ALTO WG K. Gao Internet-Draft Tsinghua University Intended status: Standards Track Y. Lee Expires: December 20, 2019 Huawei S. Randriamasy Nokia Bell Labs Y. Yang Yale University J. Zhang Tongji University June 18, 2019 ALTO Extension: Path Vector Cost Type draft-ietf-alto-path-vector-06 Abstract The Application-Layer Traffic Optimization (ALTO) protocol [RFC7285] has defined cost maps and endpoint cost maps to provide basic network information. However, they provide only scalar (numerical or ordinal) cost mode values, which are insufficient to satisfy the demands of solving more complex network optimization problems. This document introduces an extension to the base ALTO protocol, namely the path-vector extension, which allows ALTO clients to query information such as the capacity region for a given set of flows (called co-flows). A non-normative example called co-flow scheduling is presented to illustrate the limitations of existing ALTO endpoint cost maps. After that, details of the extension are defined. 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]. 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 https://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 Gao, et al. Expires December 20, 2019 [Page 1] Internet-Draft ALTO Extension: Path Vector June 2019 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 20, 2019. Copyright Notice Copyright (c) 2019 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Use Case: Capacity Region for Co-Flow Scheduling . . . . . . 5 4. Overview of Path Vector Extensions . . . . . . . . . . . . . 7 4.1. New Cost Mode to Encode Path Vectors . . . . . . . . . . 7 4.2. New ALTO Entity Domain for ANE Properties . . . . . . . . 8 4.3. Multipart/Related Resource for Consistency . . . . . . . 8 5. Path-Vector Cost Type . . . . . . . . . . . . . . . . . . . . 9 5.1. Cost Mode: path-vector . . . . . . . . . . . . . . . . . 10 5.2. Cost Metric: Link Maximum Reservable Bandwidth . . . . . 10 6. ANE Domain . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Domain Name . . . . . . . . . . . . . . . . . . . . . . . 11 6.2. Domain-Specific Entity Identifier . . . . . . . . . . . . 11 6.3. Hierarchy and Inheritance . . . . . . . . . . . . . . . . 11 7. Multipart Filtered Cost Map for Path Vector . . . . . . . . . 11 7.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . 11 7.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 11 7.3. Accept Input Parameters . . . . . . . . . . . . . . . . . 12 7.4. Capabilities . . . . . . . . . . . . . . . . . . . . . . 12 7.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.6. Response . . . . . . . . . . . . . . . . . . . . . . . . 12 8. Multipart Endpoint Cost Service for Path Vector . . . . . . . 13 8.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . 13 8.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 13 8.3. Accept Input Parameters . . . . . . . . . . . . . . . . . 13 8.4. Capabilities . . . . . . . . . . . . . . . . . . . . . . 13 Gao, et al. Expires December 20, 2019 [Page 2] Internet-Draft ALTO Extension: Path Vector June 2019 8.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . 14 8.6. Response . . . . . . . . . . . . . . . . . . . . . . . . 14 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.1. Information Resource Directory Example . . . . . . . . . 14 9.2. Example #1 . . . . . . . . . . . . . . . . . . . . . . . 16 9.3. Example #2 . . . . . . . . . . . . . . . . . . . . . . . 17 9.4. Example for Incremental Update . . . . . . . . . . . . . 19 10. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 20 10.1. Compatibility with Base ALTO Clients/Servers . . . . . . 20 10.2. Compatibility with Multi-Cost Extension . . . . . . . . 21 10.3. Compatibility with Incremental Update . . . . . . . . . 21 11. General Discussions . . . . . . . . . . . . . . . . . . . . . 21 11.1. Provide Calendar for Property Map . . . . . . . . . . . 21 11.2. Constraint Tests for General Cost Types . . . . . . . . 22 11.3. General Multipart Resources Query . . . . . . . . . . . 22 12. Security Considerations . . . . . . . . . . . . . . . . . . . 22 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 13.1. ALTO Cost Mode Registry . . . . . . . . . . . . . . . . 23 13.2. ALTO Entity Domain Registry . . . . . . . . . . . . . . 23 13.3. ALTO Property Type Registry . . . . . . . . . . . . . . 24 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 15.1. Normative References . . . . . . . . . . . . . . . . . . 24 15.2. Informative References . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 1. Introduction The base ALTO protocol [RFC7285] is designed to expose network information through services such as cost maps and endpoint cost service. These services use an extreme "single-node" network abstraction, which represents a whole network as a single node, and hosts as "endpoint groups" directly connected to the node. Although the "single-node" abstraction works well in many settings, it lacks the ability to support emerging use cases, such as co-flow scheduling for large-scale data analytics. For such a use case, applications require a more powerful network view abstraction beyond the "single-node" abstraction. To support capabilities like co-flow scheduling, this document uses a "path vector" abstraction to represent more detailed network graph information like capacity regions. A path vector is a sequence of abstract network elements (ANEs), and each ANE represents a network device that end-to-end traffic goes through, such as links, switches, middleboxes, and their aggregations. An ANE can have properties such as "bandwidth", and "delay". Providing such information can help Gao, et al. Expires December 20, 2019 [Page 3] Internet-Draft ALTO Extension: Path Vector June 2019 both applications to achieve better application performance and networks to avoid network congestion. Providing path vector abstraction using ALTO introduces the following additional requirements (ARs): AR-1: The path vector abstraction requires the encoding of array- like cost values rather than scalar cost values in cost maps or endpoint cost maps. Specifically, the path vector abstraction requires the specification of the sequence of ANEs between sources and destinations. Such a sequence, however, cannot be encoded by the scalar types (numerical or ordinal) which the base ALTO protocol supports. AR-2: The path vector abstraction requires the encoding of the properties of aforementioned ANEs. Specifically, only the sequences of ANEs are not enough for existing use cases. Properties of ANEs such as "bandwidth" and "delay" are needed by applications to properly construct network constraints or states. AR-3: The path vector abstraction requires consistent encoding of path vectors (AR-1) and the properties of the ANEs in a path vector (AR-2). Specifically, path vectors and the properties of ANEs in the vectors are dependent. A mechanism to query both of them consistently is necessary. This document proposes the path vector extension to the ALTO protocol to satisfy these additional requirements . Specifically, the extension encodes the array (AR-1) of ANEs over an end-to-end path using a new cost type, and conveys the properties of ANEs (AR-2) using unified property map [I-D.ietf-alto-unified-props-new]. The path vector and ANE properties are conveyed in a single message encoded as a multipart/ related message to satisfy AR-3. The rest of this document is organized as follows. Section 3 gives an example of co-flow scheduling and illustrates the limitations of the base ALTO protocol in such a use case. Section 4 gives an overview of the path vector extension. Section 5 introduces a new cost type. Section 6 registers a new domain in Domain Registry. Section 7 and Section 8 define new ALTO resources to support Path Gao, et al. Expires December 20, 2019 [Page 4] Internet-Draft ALTO Extension: Path Vector June 2019 Vector query by using the request format of Filtered Cost Map and Endpoint Cost Service. Section 9 presents several examples. Section 10 and Section 11 discusses compatibility issues with other existing ALTO extensions and design decisions. Section 12 and Section 13 review the security and IANA considerations. 2. Terminology Besides the terms defined in [RFC7285] and [I-D.ietf-alto-unified-props-new], this document also uses the following additional terms: Abstract Network Element and Path Vector. o Abstract Network Element (ANE): An abstract network element is an abstraction of network components. It can be an aggregation of links, middleboxes, virtualized network function (VNF), etc. An abstract network element has two types of attributes: a name and a set of properties. o Path Vector: A path vector is an array of ANEs. It presents an abstract network path between source/destination points such as PIDs or endpoints. 3. Use Case: Capacity Region for Co-Flow Scheduling Assume that an application has control over a set of flows, which may go through shared links or switches and share a bottleneck. The application hopes to schedule the traffic among multiple flows to get better performance. The capacity region information for those flows will benefit the scheduling. However, existing cost maps cannot reveal such information. Specifically, consider a network as shown in Figure 1. The network has 7 switches (sw1 to sw7) forming a dumb-bell topology. Switches sw1/sw3 provide access on one side, sw2/sw4 provide access on the other side, and sw5-sw7 form the backbone. Endhosts eh1 to eh4 are connected to access switches sw1 to sw4 respectively. Assume that the bandwidth all links are 100 Mbps. Gao, et al. Expires December 20, 2019 [Page 5] Internet-Draft ALTO Extension: Path Vector June 2019 +------+ | | --+ sw6 +-- / | | \ PID1 +-----+ / +------+ \ +-----+ PID2 eh1__| |_ / \ ____| |__eh2 | sw1 | \ +--|---+ +---|--+ / | sw2 | +-----+ \ | | | |/ +-----+ \_| sw5 +---------+ sw7 | PID3 +-----+ / | | | |\ +-----+ PID4 eh3__| |__/ +------+ +------+ \____| |__eh4 | sw3 | | sw4 | +-----+ +-----+ Figure 1: Raw Network Topology. The single-node ALTO topology abstraction of the network is shown in Figure 2. +----------------------+ {eh1} | | {eh2} PID1 | | PID2 +------+ +------+ | | | | {eh3} | | {eh4} PID3 | | PID4 +------+ +------+ | | +----------------------+ Figure 2: Base Single-Node Topology Abstraction. Consider an application overlay (e.g., a large data analysis system) which wants to schedule the traffic among a set of end host source- destination pairs, say eh1 -> eh2 and eh3 -> eh4. The application can request a cost map providing end-to-end available bandwidth, using "availbw" as cost-metric and "numerical" as cost-mode. The application will receive from ALTO server that the bandwidth of eh1 -> eh2 and eh3 -> eh4 are both 100 Mbps. But this information is not enough. Consider the following two cases: o Case 1: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw6 -> sw7 -> sw2 -> eh2 and eh3 -> eh4 uses path eh3 -> sw3 -> sw5 -> sw7 -> sw4 -> eh4, then the application will obtain 200 Mbps. Gao, et al. Expires December 20, 2019 [Page 6] Internet-Draft ALTO Extension: Path Vector June 2019 o Case 2: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw7 -> sw2 -> eh2 and eh3 -> eh4 uses the path eh3 -> sw3 -> sw5 -> sw7 -> sw4 -> eh4, then the application will obtain only 100 Mbps due to the shared link from sw5 to sw7. To allow applications to distinguish the two aforementioned cases, the network needs to provide more details. In particular: o The network needs to expose more detailed routing information to show the shared bottlenecks; o The network needs to provide the necessary abstraction to hide the real topology information while providing enough information to applications. The path vector extension defined in this document provides a solution to address the preceding issue. See [I-D.bernstein-alto-topo] for a more comprehensive survey of use cases where extended network topology information is needed. 4. Overview of Path Vector Extensions This section presents an overview of approaches adopted by the path vector extension. It assumes that the readers are familiar with cost map and endpoint cost service defined in [RFC7285]. The path vector extension also requires the support of Filtered Property Map defined in [I-D.ietf-alto-unified-props-new]. The path vector extension is composed of three building blocks: (1) a new cost mode to encode path vectors in a cost map or an endpoint cost map; (2) a new ALTO entity domain to enable ANE property encoding using the unified property extension [I-D.ietf-alto-unified-props-new]; and (3) a generic mechanism to put multiple ALTO information objects in a single response to enforce consistency, to preserve modularity and to avoid complex linking of multiple responses. 4.1. New Cost Mode to Encode Path Vectors Existing cost modes defined in [RFC7285] allow only scalar cost values. However, the "path vector" abstraction requires to convey vector format information (AR-1). To fulfill this requirement, this document defines a new "cost-mode" named path vector to indicate that the cost value is an array of ANEs. A path vector abstraction should be computed for a specific performance metric, and this is achieved using the existing "cost-metric" component of cost type. The details of the new "cost-mode" is given in Section 5. Gao, et al. Expires December 20, 2019 [Page 7] Internet-Draft ALTO Extension: Path Vector June 2019 4.2. New ALTO Entity Domain for ANE Properties A path vector of ANEs contains only the abstracted routing elements between a source and a destination. Hence, an application can find shared ANEs of different source-destination pairs but cannot know the shared ANEs' properties. For the capacity region use case in Section 3, knowing that eh1->eh2 and eh3->eh4 share ANEs but not the available bandwidth of the shared ANEs, is not enough. To encode ANE properties like the available bandwidth in a path vector query response, this document uses the unified property extension defined in [I-D.ietf-alto-unified-props-new]. Specifically, for each path vector query, the ALTO server generates a property map associated to the (endpoint) cost map as follows: o a dynamic entity domain of an entity domain type "ane" is generated to contain the generated ANEs. Each ANE has the same unique identifier in the path vectors and in the dynamic entity domain; o each entity in this dynamic entity domain has the property defined by the "cost-metric" that generated the ANEs in the query. Detailed information and specifications are given in Section 6. 4.3. Multipart/Related Resource for Consistency Path vectors and the property map containing the ANEs are two different types of objects, but they require strong consistency. One approach to achieving strong consistency is to define a new media type to contain both objects, but this violates modular design. Another approach is to provide the objects in two different information resources. Thus, an ALTO client needs to make separate queries to get the information of related services. This may cause a data synchronization problem between two queries. Also, as the generation of ANE is dynamic, an ALTO server must cache the results of a query before a client fully retrieves all related resources, which hurts the scalability and security of an ALTO server. This document uses standard-conforming usage of "multipart/related" media type defined in [RFC2387] to elegantly solve the problem. Specifically, using "multipart/related" needs to address two issues: o ALTO uses media type to indicate the type of an entry in the information resource directory (IRD) (e.g., "application/alto- costmap+json" for cost map and "application/alto- Gao, et al. Expires December 20, 2019 [Page 8] Internet-Draft ALTO Extension: Path Vector June 2019 endpointcostmap+json" for endpoint cost map). Simply putting "multipart/related" as the media type, however, makes it impossible for an ALTO client to identify the type of service provided by related entries. o The ALTO SSE extension (see [I-D.ietf-alto-incr-update-sse]) depends on resource-id to identify push updates, but resource-id is provided only in IRD and hence each entry in the IRD has only one resource-id. This design addresses the two issues as follows: o To address the first issue, the multipart/related media type includes the type parameter to allow type indication of the root object. For a cost map service, the "media-type" will be "multipart/related" with the parameter "type=application/alto- costmap+json"; for an endpoint cost map service, the parameter will be "type=application/alto-endpointcostmap+json". This design is highly extensible. The entries can still use "application/ alto-costmapfilter+json" or "application/alto- endpointcostparams+json" as the accept input parameters, and hence an ALTO client still sends the filtered cost map request or endpoint cost service request. The ALTO server sends the response as a "multipart/related" message. The body of the response includes two parts: the first one is of the media type specified by the "type" parameter; the second one is a property map associated to the first map. o To address the second issue, each part of the "multipart/related" response message has the MIME part header information including "Content-Type" and "Resource-Id". An ALTO server MAY generate incremental updates (see [I-D.ietf-alto-incr-update-sse]) for each part separately using the "Resource-Id" header. By applying the design above, for each path vector query, an ALTO server returns the path vectors and the associated property map modularly and consistently. An ALTO server can reuse the data models of the existing information resources. And an ALTO client can subscribe to the incremental updates for the dynamic generated information resources without any changes, if th ALTO server provides incremental updates for them. 5. Path-Vector Cost Type This document extends the cost types defined in Section 6.1 of [RFC7285] by introducing a new cost mode "path-vector". In the rest of the document, we use "path-vector" to indicate the cost type with the cost-mode "path-vector" for short. Gao, et al. Expires December 20, 2019 [Page 9] Internet-Draft ALTO Extension: Path Vector June 2019 5.1. Cost Mode: path-vector This document extends the CostMode defined in Section 10.5 of [RFC7285] with a new cost mode: "path-vector". This cost mode indicates that every cost value in a cost map represents an array of ANEs which are defined in Section 6.2, rather than a JSON number or a ranking order. The ANEs computed by the ALTO server associate to the cost metric for the "path-vector" cost mode. This document re-defines some cost metrics for "path-vector", which are motivated by the co-flow scheduling use case. The ALTO client SHOULD ignore the "path-vector" cost mode with any other cost metrics, unless the future documents define other cost metrics or specify the semantics of existing cost metrics for "path-vector" cost mode for some additional requirements. 5.2. Cost Metric: Link Maximum Reservable Bandwidth This document uses the same metric name, units of measurement and measurement point(s) with potential measurement domain defined by section 4.1 of [I-D.ietf-alto-performance-metrics], but specifies different metric description and method of measurement or calculation for "path-vector" cost mode only. Metric Description: When used with "path-vector" cost mode, it is to specify the path vector computed by using the spatial and temporal maximum reservable bandwidth over each network link. The value of the maximum reservable bandwidth of each ANE in the path vector is specified in the associated property map. Method of Measurement or Calculation: The value of Maximum Reservable Bandwidth is the bandwidth measured between two directly connected IS-IS neighbors, OSPF neighbors or BGP neighbors. The associated ANEs are computed by some algorithm which can guarantee the equivalent Maximum Reservable Bandwidth constraints. 6. ANE Domain This document specifies a new ALTO entity domain called "ane" in addition to the ones in [I-D.ietf-alto-unified-props-new]. The ANE domain associates property values with the ANEs in a network. The entity in ANE domain is often used in the path vector by cost maps or endpoint cost resources. Accordingly, the ANE domain always depends on a cost map or an endpoint cost map. Gao, et al. Expires December 20, 2019 [Page 10] Internet-Draft ALTO Extension: Path Vector June 2019 6.1. Domain Name ane 6.2. Domain-Specific Entity Identifier The entity identifier of ane domain is encoded as a JSON string. The string MUST be no more than 64 characters, and it MUST NOT contain characters other than US-ASCII alphanumeric characters (U+0030-U+0039, U+0041-U+005A, and U+0061-U+007A), the hyphen ("-", U+002D), the colon (":", U+003A), the at sign ("@", code point U+0040), the low line ("_", U+005F), or the "." separator (U+002E). The "." separator is reserved for future use and MUST NOT be used unless specifically indicated in this document, or an extension document. To simplify the description, we use "ANE name" to indicate the identifier of an entity in ANE domain in this document. The ANE name is usually unrelated to the physical device information. It is usually generated by the ALTO server on demand and used to distinguish from other ANEs in its dependent cost map or endpoint cost map. 6.3. Hierarchy and Inheritance There is no hierarchy or inheritance for properties associated with ANEs. 7. Multipart Filtered Cost Map for Path Vector This document introduces a new ALTO resource called Multipart Filtered Cost Map resource, which allows an ALTO server to provide other ALTO resources associated to the Cost Map resource in the same response. 7.1. Media Type The media type of the Multipart Filtered Cost Map Resource is "multipart/related;type=application/alto-costmap+json". 7.2. HTTP Method The Multipart Filtered Cost Map is requested using the HTTP POST method. Gao, et al. Expires December 20, 2019 [Page 11] Internet-Draft ALTO Extension: Path Vector June 2019 7.3. Accept Input Parameters The input parameters of the Multipart Filtered Cost Map MUST be encoded as a JSON object in the body of an HTTP POST request. The media type of the request MUST be one of "application/alto- costmapfilter+json". The format of the request body MUST be the same type as defined by section 11.3.2.3 of [RFC7285]. 7.4. Capabilities The Multipart Filtered Cost Map resource uses the same capabilities as defined by section 11.3.2.4 of [RFC7285]. But the "cost-type- names" field SHOULD only includes cost types in "path-vector" cost mode. Otherwise, the ALTO client SHOULD ignore a cost type in other cost mode, unless additional documents define the specification of it for the Multipart Filtered Cost Map resource. 7.5. Uses The resource ID of the network map based on which the PIDs in the returned cost map will be defined. 7.6. Response The response MUST indicate an error, using ALTO protocol error handling, as defined in Section 8.5 of [RFC7285], if the request is invalid. The response to a valid request MUST be a "multipart/related" message as defined by [RFC2387]. The body consists of two parts: o the first part MUST include "Resource-Id" and "Content-Type" in its header. The value of "Resource-Id" MUST be prefixed by the resource id of the Multipart Filtered Cost Map appended by a "." character. The body of this part MUST be a JSON object with the same format as defined in Section 11.2.3.6 of [RFC7285]; The JSON object MUST include the "vtag" field in the "meta" field, which provides the version tag of the returned cost map. The resource id of the version tag MUST be as same as the value of the "Resource-Id" header. The "meta" field MUST also include the "dependent-vtags" field, whose value is a single-element array to indicate the version tag of the network map used, where the network map is specified in the "uses" attribute of the Multipart Cost Map resource in IRD. o the second part MUST also include "Resource-Id" and "Content-Type" in its header. The value of "Resource-Id" MUST be prefixed by the resource id of the Multipart Filtered Cost Map appended by a "." Gao, et al. Expires December 20, 2019 [Page 12] Internet-Draft ALTO Extension: Path Vector June 2019 character. The body of this part MUST be a JSON object with the same format as defined in Section 4.6 of [I-D.ietf-alto-unified-props-new]. The JSON object MUST include the "dependent-vtags" field in the "meta" field. The value of the "dependent-vtags" field MUST be an array with a single VersionTag object as defined by section 10.3 of [RFC7285]. The "resource-id" of this VersionTag MUST be the value of "Resource-Id" header of the first part. The "tag" of this VersionTag MUST be the "tag" of "vtag" of the first part body. 8. Multipart Endpoint Cost Service for Path Vector This document introduces a new ALTO resource called Multipart Endpoint Cost resource, which allows an ALTO server to provide other ALTO resources associated to the Endpoint Cost resource in the same response. 8.1. Media Type The media type of the Multipart Endpoint Cost Resource is "multipart/related;type=application/alto-endpointcostmap+json". 8.2. HTTP Method The Multipart Endpoint Cost resource is requested using the HTTP POST method. 8.3. Accept Input Parameters The input parameters of the Multipart Endpoint Cost resource MUST be encoded as a JSON object in the body of an HTTP POST request. The media type of the request MUST be one of "application/alto- endpointcostparams+json". The format of the request body MUST be the same type as defined by section 11.5.1.3 of [RFC7285]. 8.4. Capabilities The Multipart Endpoint Cost resource uses the same capabilities as defined by section 11.3.2.4 of [RFC7285]. But the "cost-type-names" field SHOULD only includes cost types in "path-vector" cost mode. Otherwise, the ALTO client SHOULD ignore a cost type in other cost mode, unless additional documents define the specification of it for the Multipart Endpoint Cost resource. Gao, et al. Expires December 20, 2019 [Page 13] Internet-Draft ALTO Extension: Path Vector June 2019 8.5. Uses The Multipart Endpoint Cost resource MUST NOT specify the "uses" attribute. 8.6. Response The response MUST indicate an error, using ALTO protocol error handling, as defined in Section 8.5 of [RFC7285], if the request is invalid. The response to a valid request MUST be a "multipart/related" message as defined by [RFC2387]. The body consists of two parts: o the first part MUST include "Resource-Id" and "Content-Type" in its header. The value of "Resource-Id" MUST be prefixed by the resource id of the Multipart Filtered Cost Map appended by a "." character (U+002E). The body of this part MUST be a JSON object with the same format as defined in Section 11.5.1.6 of [RFC7285]; The JSON object MUST include the "vtag" field in the "meta" field, which provides the version tag of the returned endpoint cost map. The resource id of the version tag MUST be as same as the value of the "Resource-Id" header. o the second part MUST also include "Resource-Id" and "Content-Type" in its header. The value of "Resource-Id" MUST be prefixed by the resource id of the Multipart Filtered Cost Map appended by a "." character (U+002E). The body of this part MUST be a JSON object with the same format as defined in Section 4.6 of [I-D.ietf-alto-unified-props-new]. The JSON object MUST include the "dependent-vtags" field in the "meta" field. The value of the "dependent-vtags" field MUST be an array with a single VersionTag object as defined by section 10.3 of [RFC7285]. The "resource-id" of this VersionTag MUST be the value of "Resource-Id" header of the first part. The "tag" of this VersionTag MUST be the "tag" of "vtag" of the first part body. 9. Examples This section lists some examples of path vector queries and the corresponding responses. 9.1. Information Resource Directory Example Here is an example of an Information Resource Directory. In this example, the "cost-map-pv" information resource provides a Multipart Cost Map resource for path-vector; the "endpoint-cost-pv" information resource provides a MultipartEndpoint Cost resource for path-vector. Gao, et al. Expires December 20, 2019 [Page 14] Internet-Draft ALTO Extension: Path Vector June 2019 Both of them support the Maximum Reservable Bandwidth ("maxresbw") cost metric in "path-vector" cost mode. { "meta": { "cost-types": { "pv-maxresbw": { "cost-mode": "path-vector", "cost-metric": "maxresbw" } } }, "resources": { "my-default-networkmap": { "uri" : "http://alto.example.com/networkmap", "media-type" : "application/alto-networkmap+json" }, "cost-map-pv": { "uri": "http://alto.example.com/costmap/pv", "media-type": `multipart/related; type=application/alto-costmap+json`, "accepts": "application/alto-costmapfilter+json", "capabilities": { "cost-type-names": [ "pv-maxresbw" ] }, "uses": [ "my-default-networkmap" ] }, "endpoint-cost-pv": { "uri": "http://alto.exmaple.com/endpointcost/pv", "media-type": `multipart/related; type=application/alto-endpointcost+json`, "accepts": "application/alto-endpointcostparams+json", "capabilities": { "cost-type-names": [ "pv-maxresbw" ] } }, "update-pv": { "uri": "http://alto.example.com/updates/pv", "media-type": "text/event-stream", "uses": [ "endpoint-cost-pv" ], "accepts": "application/alto-updatestreamparams+json", "capabilities": { "support-stream-control": true } } } } Gao, et al. Expires December 20, 2019 [Page 15] Internet-Draft ALTO Extension: Path Vector June 2019 9.2. Example #1 Query filtered cost map to get the path vectors. POST /costmap/pv HTTP/1.1 Host: alto.example.com Accept: multipart/related; type=application/alto-costmap+json, application/alto-error+json Content-Length: [TBD] Content-Type: application/alto-costmapfilter+json { "cost-type": { "cost-mode": "path-vector", "cost-metric": "maxresbw" }, "pids": { "srcs": [ "PID1" ], "dsts": [ "PID2", "PID3" ] } } HTTP/1.1 200 OK Content-Length: [TBD] Content-Type: multipart/related; boundary=example-1; start=cost-map-pv.costmap type=application/alto-costmap+json --example-1 Resource-Id: cost-map-pv.costmap Content-Type: application/alto-costmap+json { "meta": { "vtag": { "resource-id": "cost-map-pv.costmap", "tag": "d827f484cb66ce6df6b5077cb8562b0a" }, "dependent-vtags": [ { "resource-id": "my-default-networkmap", "tag": "75ed013b3cb58f896e839582504f6228" } ], "cost-type": { "cost-mode": "path-vector", "cost-metric": "maxresbw" Gao, et al. Expires December 20, 2019 [Page 16] Internet-Draft ALTO Extension: Path Vector June 2019 } }, "cost-map": { "PID1": { "PID2": [ "ane:L001", "ane:L003" ], "PID3": [ "ane:L001", "ane:L004" ] } } } --example-1 Resource-Id: cost-map-pv.propmap Content-Type: application/alto-propmap+json { "meta": { "dependent-vtags": [ { "resource-id": "cost-map-pv.costmap", "tag": "d827f484cb66ce6df6b5077cb8562b0a" } ] }, "property-map": { "ane:L001": { "maxresbw": 100000000}, "ane:L003": { "maxresbw": 150000000}, "ane:L004": { "maxresbw": 50000000} } } 9.3. Example #2 Gao, et al. Expires December 20, 2019 [Page 17] Internet-Draft ALTO Extension: Path Vector June 2019 POST /endpointcost/pv HTTP/1.1 Host: alto.example.com Accept: multipart/related; type=application/alto-endpointcost+json, application/alto-error+json Content-Length: [TBD] Content-Type: application/alto-endpointcostparams+json { "cost-type": { "cost-mode": "path-vector", "cost-metric": "maxresbw" }, "endpoints": { "srcs": [ "ipv4:192.0.2.2" ], "dsts": [ "ipv4:192.0.2.89", "ipv4:203.0.113.45", "ipv6:2001:db8::10" ] } } HTTP/1.1 200 OK Content-Length: [TBD] Content-Type: multipart/related; boundary=example-2; start=endpoint-cost-pv.ecs type=application/alto-endpointcost+json --example-2 Resource-Id: endpoint-cost-pv.ecs Content-Type: application/alto-endpointcost+json { "meta": { "vtags": { "resource-id": "endpoint-cost-pv.ecs", "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef" }, "cost-type": { "cost-mode": "path-vector", "cost-metric": "maxresbw" } }, "endpoint-cost-map": { "ipv4:192.0.2.2": { "ipv4:192.0.2.89": [ "ane:L001", "ane:L003", "ane:L004" ], "ipv4:203.0.113.45": [ "ane:L001", "ane:L004", "ane:L005" ], Gao, et al. Expires December 20, 2019 [Page 18] Internet-Draft ALTO Extension: Path Vector June 2019 "ipv6:2001:db8::10": [ "ane:L001", "ane:L005", "ane:L007" ] } } } --example-2 Resource-Id: endpoint-cost-pv.propmap Content-Type: application/alto-propmap+json { "meta": { "dependent-vtags": [ { "resource-id": "endpoint-cost-pv.ecs", "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef" } ] }, "property-map": { "ane:L001": { "maxresbw": 50000000 }, "ane:L003": { "maxresbw": 48000000 }, "ane:L004": { "maxresbw": 55000000 }, "ane:L005": { "maxresbw": 60000000 }, "ane:L007": { "maxresbw": 35000000 } } } 9.4. Example for Incremental Update In this example, an ALTO client subscribe the incremental update for the Multipart Endpoint Cost resource "endpoint-cost-pv". POST /updates/pv HTTP/1.1 Host: alto.example.com Accept: text/event-stream Content-Type: application/alto-updatestreamparams+json Content-Length: [TBD] { "add": { "ecspvsub1": { "resource-id": "endpoint-cost-pv", "input": } } } Gao, et al. Expires December 20, 2019 [Page 19] Internet-Draft ALTO Extension: Path Vector June 2019 Based on the server process defined in [I-D.ietf-alto-incr-update-sse], the ALTO server will send the control-uri first using Server-Sent Event (SSE), and follow the full response of the multipart message. HTTP/1.1 200 OK Connection: keep-alive Content-Type: text/event-stream event: application/alto-updatestreamcontrol+json data: {"control-uri": "http://alto.example.com/updates/streams/1414"} event: multipart/related;boundary=example-3;start=pvmap; type=application/alto-endpointcost+json,ecspvsub1 data: --example-3 data: Content-ID: pvmap data: Content-Type: application/alto-endpointcost+json data: data: data: --example-3 data: Content-ID: nepmap data: Content-Type: application/alto-propmap+json data: data: data: --example-3-- Then, the ALTO server will subscribe the whole tree of the multipart message automatically. When the data updated, the ALTO server will publish the data updates for each node in this tree separately. event: application/merge-patch+json,ecspvsub1.pvmap data: event: application/merge-patch+json,ecspvsub2.nepmap data: 10. Compatibility 10.1. Compatibility with Base ALTO Clients/Servers The Multipart Filtered Cost Map resource and the Multipart Endpoint Cost resource has no backward compatibility issue with the base ALTO clients and servers. Although these two types of resources reuse the media types defined in the base ALTO protocol for the accept input parameters, they have different media types for responses. If the ALTO server provides these two types of resources, but the ALTO Gao, et al. Expires December 20, 2019 [Page 20] Internet-Draft ALTO Extension: Path Vector June 2019 client does not support them, the ALTO client will ignore the resources without conducting any incompatibility. 10.2. Compatibility with Multi-Cost Extension This document does not specify how to integrate the "path-vector" cost mode with the multi-cost extension [RFC8189]. Although there is no reason why somebody has to compound the path vectors with other cost types in a single query, there is no compatible issue doing it without constraint tests. 10.3. Compatibility with Incremental Update As this document still follows the basic request/response protocol with JSON encoding, it is surely compatible with the incremental update service as defined by [I-D.ietf-alto-incr-update-sse]. But the following details are to be noticed: o When using the compound response, updates on both cost map and property map SHOULD be notified. o When not using the compound response, because the cost map is in the "uses" attribute of the property map, once the path vectors in the cost map change, the ALTO server MUST send the updates of the cost map before the updates of the property map. 11. General Discussions 11.1. Provide Calendar for Property Map Fetching the historical network information is useful for many traffic optimization problem. [I-D.ietf-alto-cost-calendar] already proposes an ALTO extension called Cost Calendar which provides the historical cost values using Filtered Cost Map and Endpoint Cost Service. However, the calendar for only path costs is not enough. For example, as the properties of ANEs (e.g., available bandwidth and link delay) are usually the real-time network states, they change frequently in the real network. It is very helpful to get the historical value of these properties. Applications may predicate the network status using these information to better optimize their performance. So the coming requirement may be a general calendar service for the ALTO information resources. Gao, et al. Expires December 20, 2019 [Page 21] Internet-Draft ALTO Extension: Path Vector June 2019 11.2. Constraint Tests for General Cost Types The constraint test is a simple approach to query the data. It allows users to filter the query result by specifying some boolean tests. This approach is already used in the ALTO protocol. [RFC7285] and [RFC8189] allow ALTO clients to specify the "constraints" and "or-constraints" tests to better filter the result. However, the current defined syntax is too simple and can only be used to test the scalar cost value. For more complex cost types, like the "array" mode defined in this document, it does not work well. It will be helpful to propose more general constraint tests to better perform the query. In practice, it is too complex to customize a language for the general-purpose boolean tests, and can be a duplicated work. So it may be a good idea to integrate some already defined and widely used query languages (or their subset) to solve this problem. The candidates can be XQuery and JSONiq. 11.3. General Multipart Resources Query Querying multiple ALTO information resources continuously MAY be a general requirement. And the coming issues like inefficiency and inconsistency are also general. There is no standard solving these issues yet. So we need some approach to make the ALTO client request the compound ALTO information resources in a single query. 12. Security Considerations This document is an extension of the base ALTO protocol, so the Security Considerations [RFC7285] of the base ALTO protocol fully apply when this extension is provided by an ALTO server. The path vector extension requires additional considerations on two security considerations discussed in the base protocol: confidentiality of ALTO information (Section 15.3 of [RFC7285]) and availability of ALTO service (Section 15.5 of [RFC7285]). For confidentiality of ALTO information, a network operator should be aware of that this extension may introduce a new risk: the path vector information may make network attacks easier. For example, as the path vector information may reveal more network internal structures than the more abstract single-node abstraction, an ALTO client may detect the bottleneck link and start a distributed denial- of-service (DDoS) attack involving minimal flows to conduct the in- network congestion. Gao, et al. Expires December 20, 2019 [Page 22] Internet-Draft ALTO Extension: Path Vector June 2019 To mitigate this risk, the ALTO server should consider protection mechanisms to reduce information exposure or obfuscate the real information, in particular, in settings where the network and the application do not belong to the same trust domain. But the implementation of path vector extension involving reduction or obfuscation should guarantees the constraints on the requested properties are still accurate. For availability of ALTO service, an ALTO server should be cognizant that using path vector extension might have a new risk: frequent requesting for path vectors might conduct intolerable increment of the server-side storage and break the ALTO server. It is known that the computation of path vectors is unlikely to be cacheable, in that the results will depend on the particular requests (e.g., where the flows are distributed). Hence, the service providing path vectors may become an entry point for denial-of-service attacks on the availability of an ALTO server. To avoid this risk, authenticity and authorization of this ALTO service may need to be better protected. Even if there is no intentional attack, the dependent property map of path vector might be still dynamically enriched, in that every new request for path vectors will make the ALTO server generate a new property map. So the properties of the abstract network elements can consume a large amount of resources when cached. To avoid this, the ALTO server providing the path vector extension should support a time-to-live configuration for the property map, so that the outdated entries can be removed from the property map resource. 13. IANA Considerations 13.1. ALTO Cost Mode Registry This document specifies a new cost mode "path-vector". However, the base ALTO protocol does not have a Cost Mode Registry where new cost mode can be registered. This new cost mode will be registered once the registry is defined either in a revised version of [RFC7285] or in another future extension. 13.2. ALTO Entity Domain Registry As proposed in Section 9.2 of [I-D.ietf-alto-unified-props-new], "ALTO Domain Entity Registry" is requested. Besides, a new domain is to be registered, listed in Table 1. Gao, et al. Expires December 20, 2019 [Page 23] Internet-Draft ALTO Extension: Path Vector June 2019 +-------------+--------------------------+--------------------------+ | Identifier | Entity Address Encoding | Hierarchy & Inheritance | +-------------+--------------------------+--------------------------+ | ane | See Section 6.2 | None | +-------------+--------------------------+--------------------------+ Table 1: ALTO Entity Domain 13.3. ALTO Property Type Registry The "ALTO Property Type Registry" is required by the ALTO Domain "ane", listed in Table 2. +-------------+------------+----------------------------------------+ | Identifier | Intended | Dependencies and Interpretation | | | Semantics | | +-------------+------------+----------------------------------------+ | ane:maxresb | The | application/alto-costmap+json, or | | w | maximum | application/alto-endpointcostmap+json, | | | reservable | where the ANE names are used. | | | bandwidth | | | | for the | | | | ANE | | +-------------+------------+----------------------------------------+ Table 2: ALTO Abstract Network Element Property Types 14. Acknowledgments The authors would like to thank discussions with Andreas Voellmy, Erran Li, Haibin Son, Haizhou Du, Jiayuan Hu, Qiao Xiang, Tianyuan Liu, Xiao Shi, Xin Wang, and Yan Luo. The authors thank Greg Bernstein (Grotto Networks), Dawn Chen (Tongji University), Wendy Roome, and Michael Scharf for their contributions to earlier drafts. 15. References 15.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Gao, et al. Expires December 20, 2019 [Page 24] Internet-Draft ALTO Extension: Path Vector June 2019 15.2. Informative References [I-D.bernstein-alto-topo] Bernstein, G., Yang, Y., and Y. Lee, "ALTO Topology Service: Uses Cases, Requirements, and Framework", draft- bernstein-alto-topo-00 (work in progress), October 2013. [I-D.ietf-alto-cost-calendar] Randriamasy, S., Yang, Y., Wu, Q., Lingli, D., and N. Schwan, "ALTO Cost Calendar", draft-ietf-alto-cost- calendar-01 (work in progress), February 2017. [I-D.ietf-alto-incr-update-sse] Roome, W. and Y. Yang, "ALTO Incremental Updates Using Server-Sent Events (SSE)", draft-ietf-alto-incr-update- sse-16 (work in progress), March 2019. [I-D.ietf-alto-performance-metrics] Wu, Q., Yang, Y., Lee, Y., Dhody, D., and S. Randriamasy, "ALTO Performance Cost Metrics", draft-ietf-alto- performance-metrics-06 (work in progress), November 2018. [I-D.ietf-alto-unified-props-new] Roome, W., Randriamasy, S., Yang, Y., and J. Zhang, "Unified Properties for the ALTO Protocol", draft-ietf- alto-unified-props-new-07 (work in progress), March 2019. [RFC2387] Levinson, E., "The MIME Multipart/Related Content-type", RFC 2387, DOI 10.17487/RFC2387, August 1998, . [RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S., Previdi, S., Roome, W., Shalunov, S., and R. Woundy, "Application-Layer Traffic Optimization (ALTO) Protocol", RFC 7285, DOI 10.17487/RFC7285, September 2014, . [RFC8189] Randriamasy, S., Roome, W., and N. Schwan, "Multi-Cost Application-Layer Traffic Optimization (ALTO)", RFC 8189, DOI 10.17487/RFC8189, October 2017, . Authors' Addresses Gao, et al. Expires December 20, 2019 [Page 25] Internet-Draft ALTO Extension: Path Vector June 2019 Kai Gao Tsinghua University Beijing Beijing China Email: gaok12@mails.tsinghua.edu.cn Young Lee Huawei TX USA Email: leeyoung@huawei.com Sabine Randriamasy Nokia Bell Labs Route de Villejust NOZAY 91460 FRANCE Email: Sabine.Randriamasy@nokia-bell-labs.com Y. Richard Yang Yale University 51 Prospect St New Haven CT USA Email: yry@cs.yale.edu Jingxuan Jensen Zhang Tongji University 4800 Caoan Road Shanghai 201804 China Email: jingxuan.n.zhang@gmail.com Gao, et al. Expires December 20, 2019 [Page 26]