Network Working Group R. Asati Internet-Draft H. Singh Updates: 4862 (if approved) W. Beebee Intended status: Standards Track Cisco Systems, Inc. Expires: April 30, 2012 E. Dart Lawrence Berkeley National Laboratory W. George Time Warner Cable C. Pignatro Cisco Systems, Inc. October 28, 2011 Enhanced Duplicate Address Detection draft-hsingh-6man-enhanced-dad-02.txt Abstract Appendix A of the IPv6 Duplicate Address Detection (DAD) document in RFC 4862 discusses Loopback Suppression and DAD. However, RFC 4862 does not settle on one specific automated means to detect loopback of Neighbor Discovery (ND of RFC 4861) messages used by DAD. Several service provider communities have expressed a need for automated detection of looped backed ND messages used by DAD. This document includes mitigation techniques and then outlines the Enhanced DAD algorithm to automate detection of looped back IPv6 ND messages used by DAD. For network loopback tests, the Enhanced DAD algorithm allows IPv6 to self-heal after a loopback is placed and removed. Further, for certain access networks the document automates resolving a specific duplicate address conflict. 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 30, 2012. Asati, et al. Expires April 30, 2012 [Page 1]
Internet-Draft Enhanced DAD October 2011 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 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 3. Operational Mitigation Options . . . . . . . . . . . . . . . . 4 3.1. Disable DAD on Interface . . . . . . . . . . . . . . . . . 4 3.2. Dynamic Disable/Enable of DAD Using Layer 2 Protocol . . . 4 3.3. Operational Considerations . . . . . . . . . . . . . . . . 5 4. The Enhanced DAD Algorithm . . . . . . . . . . . . . . . . . . 5 4.1. General Rules . . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Processing Rules for Senders . . . . . . . . . . . . . . . 6 4.3. Processing Rules for Receivers . . . . . . . . . . . . . . 7 4.4. Impact on SEND . . . . . . . . . . . . . . . . . . . . . . 7 4.5. Changes to RFC 4862 . . . . . . . . . . . . . . . . . . . . 7 4.6. Actions to Perform on Detecting a Genuine Duplicate . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 8. Normative References . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 Asati, et al. Expires April 30, 2012 [Page 2]
Internet-Draft Enhanced DAD October 2011 1. Terminology o DAD-failed state - Duplication Address Detection failure as specified in [RFC4862]. Failure also includes if the Target Address is optimistic. Optimistic DAD is specified in [RFC4429]. o Looped back message - also referred to as a reflected message. The message sent by the sender is received by the sender due to the network or a Upper Layer Protocol on the sender looping the message back. o Loopback - A function in which the router's interface to the network is looped back, resulting in interface unavailability for regular data traffic forwarding. See more details in section 9.1 of [RFC1247]. Loopback function is commonly used to gain information on the quality of this interface, by employing mechanisms such as ICMPv6 pings, bit-error test etc. Loopback function may be done locally or remotely. o NS(DAD) - shorthand notation to denote an NS with unspecified IPv6 source-address issued during DAD. 2. Introduction Appendix A of [RFC4862] discusses Loopback Suppression and Duplicate Address Detection (DAD). However, [RFC4862] does not settle on one specific automated means to detect loopback of ND messages used by DAD. One specific DAD message is a Neighbor Solicitation (NS), specified in [RFC4861]. The NS is issued by the network interface of an IPv6 node for DAD. Another message involved in DAD is a Neighbor Advertisement (NA). The Enhanced DAD algorithm proposed in this document focuses on detecting an NS looped back to the transmitting interface during the DAD operation. Detecting a looped back NA is of no use because no problems with DAD will occur if a node receives a looped back NA. Detecting of any other looped back ND messages outside of the DAD operation is not critical and thus this document does not cover such detection. The document also includes a Mitigation section that discusses means already available to mitigate the loopback problem. Recently service providers have reported a DAD loopback problem. Loopback testing is underway on a circuit connected to an interface on a router. The interface on the router is enabled for IPv6. The interface issues a NS for the IPv6 link-local address DAD. The NS is reflected back to the router interface due to the loopback condition of the circuit, and the router interface enters a DAD-failed state. In contrast to IPv4, IPv6 will not return to operation on the Asati, et al. Expires April 30, 2012 [Page 3]
Internet-Draft Enhanced DAD October 2011 interface when the loopback condition is cleared without manual intervention. In another service provider network, two broadband modems in a home have the Ethernet ports of each modem connected to a network hub. The access concentrator serving the modems is the first-hop IPv6 router for the modems. The access concentrator also supports proxying of DAD messages. Each modem is IPv4 online. The network interface of the access concentrator serving the two broadband modems is enabled for IPv6 and the interface issues a NS(DAD) message for the IPv6 link-local address. The NS message reaches one modem first and this modem sends the message to the hub which sends the message to the second modem which forwards the message back to the access concentrator. The looped back NS message causes the network interface on the access concentrator to be in a DAD-failed state. Such a network interface typically serves over six thousand broadband modems causing all the modems (and hosts behind the modems) to fail to get IPv6 online on the access network. Additionally, it may be tedious for the access concentrator to find out which of the six thousand or more homes looped back the DAD message. Clearly there is a need for automated detection of looped back NS messages during DAD operations by a node. 3. Operational Mitigation Options Two mitigation options are described below. The mechanisms do not require any change to existing implementations. 3.1. Disable DAD on Interface One can disable DAD on an interface and then there is no NS(DAD) issued to be looped back. DAD is disabled by setting the interface's DupAddrDetectTransmits variable to zero. While this mitigation may be the simplest the mitigation has three drawbacks. It would likely require careful analysis of configuration on such point-to-point interfaces, a one-time manual configuration on each of such interfaces, and more importantly, genuine duplicates in the link will not be detected. A network operator MAY use this mitigation. 3.2. Dynamic Disable/Enable of DAD Using Layer 2 Protocol It is possible that one or more layer 2 protocols include provisions to detect the existence of a loopback on an interface circuit, usually by comparing protocol data sent and received. For example, PPP uses magic number (section 6.4 of [RFC1661]) to detect a loopback on an interface. Asati, et al. Expires April 30, 2012 [Page 4]
Internet-Draft Enhanced DAD October 2011 When a layer 2 protocol detects that a loopback is present on an interface circuit, the device MUST temporarily disable DAD on the interface, and when the protocol detects that a loopback is no longer present (or the interface state has changed), the device MUST (re-)enable DAD on that interface. This solution requires no protocol changes. This solution SHOULD be enabled by default, and MUST be a configurable option. This mitigation has several benefits. They are 1. It leverages layer 2 protocol's built-in loopback detection capability, if available. 2. It scales better (since it relies on an event-driven), requires no additional state, timer etc. This may be a significant scaling consideration on devices with hundreds or thousands of interfaces that may be in loopback for long periods of time (such as while awaiting turn-up or during long-duration intrusive bit error rate tests). 3.3. Operational Considerations The mitigation options discussed in the document do not require the devices on both ends of the circuit to support the mitigation functionality simultaneously, and do not propose any capability negotiation. Suffice to say that the mitigation options are well effective for the unidirectional loopback. The mitigation options may not be effective for the bidirectional loopback (i.e. the loopback is placed in both directions of the circuit interface, so as to identify the faulty segment) if only one device followed a mitigation option specified in this document, since the other device would follow current behavior and disable IPv6 on that interface due to DAD until manual intervention restores it. This is nothing different from what happens today (without the solutions proposed by this document) in case of unidirectional loopback. Hence, it is expected that an operator would resort to manual intervention for the devices not compliant with this document, as usual. 4. The Enhanced DAD Algorithm The Enhanced DAD algorithm covers detection of a looped back NS(DAD) message. The document proposes use of the Nonce Option specified in the SEND document of [RFC3971]. The nonce is a random number as Asati, et al. Expires April 30, 2012 [Page 5]
Internet-Draft Enhanced DAD October 2011 specified in [RFC3971]. If SEND is enabled on the router and the router also supports the new automated ND loopback detection (specified in this document), there is integration with the Enhanced DAD algorithm and SEND. See more details in the Impact on SEND section. When the IPv6 network interface issues a NS(DAD) message, the interface includes the Nonce Option in the NS(DAD) message and saves the nonce in local store. Subsequently if the interface receives an identical NS(DAD) message, the interface logs a system management message, updates any statistics counter, and drops the looped back NS(DAD). If the DupAddrDetectTransmits variable for the interface is greater than one, subsequent NS(DAD) messages for the same Target Address should be suppressed. If the interface receives a NS(DAD) message with a different nonce but TargetAddress matches a tentative or optimistic address on the interface, the interface logs a DAD- failed system management message, updates any statistics, and behaves identical to the behavior specified in [RFC4862] for DAD failure. Six bytes of random nonce is sufficiently large for nonce collisions. However if there is a collision because two nodes generated the same random nonce (that are using the same Target address in their NS(DAD)), then the algorithm will incorrectly detect a looped back NS(DAD) when the NS(DAD) was issued to signal a genuine duplicate. Since each looped back NS(DAD) event is logged to system management, the administrator of the network will have to intervene manually. The algorithm is capable of detecting any ND solicitation (NS and Router Solicitation) or advertisement (NA and Router Advertisement) that is looped back. However, saving a nonce and nonce related data for all ND messages has impact on memory of the node and also adds the algorithm state to a substantially larger number of ND messages. Therefore this document does not recommend using the algorithm outside of the DAD operation by an interface on a node. 4.1. General Rules A node MUST implement detection of looped back NS(DAD) messages during DAD for an interface address. 4.2. Processing Rules for Senders If a node has been configured to use the Enhanced DAD algorithm, when sending a NS(DAD) for a tentative or optimistic interface address the sender MUST generate a random nonce associated with the interface address, MUST save the nonce, and MUST include the nonce in the Nonce Option included in the NS(DAD). If a looped back NS(DAD) is detected by the interface, and if the DupAddrDetectTransmits variable for the Asati, et al. Expires April 30, 2012 [Page 6]
Internet-Draft Enhanced DAD October 2011 interface is greater than one, subsequent NS(DAD) messages for the same Target Address SHOULD be suppressed. 4.3. Processing Rules for Receivers If the the node has been configured to use the Enhanced DAD algorithm and an interface on the node receives any NS(DAD) message that matches the interface address (in tentative or optimistic state), the receiver compares the nonce in the message with the saved nonce. If a match is found, the node SHOULD log a system management message, SHOULD update any statistics counter, and MUST drop the received message. If the received NS(DAD) message includes a nonce and no match is found with the saved nonce, the node SHOULD log a system management message for DAD-failed and SHOULD update any statistics counter. 4.4. Impact on SEND The SEND document uses the Nonce Option in the context of matching an NA with an NS. However, no text in SEND has an explicit mention of detecting looped back ND messages. If this document updates [RFC4862], SEND should be updated to integrate with the Enhanced DAD algorithm. A minor update to SEND would be to explicitly mention that the nonce in SEND is also used by SEND to detect looped back NS messages during DAD operations by the node. In a mixed SEND environment with SEND and unsecured nodes, the lengths of the nonce used by SEND and unsecured nodes MUST be identical. 4.5. Changes to RFC 4862 The following text is added to [RFC4862] at a yet to be determined location in [RFC4862]. A router that supports IPv6 DAD MUST implement the detection of looped back NS messages during DAD operation as specified in this document. A network interface on any other IPv6 node that is not a router SHOULD implement the detection of looped back NS messages during DAD operation as specified in this document. 4.6. Actions to Perform on Detecting a Genuine Duplicate As described in paragraphs above the nonce can also serve to detect genuine duplicates even when the network has potential for looping back ND messages. When a genuine duplicate is detected, the node follows the manual intervention specified in section 5.4.5 of [RFC4862]. However, in certain networks such as an access network if the genuine duplicate matches the tentative or optimistic IPv6 address of a network interface of the access concentrator, automated Asati, et al. Expires April 30, 2012 [Page 7]
Internet-Draft Enhanced DAD October 2011 actions are proposed. One access network is a cable broadband deployment where the access concentrator is the first-hop IPv6 router to several thousand broadband modems. The router also supports proxying of DAD messages. The network interface on the access concentrator initiates DAD for an IPv6 address and detects a genuine duplicate due to receiving an NS(DAD) or an NA message. On detecting such a duplicate the access concentrator logs a system management message, drops the received ND message, and blocks the modem on whose layer 2 service identifier the NS(DAD) or NA message was received on. The network described above follows a trust model where a trusted router serves un-trusted IPv6 host nodes. Operators of such networks have a desire to take automated action if a network interface of the trusted router has a tentative or optimistic address duplicate with a host served by trusted router interface. Any other network that follows the same trust model MAY use the automated actions proposed in this section. 5. Security Considerations The nonce can be exploited by a rogue deliberately changing the nonce to fail the looped back detection specified by the Enhanced DAD algorithm. SEND is recommended for this exploit. For any mitigation suggested in the document such as disabling DAD has an obvious security issue before a remote node on the link can issue reflected NS(DAD) messages. Again, SEND is recommended for this exploit. 6. IANA Considerations None. 7. Acknowledgements Thanks to Eric Levy-Abegnoli, Erik Nordmark, and Fred Templin and Tassos Chatzithomaoglou for their guidance and review of the document. Thanks to Thomas Narten for encouraging this work. Thanks to Steinar Haug and Scott Beuker for describing the use cases. 8. Normative References [RFC1247] Moy, J., "OSPF Version 2", RFC 1247, July 1991. Asati, et al. Expires April 30, 2012 [Page 8]
Internet-Draft Enhanced DAD October 2011 [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, July 1994. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) for IPv6", RFC 4429, April 2006. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. Authors' Addresses Rajiv Asati Cisco Systems, Inc. 7025 Kit Creek road Research Triangle Park, NC 27709-4987 USA Email: rajiva@cisco.com URI: http://www.cisco.com/ Hemant Singh Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough, MA 01719 USA Phone: +1 978 936 1622 Email: shemant@cisco.com URI: http://www.cisco.com/ Asati, et al. Expires April 30, 2012 [Page 9]
Internet-Draft Enhanced DAD October 2011 Wes Beebee Cisco Systems, Inc. 1414 Massachusetts Ave. Boxborough, MA 01719 USA Phone: +1 978 936 2030 Email: wbeebee@cisco.com URI: http://www.cisco.com/ Eli Dart Lawrence Berkeley National Laboratory ESnet Network Engineering Group USA Email: dart@es.net Wes George Time Warner Cable 13820 Sunrise Valley Drive Herndon, VA 20171 USA Email: wesley.george@twcable.com Carlos Pignatro Cisco Systems, Inc. 7025 Kit Creek Road Research Triangle Park, NC 27709-4987 USA Email: cpignataro@cisco.com URI: http://www.cisco.com/ Asati, et al. Expires April 30, 2012 [Page 10]