Network Working Group S. Vinapamula Internet-Draft Juniper Networks Intended status: BCP M. Boucadair Expires: November 6, 2014 France Telecom May 5, 2014 Recommendation for Prefix Binding in the Softwire DS-Lite Context draft-vinapamula-softwire-dslite-prefix-binding-02 Abstract This document discusses issues induced by the change of the Basic Bridging BroadBand (B4) IPv6 address and sketches a set of recommendations to solve those issues. 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 November 6, 2014. Copyright Notice Copyright (c) 2014 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. Vinapamula & Boucadair Expires November 6, 2014 [Page 1] Internet-Draft Prefix Binding for DS-Lite May 2014 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The Problem . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative references . . . . . . . . . . . . . . . . . . . 6 8.2. Informative references . . . . . . . . . . . . . . . . . . 6 Vinapamula & Boucadair Expires November 6, 2014 [Page 2] Internet-Draft Prefix Binding for DS-Lite May 2014 1. Introduction IPv6 deployment models assumes IPv6 prefixes are delegated by Service Providers to the connected CPEs (Customer Premise Equipments) or hosts, which in their turn derive IPv6 addresses out of that prefix. In the case of DS-Lite [RFC6333], the Basic Bridging BroadBand (B4) element derives an IPv6 address for the softwire setup purposes. A B4 element might obtain a new external IPv6 address, for a variety of reasons including a reboot of the CPE, power outage, DHCP lease expiry, or other action undertaken by the Service Provider. If this occurs, traffic forwarded to a B4's previous address might be delivered to another B4 that now acquired that address. This affects all mapping types, whether implicit (e.g., by sending a TCP SYN) or explicit (e.g., using PCP [RFC6887]). The main goal of this document is to propose recommendations to soften the impact of such renumbering issues. Note that in some deployments, CPE renumbering may be required to accommodate some privacy-related requirements to avoid the same prefix be assigned to the same customer. It is out of scope of this document to discuss such contexts. This document complements [RFC6908]. 2. Terminology 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]. 3. The Problem Since the network behind B4 can be overlapping across multiple CPEs, B4 address plays a key role in identifying associated resources assigned for each of the connections. These resources maintain state of Endpoint-Independent Mapping (EIM), Endpoint-Independent Filtering (EIF), Address Pooling Paired (APP) in the AFTR, and Port Control Protocol (PCP) mappings and flows. However, there can be change in B4 address for any reason, may be because of change in CPE device or may be because of security extensions enabled in generating the IPv6 address. When the address change, the associated mappings created in the AFTR are no more valid. This may result in creation of new set of mappings. Service Providers may want to limit the usage of these resources on Vinapamula & Boucadair Expires November 6, 2014 [Page 3] Internet-Draft Prefix Binding for DS-Lite May 2014 per subscriber basis for fairness resources usage. To that aim , a subscriber is identified by the delegated IPv6 prefix and not the derived B4 address. These policies are used for dimensioning purposes and also to ensure that AFTR resources are not exhausted. However when there is a change in B4 address, this policy doesn't resolve stale mappings hanging around in the system, consuming not only system resources, but also reducing the available quota of resources per subscriber. Clearing those mappings can be envisaged, but that will cause a lot of churn in the AFTR and could be disruptive to existing connections. When services are hosted behind B4 element, and when there is a change in B4 address which if results in change in NAT address, these services have to advertise about their change, whenever there is a change of the B4 address. Means to discover the change of B4 address and NAT address is therefore required. Also, it doesn't address latency issues where a service has to advertise its newly assigned external IP address and port and the clients have to consume and re- initiate connections. PCP-specific failure scenarios are discussed in [I-D.boucadair-pcp-failure]. 4. Recommendations In order to mitigate the issues discussed in Section 3, the following recommendations are made: 1. A policy SHOULD be enforced at the AFTR level to limit the number of active softwires per subscriber. The default value MUST be 1. This policy aims to prevent a misbehaving subscriber to mount several softwires to consume more resources on the AFTR side. 2. Resource contexts created at the AFTR level SHOULD be based on the delegated IPv6 prefix and not based on the B4 address. Delegated prefix may be derived from the B4 address through a configured subscriber-mask. Administrators SHOULD configure per prefix limits of resource usage, instead of per tunnel limits. These resources include, number of flows, mappings including PCP, NAT pool resources, etc. 1. Subscriber-mask is an integer that indicates the length of significant bits to be applied on the source IPv6 address (internal side) to identify a subscriber. Subscriber-mask is an AFTR system-wide configuration parameter that is used to enforce generic per-subscriber policies. Applying these generic policies does not require to configure every Vinapamula & Boucadair Expires November 6, 2014 [Page 4] Internet-Draft Prefix Binding for DS-Lite May 2014 subscriber prefix. Subscriber-mask must be configurable; the default value is 56. 2. For example, suppose an IPv6 prefix 2001::/56 is delegated to a CPE. Administrator should configure resource usage limits in AFTR based on the prefix 2001::/56 and not based on any B4 address derived from the delegated prefix. AFTR will derive the prefix from B4 address through configured subscriber-mask set to 56 by the administrator. 3. In the event a new IPv6 address is assigned to B4, the AFTR SHOULD migrate existing state to be bound to the new B4's IP address. This ensures the traffic destined to the previous B4 address will be redirected to the newer B4 address. The destination address for tunneling return traffic SHOULD be the last seen as B4's address from the CPE. Doing so avoids stale mappings and minimizes the risk of service disruption. 4. In the event of change of the CPE WAN's IPv6 prefix, unsolicited PCP ANNOUNCE messages are to be sent by the B4 element to internal hosts to update their mappings. This allows internal PCP clients to update their mappings with the new B4 IPv6 address and trigger updates to rendez-vous servers (e.g., dynamic DNS). 5. When a new prefix is assigned to the CPE, stale mappings may exist in the AFTR. This will consume both implicit and explicit resources. In order to avoid such issues, stable IPv6 prefix assignment is RECOMMENDED. 6. In case for any reason an IPv6 prefix has to be reassigned, it is RECOMMENDED to reassign an IPv6 prefix only when all the resources in use associated with that prefix are cleared from the AFTR. Doing so avoids to redirect traffic, destined to the previous prefix owner, to the new one. 5. Security Considerations Security considerations related to DS-Lite are discussed in [RFC6333]. 6. IANA Considerations This document does not require any action from IANA. 7. Acknowledgements G. Krishna and C. Jacquenet reviewed document and provided useful comments. Vinapamula & Boucadair Expires November 6, 2014 [Page 5] Internet-Draft Prefix Binding for DS-Lite May 2014 8. References 8.1. Normative references [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion", RFC 6333, August 2011. [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 2013. 8.2. Informative references [I-D.boucadair-pcp-failure] Boucadair, M. and R. Penno, "Analysis of Port Control Protocol (PCP) Failure Scenarios", draft-boucadair-pcp-failure-06 (work in progress), May 2013. [RFC6908] Lee, Y., Maglione, R., Williams, C., Jacquenet, C., and M. Boucadair, "Deployment Considerations for Dual- Stack Lite", RFC 6908, March 2013. Authors' Addresses Suresh Vinapamula Juniper Networks 1194 North Mathilda Avenue Sunnyvale, CA 94089 USA Phone: +1 408 936 5441 EMail: sureshk@juniper.net Vinapamula & Boucadair Expires November 6, 2014 [Page 6] Internet-Draft Prefix Binding for DS-Lite May 2014 Mohamed Boucadair France Telecom Rennes 35000 France EMail: mohamed.boucadair@orange.com Vinapamula & Boucadair Expires November 6, 2014 [Page 7]