VIRTUAL LOCAL AREA NETWORKS WITH TRUNK STATIONS

Abstract: A switch for use in a virtual area network communications system having multiple local area networks interconnected by multiple switches that are connected by a trunk having one or more trunk stations connected directly thereto, includes a first communications port, i.e., an access port, that connects to a first local area network. The first local area network is configured within a virtual area network that also includes a second local area network and a trunk station. The switch also includes a second communications port, i.e., a trunk port, connected to the trunk to which the trunk station is connected by another trunk port. A switch control console detects a multicast communication from the first local area network, duplicates the multicast communication to form a first communication and a second communication, appends a VLAN header to the first communication to form a VLAN communication, and directs transmission of the VLAN communication and the second comminication to the second communication port, thereby facilitating delivery of the multicast communication to both the second local area network and the trunk station.

Description: VIRTUAL LOCAL AREA NETWORKS WITH TRUNK STATIONS FIELD OF THE INVENTION The present invention relates generally to communications networks and more particularly to virtual local area networks with trunk stations. BACKGROUND OF THE INVENTION Local area networks (LANs) are used to facilitate communications between a number of users. Individual LANs may be bridged together to allow a large number of users to communicate amongst themselves. These bridged LANs may be further interconnected with other bridged LANs using routers to form even larger communications networks. Figure 1 depicts an exemplary interconnected bridged LAN system. The numerals 10, 20, 30, etc., are used to identify an individual LAN. Bridges between LANs are designated by the numerals 5, 15, 25 and 35. A router between bridged LAN 100 and bridged LAN 200 is identified with the reference numeral 300. In the bridged LAN system depicted, a user A is able to communicate with a user B without leaving the LAN 10. If user A desires to communicate with user C in LAN 20 or user D in LAN 30, the communication is transmitted via bridges 5 and/or 15. If user A desires to communicate with user E, the communication must be routed via router 300 to bridged LAN 200. As will be understood by those skilled in the art, bridges operated at layer 2 of the network model and transparently bridge two LANs. It is transparent to users A and C that communications between them are ported over bridge 5 because layer 2 bridges do not modify packets, except as necessary to comply with the type of destination LAN. However, if user A wishes to communicate with user E, the communication must be ported via router 300 which operates at level 3 of the network model. Accordingly, communications over routers flow at a much slower rate than communications over a bridge, and are regulated by the routers. Therefore, LAN network administrators generally attempt to connect together those users who frequently communicate with each other in bridged LANs. However, if the bridged LAN becomes too large, it becomes unscalable and may experience various well-known problems. Accordingly, routers are used to interconnect bridged LANs so that the bridged LANs themselves can be kept to an acceptable size. This results in delays in communications between users which are transmitted via the router 300. If, for example, in Figure 1, user E and user A need to communicate frequently, it would be advantageous to interconnect LAN 10 and LAN 50 via a bridge rather than the router 300. This would require system rewiring, which is costly and may be impracticable under many circumstances, such as, if users A and E will only need to frequently communicate for a limited period of time. Virtual LANs (VLANs) have recently been developed to address the deficiencies in interconnected bridged LAN systems of the type depicted in Figure 1. VLANs allow LANs to be bridged in virtually any desired manner independent of physical topography with switches operating at layer 2. Hence, the switches are transparent to the user. Furthermore, the bridging of LANs can be changed as desired without the need to rewire the network. Because members of one VLAN cannot transmit to the members of another VLAN, a fire wall is established to provide security that would not be obtainable in a hardwired interconnected bridged LAN system. Accordingly, VLAN systems provide many advantages over interconnected bridged LANs. For example, as shown in Figure 2, individual LANs 10-90 are interconnected by layer 2 switches 5'-55'. A network management station (NMS) 290 controls the interconnection of the individual LANs such that LANs can be easily bridged to other LANs on a long-term or short- term basis without the need to rewire the network. As depicted in Figure 2, the NMS 290 has configured two VLANs by instructing, e.g., programming, and thereby configuring the switches 5 '-55' such that LANs 10-60 are bridged together by switches 5 '-45' and 55' to form VLAN 100' and LANs 70-90 are bridged together by switches 45' and 55' to form VLAN 200'. This is possible because, unlike the bridges 5-35 of Figure 1 which include only two ports, and accordingly are able to only transfer information from one LAN to another LAN, the switches 5'- 55' are multiported and programmable by the NMS 290 such that the network can be configured and reconfigured in any desired manner by simply changing the switch instructions. As shown in Figure 2, the switch 55 ' has been instructed to transmit communications from user A of LAN 10 to user E of LAN 50, since both users are configured within VLAN 100'. User A, however, is not allowed to communicate with users H or F since these users are not configured within the VLAN 100' user group. This does not, however, prohibit users F and H, both of whom are members of VLAN 200', from communicating via switches 45' and 55'. When it becomes desirable to change the network configuration, this is easily accomplished by issuing commands from NMS 290 to the applicable switches 5 '-55'. For example, if desired, user H could be easily added to VLAN 100' by simply reconfiguring VLAN 100' at the NMS 290 to cause an instruction to be issued to switch 55' to allow communications to flow between users A-D and E and user H via switch 55', i.e., to include LAN 90 in VLAN 100' and remove it from VLAN 200'. Since the switches 5 '-55' are layer 2 switches, the bridge formed by the switch is transparent to the users within the VLAN. Hence, the transmission delays normally associated with routers, such as the router 300 of Figure 1, are avoided. The power of the VLAN lies in its ability to dynamically control the network configuration through software on the NMS 290. More particularly, in accordance with its programmed instructions, the NMS 290 generates and transmits signals to instruct the switches 5'-55' to form the desired VLAN configurations. Multicasting refers to the ability of a station on a network to simultaneously communicate a single message to a number of other stations on the network. In a typical LAN protocol, as shown in Figure 3, the communication packet 400 includes a destination address 110 having six bytes, a source address 113, and a message portion 114. The message portion 114 typically includes the applicable LAN protocol. If the I/G (Individual/Group) bit 112 is set to zero, the packet is directed to a single specified address. However, if the I/G bit is set to one, the packet is identified as a multicast packet and is transmitted to all LANs of the bridged LAN. For example, referring to Figure 1, if member A of bridged LAN 100 wishes to multicast to members B and C of bridged LAN 100, the I/G bit of the destination address of the message packet would be set to one. If the I/G bit of the destination address, i.e., the multicast address designator, is at one, the bridges 5 and 15 understand that the communication is a multicast communication and direct the communication to all LANs within the bridged LAN 100 for delivery to the members of the multicast group represented by the multicast address contained in the first five bytes of the MAP address. It will be noted that multicast communications are not routed by routers such as router 300 of Figure 1. Accordingly, in a conventional interconnected bridged LAN system, multicast communications cannot be distributed between bridged LANs. Further, because multicast communications within a bridged LAN are distributed to all individual LANs, e.g.. 10-30 in Figure 1, whether or not any member of aparticular LAN within the bridged LAN is a member of the multicast group to whom the sender has addressed the message, network bandwidth may be unnecessarily utilized to communicate the message to the desired recipients. In a VLAN network, the aforementioned problems are avoided. First, because all switching is done at level 2, i.e., no level 3 routers exist in the system, multicast communications may be transmitted to network members on any LAN within the VLAN. Further, using the NMS 290, a VLAN can be configured to include only those individual LANs that include members to whom it is desired to transmit the multicast message. Accordingly, network bandwidth is not unnecessarily used to transmit multicast messages to individual LANs that lack members of the multicast group to whom the multicast message is addressed. As will be recognized by those skilled in the art, as multicasting continues to grow in popularity, the amount of wasted bandwidth utilization in conventional LAN networks has increased. Hence, multicasting in a VLAN system requires less bandwidth utilization, i.e., multicast communications can be transmitted only to LANs associated with members of the multicast member group, while providing broader user coverage, i.e., multicast communications can be transmitted to any user within a VLAN, as compared to an interconnected bridged LAN system. Hence, VLANs offer a significant advantage over standard LAN architectures in this regard. Further still, because VLANs can be rearranged or reconfigured dynamically, the members within a multicast group can be increased or decreased simply by modifying the multicast member group using the NMS 290 of Figure 2. If multicasting becomes excessive over VLAN 100', the NMS 290 can easily modify the multicast member group to exclude one or more LANs to reduce the multicasting overhead on the VLAN. VLAN 100' can also be easily reconfigured to, for example, include LAN 60, thereby extending the multicast communications capabilities of the VLAN. Figure 4 is a schematic of an exemplary VLAN system. The VLAN system includes LANs 205-260 which are connected by switches 270-280 to a high-speed LAN backbone or trunk 265. An NMS 290 is interconnected to the switches 270-280 via LAN 260. A trunk station 285 is connected to the high-speed LAN backbone 265 via a trunk port 315. The LANs 205-215, and 230-235 have designated members F-J. Each of the switches 270-280 is capable of interconnecting the respective LANs connected to the switch by an access port 305 with each other, e.g., interconnecting LANs 205-220, and with other LANs connected by an access port to another of the switches via the high-speed backbone 265, e.g., LAN 205 with LANs 225-260. For example, switch 270 can be instructed by the NMS 290 to interconnect LAN 205 to LAN 215 by configuring a VLAN including LANs 205 and 215, thereby facilitating communications between F and H. Switches 270 and 275 can also be instructed by the NMS 290 such that member F of LAN 205 can be interconnected to user I of LAN 230, by configuring a VLAN to include LANs 205 and 230. Figure 5 depicts a VLAN communications packet 400' that is identical to the LAN communications packet 400 depicted in Figure 3, except that a VLAN header 116 has been added to the packet. The header is appended by the initial switch to which the message packet is directed. The VLAN header identifies the resulting packet as a "VLAN" or "tagged" packet, and represents the particular VLAN from which the packet originated. For example, if LANs 205, 220 and 230 of Figure 4 are within a single VLAN and member F of LAN 205 desires to communicate with member I of LAN 230, the message 114 of Figure 5 with the MAP address 110 attached is directed to access port 305 of the switch 270. The switch determines, based upon instructions previously received from the NMS 290, that the member I address falls within the applicable VLAN and, accordingly, adds the appropriate VLAN header to the packet to form packet 400', as shown in Figure 5. The packet 400' is then directed via trunk port 315 to the high-speed backbone LAN 265 and detected by switches 275 and 280. Since switch 280 lacks any access ports connected to LANs within the applicable VLAN, switch 280 discards the communication. Switch 275, however, identifies the VLAN header 116 of packet 400' as associated with a VLAN that includes LAN 230. Switch 275 accordingly removes the header and directs the communication, which now appears as message 400 of Figure 3, to LAN 230 over which the member I receives the message. Traditional trunk-resident stations, such as trunk station 285, are incapable of recognizing VLAN headers. Further, since no programmable switch is disposed between a trunk station and the trunk, communications with a VLAN header appended thereto will be ignored and/or discarded by the trunk station. Hence, in conventional VLAN systems, such as that shown in Figure 4, the trunk stations, e.g., trunk station 285, form part of the default group, i.e., the group of system users not within any VLAN. Accordingly, in Figure 4, any system user on LANs 205- 260 can communicate with the trunk station. However, it may be advantageous to limit the number of users who are allowed to communicate with a particular trunk station. For example, if the trunk station 285 is a secure server, it may be appropriate to limit access to trunk station 285 to only members of particular LANs. Accordingly, although conventional VLAN systems have numerous advantages over conventional interconnected bridged LAN systems, a need remains for a VLAN system in which access to trunk stations can be limited to only members of particular LANs within the system. SUMMARY OF THE INVENTION The present invention provides a VLAN system that allows traditional trunk stations, i.e., stations resident on the trunk which are not VLAN-aware, to be configured within a VLAN. Further, the present invention provides a VLAN system that facilitates multicast communications to trunk stations configured within a VLAN without causing looping of traffic. The present invention also provides a VLAN system that facilitates both unicast and multicast communications to trunk stations configured within a VLAN and provides a VLAN system in which a trunk station communicates only with members of LANs within its own VLAN. In accordance with the present invention, a switch is provided for use in a virtual communications network having multiple local area networks interconnected by multiple switches. The multiple switches are connected by a trunk that has one or more trunk stations connected directly thereto. The switch, which is preferably a multiported reconfigurable switch, includes a first communications port, referred to as an access port, connected to a first local area network within a virtual area network, e.g., a virtual local area network (VLAN). The virtual area network includes a second local area network and a trunk station. A second communications port of the switch, referred to as a trunk port, connects to the trunk. A control console detects unicast and multicast communications from the first local area network. When the detected communication is a multicast communication, the control console duplicates the communication to form a first communication and a second communication. The console then appends a VLAN header to the first communication to form a VLAN communication. The control console directs transmission of the VLAN communication and the second communication, i.e., the same communication without the VLAN header, to the second communication port of the switch. Accordingly, the communication can be delivered to the second LAN, based upon recognition of the VLAN communication, and to the trunk station, which will recognize the second communication. Preferably, if the virtual area network is configured to include a trunk station, even if the communication is to be multicast only to multiple trunk stations or multiple local area networks within the virtual area network, the communication is duplicated, tagged with a VLAN header and directed as described above. However, if desired, only multicast communications addressed to both a trunk station and local area network included in the virtual area network could be duplicated, although this might result in increased processing overhead at the switch. When the control console detects a unicast communication from the first local area network and identifies the addressee of the message as the trunk station, the unicast communication is transmitted to the second communication port without appending a VLAN header thereto, and without duplicating the message. On the other hand, when the control console detects a unicast communication from the first local area network and identifies the addressee of the message as the second local area network, the unicast communication is transmitted to the second communication port with the VLAN header appended thereto but without duplicating the message. When the control console detects a unicast communication from the first local area network to a trunk station that is not configured within the virtual area network, the control console will not direct transmission of the unicast communication to the second communication port, unless the trunk station is a member of the default group. In accordance with other aspects of the invention, a virtual communications system includes a first switch and a second switch, each connected to the trunk by a trunk port. A trunk station is also connected to the trunk by a trunk port. A first local area network is connected to the first switch and a second local area network is connected to the second switch by access ports. A network manager is connected to the first and the second switches for configuring virtual area networks. If a network is configured to include the first local area network and the trunk station, but to exclude the second local area network, the first switch directs communications from the first local area network to the trunk station based upon the configuration of such a virtual area network by the network manager. The second switch prevents communications from the second local area network to the trunk station based upon the virtual area network configuration. Accordingly, communications from the first local area network to the trunk station are delivered by the system while delivery of communications from the second local area network to the trunk station is prohibited. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be readily appreciated as the same becomes better understood by reference to the accompanying drawings, in which like reference numerals designate like or corresponding parts throughout, and which are not limiting, wherein: Figure 1 depicts a conventional LAN configuration; Figure 2 depicts a conventional VLAN configuration; Figure 3 depicts a conventional LAN message packet; Figure 4 depicts a schematic diagram of a conventional VLAN system; Figure 5 depicts a conventional VLAN message packet; Figure 6 depicts a schematic diagram of a VLAN system in accordance with the present invention; Figure 7 depicts a switch in accordance with the present invention for use in the system as shown in Figure 6; and Figure 8 depicts a VLAN configuration in accordance with the present invention. DETAILED DESCRIPTION Figure 6 depicts a virtual communications system or network in accordance with the present invention. The network includes multiple local area networks (LANs) 205-260 interconnected by multiple multiported reconfigurable switches 270', 275' and 280', all of which are connected by a high-speed backbone LAN 265, often referred to as the trunk. Each LAN, other than the backbone LAN 265, is connected to one of the switches 270', 275' or 280' by an access port 305, while the backbone LAN 265 is connected to each switch by a trunk port 315. A network management system (NMS) 290', which may be a workstation having the network management software loaded thereon, manages the network by configuring the network via the switches 270', 275' and 280' to form one or more virtual local area networks (VLANs). Each of the trunk stations 285 and 287 is connected to the backbone LAN 265 via a trunk port 315. The trunk stations 285 and 287 may be, for example, network servers or other network resources to which some or all of the members of the LANs 205-260 may require high-speed access from time to time or on a continuous basis as is well understood in the art. Referring to Figures 6 and 7, each of switches 270', 275' and 280' is capable of linking, via the backbone LAN 265, members of each of the LANs 205-260 to members of the one or more LANs and the trunk stations within the VLANs configured by the NMS 290'. In accordance with the present invention, the NMS 290' may configure any or all of these VLANs to include the trunk stations 285 and 287, as will be further described below. As shown in Figure 7, each of the switches 270', 275' and 280' includes a control console 288 having a control module 284 and a memory 286 for storing and processing control and VLAN configuration instructions and data that may be initially programmed into the switch or transmitted to the switch by the NMS 290'. The control module 284 includes a controller 284a for controlling a switching device 282. The detector 284b detects a communication received from the backbone 265 via a trunk port 315 or from a LAN directly connected to the switch via an access port 305. Communications from the backbone 265 may or may not include a VLAN header of the type previously described with reference to Figure 5. For example, communications from a LAN to a member of the default group will not be tagged, i.e., appended with a VLAN header, by the switch to which the LAN connects via an access port 305. Thus, if one of the LANs within the system is in the default group, communications to this LAN from members of other LANs will not be tagged. The detector 284b detects all communications over the backbone LAN 265, including, in the case of switches 270' and 275', communications from the NMS 290'. Switch 280' detects communications from the NMS at the access port connected to LAN 260. If the detected communication is deliverable to a network addressee on any of the LANs connected to an access port of the applicable switch, the controller 284a of the applicable switch controls the switching device 282 to transmit the message from the trunk port 315 to the applicable access port 305. That is, if the detected communication is properly addressed to the addressee and forwarded from an authorized member of the system, e.g., from a member of a VLAN that includes the addressee's LAN or from any other member of the system if the addressee is a member of the default group, the controller 284a of the applicable switch controls the switching device 282 to transmit the message to the applicable LAN. The control module 284 also includes a tagger 284c for tagging communications received via an access port 305 for transmission from one member to another member of a configured VLAN by appending a VLAN header thereto. The tagger 284c also removes the VLAN header from a communication received from the switch's trunk port 315 that is to be forwarded to a member of a LAN connected to the switch by an access port. More particularly, the tagger 284c discards the tag by removing the VLAN header from the communication, prior to the message being transmitted to the appropriate output port 305, i.e., prior to the controller 284a controlling the switching device 282 to transmit the message from the trunk port 315 to the access port 305. When the detected communication has been received via an access port 305 of the switch and is properly addressed and deliverable to a network addressee on any of the other LANs connected to the switch, the controller 284a of the switch controls the switching device 282 to transmit the message from the input access port 305 to the applicable output access port 305. In such a case, when the sender and addressee are members of the same VLAN, there is no need to append a VLAN header to the communication before directing it to output port 305. However, when such a communication is to be multicast to one or more LANs within the applicable VLAN that are directly connected to other switches by access ports, the communication output from the trunk port 315 of the applicable switch will, of course, be tagged by the tagger before transmission via the trunk 265 as discussed above. Accordingly, all messages between LANs within configured VLANs are forwarded to the appropriate addressee LAN. This is accomplished by identifying communications between LANs within configured VLANs and tagging the communications, except for those between LANs connected by an access port to the same switch, with a VLAN header. Referring now to Figure 8, the operation of the VLAN system and the switches depicted in Figures 6 and 7 will be described. As shown, the NMS 290' has configured the VLAN system into a first VLAN 800 that includes LANs 235-250 and trunk stations 285 and 287. The NMS 290' has also configured a second VLAN 900 to include LANs 210-230. Each of the switches has accordingly been instructed and preferably stores information representing each of the VLAN configurations in its memory 286 for use by the control module 284 in detecting, tagging and removing tags from communications received via access ports 305 and trunk port 315, and in controlling the switching device 282. Since the trunk stations 285 and 287 are excluded from the VLAN 900, attempted communications between the trunk stations 285 and 287 and members of LANs 210-230 that are received by the applicable switch via an access or trunk port are ignored and/or discarded, since the sender and addressee are not within the same VLAN. Further, default group LANs 205, 255 and 260 are likewise prohibited from communicating with the trunk stations 285 and 287. Members of each of the LANs 235-250 are allowed by the applicable switch 275' or 280' to send unicast or multicast communications to the trunk stations 285 and 287. For example, when a member of LAN 250 desires to send a unicast a message to the trunk station 285, the communication received at the access port of the switch 280' will be detected by the detector 284b. The control module 284 determines, utilizing the stored configuration data, that the message is addressed to a trunk station within VLAN 800 and therefore controls, by way of the controller 284a, the switching device 282 to output the communication to the trunk 265 via the trunk port 315. Since the communication has been determined by the control module to be addressed to a trunk station on the sender's VLAN, the communication is output from the trunk port without a VLAN header being appended thereto. Accordingly, the trunk station 285, which is unable to recognize communications encapsulated with a VLAN header, is able to recognize the untagged communication from the LAN 250 and thereby receives the message from the sender. The switches 270' and 275' in the VLAN system will also receive the communication. However, since the message has been forwarded without a VLAN header, it will be ignored and/or discarded by switch 275' which has access ports connecting only to LANs within configured VLANs, i.e. LANs 225-240. The switches 270' and 280', which have access ports connecting to LANs within the default group, i.e., LANs 205, 255 and 260, after determining that the communication is not addressed to any of the members of these LANs, will likewise ignore and/or discard the communication. The trunk station 287 will also detect the communication and, after determining that the communication is not addressed to it, will ignore and/or discard the communication. Hence, since the communication is addressed only to the trunk station 285, except for the transmission by the communication by switch 280' to the trunk 265, the switches and the trunk station 287 will ignore the communication. When the trunk station 285 sends a unicast message to a member of the LAN 250, the communication received at the trunk port 315 of the switch 280' will be detected by the detector 284b. The control module 284 will determine, utilizing the stored configuration data, that the LAN 250 and the trunk station 285 are both configured within VLAN 800, and therefore will control, by way of the controller 284a, the switching device 282 to output the communication to the LAN 250 via the applicable access port 305. Accordingly, the switch 280' is able to recognize the untagged communication from the trunk station 285 and forward the message to the addressee on the LAN 250 in accordance with the instructions previously received from the NMS 290'. The switches 270' and 275' in the VLAN system will also receive the communication transmitted from trunk station 285. However, because the message has been forwarded without a VLAN header, it will be ignored and/or discarded by switch 275', which has access ports connecting only to LANs within configured VLANs, i.e., LANs 225-240. The switch 270', which has an access port connecting to a LAN within the default group, i.e. LAN 205, after determining that the communication is not addressed to any of the members of the LAN 205, will likewise ignore and/or discard the communication. The trunk station 287 will also detect the communication and, after determining that the communication is not addressed to it, will ignore and/or discard the communication. Hence, since the communication is addressed only to a member of LAN 250, except for the transmission of the communication by the switch 280' from the trunk port 315 to the applicable access port 305, the switches 270'-280' and the trunk station 287 will ignore the communication after detection. When a member of LAN 235 desires to send a multicast communication to trunk station 287 and a member of LAN 245, the switch 275', which receives the communication via an access port 305, will detect the communication by means of detector 284b. The control module 284 will then determine, based upon configuration data stored in the memory 286, that the multicast communication is addressed to members of VLAN 800. It will also recognize from the configuration data that VLAN 800 includes both trunk stations and other LANs. Accordingly, the control module 284 will duplicate the communication. One copy of the communication will be tagged by the tagger 284c with a VLAN header, thus encapsulating that copy of the communication so as to form a VLAN communication. The controller 284a will then control the switching device 282 to output both the encapsulated communication and the unencapsulated communication to the backbone 265 via the switch's trunk port 315. The encapsulated message is received by the switch 280' at the trunk port 315 connected to the backbone 265. The detector 284b of switch 280' detects the VLAN header and recognizes, based upon the configuration data stored in its memory 286, that LANs 245 and 250 are members of the VLAN 800. Accordingly, the tagger 284c of the switch removes and discards the VLAN header from the communication and the controller 284a controls the switching device 282 such that the communication, with the header now removed, is directed via output access ports 305 to LANs 245 and 250. The message is discarded by LAN 250 and delivered by LAN 245 to the appropriate addressee in the conventional manner. The unencapsulated message output from the trunk port 315 of the switch 280' is received, via the trunk 265, by the trunk station 285 and thereby delivered to the trunk station. Accordingly, by configuring the trunk stations 285 and 287 within VLAN 800, members of VLAN 800 can send unicast or multicast communications to the trunk stations. When a member of LAN 240 desires to multicast only to LANs 235, 245 and 250, the switch 275', to which the LAN 240 is connected by an access port 305, detects the message with its detector 284b and, recognizing the message as a multicast communication to members of VLAN 800 that includes trunk stations, will automatically duplicate the communication, tag one copy of the communication and transmit both the encapsulated and unencapsulated copies of the communication to the trunk 265 via the trunk port 315. Similarly, should a member of LAN 240 desire to send a multicast communication only to trunk stations 285 and 287, the switch 275', to which LAN 240 is connected via an access port 305, duplicates and tags one copy of the communication before outputting both the encapsulated and unencapsulated communications to the trunk 265 via the switch's trunk port 315. Since the trunk stations 285 and 287 are configured within the VLAN 800, a fire wall is provided between the trunk stations 285 and 287 and the members of LANs 205-230 and 255- 260. As discussed above, when desired, the LAN 800 may be easily reconfigured by the NMS 290' to delete any of the LANs 235-250 or trunk stations 285 and 287 from the VLAN 800. The system can also be easily reconfigured by the NMS 290' to add any of the LANs 205-230 and 255-260 to the VLAN 800 so as to allow other members of the system to communicate with the trunk stations 285 and 287. As described in detail above, a VLAN system is provided that allows trunk stations to be configured into VLANs. The system facilitates both secure unicast and multicast communications with trunk stations. In the described VLAN system, trunk stations communicate using unicast and multicast only with members of LANs that are configured with the trunk station(s) into a VLAN. It will also be recognized by those skilled in the art that, while the invention has been described above in terms of one or more preferred embodiments, it is not limited thereto. Various features and aspects of the above described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment and for particular purposes, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially utilized in any number of environments and implementations. Accordingly, the claims set forth below should be construed in view of the full breadth of the invention as disclosed herein.

Claims: CLAIMS 1. A switch for use in a virtual communications system having multiple local area networks interconnected by multiple switches that are connected by a trunk, having one or more trunk stations connected directly thereto, the switch comprising: a first communications port configured to connect to a first local area network within a virtual area network having a second local area network and a trunk station; a second communications port configured to connect to the trunk; and a control console configured to detect a multicast communication from the first local area network, to duplicate the multicast communication to form a first communication and a second communication, to append a VLAN header to the first communication to form a VLAN communication, and to direct transmission of the VLAN communication and the second communication to the second communication port. 2. The switch according to claim 1, wherein: the second local area network is one of multiple other local area networks within the virtual area network; and the multicast communication is only addressed to at least two of the multiple other local area networks. 3. The switch according to claim 1, wherein: the trunk station is one of multiple trunk stations within the virtual area network; and the multicast communication is only addressed to at least two of the multiple trunk stations. 4. The switch according to claim 1, wherein the control console is further configured to detect a unicast communication from the first local area network, to identify the addressee of the unicast message as the trunk station, and to direct transmission of the unicast communication, without appending a VLAN header thereto, to the second communication port. 5. The switch according to claim 1, wherein: the switch is a multiported reconfigurable switch; the first communications port is an access port; the second communications port is a first trunk port; and the trunk station is connected to the trunk by a second trunk port. 6. A method of communicating messages in a virtual area network having multiple local area networks interconnected by multiple switches that are connected by a trunk, having one or more trunk stations connected directly thereto, the method comprising: detecting a multicast communication from a first local area network configured within a virtual area network that includes a second local area network and a trunk station; duplicating the detected multicast communication to form a first communication and a second communication; appending a VLAN header to the first communication to form a VLAN communication; and directing transmission of the VLAN communication and the second communication to the trunk. 7. The method according to claim 6, wherein: the second local area network is one of multiple other local area networks within the virtual area network; and addressees of the multicast communication exclude trunk stations. 8. The method according to claim 6, wherein: the trunk station is one of multiple trunk stations within the virtual area network; and addressees of the multicast communication exclude members of local area networks. 9. The method according to claim 6, further comprising: detecting a unicast communication from the first local area network; identifying an addressee of the detected unicast communication as the trunk station; and directing transmission of the unicast communication, without appending a VLAN header thereto, to the trunk. 10. A switch for use in a virtual communications system having multiple local area networks interconnected by multiple switches that are connected by a trunk, having one or more trunk stations connected directly thereto, the switch comprising: a first communications port configured to connect to a first local area network, the first local area network being within a virtual area network; a second communications port configured to connect to the trunk; and a control console configured to detect a unicast communication from the first local area network to a trunk station, and to direct transmission of the unicast communication to the second communication port when the trunk station is determined to be within the virtual area network. 11. The switch according to claim 10, wherein, when the trunk station is determined to be within the virtual area network, the control console is further configured to direct transmission of the unicast communication, without appending a VLAN header thereto. 12. The switch according to claim 10, wherein: the switch is a multiported reconfigurable switch; the first communications port is an access port; the second communications port is a first trunk port; and the trunk station is connected to the trunk by a second trunk port. 13. A method of communicating messages in a virtual area network having multiple local area networks interconnected by multiple switches that are connected by a trunk having one or more trunk stations connected directly thereto, the method comprising: detecting a unicast communication from the first local area network to a trunk station, the first local area network being within a virtual area network; and directing transmission of the detected unicast communication to the trunk when the trunk station is determined to be within the virtual area network. 14. The method according to claim 13, wherein the unicast communication is directed to the trunk without a VLAN header appended thereto. 15. A virtual communications system, comprising: a trunk; a first switch connected to the trunk by a first trunk port; a second switch connected to the trunk by a second trunk port; a trunk station connected to the trunk by a third trunk port; a first local area network connected to the first switch by an access port; a second local area network connected to the second switch by an access port; and a network manager interconnected to the first and the second switches to configure a virtual area network including the first local area network and the trunk station and excluding the second local area network. 16. The virtual communications system according to claim 15, wherein the first switch is configured to direct communications from the first local area network to the trunk station. 17. The virtual communications system according to claim 15, wherein the second switch is configured to prevent communications from the second local area network to the trunk station. 18. A method of communicating messages in a virtual communications system having multiple local area networks interconnected by multiple switches that are connected by a trunk having one or more trunk stations connected directly thereto, the method comprising: configuring a virtual area network so as to include a first local area network and a trunk station and to exclude a second local area network; delivering communications from the first local area network to the trunk station; and prohibiting delivery of communications from the second local area network to the trunk station.

Inventors: RIJHSINGHANI ANIL G, RIJHSINGHANI, ANIL, G.
Applicants: CABLETRON SYSTEMS INC, CABLETRON SYSTEMS, INC.
Application year: 1999
Main classification: H04L12
IPC codes: H04L12