Internet Engineering Task Force H. Asai Internet-Draft H. Esaki Intended status: Informational U. Tokyo Expires: December 17, 2010 T. Momose Cisco Systems June 15, 2010 A Solution Approach for AS Relationships-aware Overlay Routing draft-asai-cross-domain-overlay-00 Abstract This document provides an idea of cross-domain cost estimation to control cross-domain traffic in overlay routing and to reduce transit traffic, which costs more for Internet service providers. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on December 17, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Asai, et al. Expires December 17, 2010 [Page 1] Internet-Draft AS Relationships-aware Overlay Routing June 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. AS . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.2. AS Relationships . . . . . . . . . . . . . . . . . . . 3 1.1.3. Transit . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.4. Peering . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.5. Overlay Network . . . . . . . . . . . . . . . . . . . 4 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Cross-Domain Traffic of Overlay Networks . . . . . . . . . 5 2.2. Cross-Domain Cooperation . . . . . . . . . . . . . . . . . 6 2.3. Non-disclosure AS Relationships . . . . . . . . . . . . . 7 2.4. Problems with the ALTO Approach . . . . . . . . . . . . . 8 3. Solution Approach . . . . . . . . . . . . . . . . . . . . . . 9 3.1. AS Path Provision Service . . . . . . . . . . . . . . . . 10 3.2. AS Relationships Estimation Service . . . . . . . . . . . 11 3.3. Cost Computation Service . . . . . . . . . . . . . . . . . 12 4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16 7. Informative References . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 Asai, et al. Expires December 17, 2010 [Page 2] Internet-Draft AS Relationships-aware Overlay Routing June 2010 1. Introduction Peer-to-peer (P2P) technologies have been introduced in many systems such as content delivery networks and video streaming systems. These P2P technologies have enabled to avoid excessive server load and to achieve effective and high-quality communication (e.g., high throughput, fault tolerance). Today, the traffic generated by P2P applications become a significant amount of the Internet traffic [RFC5693]. Since P2P applications construct their own network topologies over the Internet without taking into account the network layer topology (i.e., layer 3 topology), these P2P applications frequently utilize a larger amount of network resources than network providers expect. This document provides an idea of cross-domain cost estimation to control cross-domain traffic in overlay routing and to reduce transit traffic which costs more for network providers by taking into account the economical relationships among autonomous systems (ASes) [RFC1930], with hiding confidential information as much as possible. 1.1. Terminology We use the following terms in this document. 1.1.1. AS Autonomous System 1.1.2. AS Relationships AS relationships represent the economical relationships between interconnected ASes. AS relationships are categorized into two major types: transit and peering. 1.1.3. Transit Transit is a type of AS relationships. Transit relationships are also called provider-customer relationships. Customer ASes purchase Internet access from their transit providers over transit links by paying some amount of money according to the actual bandwidth usage. 1.1.4. Peering Peering is a type of AS relationships, and the relationships between two peering ASes are equal relationships. Traffic exchanged over peering links is free of charge. Asai, et al. Expires December 17, 2010 [Page 3] Internet-Draft AS Relationships-aware Overlay Routing June 2010 1.1.5. Overlay Network Overlay networks are constructed by application-layer nodes. We refer to not only P2P networks but also client-server content delivery networks whose servers are located at multiple points as overlay networks. 1.2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Asai, et al. Expires December 17, 2010 [Page 4] Internet-Draft AS Relationships-aware Overlay Routing June 2010 2. Problem Statement The Internet consists of thousands of ASes which are operated by distinct network providers such as commercial Internet service providers (ISPs), companies and universities. Each AS normally connects with multiple ASes, and there are distinct charging policies for each inter-AS link. These charging policies are roughly categorized into two major types of relationships; transit (with charge) and peering (without any charge). From the economical viewpoint, network providers want to reduce the traffic volume exchanged with transit providers as much as possible, and consequently, they manage the routing policies as explained in [Wang03]. However, overlay networks sometimes break the routing policies and cause problems about the cross-domain traffic. We summarize the problems with overlay networks as follows. o The cross-domain traffic generated by applications are neither controlled nor optimized. o ASes hardly cooperate with each other in computing and fairly balancing cost when ASes provide some cost information to applications as a traffic optimization metric because charging policies are complicated and each AS operates its network autonomously. o Neither AS relationships nor charging policies for transit traffic can be disclosed. 2.1. Cross-Domain Traffic of Overlay Networks Network providers cannot control nor optimize the cross-domain traffic generated by applications on overlay networks. This is because traffic is controlled by algorithms of each application such as peer/neighbor/path selection algorithms. Asai, et al. Expires December 17, 2010 [Page 5] Internet-Draft AS Relationships-aware Overlay Routing June 2010 +------+ provider | AS 1 |----------------------+ provider +------+ | transit | transit | v v customer +------+ peering +------+ +------+ customer | AS 2 |<------->| AS 3 | | AS 4 | +------+ +------+ +------+ AS 2 purchases Internet access from AS 1 via a transit link. On the contrary, the link between AS 2 and AS 3 is peering, which is lower cost link from the viewpoint of AS 2 operators. Figure 1: An example of the relationships among ASes We show an example of the problem of cross-domain traffic of overlay networks. An example of interconnections of ASes and their relationships is shown in Figure 1. Suppose mirror servers exist in both AS 3 and AS and a client in AS 2 is retrieving a file from one of these mirror servers, the client should select a mirror server in AS 3 to reduce transit charge for both the client-side and server- side ASes, but current clients which are unaware to AS relationships often select other servers. Moreover, on P2P overlay networks, the connectivity of end-point nodes (i.e., peers) is provided by residential ISPs and most of them are not transit providers but transit customers. Therefore, it is significantly important to control the transit traffic not to increase their charge to their providers though these kinds of application-layer traffic are hardly controlled by ISPs. [RFC5693] also claims the problem of the cross-domain traffic in terms of transit cost as well as congestion in intra-domain networks. 2.2. Cross-Domain Cooperation +------+ provider | AS 1 |----------------------+ provider +------+ 1 | transit 5 | transit | 30 v v 10 customer +------+ peering +------+ +------+ customer | AS 2 |<------->| AS 3 | | AS 4 | +------+ 10 20 +------+ +------+ Each number represents egress cost. Figure 2: An example of unfair cost setting Asai, et al. Expires December 17, 2010 [Page 6] Internet-Draft AS Relationships-aware Overlay Routing June 2010 The ALTO Working Group has worked on application-layer traffic optimization, and it has proposed a protocol to provide end-to-end cost between peers [I-D.ietf-alto-protocol]. Cost computation of this protocol is based on P4P [Xie08] which is an oracle-based approach of application-layer traffic optimization and has achieved the fair utilization of network resources by setting up priorities which are automatically computed from the configuration (e.g., `cost' in OSPF) in routers to links. However, there is a problem with these oracle-based approaches when they are applied to the Internet (i.e., multi-domain system). Charging policies for inter-AS links and exchanged traffic volume are so complicated that different ASes hardly cooperate with each other in computing and fairly balancing cost. This is because each AS aims to maximize its income and minimize its expense. This problem is similar to so-called hot-potato problems. For example, suppose egress cost of each inter-AS link is configured autonomously (i.e., each AS sets cost according to its own policies) as shown in Figure 2, then the accumulated cost of the path from AS 4 to AS 2 becomes larger than that of the path from AS 3 to AS 2 though the path from AS 3 to AS 2 seems to be better than the other. On the other hand, when we consider ingress cost setting, cost on the source is ignored. Thus, oracle-based approaches hardly achieve fair traffic optimization among multiple autonomous domains because the Internet is autonomously operated by each AS. 2.3. Non-disclosure AS Relationships To achieve AS relationships-aware overlay routing, applications should take into account AS relationships or charging policies among ASes. So, cross-domain cost is required to be unveiled or estimated, and provided. The ALTO protocol [I-D.ietf-alto-protocol] provides end-to-end cost based on P4P [Xie08], but it does not mention how to cooperate with each AS. Interconnections between ASes are established by commercial contracts, and consequently, most ISPs cannot disclose their commercial relationships. Hence, there is a difficulty in applying the approach of cross-domain cost computation in P4P to the real Internet because issues on disclosing topology information such as confidential commercial contracts lie upon it. Even though ASes can exchange the cost of cross-domain links, the problem of cross-domain cooperation described in Section 2.2 still exists. Asai, et al. Expires December 17, 2010 [Page 7] Internet-Draft AS Relationships-aware Overlay Routing June 2010 2.4. Problems with the ALTO Approach +-------------+-----------------------------------------------------+ | | Problems | +-------------+-----------------------------------------------------+ | Cooperation | Require to set coordinated cost onto inter-AS | | | links, but each AS is autonomously operated | | | | | Security | Require to exchange the cross-domain cost among | | | ALTO services, i.e., require to disclose AS | | | relationships, though AS relationships are | | | non-disclosure ones | +-------------+-----------------------------------------------------+ Table 1: Problems with the ALTO approach We summarize the problems with the ALTO approach in Table 1. Asai, et al. Expires December 17, 2010 [Page 8] Internet-Draft AS Relationships-aware Overlay Routing June 2010 3. Solution Approach This section describes an approach to solve the problems which have been figured out in Section 2, and the requirements. In this approach, the cost computation for AS paths between any two ASes consists of three services, as follows. 1. AS path provision service: This service provides AS paths between two arbitrary nodes (IP addresses) to applications, and it is provided by each AS. 2. AS relationships estimation service: This service provides AS relationships (i.e., cross-domain cost) of any specified inter-AS links to applications. This service is provided by its service providers which may not be ISPs but some other volunteer service providers. 3. Cost computation service: This service computes cost for an AS path according to an algorithm, and it is installed into each application. The computed cost for the AS path would be used for traffic optimization. It is true that AS paths can be resolved from IP address-based paths, which can be retrieved by network management tools (e.g., traceroute). Hence, ASes do not have to provide AS paths because applications can resolve AS paths without support of ASes. However, it is an ongoing work to assign appropriate AS numbers to routers [Huffaker10]. Moreover, some ISPs block ICMP packets including ICMP time exceed messages, and consequently, IP address- based paths are not always resolved. Therefore, provision of AS paths by ASes is enough helpful to resolve AS paths and use them for AS relationships-aware application-layer traffic optimization. Thus, it is recommended for each AS to be implemented. A method for providing AS path to applications is described in Section 3.1. This approach aims to hide information on AS relationships as much as possible; i.e., not to disclose AS relationships. So, it uses AS relationships estimated from publicly available information instead of AS relationships which are to be disclosed by ASes. This document provide one possible estimation method and the detailed description follows in Section 3.2. Cost for a path which would be used for the traffic optimization is computed from the estimated AS relationships by a certain algorithm. This document does not define any specific algorithms but provides an example as an idea in Section 3.3. Asai, et al. Expires December 17, 2010 [Page 9] Internet-Draft AS Relationships-aware Overlay Routing June 2010 +------------------------+--------------------------+---------------+ | Service | Service provider | Requirement | | | | level | +------------------------+--------------------------+---------------+ | * AS path provision | Each AS | RECOMMENDED | | | | | | * AS relationships | Volunteer service | REQUIRED | | estimation | providers etc. | | | | | | | * Cost computation | Each application | REQUIRED | +------------------------+--------------------------+---------------+ Table 2: Requirements These services and the requirements of this approach are summarized in Table 2. AS relationships estimation and cost computation services are REQUIRED ones for taking into account AS relationships. AS path provision service is not mandatory but recommended one because this function can be alternated by other mechanisms. 3.1. AS Path Provision Service +--------------+ | Applications | +--------------+ | ^ AS paths request | | AS paths response (src X, dst Y) | | (AS path from X to Y) - -- -- -- -- -- | -- | -- -- -- -- -- -- -- -- -- -- -- -- -- - v | +---------------------------+ | AS path provision service | | +---------------------+ | | | Interface w/ filter | | | +---------------------+ | | | ^ | | | | | | v | | ______ | +-----------------+ | routing table / \ | | AS paths table |<---------------------* BGP * | | lookup function | | w/ AS paths * router * | +-----------------+ | \______/ +---------------------------+ Figure 3: System overview of AS path provision service As described above, AS path provision by ASes helps applications to resolve AS paths. Here, note that AS paths can be easily retrieved Asai, et al. Expires December 17, 2010 [Page 10] Internet-Draft AS Relationships-aware Overlay Routing June 2010 from BGP routing tables at ASes' BGP routers. The overview of the AS path provision system is shown in Figure 3. The requirements of AS path provision are listed below. o AS path provision service discovery: A mechanism which enables applications to discover AS path provision servers is required. (This document does not define this service discovery protocol.) o AS path provision service: A mechanism which enables applications to resolve AS path from an IP address belonging to the AS which provides the AS path provision service to another IP address belonging to an arbitrary AS via a certain protocol is required. Here, note that the source IP address of the request must belong to the AS providing the service because AS paths are retrieved from routing tables in BGP routers and a routing table has a spanning tree from the AS as root (i.e., the source AS). (This document does not define the protocol.) o Filter: AS path provision services can deny some requests by a filter to hide their information. 3.2. AS Relationships Estimation Service Several AS relationships inference or estimation algorithms have been proposed in the research field. There are two types of these algorithms; one is based on paths analysis [Gao01] and the other is based on differences in AS' network size [Asai09]. The algorithms based on paths analysis have a difficulty in applying the inferred AS relationships to the cost computation because there are lots of missing links, which have not been inferred. The algorithms based on differences in AS' network size first quantify the network size, then estimate the relationships. Therefore, the relationships can be estimated for almost all links because one BGP routing table contains almost all ASes though there exist lots of missing links, which are not contained in the routing table but would be possibly observed at other points. Thus, this document uses the algorithms based on differences in AS' network size. Here, we provide a possible estimation method. Degree, the number of neighboring ASes, has been commonly used as an indicator which represents AS' network size. Degree for each AS is approximately counted from publicly available datasets such as public BGP routing tables (e.g., Route Views Project [RouteViews]) and Internet routing registries. If the degree of AS X is larger than that of AS Y, AS X is considered to be transit provider of AS Y. If the degree of AS X is nearly equal to that of AS Y, the link between AS X and AS Y is considered to be peering. Thus, the relationships (i.e., cost) are Asai, et al. Expires December 17, 2010 [Page 11] Internet-Draft AS Relationships-aware Overlay Routing June 2010 estimated from publicly available information. Note that [Asai09] has improved the accuracy of this estimation. +--------------+ | Applications | +--------------+ | ^ AS relationships request | | AS relationships response (AS X, AS Y) | | (AS relationships of X--Y) - -- -- -- -- -- -- -- -- | -- | -- -- -- -- -- -- -- -- -- -- - v | +-------------------------------------+ | AS relationships estimation service | | +---------------------+ | | | Interface | | | +---------------------+ | | | ^ | | | | | | v | | | +----------------------+ | +----------------+ | | AS relationships |<-------| datasets | | | estimation algorithm | | | (AS adjacency) | | +----------------------+ | +----------------+ +-------------------------------------+ Figure 4: System overview of AS relationships estimation service Figure 4 shows the system overview of AS relationships estimation service. In this figure, the AS relationships estimation service calculates degree from AS adjacency datasets, which can be approximated from public BGP routing tables etc., and then it provides the estimated AS relationships from degree. Note that degree can be replaced by the magnitude defined in [Asai09]. 3.3. Cost Computation Service Cost for a path is computed from the estimated AS relationships by a certain cost computation algorithm. Cost computation services on applications compute the cost. +------+ +------+ +------+ +------+ | AS S |-->| AS X |--> ... -->| AS Y |-->| AS T | +------+ +------+ +------+ +------+ Suppose AS S and AS T are the source AS and the destination AS, respectively, on this AS path. The cost computation algorithm takes into account only edge relationships, i.e., the relationships between AS S and AS X, and AS Y and AS T. Asai, et al. Expires December 17, 2010 [Page 12] Internet-Draft AS Relationships-aware Overlay Routing June 2010 Figure 5: AS path and a cost computation algorithm This document provides an example of cost computation algorithms with a paper in research field. There is a research on application-layer traffic optimization in content delivery networks for reducing transit traffic by taking into account the AS relationships with degree [Asai10]. In [Asai10], only the relationships between edge (i.e., source and destination) AS and their neighbors are considered for the cost computation. The cost for the AS path shown in Figure 5 can be computed in the following equation: cost = {log(degree-of(S)) - log(degree-of(X))} + {log(degree-of(T)) - log(degree-of(Y))}. Here, function ``degree-of(X)'' returns the degree of AS X, and AS relationships (i.e., cross-domain cost) for each inter-AS link (e.g., {log(degree-of(S)) - log(degree-of(X))} and {log(degree-of(T)) - log(degree-of(Y))} in Figure 5) are resolved via AS relationships estimation services described in Section 3.2. [Asai10] has shown from a simulation that their method has reduced the percentage of high-cost transit traffic (i.e., traffic from/to provider) in inter-domain traffic on residential ASes by 8.46 percentage point compared to minimum AS hop selection though the total amount of inter-domain traffic has not been changed. Cost computation services run on not any servers but applications, so the algorithms can be modified by applications. Note that application service providers can provide the cost computation service if they need to control the computation algorithm. Asai, et al. Expires December 17, 2010 [Page 13] Internet-Draft AS Relationships-aware Overlay Routing June 2010 4. Discussion This section discusses the cooperation with the ALTO approach. The proposed solution approach in this document is applicable only for cross-domain cost estimation. In another word, The proposed solution approach does not mention the intra-domain traffic optimization. This document figured out the problem with the ALTO approach for cross-domain cost estimation in Section 2. Hence, the proposed solution approach can be used as a complementary element of the ALTO approach to compute cross-domain cost. Asai, et al. Expires December 17, 2010 [Page 14] Internet-Draft AS Relationships-aware Overlay Routing June 2010 5. IANA Considerations No need to describe any request regarding number assignment. Asai, et al. Expires December 17, 2010 [Page 15] Internet-Draft AS Relationships-aware Overlay Routing June 2010 6. Security Considerations This document requests that all residential ISPs should provide AS paths in their routing tables. Some ISPs do not want to reveal the information on the AS paths because they consider that it can cause security problems. On the other hand, AS paths are probably resolved by network management tools such as ``traceroute'' though they sometimes fail. Therefore, AS path provision service can be OPTIONAL. The requirement level of AS path provision should be discussed in greater detail by considering the trade-off between security and accuracy.. Asai, et al. Expires December 17, 2010 [Page 16] Internet-Draft AS Relationships-aware Overlay Routing June 2010 7. Informative References [RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, selection, and registration of an Autonomous System (AS)", BCP 6, RFC 1930, March 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic Optimization (ALTO) Problem Statement", RFC 5693, October 2009. [I-D.ietf-alto-protocol] Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol", draft-ietf-alto-protocol-04 (work in progress), May 2010. [Asai09] Asai, H. and H. Esaki, "A Methodology for Magnitude-based Inter-AS Distance Estimation", The Tenth Workshop on Internet Technology - WIT2009, 2009. [Asai10] Asai, H. and H. Esaki, "Towards Interdomain Transit Traffic Reduction in Peer-assisted Content Delivery Networks", 14th International Telecommunications Network Strategy and Planning Symposium, 2010 (to appear). [Gao01] Gao, L., "On inferring autonomous system relationships in the Internet", IEEE/ACM Transactions on Networking, Vol. 9, No. 6, pp. 733-745, 2001. [Huffaker10] Huffaker, B., Dhamdhere, A., and Fomenkov, M., "Toward Topology Dualism: Improving the Accuracy of AS Annotations for Routers", Passive and Active Measurement: 11th International Conference, PAM 2010, pp. 101-110, 2010. [RouteViews] University of Oregon, "University of Oregon Route Views Project", . [Wang03] Wang, F. and L. Gao, "On Inferring and Characterizing Internet Routing Policies", IMC '03: Proceedings of the 3rd ACM SIGCOMM conference on Internet measurement, pp. 15-26, 2003. [Xie08] Xie, H., Yang, Krishnamurthy, A., Liu, and A. Silberschatz, "P4P: provider portal for applications", SIGCOMM '08: Proceedings of the ACM SIGCOMM 2008 Asai, et al. Expires December 17, 2010 [Page 17] Internet-Draft AS Relationships-aware Overlay Routing June 2010 conference on Data communication, pp. 351-362, 2008. Asai, et al. Expires December 17, 2010 [Page 18] Internet-Draft AS Relationships-aware Overlay Routing June 2010 Authors' Addresses Hirochika Asai The University of Tokyo 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656 JP Phone: +81 3 5841 6748 Email: panda@hongo.wide.ad.jp Hiroshi Esaki The University of Tokyo 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656 JP Phone: +81 3 5841 6748 Email: hiroshi@wide.ad.jp Tsuyoshi Momose Cisco Systems G.K. 2-1-1 Nishi-Shinjuku Shinjuku-ku, Tokyo 163-0409 JP Phone: +81 3 5324 4154 Email: tmomose@cisco.com Asai, et al. Expires December 17, 2010 [Page 19]