Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing
Reexamination Certificate
1998-06-09
2001-10-16
Harrell, Robert B. (Department: 2758)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
C709S227000, C709S238000, C709S242000, C370S351000, C370S392000, C370S409000, C370S474000, C340S870030, C340S870030
Reexamination Certificate
active
06304912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention firstly relates to a process for storing, in a first communication apparatus, data-link-layer path information indicating a communication path in a data link layer (layer
2
) from the first communication apparatus to one of at least one second communication apparatus, where the first and at least one second communication apparatuses are each connected to a network which is logically divided into a plurality of subnetworks based on network-layer addresses. The present invention also relates to a product which, when used with a communication apparatus, is able to output control information which directs the communication apparatus to execute the above process. The present invention further relates to a communication apparatus generated by the above process.
The present invention secondly relates to a process for searching, at a first communication apparatus, for one of at least one piece of data-link-layer (layer-
2
) or network-layer (layer-
3
) path information indicating a communication path in a data link layer or in a network layer from the first communication apparatus to one of at least one second communication apparatus, based on a network-layer (layer-
2
) address of the one of the at least one second communication apparatus, where the first communication apparatus and the at least one second communication apparatuses are each connected to a network as above. The present invention also relates to a product which, when used with a communication apparatus, is able to output control information which directs the communication apparatus to execute the above process.
The present invention thirdly relates to a process and an apparatus for determining layer-
2
(data-link-layer) reachability between first and second communication apparatuses, where each of the first and second communication apparatuses are connected to a layer-
3
(network-layer) communication network comprised of at least one router and a plurality of subnetworks which are logically defined over at least one layer-
2
-connected communication network. The present invention also relates to a product which, when used with a communication apparatus, is able to output control information which directs the communication apparatus to execute the functions of the above apparatus for determining layer-
2
reachability.
The present invention fourthly relates to an apparatus, for use with each of at least one router provided in a layer-
3
communication network comprised of a plurality of subnetworks which are logically defined over at least one layer-
2
-connected communication network, and for determining layer-
2
reachability between first and second communication apparatuses each connected to the layer-
3
communication network, where a layer-
3
communication path passing a portion or all of the at least one router can be determined by the portion or all of the at least one router based on a layer-
3
address of the second communication apparatus. The present invention also relates to a product which, when used with a communication apparatus, is able to output control information which directs the communication apparatus to execute the functions of the above apparatus for use with each router in determining layer-
2
reachability.
2. Description of the Related Art
2.1 LANs (local area networks) are constructed in respective sections or task groups in many companies and campuses, and those LANs are interconnected through relaying apparatuses called routers to form a company network or a campus network. Each LAN in such a network is an example of a subnetwork. Namely, a plurality of subnetworks are interconnected to a plurality of routers to form a network.
Each terminal connected to one of the above subnetworks can communicate with another terminal connected to the same subnetwork by directly sending a packet, while each terminal sends a packet to one of the plurality of routers which is located at a boundary of the subnetwork to which the terminal is connected, when the said each terminal communicates to another terminal which is connected to a different subnetwork. When the router receives the packet, the router determines to which router the packet is to be transferred, and then transfers the packet to the determined router. Thus, communication to a terminal connected to a different subnetwork is possible.
In a typical terminal, transmission processing of a packet is performed by an operating system (OS). The packet is transmitted based on a network-layer address, For example, according to the Internet protocol (IP), an IP address is used in transmission. The transmission processing of a packet according to the Internet protocol (IP) is explained below.
The operating system (OS) has a routing table corresponding to all the network-layer addresses which are reachable from the host (router) which contains the operating system, and each entry of the routing table contains a network address, an output interface of the host, a gateway address, and the like. The gateway address is an IP address of a router to which the packet is to be sent first from the its own (source) host, when a destination host belongs to a subnetwork which is different from the subnetwork to which the source host belongs. When the destination host and the source host belong to the same subnetwork, the gateway address is not an IP address of a router and, instead, is an IP address of the destination host or an IP address of its own host. The operating system (OS) searches the routing table using the IP address of the destination host as a search key, to obtain the output interface and the gateway address.
In addition, the operating system (OS) contains a data-link-layer address table for each interface, to indicate correspondence between the network-layer addresses and the data-link-layer addresses. For example, ARP (address resolution protocol) tables in UNIX systems having Ethernet interfaces, indicate correspondences between IP addresses and MAC (media access control) addresses. MAC addresses of L
2
(layer
2
) reachable hosts or gateways can be obtained from their IP addresses, to enable the source host to communicate with these L
2
reachable hosts or gateways. When no entry corresponding to an IP address is found, an APR request is sent to all the hosts and gateways in the same subnetwork in accordance with the ARP protocol to obtain the MAC address corresponding to the IP address.
A similar protocol called ATMARP has been proposed for ATM networks. ATM addresses corresponding to IP addresses can be obtained in accordance with the ATMARP protocol. In addition, a procedure for management and control of a plurality of subnetworks over an ATM network, called IPOA (IP over ATM) has been proposed by M. Laubach, “Classical IP and ARP over ATM”, Request for comments: 1577, January 1994. According to the IPOA, a plurality of subnetworks, called LIS (Logical IP Subnetwork), are logically defined on an ATM network, and an ATMARP server is provided for each LIS to register and control ATM addresses of terminals in the LIS. Before each terminal sends a packet, the terminal searches its own routing table to determine an output interface, and then searches an ATMARP table which is provided corresponding to the determined output interface to obtain an ATM address or a VC (virtual connection) number of a host or router in the same LIS to which a packet is to be transferred next. When no ATM address corresponding to the IP address is found in the ATMARP table, the terminal inquires of the ATMARP server an ATM address corresponding to the IP address. After the terminal receives a response from the ATMARP server together with the ATM address to the router, each terminal can send the packet to the router as a next hop, and then the packet can be transferred through at least one router to a destination host in a different subnetwork (LIS) based on the IP address of the destination host.
However, the LISs are logically defined on an ATM network in which communication based on a data-
Oguchi Naoki
Tsuruoka Tetsumei
Fujitsu Limited
Harrell Robert B.
Helfgott & Karas P.C.
Willett Stephan
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