MOSPF: Analysis and Experience (RFC1585)
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2000-Sep-12
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]).
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
Please send comments to firstname.lastname@example.org.
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
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
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
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 ...