Softwires Working Group C. Metz, Ed. Internet-Draft Cisco Systems Intended status: Informational Y. Cui, Ed. Expires: August 18, 2008 M. Xu, Ed. Tsinghua University February 15, 2008 Softwires Mesh Multicast Problem Statement draft-metz-softwires-multicast-problem-statement-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 18, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Metz, et al. Expires August 18, 2008 [Page 1] Internet-Draft Softwires Multicast Problem Statement February 2008 Abstract This document defines a problem statemet for Softwires Mesh Multicast. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Scenarios of Interest . . . . . . . . . . . . . . . . . . 4 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Considerations . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Optimality vs Scalability . . . . . . . . . . . . . . . . 6 3.2. Single-Source Multicast vs Any-Source Multicast . . . . . 7 3.3. E-IP Client Networks and MPLS Multicast . . . . . . . . . 7 3.4. Client E-IP Multicast Signaling between AFBR Nodes . . . . 7 3.5. I-IP Unicast Core . . . . . . . . . . . . . . . . . . . . 7 4. Problem Examples . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. Client E-IP = IPv6 and I-IP Backbone = IPv4 . . . . . . . 9 4.2. Client E-IP = IPv4 and I-IP Backbone = IPv6 . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 8.1. Normative References . . . . . . . . . . . . . . . . . . . 14 8.2. Informative References . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 16 Metz, et al. Expires August 18, 2008 [Page 2] Internet-Draft Softwires Multicast Problem Statement February 2008 1. Introduction The Internet will need to support IPv4 and IPv6 packets. Both address families and their attendent protocol suites support multicast of the single-source and any-source varieties. As part of the transition to IPv6, there will be scenarios where a backbone network running one IP address family internally (referred to as internal IP or I-IP) will provide transit services to attached client networks running another IP address family (referred to as external IP or E-IP). It is expected that the I-IP backbone will offer unicast and multicast transit services to the client E-IP networks. The Softwires Working Group has defined a framework by which E-IP unicast and multicast packets can be tunneled across an I-IP backbone network [I-D.draft-ietf-softwire-mesh-framework-03]. The tunnels are referred to as Softwires. The Softwires Problem Statement [RFC4925] calls out multicast as a requirement. The charter for the Softwires working group explicitly mentions multicast and at the Vancouver IETF meeting, a healthy discussion on Softwire Multicast ensued. It was suggested and agreed to at the time that a problem statement for softwire mesh multicast be created and discussed at the next IETF meeting in Philadelphia. This document describes the softwires mesh multicast problem statement. 1.1. Terminology The following terminology will be used in this document. o Softwire (SW) - A "tunnel" that is created on the basis of a control protocol setup between softwire endpoints with a shared point-to- point, multipoint-to-point, point-to-multipoint or multipoint-to-multipoing state. Softwires are generally dynamic in nature (they may be initiated and terminated on demand), but may be very long-lived. o Address Family Border Router (AFBR) - The dual-stack router that interconnects two networks that use different address families. In the context of softwires multicast, the AFBR runs E-IP and I-IP control planes to maintain E-IP and I-IP multicast state respectively and performs the appropriate encapsulation/ decapsultion client E-IP multicast packets for transport across the I-IP backbone. o I-IP ("Internal IP"). This refers to the form of IP (i.e., either IPv4 or IPv6) that is supported by the transit (or backbone) network. Metz, et al. Expires August 18, 2008 [Page 3] Internet-Draft Softwires Multicast Problem Statement February 2008 o E-IP ("External IP") This refers to the form of IP (i.e. either IPv4 or IPv6) that is supported by the client networks. o I-IP Core Tree. A single-source or multi-source distribution tree rooted at one or more AFBR source nodes and branching out to one or more AFBR leaf nodes. An I-IP core tree is built using standard IP or MPLS multicast signaling protocols operating exclusively inside the I-IP backbone network. An I-IP core tree is used to tunnel E-IP multicast packets belonging to E-IP trees across the I-IP backbone. Another name for an I-IP core tree is multicast or multipoint softwire. o E-IP client tree. A single-source or multi-source distribution tree rooted at one or more hosts or routers located inside a client E-IP network and branching out to one or more leaf nodes located in the same or different client E-IP networks. 1.2. Scenarios of Interest The scenarios of interest are the following: o IPv6-over-IPv4. This is the case when the I-IP backbone is IPv4 and the client E-IP networks are global IPv6 o IPv4-over-IPv6. This is the case where the I-IP backbone is IPv6 and the client E-IP networks are global IPv4 While the focus on Softwires is IPv6 transition, it should be noted that the mechanisms defined so far in the softwire mesh framework and any additional protocol machinery required for softwire mesh multicast can and should work in the cases where E-IP and I-IP networks support the same IP address family. Metz, et al. Expires August 18, 2008 [Page 4] Internet-Draft Softwires Multicast Problem Statement February 2008 2. Motivation The fundamental objective of any I-IP backbone, in particular as it relates to Softwires Mesh and IPv6 transition is to provide transit connectivity between constituent client E-IP networks. The transit connectivity between client E-IP networks must support both IP unicast and multicast packets. With respect to the latter it is possible, although highly undesirable for provisioning and scalability reasons, to accomodate multicast connectivity across the I-IP backbone via a series of inter-AFBR point-to-point tunnels using mechanisms such as GRE [RFC2784] or L2TPv3 [RFC3931] The preferred solution is to leverage the multicast functions, inherent in the I-IP backbone, to efficiently and scalably tunnel encapsulated client E-IP multicast packets inside an I-IP core tree rooted at one or more ingress AFBR nodes and branching out to one or more egress AFBR leaf nodes. Thus we require protocol machinery capable of dynamically building single-source or multi-source I-IP core trees (aka multipoint softwires) capable of providing client E-IP multicast connectivity. Metz, et al. Expires August 18, 2008 [Page 5] Internet-Draft Softwires Multicast Problem Statement February 2008 3. Considerations This section lays out several areas to consider when addressing the softwires mesh multicast problem. 3.1. Optimality vs Scalability The issues regarding optimality versus scalability have been discussed ad nauseum. [I-D.draft-ietf-l3vpn-2547bis-mcast-06]At one end of the spectrum each E-IP client tree maps to one I-IP core tree on a 1:1 basis so the amount of multicast state inside the core is O(# of E-IP client trees). 1:1 mapping infers E-IP client and I-IP core branch and/or leaf routers will be contiguous on the AFBR nodes thus contributing to an optimal delivery. In addition 1:1 mapping is consistent with Internet-style multicast in that there is no aggregation of E-IP client state performed by routers. At the other end of the spectrum we have aggregation where a set of AFBR-rooted single-source trees or even an individual any-source tree could serve to deliver all client E-IP multicast packets to all AFBR leaf nodes where a decision to forward to downstream client E-IP routers will be determined by E-IP multicast state. This N:1 mapping of N number of E-IP client trees mapped to one or a few I-IP core trees is scalable from a state perspective. However it could be sub- optimal because some AFBR nodes might have to discard E-IP multicast packets received through an I-IP core tree for which there are no downstream receivers. Aggregation is appropriate for the L3VPN cases where the backbone needs to handle potentially a large number of VPN-specific, receiver- dense, low-volume multicast trees. The advantages of state containment in the backbone at the expense of low-volume packet drops on uninterested leaf routers is acceptable. This is not the case for Internet multicast where receiver populations are sparse and per-tree traffic volumes tend towards higher-bandwidth consuming multimedia streams. The mission for softwires is to support global E-IP connectivity across an I-IP backbone network. We extend this notion naturally in support of multicast which leads to the conclusion that only Internet-style multicast (i.e 1:1 mapping with no aggregation ) should be addressed in Softwires. If the IETF community under the auspices of another working group (e.g. MBONED) deems that aggregation of Internet multicast is a problem needing a solution,then those requirements should be documented and disseminated to other working groups for consideration. Metz, et al. Expires August 18, 2008 [Page 6] Internet-Draft Softwires Multicast Problem Statement February 2008 It should also be noted that a solution for multicast state aggregation exists today in the form of multicast VPNs. 3.2. Single-Source Multicast vs Any-Source Multicast Noting again that softwires must address Internet multicast, it is required that singles-source multicast (e.g. PIM-SSM) be supported. Any-source multicast (ASM) could be considered but we observe that there is a decided lack of security in the current schemes. One could have unauthorized sources blasting multicast packets into a shared tree in a benign or malicious denial-of-service attack. The use embedded RP [RFC3956]in which the address of the rendezvous point (RP) for the shared tree is embedded in the group address is one way that ASM could scale for the Internet but the security issue still remains. 3.3. E-IP Client Networks and MPLS Multicast Client E-IP networks will run native IPv4 or native IPv6 multicast to build E-IP client trees and to replicate and forward client E-IP multicast packets. No requirement or statement has been put forth to date suggesting that the client E-IP networks will run MPLS multicast. It is noted that MPLS multicast is permitted to run in I-IP backbone networks. 3.4. Client E-IP Multicast Signaling between AFBR Nodes AFBR nodes might need to establish some form of control plane interaction to exchange client E-IP multicast configuration and/or routing information. Configuring and running a full mesh of inter- AFBR E-IP PIM adjacencies in an overlay fashion is one possible solution. Another solution is to extend MP-BGP to distribute E-IP multicast routing information between AFBR nodes. [I-D.draft-ietf-l3vpn-2547bis-mcast-bgp-04] 3.5. I-IP Unicast Core It is possible that the I-IP backbone only supports softwire mesh unicast routing and forwarding. In such a scenario, the ingess AFBR node(s) will need to replicate, map and then encapsulate E-IP client multicast packets in softwire unicast tunnel headers for transport to the appropriate egress AFBR node(s). There the softwire tunnel header is removed and E-IP client multicast packet process occurs. Metz, et al. Expires August 18, 2008 [Page 7] Internet-Draft Softwires Multicast Problem Statement February 2008 A method for mapping E-IP client multicast group addresses to the I-IP unicast addresses of the one or more egress AFBR nodes will be required. Metz, et al. Expires August 18, 2008 [Page 8] Internet-Draft Softwires Multicast Problem Statement February 2008 4. Problem Examples This section outlines several examples of where softwire mesh multicast would apply. 4.1. Client E-IP = IPv6 and I-IP Backbone = IPv4 This first example will likely be the most common one encountered. The client E-IP networks are running global IPv6 routing and are attached via single-homed or multi-homed connections to dual-stack AFBR nodes positioned at the edges of a backbone I-IP network running IPv4. The client E-IP IPv6 networks are capable of running single-source and any-source multicast applications and support PIM-SM and PIM-SSM for building and maintaining E-IP client trees. Multicast sources (hosts or routers) are rooted in one or more client E-IP networks and leafs or receivers are located in the same or remote client E-IP networks on the other side of the I-IP IPv4 backbone network. The I-IP IPv4 backbone runs PIM or mLDP to build and maintain I-IP core trees. The encapsulations applied to client E-IP IPv6 multicast packets tunneled inside the I-IP core trees are IPv4 multicast or MPLS labels. The core routers do not hold client E-IP routes so support for the RPF Vector is needed. This enables core routers to forward I-IP PIM IPv4 join/prune messages towards the AFBR leading to the E-IP source or RP. The dual-stack AFBR nodes run E-IP PIM to exchange client E-IP multicast routing information with attached client E-IP routers. The AFBR nodes must also exchange client E-IP routing information with other AFBR nodes. And finally an AFBR is expected to participate in the signaling (I-IP PIM or I-IP mLDP) necessary to establis the I-IP core tree. The encapsulation and decapsulation of client E-IP multicast packets in I-IP multipoint softwire packets is performed by the AFBR. 4.2. Client E-IP = IPv4 and I-IP Backbone = IPv6 This second example will be encountered as well. The client E-IP networks are running global IPv4 routing and are attached via single- homed or multi-homed connections to dual-stack AFBR nodes positioned at the edges of a backbone I-IP network running native IPv6. Now client E-IP IPv4 networks will have multicast connectivity Metz, et al. Expires August 18, 2008 [Page 9] Internet-Draft Softwires Multicast Problem Statement February 2008 extended across an I-IP IPv6 backbone network with the same general interactions in place as described in the previous scenario. The one exception is the strong likelihood that MPLS multicast will not operate in the I-IP IPv6 backbone network. Metz, et al. Expires August 18, 2008 [Page 10] Internet-Draft Softwires Multicast Problem Statement February 2008 5. IANA Considerations This document makes no request of IANA. Note to RFC Editor: this section may be removed on publication as an RFC. Metz, et al. Expires August 18, 2008 [Page 11] Internet-Draft Softwires Multicast Problem Statement February 2008 6. Security Considerations TBA .. Metz, et al. Expires August 18, 2008 [Page 12] Internet-Draft Softwires Multicast Problem Statement February 2008 7. Acknowledgements Toerless Eckert, Greg Shephard, Eric Rosen and Vasu Kengeri provided useful input. Metz, et al. Expires August 18, 2008 [Page 13] Internet-Draft Softwires Multicast Problem Statement February 2008 8. References 8.1. Normative References [I-D.draft-ietf-l3vpn-2547bis-mcast-06] Rosen, E., Ed., "Multicast in MPLS/BGP IP VPNs", . [I-D.draft-ietf-l3vpn-2547bis-mcast-bgp-04] Rosen, E. and R. Aggarwal, "BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNs", November 2007, . [I-D.draft-ietf-softwire-mesh-framework-03] Rosen, E., Ed., "Softwire Mesh Framework", January 2008, . [RFC2784] Farinacci, D., "Generic Router Encapsulation", March 2000. [RFC3931] Townsley, M., Ed., "Layer-2 Tunneling Protocol - Version 3", March 2005. [RFC3956] Savola, P., "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", November 2004. [RFC4925] Li, X., Ed., "Softwire Problem Statement", July 2007. 8.2. Informative References Metz, et al. Expires August 18, 2008 [Page 14] Internet-Draft Softwires Multicast Problem Statement February 2008 Authors' Addresses Chris Metz (editor) Cisco Systems 170 West Tasman Drive San Jose, California 95134-1706 USA Phone: +1-408-525-3275 Email: chmetz@cisco.com Yong Cui (editor) Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 P.R.China Phone: +86-10-6278-5822 Email: cuiyong@tsinghua.edu.cn Mingwei Xu (editor) Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 P.R.China Phone: +86-10-6278-5822 Email: xmw@csnet1.cs.tsinghua.edu.cn Metz, et al. Expires August 18, 2008 [Page 15] Internet-Draft Softwires Multicast Problem Statement February 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Metz, et al. Expires August 18, 2008 [Page 16]