|Document||Charter||Extensions for Scalable DNS Service Discovery WG (dnssd)|
|IESG||Responsible AD||Éric Vyncke|
|Charter edit AD||Éric Vyncke|
|Send notices firstname.lastname@example.org, email@example.com|
Background ---------- Zero configuration networking protocols are currently well suited to discover services within the scope of a single link. In particular, the DNS-SD [RFC 6763] and mDNS [RFC6762] protocol suite (sometimes referred to using Apple Computer Inc.'s trademark, Bonjour) are widely used for DNS-based service discovery and host name resolution on a single link. The DNS-SD/mDNS protocol suite is used in many scenarios including home, campus, and enterprise networks. However, the zero configuration mDNS protocol is constrained to link-local multicast scope by design, and therefore cannot be used to discover services on remote links. In a home network that consists of a single (possibly bridged) link, users experience the expected discovery behavior; available services appear because all devices share a common link. However, in multi-link home networks (as envisaged by the homenet WG) or in routed campus or enterprise networks, devices and users can only discover services on the same link, which is a significant limitation. This has led to calls, such as the Educause petition, to develop an appropriate service discovery solution to span multiple links or to perform discovery across a wide area, not necessarily on directly connected links. In addition, the "Smart Energy Profile 2 Application Protocol Standard", published by ZigBee Alliance and HomePlug Powerline Alliance specifies the DNS-SD/mDNS protocol suite as the basis for its method of zero configuration service discovery. However, its use of wireless mesh multi-link subnets in conjunction with traditional routed networks will require extensions to the DNS-SD/mDNS protocols to allow operation across multiple links. The scenarios in which multi-link service discovery is required may be zero configuration environments, environments where administrative configuration is supported, or a mixture of the two. As demand for service discovery across wider area routed networks grows, some vendors are beginning to ship proprietary solutions. It is thus both timely and important that efforts to develop improved, scalable, autonomous service discovery solutions for routed networks are coordinated towards producing a single, standards-based solution. Working Group Description ------------------------- The focus of the WG is to develop a solution for extended, scalable DNS-SD. This work is likely to highlight problems and challenges with naming protocols, as some level of coexistence will be required between local zero configuration name services and those forming part of the global DNS. It is important that these issues are captured and documented for further analysis; solving those problems is however not within the scope of this WG. The WG will consider the tradeoffs between reusing/extending existing protocols and developing entirely new ones. It is highly desirable that any new solution is backwardly compatible with existing DNS-SD/mDNS deployments. Any solution developed by the dnssd WG must not conflict or interfere with the operation of other zero-configuration service and naming protocols such as uPnP or LLMNR. Integration with such protocols is out of scope for this WG. Current zero configuration discovery protocols are constrained to operate within a single link, which implicitly limits the scope of discovery. In extending service discovery protocols to operate over multiple links, devices will inherently become discoverable over a wider area, which may introduce security or privacy concerns. The WG will consider such concerns when exploring the solution space for multi-link service discovery. To that end, the primary goals of the dnssd WG are as follows: 1. To document a set of requirements for scalable, autonomous DNS-based service discovery in routed, multi-link networks in the following five scenarios: (A) Personal Area networks, e.g., one laptop and one printer. This is the simplest example of a service discovery network, and may or may not have external connectivity. (B) Home networks, as envisaged by the homenet WG, consisting of one or more exit routers, with one or more upstream providers or networks, and an arbitrary internal topology with heterogeneous media where routing is automatically configured. The home network would typically be a single zero configuration administrative domain with a relatively limited number of devices. (C) Wireless 'hotspot' networks, which may include wireless networks made available in public places, or temporary or permanent infrastructures targeted towards meeting or conference style events, e.g., as provided for IETF meetings. In such environments other devices may be more likely to be 'hostile' to the user. (D) Enterprise networks, consisting of larger routed networks, with large numbers of devices, which may be deployments spanning over multiple sites with multiple upstreams, and one more more administrative domains (depending on internal administrative delegation). The large majority of the forwarding and security devices are configured. These may be commercial or academic networks, with differing levels of administrative control over certain devices on the network, and BYOD devices commonplace in the campus scenario. (E) Mesh networks such as RPL/6LoWPAN, with one or more links per routable prefix, which may or may not have external connectivity. The topology may use technologies including 802.11 wireless, HomePlug AV and GP, and ZigBee IP. In the above scenarios, the aim is to facilitate service discovery across the defined site. It is also desirable that a user or device, when away from such a site, is still able to discover services within that site, e.g. a user discovering services in their home network while remote from it. It is also desirable that multiple discovery scopes are supported, from the point of view of either performing discovery within a specified scope or advertisement within a specified scope, and being able to discover (enumerate) the set of scopes such that an application could then choose to do either. It should be noted that scope in this sense might refer to 'building' or 'room' and thus might have no correlation to network topology. 2. To develop an improved, scalable solution for service discovery that can operate in multi-link networks, where devices may be in neighboring or non-neighboring links, applicable to the scenarios above. The solution will consider tradeoffs between reusing/extending existing protocols and developing entirely new protocols. The solution should include documentation or definition of the interfaces that can be implemented, separately to transport of the information. 3. To document challenges and problems encountered in the coexistence of zero configuration and global DNS name services in such multi-link networks, including consideration of both the name resolution mechanism and the namespace. It is important that the dnssd WG takes input from stakeholders in the scenarios it is considering. For example, the homenet WG is currently evaluating its own requirements for naming and service discovery; it is up to the homenet WG as to whether it wishes to recommend adoption of the solution developed in the dnssd WG, but coordination between the WGs is desirable.