Background Intelligent Transfer Service (BITS) Peer-Caching: Peer Discovery Protocol

[MS-BPDP]:

Background Intelligent Transfer Service (BITS) Peer-Caching: Peer Discovery Protocol

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Revision Summary

Table of Contents

1Introduction

1.1Glossary

1.2References

1.2.1Normative References

1.2.2Informative References

1.3Overview

1.4Relationship to Other Protocols

1.5Prerequisites/Preconditions

1.6Applicability Statement

1.7Versioning and Capability Negotiation

1.8Vendor-Extensible Fields

1.9Standards Assignments

2Messages

2.1Transport

2.2Common Message Syntax

2.2.1Namespaces

2.2.2Messages

2.2.3Elements

2.2.4Complex Types

2.2.5Simple Types

2.2.6Attributes

2.2.7Groups

2.2.8Attribute Groups

3Protocol Details

3.1Server Details

3.1.1Abstract Data Model

3.1.1.1Protocol Metadata

3.1.1.2Table of Connected Subnets

3.1.2Timers

3.1.3Initialization

3.1.4Message Processing Events and Sequencing Rules

3.1.4.1Hello

3.1.4.1.1Messages

3.1.4.2Bye

3.1.4.2.1Messages

3.1.4.3Probe

3.1.4.3.1Messages

3.1.4.4ProbeMatch

3.1.4.4.1Messages

3.1.4.5Resolve

3.1.4.5.1Messages

3.1.4.6ResolveMatch

3.1.4.6.1Messages

3.1.5Timer Events

3.1.6Other Local Events

3.1.6.1Shutdown

3.1.6.2Add a Local IP Address

3.1.6.3Remove an IP Address

3.2Client Details

3.2.1Abstract Data Model

3.2.1.1Table of Subnets

3.2.1.2Table of Servers

3.2.1.3Tables of Server Addresses

3.2.1.4Scope List

3.2.2Timers

3.2.2.1Discovery Timer

3.2.2.2Discovery Suppression Timer

3.2.2.3Address Scavenger Timer

3.2.3Initialization

3.2.4Message Processing Events and Sequencing Rules

3.2.4.1Hello

3.2.4.2Bye

3.2.4.3Probe

3.2.4.4ProbeMatch

3.2.5Timer Events

3.2.5.1Discovery Time-Out

3.2.5.2Discovery Suppression Time-Out

3.2.5.3Address Scavenger Time-Out

3.2.6Other Local Events

3.2.6.1Attach to a Subnet

3.2.6.2Detach from a Subnet

3.2.6.3Clear the Table of Servers

3.2.6.4Discovery Request

3.2.6.5Cancel Discovery Request

3.2.6.6Enumerate Server Addresses

3.2.6.7Update Server Address Time Stamp

3.2.6.8Shut Down

4Protocol Examples

4.1Hello Message at Server Startup and Bye Message at Shutdown

4.2Client Probe with Probe-Match Replies

5Security

5.1Security Considerations for Implementers

5.1.1Potential for High Unicast Traffic

5.1.2Lack of Message Authentication

5.2Index of Security Parameters

6Appendix A: Full WSDL

7Appendix B: Product Behavior

8Change Tracking

9Index

1 Introduction

This document describes the Background Intelligent Transfer Service (BITS) Peer-Caching: Peer Discovery Protocol. This protocol is used to locate hosts in a domain that supports the URL-caching protocol implemented by BITS. The protocol is implemented by using the Web Services Dynamic Discovery (WS-Discovery) Protocol, as specified in [WS-Discovery].

Sections 1.5, 1.8, 1.9, 2, and 3 of this specification are normative. All other sections and examples in this specification are informative.

1.1 Glossary

This document uses the following terms:

Active Directory: A general-purpose network directory service. Active Directory also refers to the Windows implementation of a directory service. Active Directory stores information about a variety of objects in the network. Importantly, user accounts, computer accounts, groups, and all related credential information used by the Windows implementation of Kerberos are stored in Active Directory. Active Directory is either deployed as Active Directory Domain Services (AD DS) or Active Directory Lightweight Directory Services (AD LDS). [MS-ADTS] describes both forms. For more information, see [MS-AUTHSOD] section 1.1.1.5.2, Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Kerberos, and DNS.

Coordinated Universal Time (UTC): A high-precision atomic time standard that approximately tracks Universal Time (UT). It is the basis for legal, civil time all over the Earth. Time zones around the world are expressed as positive and negative offsets from UTC. In this role, it is also referred to as Zulu time (Z) and Greenwich Mean Time (GMT). In these specifications, all references to UTC refer to the time at UTC-0 (or GMT).

domain: A set of users and computers sharing a common namespace and management infrastructure. At least one computer member of the set must act as a domain controller (DC) and host a member list that identifies all members of the domain, as well as optionally hosting the Active Directory service. The domain controller provides authentication of members, creating a unit of trust for its members. Each domain has an identifier that is shared among its members. For more information, see [MS-AUTHSOD] section 1.1.1.5 and [MS-ADTS].

fully qualified domain name (FQDN): An unambiguous domain name that gives an absolute location in the Domain Name System's (DNS) hierarchy tree, as defined in [RFC1035] section 3.1 and [RFC2181] section 11.

globally unique identifier (GUID): A term used interchangeably with universally unique identifier (UUID) in Microsoft protocol technical documents (TDs). Interchanging the usage of these terms does not imply or require a specific algorithm or mechanism to generate the value. Specifically, the use of this term does not imply or require that the algorithms described in [RFC4122] or [C706] must be used for generating the GUID. See also universally unique identifier (UUID).

Internet Protocol version 4 (IPv4): An Internet protocol that has 32-bit source and destination addresses. IPv4 is the predecessor of IPv6.

Internet Protocol version 6 (IPv6): A revised version of the Internet Protocol (IP) designed to address growth on the Internet. Improvements include a 128-bit IP address size, expanded routing capabilities, and support for authentication and privacy.

SOAP fault: A container for error and status information within a SOAP message. See [SOAP1.2-1/2007] section 5.4 for more information.

Uniform Resource Identifier (URI): A string that identifies a resource. The URI is an addressing mechanism defined in Internet Engineering Task Force (IETF) Uniform Resource Identifier (URI): Generic Syntax [RFC3986].

universally unique identifier (UUID): A 128-bit value. UUIDs can be used for multiple purposes, from tagging objects with an extremely short lifetime, to reliably identifying very persistent objects in cross-process communication such as client and server interfaces, manager entry-point vectors, and RPC objects. UUIDs are highly likely to be unique. UUIDs are also known as globally unique identifiers (GUIDs) and these terms are used interchangeably in the Microsoft protocol technical documents (TDs). Interchanging the usage of these terms does not imply or require a specific algorithm or mechanism to generate the UUID. Specifically, the use of this term does not imply or require that the algorithms described in [RFC4122] or [C706] must be used for generating the UUID.

UTC (Coordinated Universal Time): A high-precision atomic time standard that approximately tracks Universal Time (UT). It is the basis for legal, civil time all over the Earth. Time zones around the world are expressed as positive and negative offsets from UTC. In this role, it is also referred to as Zulu time (Z) and Greenwich Mean Time (GMT). In these specifications, all references to UTC refer to the time at UTC–0 (or GMT).

Web Services Description Language (WSDL): An XML format for describing network services as a set of endpoints that operate on messages that contain either document-oriented or procedure-oriented information. The operations and messages are described abstractly and are bound to a concrete network protocol and message format in order to define an endpoint. Related concrete endpoints are combined into abstract endpoints, which describe a network service. WSDL is extensible, which allows the description of endpoints and their messages regardless of the message formats or network protocols that are used.

MAY, SHOULD, MUST, SHOULD NOT, MUST NOT: These terms (in all caps) are used as defined in [RFC2119]. All statements of optional behavior use either MAY, SHOULD, or SHOULD NOT.

1.2 References

Links to a document in the Microsoft Open Specifications library point to the correct section in the most recently published version of the referenced document. However, because individual documents in the library are not updated at the same time, the section numbers in the documents may not match. You can confirm the correct section numbering by checking the Errata.

1.2.1 Normative References

We conduct frequent surveys of the normative references to assure their continued availability. If you have any issue with finding a normative reference, please contact . We will assist you in finding the relevant information.

[MS-DTYP] Microsoft Corporation, "Windows Data Types".

[RFC1035] Mockapetris, P., "Domain Names - Implementation and Specification", STD 13, RFC 1035, November 1987,

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997,

[RFC3513] Hinden, R. and Deering, S., "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003,

[SOAP-UDP] Combs, H., Justice, J., Kakivaya, G., et al., "SOAP-over-UDP", September 2004,

[SOAP1.2-2/2003] Gudgin, M., Hadley, M., Mendelsohn, N., et al., "SOAP Version 1.2 Part 2: Adjuncts", W3C Recommendation, June 2003,

[WS-Discovery] Beatty, J., Kakivaya, G., Kemp D., et al., "Web Services Dynamic Discovery (WS-Discovery)", April 2005,

[WSAddressing] Box, D., et al., "Web Services Addressing (WS-Addressing)", August 2004,

[WSDL] Christensen, E., Curbera, F., Meredith, G., and Weerawarana, S., "Web Services Description Language (WSDL) 1.1", W3C Note, March 2001,

[XMLNS] Bray, T., Hollander, D., Layman, A., et al., Eds., "Namespaces in XML 1.0 (Third Edition)", W3C Recommendation, December 2009,

[XMLSCHEMA1] Thompson, H., Beech, D., Maloney, M., and Mendelsohn, N., Eds., "XML Schema Part 1: Structures", W3C Recommendation, May 2001,

[XMLSCHEMA2] Biron, P.V., Ed. and Malhotra, A., Ed., "XML Schema Part 2: Datatypes", W3C Recommendation, May 2001,

1.2.2 Informative References

[MS-BPAU] Microsoft Corporation, "Background Intelligent Transfer Service (BITS) Peer-Caching: Peer Authentication Protocol".

[MS-BPCR] Microsoft Corporation, "Background Intelligent Transfer Service (BITS) Peer-Caching: Content Retrieval Protocol".

[MSDN-BITS] Microsoft Corporation, "Background Intelligent Transfer Service",

1.3 Overview

The BITS Peer-Caching: Peer Discovery Protocol is used to locate networked hosts or devices that are implementing the server role of the BITS Peer-Caching: Content Retrieval Protocol. The BITS Peer-Caching: Peer Discovery Protocol provides a way for peer servers to announce their presence to connected subnets and a way for peer clients to locate servers in connected subnets.

The BITS Peer-Caching: Peer Discovery Protocol is a specialization of Web Services Dynamic Discovery (WS-Discovery), as specified in [WS-Discovery], and follows its model for announcing and locating resources. The protocol defines a client role and a server role. A server announces its presence to connected IP subnets via a multicasted Hello message to UDP port 3702. A client discovers servers passively by listening for Hello messages. A client can also solicit for servers by multicasting a Probe message to the same UDP port; servers with matching characteristics reply to the client with unicast Probe-Match messages.

Windows uses the BITS Peer-Caching: Peer Discovery Protocol to implement a distributed peer-to-peer cache of URL content for use by the Background Intelligent Transfer Service (BITS) component. For more information about BITS, see [MSDN-BITS].

1.4 Relationship to Other Protocols

The BITS Peer-Caching: Peer Discovery Protocol does not authenticate computers to each other; Windows uses the Background Intelligent Transfer Service (BITS) Peer-Caching: Peer Authentication Protocol Specification for mutual authentication of potential peers. For more information, see [MS-BPAU].

WS-Discovery, and therefore the BITS Peer-Caching: Peer Discovery Protocol, uses SOAP-over-UDP as its network transport. For more information, see [SOAP-UDP].

A host implementing the client or server role of the BITS Peer-Caching: Peer Discovery Protocol typically also implements the same role of the BITS Peer-Caching: Content Retrieval Protocol, as a higher level protocol.

Figure 1: Relationship to other protocols

1.5 Prerequisites/Preconditions

This protocol defines no prerequisites.

1.6 Applicability Statement

The primary purpose of the BITS Peer-Caching: Peer Discovery Protocol is to locate peer servers for use by the BITS Peer-Caching: Content Retrieval Protocol, as specified in [MS-BPCR]. The BITS Peer-Caching: Peer Discovery Protocol is intended for use by hosts that are members of an Active Directory domain.

1.7 Versioning and Capability Negotiation

This document covers versioning issues in the following areas:

 Protocol Versions: A server advertises the versions of the protocol it supports via Hello and Probe-Match messages.

A client does not advertise the protocol versions it supports.

This specification defines version 1 of the BITS Peer-Caching: Peer Discovery Protocol. The format of each message in version 1 is defined in section 2 and 3. Because this is the initial release of the protocol, no additional versions are defined at time of publication.