Network Working Group D. Meyer, Ed. Internet-Draft L. Zhang, Ed. Intended status: Informational K. Fall, Ed. Expires: June 18, 2007 December 15, 2006 Report from the IAB Workshop on Routing and Addressing draft-iab-raws-report-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 June 18, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document reports the outcome of the Routing and Addressing Workshop which the Internet Architecture Board (IAB) held on October 18-19, 2006 in Amsterdam, Netherlands. The primary goal of the workshop was to develop a shared understanding of the problems that the large backbone operators are facing regarding the scalability of today's Internet routing system. The key workshop findings include an analysis of the major factors that are driving routing table growth, constraints in router technology, and the limitations of Meyer, et al. Expires June 18, 2007 [Page 1] Internet-Draft IAB Workshop on Routing & Addressing December 2006 today's Internet addressing architecture. It is hoped that these findings will serve as input to the IETF community and help identify next steps towards effective solutions. Note that this document is a report on the proceedings of the workshop, and it is not an IAB document. The views and positions documented in this report are those of the workshop participants and not the IAB. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Key Findings from the Workshop . . . . . . . . . . . . . . . . 4 2.1. Problem #1: The Scalability of the Routing System . . . . 5 2.1.1. Implications of DFZ RIB Growth . . . . . . . . . . . . 5 2.1.2. Implications of DFZ FIB Growth . . . . . . . . . . . . 6 2.2. Problem #2: The Overloading of IP Address Semantics . . . 7 2.3. Other Concerns . . . . . . . . . . . . . . . . . . . . . . 8 2.4. How Urgent are these Problems? . . . . . . . . . . . . . . 8 3. Current Stresses on the Routing and Addressing System . . . . 9 3.1. Major Factors Driving Routing Table Growth . . . . . . . . 9 3.1.1. Avoiding Renumbering . . . . . . . . . . . . . . . . . 10 3.1.2. Multihoming . . . . . . . . . . . . . . . . . . . . . 10 3.1.3. Traffic Engineering . . . . . . . . . . . . . . . . . 11 3.2. IPv6 and its potential impact on routing table size . . . 12 4. Implications of Moore's Law on the Scaling Problem . . . . . . 12 4.1. Integrated Circuits . . . . . . . . . . . . . . . . . . . 12 4.2. Heat and Power . . . . . . . . . . . . . . . . . . . . . . 13 5. What is on the Horizon . . . . . . . . . . . . . . . . . . . . 13 5.1. Continual Growth . . . . . . . . . . . . . . . . . . . . . 14 5.2. Large Numbers of Mobile Networks . . . . . . . . . . . . . 14 5.3. Orders of magnitude increase in mobile edge devices . . . 14 6. What Approaches Have Been Investigated . . . . . . . . . . . . 15 6.1. Lessons from MULTI6 . . . . . . . . . . . . . . . . . . . 15 6.2. SHIM6: Pros and Cons . . . . . . . . . . . . . . . . . . . 16 6.3. GSE/indirection solutions: Costs and Benefits . . . . . . 17 6.4. Futures for Indirection . . . . . . . . . . . . . . . . . 18 7. Problem Statements . . . . . . . . . . . . . . . . . . . . . . 19 7.1. Problem 1: Routing Scalability . . . . . . . . . . . . . . 19 7.2. Problem 2: The overloading of IP address semantics . . . . 20 7.2.1. Definition of Locator and Identifier . . . . . . . . . 20 7.2.2. Consequence of Locator and Identifier Overloading . . 21 7.2.3. Traffic Engineering and IP Address Semantics Overload . . . . . . . . . . . . . . . . . . . . . . . 21 7.3. Routing Convergence . . . . . . . . . . . . . . . . . . . 22 7.4. Misaligned Costs and Benefits . . . . . . . . . . . . . . 23 7.5. Other Issues . . . . . . . . . . . . . . . . . . . . . . . 23 Meyer, et al. Expires June 18, 2007 [Page 2] Internet-Draft IAB Workshop on Routing & Addressing December 2006 7.6. Problem Recognition . . . . . . . . . . . . . . . . . . . 24 8. Criteria for Solution Development . . . . . . . . . . . . . . 24 8.1. Criteria on Scalability . . . . . . . . . . . . . . . . . 24 8.2. Criteria on Incentives and Economics . . . . . . . . . . . 25 8.3. Criteria on Timing . . . . . . . . . . . . . . . . . . . . 26 8.4. Consideration on Existing Systems . . . . . . . . . . . . 26 8.5. Consideration on Security . . . . . . . . . . . . . . . . 27 8.6. Other Criteria . . . . . . . . . . . . . . . . . . . . . . 27 8.7. Understanding the Tradeoff . . . . . . . . . . . . . . . . 27 9. Workshop Recommendations . . . . . . . . . . . . . . . . . . . 28 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29 11. Security Considerations . . . . . . . . . . . . . . . . . . . 29 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Appendix A. Suggestions for Specific Steps . . . . . . . . . . . 31 Appendix B. Workshop Participants . . . . . . . . . . . . . . . . 32 Appendix C. Workshop Agenda . . . . . . . . . . . . . . . . . . . 33 Appendix D. Presentations . . . . . . . . . . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34 Intellectual Property and Copyright Statements . . . . . . . . . . 35 Meyer, et al. Expires June 18, 2007 [Page 3] Internet-Draft IAB Workshop on Routing & Addressing December 2006 1. Introduction It is commonly recognized that today's Internet routing and addressing system is facing serious scaling problems. The ever increasing user population, as well as multiple other factors including multi-homing, traffic engineering, and policy routing, have been driving the growth of Default Free Zone (DFZ) routing table size at an alarming rate [DFZ]. While it has been long recognized that the existing routing architecture may have serious scalability problems, effective solutions have yet to be identified, developed, and deployed. As a first step towards tackling these long standing concerns, the IAB held a "Routing and Addressing Workshop" in Amsterdam, Netherlands on October 18-19, 2006. The main objectives of the workshop were to identify existing and potential factors that have major impacts on routing scalability, and to develop a concise problem statement that could serve as input to a set of follow-on activities. This document reports on the outcome from that workshop. The remainder of the document is organized as follows: Section 2 captures the high level findings from the workshop. Section 3 describes the sources of stress in the current global routing and addressing system. Section 4 discusses the relationship between Moore's law and our ability to build large routers. Section 5 describes some of the factors that could exacerbate the current problems outlined in Section 2. Section 6 describes previous work in this area. Section 7 describes the problem statements in more detail, and Section 8 discusses the criteria that constrain the solution space. Finally, Section 9 summarizes the recommendations made by the workshop participants. The workshop participant list is attached in Appendix B. The agenda can be found in Appendix C, and Appendix D provides pointers to the presentations from the workshop. Finally, note that this document is a report on the outcome of the workshop, not an official document of the IAB. Any opinions expressed are those of the workshop participants and not the IAB. 2. Key Findings from the Workshop This section provides a concise summary of the key findings from the workshop. While many other aspects of a routing and addressing system were discussed, the findings described here were deemed most important by the workshop participants. Meyer, et al. Expires June 18, 2007 [Page 4] Internet-Draft IAB Workshop on Routing & Addressing December 2006 The clear highest priority takeaway from the workshop was the need to devise a scalable routing and addressing system, one which is scalable in the face of multihoming, and which facilitates a wide spectrum of traffic engineering (TE) requirements. While several scalability features of the routing and addressing systems were discussed, most related to the size of the DFZ routing table (frequently referred to as the Routing Information Base, or RIB) and its implications. Those implications included (but were not limited to) the sizes of the DFZ RIB and FIB (the Forwarding Information Base), the cost of recomputing the FIB, concerns about the BGP convergence times in the presence of growing RIB and FIB sizes, and the costs and power (and hence heat dissipation) properties of the hardware needed to route traffic in the core of the Internet. 2.1. Problem #1: The Scalability of the Routing System The shape of the growth curve of the DFZ RIB has been the topic of much research and discussion since the early days of the Internet [DFZ]. There have been various hypotheses regarding the sources of this growth. The workshop consensus is that the following factors are the main driving forces behind the rapid growth of the DFZ RIB: o Multihoming, o Traffic engineering, o Suboptimal RIR address allocations, and o Business events such as mergers and acquisitions. All of the above factors can lead to prefix de-aggregation and/or the injection of unaggregatable prefixes into the DFZ RIB. This de- aggregation leads to routing scalability problem because, absent some non-topologically based routing technology (for example, Routing On Flat Labels [ROFL], or Compact Routing [CNIR]), topological aggregation is the only known practical approach to control the growth of the DFZ RIB. The following section reviews the workshop discussion of the implications of the growth of the DFZ RIB. 2.1.1. Implications of DFZ RIB Growth Presentations made at the workshop showed that the DFZ RIB has been growing at greater than linear rates for several years [DFZ]. While this has the obvious effects on the requirements for RIB and FIB memory sizes, the growth driven by prefix de-aggregation also exposes the core of the network to the dynamic nature of the edges. One particularly troublesome result of prefix de-aggregation is that Meyer, et al. Expires June 18, 2007 [Page 5] Internet-Draft IAB Workshop on Routing & Addressing December 2006 it leads to an increased number of BGP UPDATE messages injected into the DFZ (frequently referred to as "UPDATE churn") and consumes the corresponding processing resources. This additional processing is required to maintain state for the longer prefixes and to compute the FIB. Note that, although the size of the RIB is bounded by the given address space size (i.e. O(m*2^32) for IPv4, where is a slow moving function that describes the interconnection mesh of the Internet), the dynamic nature of the edges is not. As a result, the amount of BGP UPDATE churn that the network can experience is essentially unbounded. It was also noted that the UPDATE churn, as currently measured, is heavy-tailed [ATNAC2006]. That is, a relatively small number of Autonomous Systems (ASes) are responsible for a disproportionately large fraction of the UPDATE churn that we observe today. Furthermore, much of the churn may turn out to be unnecessary information, possibly injected to arbitrage some bandwidth pricing model or the like (see [GIH], for example, or the discussion of the behavior of AS 9121 in [BGP2005]). Finally, it was noted by the workshop participants that the UPDATE churn situation may be exacerbated by the current Regional Internet Registry (RIR) policy in which end sites are allocated Provider Independent (PI) addresses. These addresses are not topologically aggregatable, and as such bring the churn problem described above into the core routing system. Of course, as noted by several participants, the RIRs have no real choice in this matter, as many enterprises demand PI addresses which allow them to multihome without the "provider lock" that Provider Allocated (PA) [PIPA] address space creates. Some enterprises also find the renumbering cost associated with PA address assignments unacceptable. 2.1.2. Implications of DFZ FIB Growth [Editor's note: The conclusions reviewed in this section have been the subject of considerable debate since the workshop. As such, more exploration of these topics is indicated.] Perhaps the most surprising outcome of the workshop was the observation made by Tony Li about the relation between "Moore's Law" [ML] and our ability to build large scale routers. "Moore's Law" is the empirical observation that the transistor density of integrated circuits doubles roughly every 24 months, and many people believe that Moore's Law solves the problem of scaling core router hardware. However Li pointed out that Moore's Law does not necessarily apply to building high-end routers. In particular, Moore's Law applies specifically to on-chip transistor density and is applicable only to high-volume processors. It is not necessarily applicable to the low- volume, custom processors needed to forward traffic at the rates commonly found in the core of the Internet. Furthermore, Moore's Law Meyer, et al. Expires June 18, 2007 [Page 6] Internet-Draft IAB Workshop on Routing & Addressing December 2006 does not apply to the clock speeds of the chip. While DRAM capacity has grown in accordance with Moore's law (at a rate of approximately 2.4 times every 2 or so years), memory clock rates have grown at a much lower rate (roughly 1.2 times every two years according to Tony Li's presentation; see Appendix D). 2.2. Problem #2: The Overloading of IP Address Semantics One of the fundamental assumptions underlying the scalability of routing systems was eloquently stated by Yakov Rekhter (and is sometimes referred to as "Rekhter's Law"), namely that, in general: "Addressing can follow topology or topology can follow addressing. Choose one." The same idea was expressed by Mike O'Dell in his design of GSE (formerly 8+8) [GSE], where the address structure was designed explicitly to scale the routing system by providing for "aggressive topological aggregation". Noel Chiappa has also written extensively on this topic (see, e.g., [EID]). There is, however, a difficulty in creating (and maintaining) the kind of congruency envisioned by Rekhter's Law in today's Internet. The difficulty arises from the overloading of addressing with the semantics of both "who" (endpoint identifier for the transport layer) and "where" (locators for the routing system); some might also add that IP addresses are also overloaded with "how" [GIH]. In any event, this kind of overloading is felt to have had deep implications for the scalability of the global routing system. A refinement to Rekhter's Law, then, is that for a routing system to scale, the locator part of IP address must be assigned in such a way that it is congruent with the Internet's topology. However, as identifiers are typically assigned based upon organizational (not topological) structure and have stability as a desirable property, a "natural incongruence" arises. As a result, it is difficult (if not impossible) to make a single number space serve both purposes efficiently. Of course this conclusion assumes, as mentioned above, that no effective "non-topological routing system" exists. Following the logic of the previous paragraphs, workshop participants concluded that the so-called "locator/identifier overload" of the IP address semantics one of the causes of the routing scalability problem as we see today. Thus such a "split" seems necessary to scale the routing system, although how to actually architect and implement such a split was not explored in detail. Meyer, et al. Expires June 18, 2007 [Page 7] Internet-Draft IAB Workshop on Routing & Addressing December 2006 2.3. Other Concerns In addition to the issues described in Section 2.1 and Section 2.2, the workshop participants identified several pressing issues that were considered "second tier" issues. These included o General concerns with IPv6 deployment, o Slow routing convergence, and o Misalignment of costs and benefits in the current routing system. The primary issue with IPv6 deployment was that, in the absence of a scalable routing strategy, IPv6 has the potential to exacerbate today's problems simply by the virtue of its much larger address space. The only routing paradigm available today for IPv6 is a combination of CIDR [RFC4632] and provider independent (PI) address allocation strategies [PIPA] (and possibly SHIM6 [SHIM6] when that technology is developed and deployed). Thus the opportunity exists to create a "swamp" (unaggregatable address space) that can be many orders of magnitude larger than what we faced with IPv4. Of course, this is not independent of the concerns raised in both Section 2.1 and Section 2.2. The key takeaway was that the advent of IPv6 and its larger address space has the potential to make these problems much worse if a solution isn't found. Routing convergence was also seen to be an issue that the workshop participants felt needed attention. In particular, the concern was that the growth in the number of routes that service providers must carry will cause routing convergence to become a significant problem. Finally, the workshop participants felt that the costs and benefits in today's routing system are misaligned. While the IETF does not typically consider the "business model" impacts various technology choices directly, many participants felt that perhaps the time has come to review that philosophy. 2.4. How Urgent are these Problems? There was a fairly universal agreement among the workshop participants that the problems outlined in Section 2.1 and Section 2.2 need immediate attention. This need was not because the participants perceived a looming, well-defined "hit the wall" date, but rather because these are difficult problems that to date have resisted solution, that are likely to get more unwieldy as IPv6 deployment proceeds, and that the development and deployment of an effective solution will necessarily take at least a few years. Meyer, et al. Expires June 18, 2007 [Page 8] Internet-Draft IAB Workshop on Routing & Addressing December 2006 3. Current Stresses on the Routing and Addressing System The primary concern voiced by the workshop participants regarding the state of the current Internet routing system was the rapid growth of the DFZ RIB. The number of entries in 2005 ranged from about 150,000 entries to 175,000 entries [BGP2005]; this number has reached 200,000 today [CIDRRPT], and is projected to increase to 370,000 or more within 5 years. Some workshop participants projected that the DFZ could reach 2 million entries within 15 years, and with as many as 10 million multihomed sites by 2050. Another related concern was the number of prefixes changed, added, and withdrawn as a function of time (i.e., BGP UPDATE churn). This has a detrimental impact on routing convergence, since UPDATEs frequently necessitate a re-computation and download of the FIB. For example, in August 2005 alone some 400,000 changes were recorded [BGP2005]. Such UPDATE churn problems are not limited to DFZ routes; indeed, the number of internal routes carried by large ISPs also threatens convergence times, given that such internal routes include more specifics, VPN routes, and other routes that do not appear in the DFZ [ATNAC2006]. Furthermore, some of the properties of BGP were seen as problematic. Although BGP routing updates are propagated between AS neighbors, the number of elements in a RIB or FIB is determined by the total number of IP prefixes being routed in the Internet, and not by the number of ASes or length of AS paths. It was noted that a number of large ASes advertise over 1000 prefixes each [BGP2005]. 3.1. Major Factors Driving Routing Table Growth The growth of the DFZ RIB results from the addition of more prefixes to the table. Although some of this growth is organic (i.e., results simply from growth of the Internet), a large portion of the growth results from de-aggregation of address prefixes (i.e., more specific prefixes). In this section, we discuss in more detail why this alarming trend is accelerating. An increasing fraction of the more-specific prefixes found in the DFZ are due to deliberate action on the part of operators [ATNAC2006]. Motivations to advertise these more-specifics include: o Traffic Engineering, where load is balanced across multiple links through selective advertisement of more-specific routes on different links to adjust the amount of traffic received on each; and Meyer, et al. Expires June 18, 2007 [Page 9] Internet-Draft IAB Workshop on Routing & Addressing December 2006 o Attempts to prevent prefix-hijacking by other operators who might advertise more-specifics to steer traffic toward them; there are several known instances of this behavior today. 3.1.1. Avoiding Renumbering The workshop participants noted that customers generally prefer to have PI address space. Doing so gives them additional agility in selecting ISPs and helps them avoid the need to renumber. Many end- systems use DHCP to assign addresses, so a cursory analysis might suggest renumbering might involve modification of a modest number of routers and servers (perhaps rather than end hosts) at a site that was forced to renumber. In reality, however, renumbering can be more cumbersome because IP addresses are often used for other purposes such as access control lists. They are also sometimes hard-coded into applications used in environments where failure of the DNS would be catastrophic (e.g. some remote monitoring applications). Although renumbering may be a mild inconvenience for some sites and guidelines have been developed for renumbering a network without a flag day [RFC4192], for others the necessary changes are sufficiently difficult that makes renumbering effectively impossible. For these reasons, PI address space is sought by a growing number of customers. Current RIR policy reflects this trend, and their policy is to allocate PI prefixes to all customers who claim a need. Routing PI prefixes requires additional entries in the DFZ routing and forwarding tables. At present, ISPs do not typically charge to route PI prefixes. Therefore, the "costs" of the additional prefixes, in terms of routing table entries and processing overhead, is not born directly by the users of PI space; rather the cost is borne by the global routing system as a whole. Finally, workshop participants observed that no strong disincentive exists to discourage the increasing use of PI address space. 3.1.2. Multihoming Multihoming refers generically to the case in which a site is served by more than one ISP [RFC4116]. There are several reasons for the observed increase in multihoming, including the increased reliance on the Internet for mission and business-critical applications and the general decrease in cost to obtain Internet connectivity. Multihoming provides backup routing-- Internet connection redundancy; in some circumstances multihoming is mandatory due to contract or law. Multihoming can be accomplished using either PI or PA address space, and multihomed sites generally have their own AS numbers (although some do not; this generally occurs when such customers are Meyer, et al. Expires June 18, 2007 [Page 10] Internet-Draft IAB Workshop on Routing & Addressing December 2006 statically routed). A multihomed site using PI address space has its prefixes present in the forwarding and routing tables of each of its providers. For PA space, each prefix allocated from one provider's address allocation will be aggregatable for that provider but not the others. If the addresses are allocated from a 'primary' ISP (i.e. one that the site uses for routing unless a failure occurs), then the additional routing table entries only appear during path failures to that primary ISP. A problem with multihoming arises when a customer's PA IP prefixes are advertised by AS(es) other than their 'primary' ISPs, as the longest-match forwarding rule would force the primary ISPs to de-aggregate its prefixes. 3.1.3. Traffic Engineering Traffic engineering (TE) is the act of arranging for certain Internet traffic to use or avoid certain network paths (that is, TE puts traffic where capacity exists, or where some set of parameters of the path is more favorable to the traffic being placed there). TE is performed by both ISPs and customer networks, for three primary reasons: o First, as mentioned above, to match traffic with network capacity, or spreading the traffic load across multiple links (frequently referred to as "load balancing"). o Second, to reduce the cost by shifting traffic to lower cost paths or by balancing the incoming and outgoing traffic volume to maintain appropriate peering relations. o Finally, TE is sometimes deployed to enforce certain forms of policy (e.g., Canadian government traffic is not permitted to transit through the United States). BGP and the common IGPs (OSPF, IS-IS) provide few tools for traffic engineering, so network operators usually achieve traffic engineering by "tweaking" the processing of routing protocols to achieve desired results. At the BGP level, if the address range requiring TE is a portion of a larger PA address aggregate, network operators implementing TE are forced to de-aggregate otherwise aggregatable prefixes in order to steer the traffic of the particular address range to specific paths. In today's highly competitive environment, the use of TE is mandatory for providers to keep good performance and low cost for each one's own network. However the resulting increase of the DFZ RIB leads to the increased cost of the Internet routing infrastructure as a whole. Meyer, et al. Expires June 18, 2007 [Page 11] Internet-Draft IAB Workshop on Routing & Addressing December 2006 3.2. IPv6 and its potential impact on routing table size Due to the increased IPv6 address size over IPv4, a full immediate transition to IPv6 is estimated to lead to the RIB and FIB sizes increasing by a factor of about four. The size of the routing table based on a more realistic assumption, that of parallel IPv4 and IPv6 routing for many years, is less clear. An increasing amount of allocated IPv6 address prefixes is in PI space. ARIN [ARIN] has relaxed their policy for allocation of such space and has been allocating /48 prefixes when customers request for PI prefixes. Thus, the same pressures affecting IPv4 address allocations also affect IPv6 allocations. 4. Implications of Moore's Law on the Scaling Problem [Editor's note: The information in this section is gathered from presentations given at the workshop. The presentation slides can be retrieved from the pointer provided in Appendix D. It is worth noting that this information has generated quite a bit of discussion since the workshop, and as such requires further community input.] The workshop heard from Tony Li about the relationship between Moore's law and the ability to build cost-effective high-performance routers. Routers are generally required to hold a data structure to encode the FIB in fast memory in a way convenient to execute the longest prefix match (LPM) lookup algorithm. In executing LPM, dedicated hardware will access relatively large fast memories (SRAM) containing the required data structures (e.g. radix tries [RADIX]). [Editor's note: The exact implementation of a high-performance router's RIB and FIB memories is the subject of much debate.] 4.1. Integrated Circuits In 1965 Gordon Moore projected that the density of transistors in integrated circuits could double every two years, with respect to minimum component cost. The period was subsequently adjusted to be between 18-24 months and this conjecture became known as Moore's Law [ML]. The semiconductor industry has been following this density trend for the last 40 or so years. This technology performance trend can, in principal, be achieved by anyone involved in the design and production of integrated circuits. However, the costs are not equal to all players. It is much easier for large-volume manufacturing to track the technology trend at reasonable cost. In particular, large-volume Integrated Circuits (ICs) such as CPUs have been aggressively doing so, sometimes Meyer, et al. Expires June 18, 2007 [Page 12] Internet-Draft IAB Workshop on Routing & Addressing December 2006 improving over the 24 month prediction of Moore's Law. However smaller volume devices (i.e. custom-built router forwarding engine ASICs) cannot ride the same cost curve. In earlier times, high volume production of SRAM was more common due to its use as off-chip cache for supporting commodity CPUs. With the migration of most cache memories to on-chip implementations, the relative cost of off-chip SRAMs has increased due to their decreased volumes. For DRAM, which is used to store RIB data for BGP and IGPs, the speed only improves about 10%/year. Routing performance (i.e. route computation time) scales as approximately T/D where T is the table growth rate and D is the speed improvement of DRAM, and the performance degrades when the value of T is greater than that of D. See [ATNAC2006] for a discussion of some metrics around routing performance. [Editor's note: [ATNAC2006] was not input to the workshop, and is being cited by the editors as additional information for the reader.] 4.2. Heat and Power Transistors consume power both when idle ("leakage current") and when switching. The smaller the transistors, the larger the leakage current. The overall power consumption is not linear with the density increase. Thus, as the need for more powerful routers increases, cooling technology grows more taxed. At present, the existing air cooling system is starting to be a limiting factor for scaling high-performance routers. A key metric for system evaluation is now the unit of forwarding bandwidth per Watt-- [(Mb/s)/W]. About 60% of the power goes to the forwarding engine circuits, with the rest divided between the memories, route processors, and interconnect. Using parallelization to achieve higher bandwidths can aggravate the situation, due to increased power and cooling demands. [Editor's note: Many in the community have commented that heat power utilization and the attendant heat dissipation, along with size limitations of fabrication processes are the current limiting factors.] 5. What is on the Horizon Routing and addressing are two fundamental pieces in the Internet architecture, thus any changes to them will likely impact almost all of the "IP stack", from applications to packet forwarding. In resolving the routing scalability problems, as agreed upon by the workshop attendees, we should aim at a long term solution. This Meyer, et al. Expires June 18, 2007 [Page 13] Internet-Draft IAB Workshop on Routing & Addressing December 2006 requires a clear understanding of various trends in the foreseeable future: the growth in Internet user population, the applications, and the technology. 5.1. Continual Growth The backbone operators expect that the current Internet user population base will continue to expand, as measured by the traffic volume, the number of hosts connected to the Internet, the number of customer networks, and the number of regional providers. 5.2. Large Numbers of Mobile Networks Boeing's Connexion service pioneered the deployment of mobile networks that may change their attachment points to the Internet in a global scale. It is believed that such in-flight Internet connectivity would likely become commonplace in the not-too-distant future. When that happens, there can be multiple thousands of airplane networks in the air at any given time. Given today's DFZ RIB already handles over 200,000 prefixes [CIDRRPT], several thousands of mobile networks, each represented by a single prefix announcement, may not necessarily raise serious routing scalability or stability concerns. However there is an open question regarding whether this number can become substantially larger, if other types of mobile networks, such as networks on trains, come into play. If such mobile networks become commonplace, then their impact on the global routing needs to be assessed. 5.3. Orders of magnitude increase in mobile edge devices Today's technology trend indicates that billions of hand-held gadgets may come on-line in the next several years. There were different opinions regarding whether this would, or would not, bring a significant impact on the global routing scalability. The current solutions for mobile hosts, namely Mobile IP (e.g., [RFC3775]), handle the mobility by one-level of indirection through home agents, thus mobile hosts do not appear any different from a routing perspective than stationary hosts. If we follow the same approach, new mobile devices should not present challenges beyond the increase in the size of the network. The workshop participants recognized that the increase in the number of mobile devices can be significant, and that the introduction of a scalable routing system supporting generic identity-locator separation would enable the support for these billions of mobile gadgets without bringing undue impact on the global routing scalability and stability. Meyer, et al. Expires June 18, 2007 [Page 14] Internet-Draft IAB Workshop on Routing & Addressing December 2006 Further investigation is needed to gain a complete understanding of the implications on the global routing system of connecting many new hand-held devices and sensor networks to the Internet. 6. What Approaches Have Been Investigated Over the years there have been many efforts designed to investigate scalable inter-domain routing for the Internet [I-D.irtf-routing-history]. To benefit from the insights obtained from these past results, the workshop reviewed several major previous and ongoing efforts: 1. The MULTI6 working group's exploration of the solution space and the lessons learned, 2. The solution to multihoming being developed by the SHIM6 Working Group and its pro's and con's, 3. The GSE proposal made by O'Dell in 1997 and its pro's and con's, and 4. Map-and-Encap [RFC1955], a general indirection-based solution to scalable multihoming support. 6.1. Lessons from MULTI6 The MULTI6 working group was chartered to explore the solution space for scalable support of IPv6 multihoming. The numerous proposals collected by MULTI6 Working group generally fell into one of two major categories: resolving the above mentioned conflict by provider- independent address assignments, or by assigning multiple address prefixes to multihomed sites, one for each of its providers, so that all the addresses can be topologically aggregatable. The first category includes proposals of (1) simply allocating provider independent address space, which is effectively the current practice, and (2) assigning IP addresses based on customers geographical locations. The first approach does not scale; the second approach represents a fundamental change to the Internet routing system and its economic model, and imposes undue constraints on ISPs. These proposals were found to be incomplete as they offered no solutions to the new problems they introduced. The majority of the proposals fell into the second category-- assigning multiple address blocks per site. Because IP addresses have been used as identifiers by higher level protocols and applications, these proposals face a fundamental design decision Meyer, et al. Expires June 18, 2007 [Page 15] Internet-Draft IAB Workshop on Routing & Addressing December 2006 regarding which layer should be responsible for mapping the locators (i.e. the multiple addresses received from ISPs) to an identifier. A related question involves which nodes are responsible for handling multiple addresses. One can implement a multi-address scheme at either each individual host or at edge routers of a site, or even both. Handling multiple addresses by edge routers provides the ability to control the traffic flow of the entire site. Conversely, handling multiple addresses by individual hosts offers each host the flexibility to choose different policies for selecting a provider; it also implies changes to all the hosts of a multihomed site. During the process of evaluating all the proposals, two major lessons were learned: o Changing anything in the current practice is hard: for example, inserting an additional header into the protocol would impact IP fragmentation processing, and the current congestion control assumes that each TCP connection follows a single routing path. In addition, operators ask for the ability to perform traffic engineering on a per site basis, and specification of site policy is often interdependent with the IP address structure. o The IP address has been used as an identifier and has been codified into many Internet applications that manipulate IP addresses directly or include IP addresses within the application layer data stream. Thus changing the semantics of an IP address, for example using only the last 64-bit as identifiers as proposed by GSE, will require changes to all such applications. 6.2. SHIM6: Pros and Cons The SHIM6 working group took the second approach from the MULTI6 working group's investigation, i.e. supporting multihoming through the use of multiple addresses. SHIM6 adopted a host-based approach where the host IP stack includes a "shim" that presents a stable "upper layer identifier" (ULID) to the upper layer protocols, but may rewrite the IP packets sent and received so that a currently-working IP address is used in the transmitted packets. When needed, a SHIM6 header is also included in the packet itself, to signal to the remote stack. With SHIM6, protocols above the IP layer use the ULID to identify endpoints (e.g., for TCP connections). The current design suggests choosing one of the locators as the ULID (borrowing a locator to be used as an identifier). This approach makes the implementation compatible with existing IPv6 upper layer protocol implementations and applications. Many of these applications have inherited the long time practice of using IP addresses as identifiers. Meyer, et al. Expires June 18, 2007 [Page 16] Internet-Draft IAB Workshop on Routing & Addressing December 2006 SHIM6 is able to isolate upper layer protocols from multiple IP layer addresses. This enables a multihomed site to use provider-allocated prefixes, one from each of its multiple providers, to facilitate provider-based prefix aggregation. However this gain comes with considerable costs. First, SHIM6 requires modifications to all host stack implementations to support the shim processing. Second, the shim layer must maintain the mapping between the identifier and the multiple locators returned from IPv6 AAAA name resolution, and must take the responsibility to try multiple locators if failures ever occur during the end-to-end communication. At this time the host has little information to determine the order of locators it should use in reaching a multihomed destination, however there is ongoing effort in addressing this issue. As a host-based approach, SHIM6 provides little control to the service provider for effective traffic engineering. At the same time, it also imposes additional state information on the host regarding the multiple locators of the remote communication end. Such state information may not be a significant issue for individual user hosts, but can lead to larger resource demands on large application servers which handle hundreds of thousands simultaneous TCP connections. Yet another major issue with the SHIM6 solution is the need for renumbering when a site changes providers. Although a multihomed site is assigned multiple address blocks, none of them can be treated as a persistent identifier for the site. When the site changes one of its providers, it must purge the address block of that provider from the entire site. The current practice of using the IP address as both an identifier and a locator has been strengthened by the use of IP addresses in access control lists present in various types of policy-enforcement devices (e.g. firewalls). If SHIM6's ULIDs are to be used for policy enforcement, a change of providers may necessitate the re-configuration of many such devices. 6.3. GSE/indirection solutions: Costs and Benefits The use of indirection for scalable multihoming was discussed at the workshop, including the GSE [GSE] and indirection approaches in general. The GSE proposal changes the IPv6 address structure to bear the semantics of both an identifier and a locator. The first n bytes of the 16-byte IPv6 address are called the Routing Goop (RG), and are used by the routing system exclusively as a locator. The last 8 bytes of the IPv6 address specify an interface on an end-system. The middle (16 - n - 8) bytes are used to identify site local topology. The border routers of a site re-write the source RG of each outgoing packet to make the source address part of the source provider's address aggregation; they also re-write the destination RG of each Meyer, et al. Expires June 18, 2007 [Page 17] Internet-Draft IAB Workshop on Routing & Addressing December 2006 incoming packet to hide the site's RG from all the internal routers and hosts. All identifier/locator split proposals require a mapping service that can return a set of locators corresponding to a given identifier. In addition, these proposals must also address the problem of detecting locator failures and redirecting data flows to remaining locators for a multihomed site. GSE proposed to use DNS for providing the mapping service, but it did not offer an effective means for locator failure recovery. GSE also requires host stack modifications, as the upper layers and applications are only allowed to use the lower 8-bytes, rather than the entire, IPv6 address. Finally, the extent to which GSE could be made compatible with increasingly-popular cryptographically-generated addresses (CGA) remains to be determined [dGSE]. 6.4. Futures for Indirection As the saying goes, "There is no problem in computer science that cannot be solved by an extra level of indirection". The GSE proposal can be considered a specific instantiation of a class of indirection based solutions to scalable multihoming. A more general form of this indirection solution, Map-and-Encap [RFC1955], uses tunneling, instead of locator rewriting, to cross the DFZ and support provider- based prefix aggregation. This solution avoids the provider and customer conflicts regarding PA and PI prefixes by putting each in a separate name space, so that ISPs can use topologically aggregatable addresses while customers can have their globally unique and provider-independent identifiers. Thus it supports scalable multihoming, and requires no changes to the end systems when the encapsulation is performed by the border routers of a site. It also requires no changes to the current practice of both applications as well as backbone operations. However, all gains of an effective solution are accompanied with certain associated costs. As stated earlier in the GSE discussion, a mapping service must be provided. This mapping service not only brings with it the associated complexity and cost, but it also adds another point of failure and is a potential target for malicious attacks. Any solution to routing scalability is necessarily a cost/ benefit trade-off. Given the high potential of its gains, this indirection approach deserves special attention in our search for scalable routing solutions. Meyer, et al. Expires June 18, 2007 [Page 18] Internet-Draft IAB Workshop on Routing & Addressing December 2006 7. Problem Statements The fundamental goal of this workshop was to develop a prioritized problem statement regarding the scalability problems facing us today, and the workshop spent a considerable amount of time on reaching that goal. This section provides a description of the prioritized problem statement, together with elaborations on both the rationale and open issues. The workshop participants noted that there exist different classes of stakeholders in the Internet community who view today's global routing system from different angles, and assign different priorities to different aspects of the scalability problem set. The prioritized problem statement in this section is the consensus of the participants in this workshop, which was comprised primarily of large network operators (and a few vendors). It is likely that a different group of participants would produce a different list, or with different priorities. For example, freedom of changing providers without renumbering might make top of the priority list assembled by a workshop of end users and enterprise network operators. 7.1. Problem 1: Routing Scalability The workshop participants believe that routing scalability is the most important problem facing the Internet today and must be solved (note that the time frame in which these problems need solutions was not directly specified). These scalability problems include the size of the DFZ RIB and FIB, the implications of the growth of the RIB and FIB on routing convergence times, and the cost, power (and hence heat dissipation) and ASIC real estate requirements of core router hardware. Another interesting observation is that the power requirements of an ASIC are related to the feature set implemented by that ASIC. [Editor's note: Need citation here?] The DFZ IPv4 RIB has been growing at what appears to be an accelerating rate [DFZ]. If/when IPv6 becomes widely deployed, this problem is expected to get much worse. It is commonly believed that the limited IPv4 address space has imposed constraints on IPv4 RIB growth. Given that the IPv6 routing architecture is the same as the IPv4 architecture (with substantially larger address space), it is natural to predict that routing table growth for IPv6 will only exacerbate the situation. The increasing deployment of VPN/VRF is considered another major factor driving the routing system growth. However there are different views regarding whether this factor has, or does not have, a direct impact to the DFZ RIB. A common practice is to delegate specific routers to handle VPN connections, thus backbone routers do Meyer, et al. Expires June 18, 2007 [Page 19] Internet-Draft IAB Workshop on Routing & Addressing December 2006 not necessarily hold state for individual VPNs. Nevertheless VPNs do represent a scalability challenges in network operations. 7.2. Problem 2: The overloading of IP address semantics As we have reported in Section 3, multihoming, along with traffic engineering, appear to be the major driving factors driving the growth of the DFZ RIB. As mentioned above, computing the FIB, along with the power and real estate requirements of core router ASICs, has become challenging. [Editors note: Need citation] 7.2.1. Definition of Locator and Identifier [Editor's note: pending approval of the workshop participants, we may change the "Locator" and "Identifier" to different names.] Roughly speaking, the Internet comprises a transit backbone network and a large number of customer networks containing hosts that are attached to the backbone. Viewing the Internet as a graph, transit networks have branches and customer networks with hosts hang at the edges as leaves. As its name suggests, locators identify locations in the topology and a network's or host's locator is topologically constrained by its present position. Identifiers, in principal, should be network- topology independent. That is, even though a network or host may need to change its locator because it becomes attached to a different set of points in the Internet, its identifier should remain constant. From an ISP's viewpoint, identifiers identify customer networks and customer hosts. As an example, a non-routable, provider-independent IP prefix for an enterprise network serves as an identifier for that enterprise. This block of IP addresses can be used to route packets inside the enterprise network, however they are are independent from the DFZ topology, that is why they are not globally routable on the Internet. Note that in cases such as the last example, the definition of locators and identifiers can be context-dependent. Following the example further, a PI address may be routable in an enterprise but not the global network. If allowed to be visible in the global network, such addresses might act as identifiers from a backbone operator's point of view but locators from an enterprise operator's point of view. Meyer, et al. Expires June 18, 2007 [Page 20] Internet-Draft IAB Workshop on Routing & Addressing December 2006 7.2.2. Consequence of Locator and Identifier Overloading In today's Internet architecture, IP addresses have been used as both locators and identifiers. Combined with the use of CIDR to perform route aggregation, a problem arises for either providers or customers (or both). Consider, for example, a campus network C that received prefix x.y.z/24 from provider P1. When C multi-homes with a second provider P2, both P1 and P2 must announce x.y.z/24 so that C can be reached through both providers. In this example the prefix x.y.z/24 serves both as an identifier for C, as well as a (non-aggregatable) locator for C's two attachments to the transit system. As far as the DFZ RIB is concerned, the above example shows that customer multihoming blurs the distinction between PA and PI prefixes: although C received a PA prefix x.y.z/24 from P1, nevertheless C's multihoming forced this prefix to be announced globally (equivalent to a PI prefix), and forced the prefix's original owner, provider P1, to de-aggregate. As a result, today's multihoming practice leads to a growth of the routing table size in proportion to the number of multihomed customers. The only practical way to scale a routing system today is topological aggregation, which gets destroyed by customer multihoming. Although multi-homing may blur the PA/PI distinction, there exists a big difference between PA and PI prefixes when a customer changes its provider(s): if the customer has used a PA prefix from a former provider P1, the prefix is supposed to be returned to P1 upon completion of the change. The customer is supposed to get a new prefix from its new provider, i.e. renumbering its network. It is necessary for providers to reclaim their PA prefixes from former customers in order to keep the topological aggregatiblity of their prefixes. On the other hand, renumbering is considered very painful, if not impossible, by many Internet users, especially large enterprise customers. It is not uncommon for IP addresses in such enterprises to penetrate deeply into variously parts of the networking infrastructure, ranging from applications to network management (e.g., policy databases, firewall configurations, etc.). This shows how fragile the system becomes due to the overloading of IP address as both locators and identifiers; significant enterprise operations could be disrupted due to the otherwise simple operation of switching IP address prefix assignment. 7.2.3. Traffic Engineering and IP Address Semantics Overload In today's practice, traffic engineering (TE) is achieved by de- aggregating IP prefixes. One can effectively adjust the traffic Meyer, et al. Expires June 18, 2007 [Page 21] Internet-Draft IAB Workshop on Routing & Addressing December 2006 volume along specific routing paths by adjusting the prefix lengths and the number of prefixes announced through those paths. Thus the very means of TE practice directly conflicts with constraining the routing table growth. On the surface, traffic engineering induced prefix de-aggregation seems orthogonal to the locator-identifier overloading problem. However this may not necessarily be true. Had all the IP prefixes been topologically aggregatable to start with, it would make re- aggregation possible or easier, when the finer granularity prefix announcements propagate further away from their origins. 7.3. Routing Convergence There are two kinds of routing convergence issues, eBGP (global routing) convergence and IGP (enterprise or provider) routing convergence. Generally speaking, eBGP convergence is relatively fast in most cases if one ignores the delay caused by the minimum route advertisement interval (MRAI) timer [RFC4098], except those cases when a route is withdrawn. Route withdrawals tend to suffer from slow convergence; one participant's experience suggests that the withdrawal delays often last a couple of minutes. One may argue that, if the destination becomes unreachable, a long convergence delay would not bring further damage to applications. However, there are cases where a more specific route (a longer prefix) has failed, yet the destination can still be reachable through an aggregated route (a shorter prefix). In these cases the long convergence delay does impact application performance. The IGP convergence can also be very slow, which can lead to intolerable performance problems for real time applications such as VoIP. The cause for this slow convergence can be due to multiple factors, including 1. Delays in detecting physical failures, 2. The delay in loading updated information into the FIB, and 3. The large size of the internal RIB, often twice as big as the DFZ RIB, which can lead to both longer route computation time and the longer FIB loading time. The workshop participants hold different views regarding (1) the severity of the routing convergence problem; and (2) whether it is an architectural problem, or an implementation issue. However, people generally agree that if we solve the routing scalability problem, that will certainly help reduce the convergence delay or make the problem a much easier one to handle simply by reducing the number of Meyer, et al. Expires June 18, 2007 [Page 22] Internet-Draft IAB Workshop on Routing & Addressing December 2006 routes to handle. 7.4. Misaligned Costs and Benefits Today's rapid growth of the DFZ RIB is driven by several major factors, including multihoming, traffic engineering, and organic growth of the Internet's user base. There is a powerful incentive to deploy each of the above features as they bring direct benefits to the parties who make use of them. However, the beneficiaries may not bear the direct costs of the resulting routing table size increase, and there is no measurable or enforceable constraint to limit such increase. For example, suppose that a service provider bandwidth-constrained transoceanic links and wants to splits its prefix announcements in order to fully load each link. The origin AS benefits from performing the de-aggregation, however if the de-aggregated announcements propagate globally, the cost is born by all other ASes. That is, the costs and benefits of this type of TE are not contained. Multihoming provides a similar example (in this case, the multihomed site achieves a benefit, but the global Internet incurs the cost of carrying the additional prefix(es)). The mis-alignment of cost and benefit in the current routing system has been a driver for acceleration of the routing system size growth. 7.5. Other Issues Mobility was among the most frequently mentioned issues at the workshop. It is expected that billions of mobile gadgets may be connected to the Internet in the near future. There was also a discussion on the network connectivity for air travel, such as the Connexion service provided by Boeing over the last few years. However, at this time it seems unclear (1) whether the Boeing-like network mobility support would cause a scaling issue in the routing system (the number of aircraft in the sky is relatively small compared to the current routing table size), and (2) exactly what would be the impact of billions of mobile hosts on the global routing system. These discussions were covered in Section 5 of this report. Routing security is another issue that was brought up a number of times during the workshop. However important routing security may be, it seems out of scope for this workshop given the workshop's goal was to produce a problem statement about routing scalability. It was duly considered that security must be one of the top goals when we get to a solution development stage. It was also noted that, if we continue to allow the routing table to grow indefinitely, then it may be impossible to add security enhancements in the future. Meyer, et al. Expires June 18, 2007 [Page 23] Internet-Draft IAB Workshop on Routing & Addressing December 2006 7.6. Problem Recognition The first step in solving a problem is recognizing its existence. However, recognizing the severity of the routing scaling issue can be a challenge by itself. There does not exist a specific hard limit in the routing system scalability that can be easily demonstrated, nor is there any specific answer to the question of how much time we may have in developing a solution. However, a general consensus among the workshop participants is that we are running out of time. As explained in Section 4, the current RIB growth trend is leading towards cost increases at a rate greater than the nominal depreciation cycle. [Editor's note: There has been quite a bit of discussion about the exact effect of Moore's law on the design and cost of high-end routers. This topic requires more discussion.] 8. Criteria for Solution Development Any common problem statement may admit multiple different solutions. This section provides a set of considerations, as identified from the workshop discussion, over the solution space. Given the heterogeneity among customers and providers of the global Internet, and the elasticity of the problem (as mentioned in the previous section), none of these considerations should inherently preclude any specific solution. Consequently, although the following considerations were initially considered as constraints on solutions, we have instead opted to adopt the term 'criteria' to be used in guiding solution evaluations. 8.1. Criteria on Scalability Clearly, any proposed solution must solve the problem at hand, and our number one problem concerns the scalability of the Internet's routing and addressing system(s) (as outlined in previous sections). Under the assumption of continued increases of multihoming and RFC 2547 VPN [RFC2547] deployment, the solution must enable the routing system to scale gracefully as measured by the number of o DFZ Internet routes, and o Internal routes. In addition, scalable support for traffic engineering (TE) must be considered as a business necessity, not an option. Capacity planning involves placing circuits based on traffic demand over a relatively long time scale, while TE must work more immediately to match the Meyer, et al. Expires June 18, 2007 [Page 24] Internet-Draft IAB Workshop on Routing & Addressing December 2006 traffic load to the existing capacity and to match the routing policy requirements. It was recognized that different parties in the Internet may have different specific TE requirements. For example, o End site TE: based on locally determined performance or cost policies, end sites may wish to control the traffic volume exiting to, or entering from specific providers. o Small ISP to transit ISP TE: operators may face tight resource utilization and wish to influence the volume of entering traffic from both customers and providers along specific routing paths to best utilize the limited resources o Large ISP TE: given the densely connected nature of the Internet topology, a given destination normally can be reached through different routing paths. An operator may wish to be able to adjust the traffic volume sent to each of its peers based on business relations with its neighbor ASes. At this time, it remains an open issue whether a scalable TE solution would be necessarily inside the routing protocol, or can be accomplished through means that are external to the routing system. 8.2. Criteria on Incentives and Economics The workshop attendees concluded that one important reason for uncontrolled routing growth was the misalignment of incentives. New entries are added to the routing system to provide benefit to specific parties, while the cost is born by everyone in the global routing system. The consensus of the workshop was that any proposed solutions should strive to provide incentives to reward practices that reduce the overall system cost, and punish the "bad" behavior which impose undue burden on the global system. [0] The consensus of the workshop was that there no longer can (ever) be a flag day on the Internet. Rather, attendees felt that to bootstrap the deployment of the new solutions, the solutions should provide incentives to first movers. That is, even when a single party starts to deploy the new solution, there should be measurable benefits to balance the costs. Independent of what kind of solutions the IETF develops, if any, attendees felt it was unlikely that the resulting routing system would stay constant in size. Instead, they believed it will continue to grow, and that ISPs will continue to go through system and hardware upgrade cycles. Many attendees expressed a desire that the Meyer, et al. Expires June 18, 2007 [Page 25] Internet-Draft IAB Workshop on Routing & Addressing December 2006 scaling properties of the system can allow the hardware to keep up with the Internet growth at rate comparable to current costs, for example allowing one to keep a 5-year hardware depreciation cycle, as opposed to a situation where scaling leads to accelerating cost increases. 8.3. Criteria on Timing Although there does not exist a specific hard deadline, the unanimous consensus among the workshop participants is that the solution development must start now. That is, even if we can have the solution specification ready within a 1 - 2 year time frame, that will be followed by another 2-year certification cycle. As a result, even in the best case scenario, the workshop participants felt that we are faced with a 3 - 5 year time frame in getting the solutions deployed. 8.4. Consideration on Existing Systems The routing scalability problem is a shared one between IPv4 and IPv6, as IPv6 simply inherited IPv4's CIDR-style "Provider-based Addressing." The proposed solutions should, and are also expected to, solve the problem for both IPv4 and IPv6. Backwards compatibility with the existing IPv4 and IPv6 protocol stack is a necessity. Although a wide deployment of IPv6 is yet to happen, there has been substantial investment into IPv6 implementation and deployment by various parties. IPv6 is considered a legacy with shipped code. Thus a highly desired feature of any proposed solution is to avoid imposing backwards incompatible changes on end hosts (either IPv4 or IPv6). In the routing system itself, the solutions must allow incremental changes from the current operational Internet. The solutions should be backward compatible with the routing protocols in use today, including BGP, OSPF, IS-IS, and others, possibly with incremental enhancements. The data path should support IPv4 and IPv6. The above backward compatibility considerations should not constrain the exploration of the solution space. We need to first find right solutions, and look into their backward compatibility issues after that. This way enables us to gain a full understanding of the tradeoffs, and what potential gains, if any, that we may achieve by relaxing the backward compatibility concerns. As a rule of thumb for successful deployment, for any new design, its chance of success is higher if it makes fewer changes to the existing system. Meyer, et al. Expires June 18, 2007 [Page 26] Internet-Draft IAB Workshop on Routing & Addressing December 2006 8.5. Consideration on Security Securing the routing system is not considered a requirement for the solution development. Security is important; having a working system in the first place is even more important. Security should be considered from day one of solution development. If nothing else, the solutions must not make securing the routing system any worse than the situation today. It is highly desirable to have a solution that makes it more difficult to inject false routing information, and makes it easier to filter out DoS traffic. 8.6. Other Criteria A number of other criteria were also raised which fall into various different categories. They are summarized below. o Site renumbering forced by the routing system should be avoided. o Site reconfiguration driven by the routing system should be minimized. o The solutions should not force ISPs to reveal internal topology. o Routing convergence delay must be under control. o End-to-end data delivery paths should be stable enough for good VoIP performance. 8.7. Understanding the Tradeoff As the old saying goes, every coin has two sides. If we let the routing table continue to grow at its present rate, rapid hardware and software upgrade and replacement cycles for deployed core routing equipment may become cost prohibitive. In the worst case, routing table growth may exceed our ability to engineer the global routing system in an effectively way. On the other hand, solutions for stopping or substantially slowing down the growth in the Internet routing table will necessarily bring their own costs, perhaps elsewhere and in different forms. Examples of such tradeoffs among approaches are presented in Section 6, where we examined the gains and costs of a few different approaches to multihoming (SHIM6, GSE, and a general tunneling approach). A major task in the solution development is to understand who may have to give up what and whether that makes a worthy tradeoff. Before ending this discussion on the solution criteria, it is worth mentioning the shortest presentation at the workshop, which was made Meyer, et al. Expires June 18, 2007 [Page 27] Internet-Draft IAB Workshop on Routing & Addressing December 2006 by Tony Li. He asked a fundamental question: what is at stake? It is the Internet itself. If the routing system does not scale with the continued growth of the Internet, eventually the costs might spiral out of control, the digital divide widen, and the Internet growth slow down, stop, or retreat. Compared to this problem, he considered that none of the criteria mentioned so far (except solving the problem) was important enough to block the development and deployment of an effective solution. 9. Workshop Recommendations The workshop attendees would like to make the following recommendations: First, the workshop participants noted that the concern over the scalability of the routing and addressing system has been with us for a very long time. The factors contributing to these concerns are outlined in Section 3. Further, the participants expressed concern that the current growth rate of the DFZ RIB is exceeding our ability to engineer the routing infrastructure in an economically feasible way. Second, because the participants of this workshop consisted of mostly large service providers and major router vendors, the workshop participants recommend that IAB/IESG organize additional workshops or use other venues of communication to reach out to other stakeholders such as content providers, retail providers, and enterprise operators, both to communicate to them the outcome of this workshop, and to solicit the routing/addressing problems they are facing today, and their requirements on the solution development. Third, the workshop participants recommend conducting the solution development in an open, transparent way, with broad ranging participation from the larger networking community. A majority of the participants indicated their willingness to commit resources toward developing a solution. We must also invite the participation from the research community in this process. The locator-identifier split represents a fundamental architectural issue and IAB should lead the investigation into understanding of both how to make this architectural change and the overall impact of the change. Fourth, given the goal of developing a long term solution, and the fact that development and deployment cycles will necessarily take some time, it may be helpful (or even necessary) to buy some time through engineering feasible short or intermediate term solutions (e.g., FIB compression). Meyer, et al. Expires June 18, 2007 [Page 28] Internet-Draft IAB Workshop on Routing & Addressing December 2006 Fifth, the workshop participants believe the next step is to develop a roadmap from here to the solution deployment. The IAB and IESG are expected to take on the leadership role in this roadmap development, and to leverage on the momentum from this successful workshop to move forward quickly. The roadmap should provide clearly defined short, medium, and long term objectives to guide the solution development process, so that the community as a whole can proceed in an orchestrated way, seeing exactly where we are going when engineering necessary short term fixes. Finally, the workshop participants also made a number of suggestions to IETF regarding specific steps towards a quick solution development. These suggestions are captured in Appendix A. 10. Acknowledgments Jari Arkko, Vince Fuller, Darrel Lewis, Tony Li, Eric Rescorla, and Ted Seely made many insightful comments on earlier versions of this document. Finally, many thanks to Wouter Wijngaards for the fine notes he took during the workshop. 11. Security Considerations While the security of the routing system is of great concern, this document introduces no new protocol or protocol usage and as such presents no new security issues. 12. References [RFC1955] Hinden, R., "New Scheme for Internet Routing and Addressing (ENCAPS) for IPNG", RFC 1955, June 1996. [RFC2547] Rosen, E. and Y. Rekhter, "BGP/MPLS VPNs", RFC 2547, March 1999. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [RFC4098] Berkowitz, H., Davies, E., Hares, S., Krishnaswamy, P., and M. Lepp, "Terminology for Benchmarking BGP Device Convergence in the Control Plane", RFC 4098, June 2005. [RFC4116] Abley, J., Lindqvist, K., Davies, E., Black, B., and V. Gill, "IPv4 Multihoming Practices and Limitations", RFC 4116, July 2005. Meyer, et al. Expires June 18, 2007 [Page 29] Internet-Draft IAB Workshop on Routing & Addressing December 2006 [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering an IPv6 Network without a Flag Day", RFC 4192, September 2005. [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, August 2006. [I-D.irtf-routing-history] Doria, A. and E. Davies, "Analysis of IDR requirements and History Group B contribution", draft-irtf-routing-history-00 (work in progress), February 2002. [ARIN] "American Registry for Internet Numbers", http://www.arin.net/index.shtml. [ROFL] "ROFL: Routing on Flat Labels", SIGCOMM 2006, http:// sigcomm06.stanford.edu/discussion-beta/ getpaper.php?paper_id=34& PHPSESSID=10ece185c9ee5f7e136921fc743b2401, 2006. [CNIR] "Compact Name-Independent Routing with Minimum Stretch", ACM Symposium on Parallel Algorithms and Architectures, http://citeseer.ist.psu.edu/710757.html, 2004. [GSE] "GSE - An Alternate Addressing Architecture for IPv6", Internet Draft, http://www.watersprings.org/pub/id/ draft-ietf-ipngwg-gseaddr-00.txt, 1997. [dGSE] "An Overview of Multihoming and Open Issues in GSE", http://www.isoc.org/tools/blogs/ietfjournal/ ?p=98#more-98, 2006. [PIPA] "IPv4 Address Allocation and Assignment Policies for the RIPE NCC Service Region", RIPE-387 http://www.ripe.net/docs/ipv4-policies.html, 2006. [SHIM6] "Site Multihoming by IPv6 Intermediation (shim6)", http://www.ietf.org/html.charters/shim6-charter.html, 2006. [DFZ] "Growth of the BGP Table - 1994 to Present", Huston, G., http://bgp.potaroo.net, 2006. [GIH] "Wither Routing?", Huston, Meyer, et al. Expires June 18, 2007 [Page 30] Internet-Draft IAB Workshop on Routing & Addressing December 2006 G., http://www.potaroo.net/ispcol/2006-11/raw.html, 2006. [ATNAC2006] "Projecting Future IPv4 Router Requirements from Trends in Dynamic BGP Behaviour", Huston, G., http:// www.potaroo.net/papers/phd/atnac-2006/bgp-atnac2006.pdf, 2006. [CIDRRPT] "The CIDR Report", http://www.cidr-report.org, 2006. [BGP2005] "2005 -- A BGP Year in Review", Huston, G., http://potaroo.net/presentations/index.html, 2005. [ML] "Moore's Law", Wikipedia http://en.wikipedia.org/wiki/Moore's_law, 2006. [RADIX] "Radix Tree", Wikipedia http://en.wikipedia.org/wiki/Patricia_trie, 2006. [EID] "Endpoints and Endpoint Names: A Proposed Enhancement to the Internet Architecture", Chiappa, N. http://www.chiappa.net/~jnc/tech/endpoints.txt, 1999. Appendix A. Suggestions for Specific Steps At the end of the workshop there was a lively round-table discussion regarding specific steps that IETF may consider undertaking towards a quick solution development, as well as potential issues to avoid. Those steps included: o Finding a home (mailing list) to continue the discussion started from the workshop with wider participation. [Editor's note: Done -- This action has been completed. The list is ram@iab.org.] o Considering a special process to expedite solution development, avoiding the lengthy protocol standardization cycles. For example IESG may charter special design teams for the solution investigation. o If a working group is to be formed, care must be taken to ensure that the scope of the charter is narrow and specific enough to allow quick progress, and that the WG chair be forceful enough to keep the WG activity focused. There was also a discussion on which area this new WG should belong to; both routing area ADs and Internet area AD are willing to host it. Meyer, et al. Expires June 18, 2007 [Page 31] Internet-Draft IAB Workshop on Routing & Addressing December 2006 o It is desirable that the solutions be developed in open environment and free from any Intellectual property right claims. Finally, given the perceived severity of the problem at hand, the workshop participants trust that IAB/IESG/IETF will take prompt actions. However if that were not to happen, operators and vendors would be most likely to act on their own and get a solution deployed. Appendix B. Workshop Participants Loa Anderson (IAB) Jari Arkko (IESG) Ron Bonica Ross Callon (IESG) Brian Carpenter (IESG Chair) David Conrad (IANA) Leslie Daigle (IAB Chair) Elwyn Davies (IAB) Terry Davis Weisi Dong Kevin Fall (IAB) Aaron Falk (IRTF Chair) Dino Farinacci Vince Fuller Vijay Gill Russ Housely (IESG) Geoff Huston Daniel Karrenberg Dorian Kim Olaf Kolkman (IAB) Darrel Lewis Kurtis Lindqvist (IAB) Tony Li Peter Lothberg David Meyer (IAB) Christopher Morrow Dave Oran (IAB) Phil Roberts (IAB Executive Director) Jason Schiller Peter Schoenmaker Ted Seely Mark Townsley (IESG) Iljitsch van Beijnum Ruediger Volk Magnus Westerlund (IESG) Lixia Zhang (IAB) Meyer, et al. Expires June 18, 2007 [Page 32] Internet-Draft IAB Workshop on Routing & Addressing December 2006 Appendix C. Workshop Agenda IAB Routing and Addressing Workshop Agenda October 18-19 Amsterdam, Netherlands DAY 1: the proposed goal is to collect, as complete as possible, a set of scalability problems in the routing and addressing area facing the Internet today. 0815-0900: Welcome, framing up for the 2 days Moderator: Leslie Daigle 0900-1200: Morning session Moderator: Elwyn Davies Strawman topics for the morning session: - Scalability - Multihoming support - Traffic Engineering - Routing Table Size: Rate of growth, Dynamics (this is not limited to DFZ, include iBGP) - Causes of the growth - Pains from the growth (perhaps "Impact on routers" can come here?) - How big a problem is BGP slow convergence? 1015-1030: Coffee Break 1200-1300: Lunch 1330-1730: Afternoon session: What are the top 3 routing problems in your network? Moderator: Kurt Erik Lindqvist 1500-1530: Coffee Break Dinner at Indrapura (http://www.indrapura.nl), sponsored by Cisco --------- DAY 2: The proposed goal is to formulate a problem statement 0800-0830: Welcome 0830-1000: Morning session: What's on the table Moderator: TBD - shim6 - GSE Meyer, et al. Expires June 18, 2007 [Page 33] Internet-Draft IAB Workshop on Routing & Addressing December 2006 1000-1030: Coffee Break 1030-1200: Problem Statement session #1: document the problems Moderator: David Meyer 1200-1300: Lunch 1300-1500: Problem Statement session # 2, cont; Moderator: TBD - Constraints on solutions 1500-1530: Coffee Break 1530-1730: Summary and Wrap-up Moderator: Leslie Daigle Appendix D. Presentations The presentations from the workshop can be found on http://www.iab.org/about/workshops/routingandaddressing Authors' Addresses David Meyer (editor) Email: dmm@1-4-5.net Lixia Zhang (editor) Email: lixia@cs.ucla.edu Kevin Fall (editor) Email: kfall@intel.com Meyer, et al. Expires June 18, 2007 [Page 34] Internet-Draft IAB Workshop on Routing & Addressing December 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). 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 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. 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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). Meyer, et al. Expires June 18, 2007 [Page 35]