address sharing function can re-write the IP-ID field to insert a value unique to the user (16 bits are sufficient to uniquely disambiguate users sharing the same IP address). Note that this field is not altered by some NATs; hence some side effects such as counting hosts behind a NAT as reported in [Count]. A variant of this approach relies upon the format of certain packets, such as TCP SYN, where the IP-ID can be modified to contain a 16 bit user-hint. Address sharing devices performing this function would require to indicate they are performing this function out of band, possibly using a special DNS record. 3.3.2. Analysis This usage is not compliant with what is recommended in [I-D.ietf-intarea-ipv4-id-update]. [TBC]. [[Touch.NOTE: One other problem - picking an ID value here *requires* coordination, i.e., that no other IP packet with this IP address uses that ID within 2MSL. Unless fragmentation is disabled for all packets all the time, you can't use *any* ID Boucadair, et al. Expires September 15, 2011 [Page 9] Internet-Draft Revealing the origin IP address March 2011 value without that coordination.]] [[Wing.NOTE: Most OSes today are emitting TCP packets with DF=1 (OSX, Windows XP and 7, Linux, etc.). So, we can assume the TCP SYN is going to have DF=1, and only insert IP-ID if DF=1 and it's a TCP SYN. Doing that, I don't see any disagreement with Joe's IP-ID document.]] 3.4. Inject Application Headers 3.4.1. Description Another option is to not require any change at the transport nor the IP levels but to convey at the application payload the required information which will be used to disambiguate users. This format and the related semantics depend on its application (e.g., HTTP, SIP, SMTP, etc.). For HTTP, the X-Forwarded-For (XFF) header can be used to display the original IP address when an address sharing device is involved. Service Providers operating address sharing devices can enable the feature of injecting the XFF header which will enclose the original IPv4 address or the IPv6 prefix part. The address sharing device has to strip all included XFF headers before injecting their own. Servers may rely on the contents of this field to enforce some policies such as blacklisting misbehaving users. Note that XFF can also be logged by some servers (this is for instance supported by Apache). 3.4.2. Analysis Not all applications impacted by the address sharing can support the ability to disclose the original IP address. Only a subset of protocols (e.g., HTTP) can rely on this solution. For the HTTP case, to prevent users injecting invalid user-hints, an initiative has been launched to maintain a list of trusted ISPs using XFF: See for example the list available at: [Trusted_ISPs] of trusted ISPs as maintained by Wikipedia. If an address sharing device is on the trusted XFF ISPs list, users editing Wikipedia located behind the address sharing device will appear to be editing from their "original" IP address and not from the NATed IP address. If an offending activity is detected, individual users can be blacklisted instead of all users sharing the same IP address. XFF header injection is a common practice of load balancers. When a load balancer is in the path, the original content of any included XFF header should not be stripped. Otherwise the information about Boucadair, et al. Expires September 15, 2011 [Page 10] Internet-Draft Revealing the origin IP address March 2011 the "origin" IP address will be lost. When several address sharing devices are crossed, XFF header can convey the list of IP addresses. The origin USER_HINT can be exposed to the target server. XFF also introduces some implementation complexity if the HTTP packet is at or close to the MTU size. It has been reported that some "poor" implementation may encounter some parsing issues when injecting XFF header. For encrypted HTTP traffic, injecting XFF header may be broken. 3.5. PROXY Protocol 3.5.1. Description The solution, referred to as Proxy Protocol [Proxy], does not require any application-specific knowledge. The rationale behind this solution is to prepend each connection with a line reporting the characteristics of the other side's connection as shown in the example below (excerpt from [Proxy]): PROXY TCP4 192.168.0.1 192.168.0.11 56324 443\r\n Upon receipt of a message conveying this line, the server removes the line. The line is parsed to retrieve the transported protocol. The content of this line is recorded in logs and used to enforce policies. 3.5.2. Analysis This solution can be deployed in a controlled environment but it can not be deployed to all access services available in the Internet. If the remote server does not support the Proxy Protocol, the session will fail. Other complications will raise due to the presence of firewalls for instance. As a consequence, this solution is broken and can not be recommended. 3.6. Enforce a Source-based Selection Algorithm at the Server Side 3.6.1. Description This solution proposal does not require any action from the address sharing function to disclose an user identifier. Instead of assuming all the ports are associated with the same user, a random-based Boucadair, et al. Expires September 15, 2011 [Page 11] Internet-Draft Revealing the origin IP address March 2011 algorithm (or any port selection method) is run to generate the set of ports (including the source port of the received packet). The length of the ports set to be generated by the server may be configurable (e.g., 8, 32, 64, 512, 1024, etc.). Instead of a random-based scheme, the server can use contiguous port ranges to form the port sets. The server may reduce (or enlarge) the width of the ports set of the misbehaving action is (not) mitigated. A variant of this proposal is to announce by off-line means the port set assignment policy of an operator. 3.6.2. Analysis In nominal mode, no coordination is required between the address sharing function and the server side but the efficiency of the method depends on the port set selection algorithm. The method is more efficient if the provider that operates the address sharing device advertises its port assignment policy but this may contradicts the port randomization as identified in [I-D.ietf-intarea-shared-addressing-issues]. The server is free to implement the actions (e.g., blacklist all the ports) it judges required to mitigate an abuse attack. 3.7. Host Identity Protocol (HIP) 3.7.1. Description [RFC5201] specifies an architecture which introduces a new namespace to convey an identity information. 3.7.2. Analysis This solution requires both the client and the server to support HIP [RFC5201]. Additional architectural considerations are to be taken into account such as the key exchanges, etc. If the address sharing function is required to act as a UDP/TCP-HIP relay, this is not a viable option. 4. IANA Considerations This document does not require any action from IANA. Boucadair, et al. Expires September 15, 2011 [Page 12] Internet-Draft Revealing the origin IP address March 2011 5. Security Considerations The same security concerns apply for the injection of an IP option, TCP option and application-related content (e.g., XFF) by the address sharing device. If the server trusts the content of the user-hint field, a third party user can be impacted by a misbehaving user to reveal a "faked" original IP address. 6. Acknowledgments Many thanks to D. Wing and C. Jacquenet for their review, comments and inputs. Some of the issues related to defining a new TCP option have been raised by L. Eggert. 7. References 7.1. Normative References [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, January 2001. [RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport- Protocol Port Randomization", BCP 156, RFC 6056, January 2011. 7.2. Informative References [Count] "A technique for counting NATted hosts", . [I-D.ietf-intarea-ipv4-id-update] Touch, J., "Updated Specification of the IPv4 ID Field", draft-ietf-intarea-ipv4-id-update-01 (work in progress), October 2010. [I-D.ietf-intarea-server-logging-recommendations] Durand, A., Gashinsky, I., Lee, D., and S. Sheppard, Boucadair, et al. Expires September 15, 2011 [Page 13] Internet-Draft Revealing the origin IP address March 2011 "Logging recommendations for Internet facing servers", draft-ietf-intarea-server-logging-recommendations-03 (work in progress), February 2011. [I-D.ietf-intarea-shared-addressing-issues] Ford, M., Boucadair, M., Durand, A., Levis, P., and P. Roberts, "Issues with IP Address Sharing", draft-ietf-intarea-shared-addressing-issues-05 (work in progress), March 2011. [I-D.wing-nat-reveal-option] Yourtchenko, A. and D. Wing, "Revealing hosts sharing an IP address using TCP option", draft-wing-nat-reveal-option-01 (work in progress), February 2011. [Not_An_Option] R. Fonseca, G. Porter, R. Katz, S. Shenker, and I. Stoica,, "IP options are not an option", 2005, . [Options] Alberto Medina, Mark Allman, Sally Floyd, "Measuring Interactions Between Transport Protocols and Middleboxes", 2005, . [Proxy] Tarreau, W., "The PROXY protocol", November 2010, . [RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson, "Host Identity Protocol", RFC 5201, April 2008. [Trusted_ISPs] "Trusted XFF list", . Authors' Addresses Mohamed Boucadair France Telecom Rennes, 35000 France Email: mohamed.boucadair@orange-ftgroup.com Boucadair, et al. Expires September 15, 2011 [Page 14] Internet-Draft Revealing the origin IP address March 2011 Joe Touch USC/ISI Email: touch@isi.edu Pierre Levis France Telecom Caen, 14000 France Email: pierre.levis@orange-ftgroup.com Boucadair, et al. Expires September 15, 2011 [Page 15]