INTERNET-DRAFT David Meyer draft-ietf-mboned-admin-ip-space-00.txt University of Oregon Category: Informational November 1996 Expire in six months Administratively Scoped IP Multicast Status of this Memo This document provides information for the Internet Community. It does not define a standard of any kind. Distribution of this memo is unlimited. Internet Drafts This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract This document defines the "administratively scoped IP multicast space" to be the range 239.0.0.0 to 239.255.255.255. In addition, it describes a simple set of semantics for the implementation of Admin- istratively Scoped IP Multicast. This memo is a product of the MBONE Deployment Working Group (MBONED) in the Operational Requirements area of the Internet Engineering Task Force. Submit comments to or the author. Acknowledgments Much of this memo is taken from "Administratively Scoped IP Multi- cast", Van Jacobson and Steve Deering, presented at the 30th IETF, Toronto, Canada, 25 July 1994. Introduction Most current IP multicast implementations achieve some level of scop- ing by using the TTL field in the IP header. Typical MBONE (Multicast Backbone) usage has been to engineer TTL thresholds that confine traffic to some administratively defined topological region. The basic forwarding rule for interfaces with configured TTL thresholds is that for a packet is not forwarded across the interface unless its remaining TTL greater than the threshold. TTL scoping has been used to control the distribution of multicast traffic with the objective of easing stress on scarce resources (e.g., bandwidth), or to achieve some kind of improved privacy or scaling properties. In addition, the TTL is also used in its tradi- tional role to limit datagram lifetime. Given these often conflicting roles, TTL scoping has proven difficult to implement reliably, and the resulting schemes have often been complex and difficult to under- stand. On the other hand, by using administratively scoped IP multicast, one can achieve locally scoped multicast with simple, clear semantics. The key properties of any implementation of administratively scoped IP multicast are that (i). packets addressed to administratively scoped multicast addresses do not cross configured administrative boundaries, and (ii). administratively scoped multicast addresses are locally assigned, and hence are not guaranteed to be unique across administrative boundaries. These properties are sufficient to imple- ment administrative scoping. Allocation of the Administratively Scoped IP Multicast Address Space IANA should allocate the range 239.0.0.0 to 239.255.255.255 to be the "Administratively Scoped IP Multicast" address space. Discussion In order to support administratively scoped IP multicast, a router should support the configuration of scoped IP multicast boundaries. Such a router, called a boundary router, does not forward packets matching its boundary definition in either direction across its border (the bi-directional check prevents problems with multicaccess networks). In addition, a boundary router always prunes the boundary for dense-mode groups, or doesn't accept joins for sparse-mode groups [PIMSM]. Topological Requirements for Administrative Boundaries An administratively scoped IP multicast region is defined to be a topological region in which there are one or more boundary routers with common boundary definitions. Such a router is said to be a boun- dary for scoped addresses in the range defined in its configuration. Network administrators may configure a scope region whenever local multicast scope is required. In addition, an administrator may con- figure overlapping scope regions (networks can be in multiple scope regions) where convenient, with the only limitations being that a scope region must be connected (there must be a path between any two nodes within a scope region that doesn't leave that region), and con- vex (i.e., no path between any two points can cross a region boun- dary). Example: DVMRP DVMRP [DVMRP] implementations could be extended to support a boundary attribute in the interface configuration [ASMA]. The boundary attribute that includes a prefix and mask, and has the semantics that packets matching the prefix and mask do not not pass the boundary. As mentioned above, the implementation would also prune the boundary. Security Considerations While security considerations are not explicitly discussed in this memo, it is important to note that a boundary router as described here should not be considered to provide any kind of firewall func- tionality. References [ASMA] V. Jacobson, S. Deering, "Administratively Scoped IP Multicast", , presented at the 30th IETF, Toronto, Canada, 25 July 1994. [DVMRP] T. Pusateri, "Distance Vector Multicast Routing Protocol", draft-ietf-idmr-dvmrp-v3-03, September, 1996. [PIMSM] Estrin, D, et. al., "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification", draft-ietf-idmr-pim-sm-spec-08.txt, October, 1996. Author's Address David Meyer University of Oregon 1225 Kincaid St. Eugene, OR 97403 phone: +1 541.346.1747 email: meyer@ns.uoregon.edu