Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing
Reexamination Certificate
1999-10-13
2003-10-21
Alam, Hosain T. (Department: 2155)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
C709S239000, C709S240000, C709S243000, C709S244000, C370S351000
Reexamination Certificate
active
06636895
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to communication systems, and more particularly to distributing multicast routing information in a protocol independent multicast network.
BACKGROUND OF THE INVENTION
In today's information age, communication networks are often used for transporting information from an information provider to one or more information consumers.
One technique for transporting information from an information provider to a group of information consumers over the communication network is known as “multicasting.” Multicasting allows the information provider (referred to hereinafter as a “multicast source”) to transmit a single unit of multicast information (referred to hereinafter as a “multicast packet”) simultaneously to all information consumers (referred to hereinafter individually as a “multicast client” and collectively as “multicast clients”) in the multicast group, specifically by addressing the multicast packet to the multicast group using a multicast address. The multicast clients monitor the communication network for multicast packets addressed to the multicast group.
In order to distribute multicast packets from a particular multicast source S to the multicast clients for a particular multicast group G, the multicast packet is routed through the communication network by a number of routers. The communication network may include multiple routing domains, and therefore the multicast packet may traverse multiple routing domains. Each router runs various routing protocols to determine, among other things, a “next hop” for each packet based upon address information in the packets. Such routing information is used to establish a multicast distribution tree, and is maintained by each router in one or more routing tables (often referred to as a “routing information base”). In particular, each router maintains a unicast routing information base (URIB) that is used to determine the “next hop” for unicast packets. Also, each multicast router maintains a multicast routing information base (MRIB) that is used to determine the “next hop” for multicast packets. Upon receiving a packet, the router uses the appropriate routing information base to determine the “next hop” router for the packet.
One well-known protocol for routing multicast packets within a multicast routing domain is known as Protocol Independent Multicast (PIM). PIM is so named because it is not dependent upon any particular unicast routing protocol for setting up a multicast distribution tree within the multicast routing domain. PIM has two modes of operation, specifically a sparse mode and a dense mode. PIM Sparse Mode (PIM-SM) is described in the document Internet Engineering Task Force (IETF) Request For Comments (RFC) 2362 entitled
Protocol Independent Multicast
-
Sparse Mode
(
PIM
-
SM
):
Protocol Specification
and published in June 1998, hereby incorporated by reference in its entirety. PIM Dense Mode (PIM-DM) is described in an Internet Draft of the Internet Engineering Task Force (IETF) entitled
Protocol Independent Multicast Version
2
Dense Mode Specification
, document draft-ietf-pim-v2-dm-03.txt (Jun. 7, 1999), hereby incorporated by reference in its entirety
In accordance with the PIM protocol, the various routers within a particular PIM domain establish a default multicast distribution tree, referred to as a “shared tree,” for each multicast group. Each shared tree is rooted at a Rendezvous Point (RP) router that acts as the distribution point of all multicast packets for the multicast group. Before a router can join the shared tree for a particular multicast group, the router must learn the identity of the multicast group RP router. A router learns the identity of the multicast group RP router by receiving a PIM Bootstrap Message including a list of all RP routers in the PIM domain. The router receives the PIM Bootstrap Message either from a Bootstrap Router (BSR), which sends the PIM Bootstrap Message to all routers in the PIM domain at predetermined intervals (typically every 60 seconds), or from a neighboring router, which sends the PIM Bootstrap Message to the router if and only if the neighboring router has lost contact with the router for a predetermined period of time (typically 105 seconds). Upon learning the identity of the multicast group RP router, or at any time thereafter, each router that supports a downstream multicast group member (i.e., multicast client) joins the shared tree by sending a PIM Join/Prune Message hop-by-hop toward the multicast group RP router. Each intermediate router that receives the PIM Join/Prune Message from a downstream router also joins the shared tree by forwarding the PIM Join/Prune Message toward the multicast group RP router.
The PIM domain may have a number of source networks that belong to the PIM domain itself. Multicast packets that originate within such intradomain source networks are not routed to other PIM domains. The routes associated with such intradomain source networks (referred to hereinafter as intra-source routes) are distributed by a unicast routing protocol and maintained in the URIB.
In order to route the multicast packet between PIM domains, border routers in each PIM domain (each referred to hereinafter as a Multicast Border Gateway Protocol or MBGP router) determine interdomain routes (referred to hereinafter as MBGP routes) for the (source, group) pair. The MBGP router is typically a Multicast Source Discovery Protocol (MSDP) router or a PIM Multicast Border Router (PMBR) that functions as a Border Gateway Protocol (BGP) router to receive and install MBGP routes. MSDP, PMBR, and BGP are described in IETF documents and are well-known in the art. The MBGP routes need to be distributed to all PIM routers in the PIM domain so that all PIM routers will have consistent routing information.
One way to distribute the MBGP routes to the PIM routers in the PIM domain is to manually configure each PIM router to include the MBGP routes. Such manual configuration is a significant burden on the network administrator, and is therefore not a viable approach. Another way to distribute the MBGP routes to the PIM routers in the PIM domain is using any of a number of interior routing protocols, including, but not limited to, Interior Border Gateway Protocol (IBGP), Routing Information Protocol (RIP), and Open Shortest Path First (OSPF). These interior routing protocols have certain drawbacks, and are therefore not viable alternatives. Yet another way to distribute the MBGP routes to the PIM routers in the PIM domain is using a multicast routing protocol such as Distance Vector Multicast Routing Protocol (DVMRP). Unfortunately, such a multicast routing protocol may not be in use within the PIM domain.
Thus, a need remains for a system, device, and method for distributing MBGP routes to all of the PIM routers in the PIM domain.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, a PIM router distributes MBGP routes over the PIM domain by opening a TCP connection to each MBGP router, obtaining the MBGP routes from the MBGP routers using IBGP, and sending a bootstrap message including the MBGP routes. In a preferred embodiment, the PIM router periodically sends a bootstrap message including all MBGP routes, and also sends a bootstrap message including only changed MBGP routes whenever the PIM router detects a MBGP route change. The bootstrap messages are propagated to all PIM routers in the PIM domain.
REFERENCES:
patent: 6055561 (2000-04-01), Feldman et al.
patent: 6069889 (2000-05-01), Feldman et al.
patent: 6321270 (2001-11-01), Crawley
patent: 6343326 (2002-01-01), Acharya et al.
Estrin et al., Internet Engineering Task Force (IETF) Request for Comments (RFC) 2362, Protocol Independent Multicast—Sparse Mode (PIM-SM): Protocol Specification, Jun. 1998.
Deering et al., Internet Engineering Task Force (IETF) Internet Draft draft-ietf-pim-v2-dm-03.txt, Protocol Independent Multicast Version 2 Dense Mode Specification, Jun. 7, 1999.
Bates et al., Internet Engineering Task Force (IETF)
Li Yunzhou
Ng Billy C.
Alam Hosain T.
Gorecki John C.
Nortel Networks Limited
Won Young N.
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