« ZurückWeiter »
SYSTEM FOR EXTENDING NETWORK
RESOURCES TO REMOTE NETWORKS
This application is a continuation of application Ser. No. 08/203,691, filed Feb. 28, 1994, now U.S. Pat. No. 5,423, 002 which is a continuation of application Ser. No. 07/871, 113, filed Apr. 20, 1992 now abandoned.
FIELD OF THE INVENTION 10
The present invention relates to the extension of network resources in computer networks; and more particularly to extending interfaces to systems such as routers in widely distributed networks to remote networks. 15
DESCRIPTION OF RELATED ART
A widely accepted series of international standards describing network architectures is known as the OSI reference model. See, generally, Tannenbaum, Computer Networks, 2nd Ed., 1988, Prentice-Hall. According to this model, network communications are divided into a plurality of protocols within layers of the model. Local Area Networks (LANs) operate using protocols within the lower layers, layers 1 and 2, of the OSI model, such as the carrier sense multiple access with collision detection CSMA/CD, IEEE Standard 802.3, also known as ETHERNET, and the token ring access ring method of IEEE Standard 802.5. These two lower layers are typically broken down into the physical layer and the data link layer, with the data link layer being further broken down into a media access control (MAC) layer, and a logical link layer. All MAC frames transmitted on a LAN contain distinct source and destination LAN addresses.
End systems, such as personal computers, workstations, and mainframe computers, attached to the LANs each have a distinct LAN address. LAN frames forwarded to an end system contain its address as a destination. LAN frames forwarded from an end system contain its address as a source address. Systems communicate by encapsulating additional protocols (OSI layers 3-7) within the lower layer LAN frames. These higher level protocols are grouped into suites such as the TCP/IP protocol suite and the XNS protocol suite. Many LANs contain groups of end systems that use different higher level protocol suites.
Today, LANs in remote sites are connected together using devices referred to as intermediate systems. Two of the most common types of intermediate systems used in this context are called remote bridges and routers. See, Hart, "Extending the IEEE 802.1 MAC Bridging Standard to Remote Bridges," IEEE Network, the Magazine of Communications, January, 1988, Vol. II, No. 1, pp. 10-15; Benhamou, "Integrating Bridges and Routers in a Large Internetwork," IEEE Network, January, 1988, Vol. I, No. 2, pp. 65-71; and Tannenbaum, supra, §5.4, "Internetworking", pp. 320-350.
802.1 bridges operate so that they appear transparent to the higher level protocol suites. Thus, they interconnect LANs transparently, from the perspective of the end systems attached to the LANs. That is, using a bridge, two interconnected LANs appear as if they were a single LAN to attached end systems operating in a single higher level protocol suite, such as the TCP/IP suite. Because of inherent self learning, automatic operation, and independence from the higher level protocol suites, remote bridges are easy to install and support in a multiple protocol suite environment.
There are two primary classes of LAN frames from the point of view of the higher level protocol suites. Single destination frames, which are received and processed by a single LAN end system, and multicast frames which are received and processed by a group of LAN end systems. Bridges learn the layer 2 end system LAN addresses, and can thereby identify the single destination LAN frames that need to be forwarded to remote interconnected LANs through the bridge independent of the LAN end system protocol suite. On the other hand, bridges automatically forward all multicast LAN end system frames to remote interconnected LANs.
When the number of interconnected LANs is small (e.g., less than 10) and interconnection media high speed (e.g., greater than or equal to 56,000 bits per second) the automatic forwarding of multicast frames by bridges is not a problem. However, as the number of interconnected LANs increases and/or the interconnection media speeds decrease, more and more of the interconnection media bandwidth is consumed by multicast frame traffic. Thus, less and less of the interconnection media bandwidth is available fqr single destination frames, which carry the bulk of the end system to end system workload. In contrast, routers do not forward LAN frames generated by LAN end systems. Rather, they forward higher level protocol suite information in the LAN frames that is destined for remote end system. The higher level protocol suite information is received by a router in single destination LAN frames addressed to it by a connected LAN end system or other intermediate system, such as a router. Also, routers do not forward multicast frames. Rather, they receive multicast frames containing higher level protocol suite information which must be processed locally by the router. Consequently, low speed links are more effectively utilized by routers which do not propagate multicast frames. Also, because routers operate according to higher level protocols, and have access to protocol suite dependent information, routers have traffic control ability to support very large numbers of interconnected LANs. However, the protocol suite dependent operation of routers makes them more difficult to install and support than bridges, particularly as the number of routed protocol suites increase.
In many of today's corporate networks, large and medium sized data network sites are interconnected remotely using routers, while bridges handle local LAN to LAN interconnection. These large and medium sized sites typically employ data network specialists who are responsible for the installation and maintenance of the data network equipment, including the routers.
However, many LANs in smaller sites are not interconnected with networks in the large and medium sized sites. Thus, these smaller sites are isolated from effective communication through the corporate networks. The isolated sites are relatively large in number, often use multiple protocol suites, and may have little or no local data networking expertise. Further, these small sites may comprise a single LAN which will not have a need for high volume communications with the wider network and may not support the expense of high speed links to remote sites. Thus, it can be expected that these smaller sites will use low speed (e.g., 9600 to 19,200 bits per second) full period or switched communication circuits for linking to remote LANs.
Because of the large number of small sites and associated low speed links that will be utilized for interconnecting them with wider networks, routers appear to be the right type of intermediate system for internetworking. However, the lack of networking expertise to install and maintain routers in
small sites conflicts with their use. Therefore, it is desirable to provide an optimal interconnection solution for these small sites which has the effective traffic control of a multi-protocol router, and protocol suite independent simplicity of a bridge. 5
SUMMARY OF THE INVENTION
The present invention provides system for transparently extending network resources, such as the multi-protocol 10 routing functionality of a router, to a remote LAN, while requiring a device on the remote LAN which operates independent of the higher level protocol suites under which the extended network resources operate.
Thus, two new classes of intermediate systems are pro- 15 vided which support internetwork multiprotocol routing, termed herein a routing adapter and a-boundary router. From the perspective of the end systems on interconnected LANs, a routing adapter and a boundary router provide the same functionality as two interconnected routers. Using this tech- 20 nique, a small site LAN may install a routing adapter which operates independent of the higher level protocol suites without the network management responsibility that is attendant with those higher level protocol functions. The routing adapter is coupled to a communication link which provides 25 point to point communication from the routing adapter to the boundary router. The boundary router provides the higher level protocol suite services by way of the direct communication link and the routing adapter to the remote LAN. The boundary router also provides the higher level protocol suite 30 services to the attached local LAN directly.
According to one aspect of the present invention, an apparatus for connecting a first LAN to a second LAN comprises a communication link, a boundary router, having a local routing interface coupled to the first LAN, and a remote routing interface coupled to the communication link, and providing the higher level protocol suite services for routing frames of data to end systems in the first and second LAN. The system also includes a routing adapter for extending the remote routing interface of the boundary router transparently across the communication link to the second LAN.
The boundary router applies a LAN address for the local routing interface as source address of frames routed to the 4J local LAN, and a network address of the remote routing interface/routing adapter as the source address to frames routed to the second network.
According to another aspect, the routing adapter comprises an intermediate system on the second network which 50 is responsive to destination addresses in frames that fall within a programmed set of addresses, for forwarding frames of data having a destination address within the programmed set from the second LAN across the communication link to the boundary router, and forwarding frames 55 received from the boundary router by way of the communication link to the second LAN. The programmed set of addresses includes a unique LAN address for the routing adapter/remote routing interface pair, and a set of group addresses for multicast frames which need to be processed go by the higher level protocol suite services in the boundary router.
By transparently extending an interface to routing resources across a communication link to a device which operates independent of the higher level protocol suites, a 65 small remote LAN can be effectively coupled to a wider network, without the expense and complexity of installing a
router or other intermediate system requiring sophisticated local support, or without requiring expensive higher speed links between the small remote LAN and the wider corporate data network that a remote bridge could require because it forwards all multicast frames.
Other aspects and advantages of the present invention can be seen upon review of the figures, the detailed description, and the claims which follow.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a schematic diagram of a network interconnected with a boundary router and routing adapter according to the present invention.
FIGS. 2A and 2B illustrate the prior art multi-protocol router to router configuration, and the boundary router to routing adapter configuration of the present invention, respectively.
FIG. 3 is a functional block diagram of a boundary router and routing adapter according to the present invention.
FIG. 4 schematically illustrates the configuration of a network using a routing adapter with multiple LAN interfaces.
FIG. 5 schematically illustrates a network utilizing a routing adapter with multiple LAN and link interfaces according to the present invention.
FIG. 6 is a functional block diagram of a boundary router and routing adapter for systems including a plurality of boundary LANs coupled to the routing adapter.
FIG. 7 is a functional block diagram of a boundary router and routing adapter configuration using a plurality of boundary routers coupled to a routing adapter.
DESCRIPTION OF THE PREFERRED
A detailed description of preferred embodiments of the present invention is provided with respect to FIGS. 1-7.
I. System Overview
FIG. 1 provides a schematic diagram of an apparatus for connecting a first network 10 to a second network 11. The first network 10 includes a first LAN 9 which includes a plurality of end systems and a server, and may be interconnected to other LANs using intermediate systems (not shown) known in the art. Coupled to the LAN 9 is a boundary router 12. The boundary router 12 is an intermediate system in the network which provides network resources serving higher level protocol suites, which, in one unique embodiment, constitute routing resources. As such, the boundary router 12 maintains end system directories 13 for the local LAN 9 and global routing information 14 to serve the routing functions according to the higher level protocol suites. Thus, the end system directories will include DEC end system tables, IPX end system tables, IP end system tables, and others to serve other protocol suites that are operating in the network 10. The boundary router 12 may also be coupled to other portions of the corporate data network as schematically illustrated at arrow 15.
The boundary router 12 includes a local interface 16 which serves the local LAN 9 providing access to the network resources within the boundary router to end systems on LAN 9. The boundary router could also interface to other local LANs as well. In addition, the boundary router 12 includes a remote routing interface 17, which provides an