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MOSPF: Analysis and Experience (RFC1585)

IP.com Disclosure Number: IPCOM000002419D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2000-Sep-12
Document File: 10 page(s) / 28K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J. Moy: AUTHOR

Abstract

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 text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 11% of the total text.

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.

Abstract

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]).

Please send comments to mospf@gated.cornell.edu.

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

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 ...