MOSPF: Analysis and Experience (RFC1585)
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2019-Feb-13
Internet Society Requests For Comment (RFCs)
This memo documents how the MOSPF protocol satisfies the requirements imposed on Internet routing protocols by "Internet Engineering Task Force internet routing protocol standardization criteria" ([RFC 1264]). This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.
Network Working Group J. Moy Request for Comments: 1585 Proteon, Inc. Category: Informational March 1994
MOSPF: Analysis and Experience
Status of this Memo
This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
This memo documents how the MOSPF protocol satisfies the requirements imposed on Internet routing protocols by "Internet Engineering Task Force internet routing protocol standardization criteria" ([RFC 1264]).
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1. Summary of MOSPF features and algorithms
MOSPF is an enhancement of OSPF V2, enabling the routing of IP multicast datagrams. OSPF is a link-state (unicast) routing protocol, providing a database describing the Autonomous System’s topology. IP multicast is an extension of LAN multicasting to a TCP/IP Internet. IP Multicast permits an IP host to send a single datagram (called an IP multicast datagram) that will be delivered to multiple destinations. IP multicast datagrams are identified as those packets whose destinations are class D IP addresses (i.e., addresses whose first byte lies in the range 224-239 inclusive). Each class D address defines a multicast group.
The extensions required of an IP host to participate in IP multicasting are specified in "Host extensions for IP multicasting" ([RFC 1112]). That document defines a protocol, the Internet Group Management Protocol (IGMP), that enables hosts to dynamically join and leave multicast groups.
MOSPF routers use the IGMP protocol to monitor multicast group membership on local LANs through the sending of IGMP Host Membership Queries and the reception of IGMP Host Membership Reports. A MOSPF router then distributes this group location information throughout the routing domain by flooding a new type of OSPF link state advertisement, the group-membership-LSA (type 6). This in turn enables the MOSPF routers to most efficiently forward a multicast
Moy [Page 1]
RFC 1585 MOSPF: Analysis and Experience March 1994
datagram to its multiple destinations: each router calculates the path of the multicast datagram as a shortest-path tree whose root is the datagram source, and whose terminal branches are LANs containing group members.
A separate tree is built for each [source network, multicast destination] combination. To ease the computational demand on the routers, these trees are built "on demand", i.e., the first time a datagram having a particular combination of source network and multicast destination is received. The results of these "on demand" tree calculations are then cached for later use by subsequent matching datagrams.
MOSPF is meant to be used internal to a single Autonomous System. When supporting IP multicast over the entire Internet, MOSPF would have to be used in concert with an inter-AS multicast routing protocol (something like DVMRP would work).
The MOSPF protocol is based on the work of Steve Deering in [Dee...