Mboned T. Chown Internet-Draft University of Southampton Intended status: Informational July 4, 2011 Expires: January 5, 2012 Multicast Filtering Practices draft-chown-mboned-multicast-filtering-00 Abstract Operators of multicast networks may apply various filters to multicast traffic at boundary routers or on MSDP peerings. The aim of this text is to document existing filtering practices, with a view to generating some discussion towards producing guidance on best filtering practice. 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/. 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Chown Expires January 5, 2012 [Page 1] Internet-Draft Multicast Filtering Practices July 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Border and MSDP Filtering . . . . . . . . . . . . . . . . . . . 3 3. Subnet filtering . . . . . . . . . . . . . . . . . . . . . . . 5 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 8. Informative References . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Chown Expires January 5, 2012 [Page 2] Internet-Draft Multicast Filtering Practices July 2011 1. Introduction Multicast filtering can be applied at a multicast boundary or on an MSDP peering as a means to prevent unintended leakage of multicast traffic beyond its desired scope. An informal discussion of filtering practices suggested that those practices vary from organisation to organisation. The aim of this text is to gather and document commonly used existing filtering practices. Whether it is then possible to draw up a definitive best practice is to be determined; it is quite possible that due to the shifting nature of the target that a point-in-time recommendation would quickly be overtaken by events. For example, the recent addition of unicast prefix-based IPv4 multicast addresses [RFC6034] meant that filtering of all of 234.0.0.0/8 became undesirable. However, general principles may remain valid over time. For sites on academic research networks, some examples of filtering recommendations already exists, e.g. in documentation [I2multicast] from the Internet2 Multicast WG, and in the JANET IPv4 Multicast Guide [JANETmulticast]. An additional resource is the registry of IPv4 multicast address space held by IANA [IANAmulticast]. This registry should be a definitive guide to the formal use of ranges of addresses within the overall IPv4 multicast address space. A similar registry is maintained for IPv6 multicast address space [IANA6multicast]. This text is a very early draft, aimed at soliciting feedback, both on content and whether the goal of the draft is actually worthwhile. Different sites may have different requirements. There may also be issues with handling scope boundaries that need to be considered. So there may be general principles that could be captured in a document such as this, even if specific filtering rules are not included. 2. Border and MSDP Filtering In this section we summarise IPv4 multicast addresses that are commonly filtered at site borders or on MSDP peerings. Based on responses we received from a couple of multicast community lists, it wasn't clear which filters are applied on border routers and which on MSDP SA messages. Some sites apply minimal traffic filters, but heavier MSDP filtering. Some sites choose to route multicast around their unicast firewalls, for performance or other operational reasons, but this shouldn't alter the requirement to filter groups appropriately where necessary. Chown Expires January 5, 2012 [Page 3] Internet-Draft Multicast Filtering Practices July 2011 In this section we draw on the small number contributions so far; we hope to get more inputs in time. In general, many 224.0.0.* addresses that are used by infrastructure are typically blocked, as well as some addresses that are global scope but should not be, like Ghostcast. Local scope multicast should also generally be constrained to the intended site scope. The following list currently includes multicast IP addresses that are being filtered based on the union of responses received so far (hence the apparent duplication of certain prefixes). The list of filters applied by all respondents would be somewhat shorter. 224.0.1.2 SGI-Dogfight 224.0.1.3 Rwhod 224.0.1.8 SUN NIS+ 224.0.1.20 any private experiment 224.0.1.22 SVRLOC 224.0.1.24 microsoft-ds 224.0.1.25 nbc-pro 224.0.1.35 SVRLOC-DA 224.0.1.39 cisco-rp-announce 224.0.1.40 cisco-rp-discovery 224.0.1.41 gatekeeper 224.0.1.60 hp-device-disc 224.0.1.65 iapp 224.0.1.76 IAPP 224.0.2.1 rwho 224.0.2.2 SUN RPC 224.0.2.3 EPSON-disc-set 224.0.23.1 Ricoh-device-ctrl 224.0.23.2 Ricoh-device-ctrl 224.1.0.1 ? 224.77.0.0/16 Norton Ghost 224.101.101.101 ? 225.1.2.3 Altiris 226.77.0.0/16 ? 229.55.150.208 Norton Ghost 234.42.42.0/30 ? 234.42.42.40/30 ImageCast 234.142.142.42/31 ImageCast 234.142.142.44/30 ImageCast 234.142.142.48/28 ImageCast 234.142.142.64/26 ImageCast 234.142.142.128/29 ImageCast 234.142.142.136/30 ImageCast 234.142.142.140/31 ImageCast 234.142.142.142 ImageCast 239.0.0.0/8 Scoped groups Chown Expires January 5, 2012 [Page 4] Internet-Draft Multicast Filtering Practices July 2011 239.252.0.0/14 Scoped groups Different networks make different use of the scoped address space under 239.0.0.0/8, which may lead to different organisational filters in different scenarios. The SSM range 232.0.0.0/8 should not be carried in MSDP peerings. As a general principle, multicast sourced from private address ranges [RFC1918] or from 169.254.0.0/16, 192.0.2.0/24 or 127.0.0.0/8 should be dropped, regardless of the multicast destination. In certain cases, rate limiting may be desirable, where complete filtering might not, e.g. in mitigating against SAP [RFC2974] storms, or against unintended MSDP SA bursts. 3. Subnet filtering Two respondents are currently filtering uPNP between subnets, and one is filtering mDNS. One reason for the uPNP filtering was due to issues with errant Ricoh printers which flood announcements with too- large TTLs. 4. Conclusions This text is a very drafty first version of a document aimed to summarise the use of multicast filtering practices in the wild. It includes filters at various boundaries as well as MSDP SA filters. Further feedback on the text, and the practices reported to date is welcomed. 5. Security Considerations There are no extra security consideration for this document. 6. IANA Considerations There are no extra IANA consideration for this document. 7. Acknowledgments The author would like to thank the following people for their contributions to this text: Scott Bertilson, Alan Buxey, Bruce Chown Expires January 5, 2012 [Page 5] Internet-Draft Multicast Filtering Practices July 2011 Curtis, Andy Gatward, Jeffry J. Handal, Lonnie Leger, and William F. Maton Sotomayor. 8. Informative References [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. [RFC6034] Thaler, D., "Unicast-Prefix-Based IPv4 Multicast Addresses", RFC 6034, October 2010. [JANETmulticast] Price, D., "IPv4 Multicast on JANET", 2006, . [IANA6multicast] "IPv6 Multicast Address Space Registry", . [IANAmulticast] "IPv4 Multicast Address Space Registry", . [I2multicast] "Enabling IP Multicast with Internet2", . Author's Address Tim Chown University of Southampton Highfield Southampton, Hampshire SO17 1BJ United Kingdom Email: tjc@ecs.soton.ac.uk Chown Expires January 5, 2012 [Page 6]