Abstract:
Provided is a management computer which reduces the workload of an administrator of a network in setting node when the normal network is changed to a network with redundancy. The management computer manages a plurality of nodes that constitute a network accommodating VLANs. The plurality of nodes include a first node and a second node which make a redundancy pair and which divides the network into an active path and a standby path. The management computer stores port management information showing connection relations for respective nodes and identifiers of VLANs allocated to ports of the nodes, and creates the redundancy pair by updating the port management information of the first node such that a VLAN allocated to one of ports of a connected node that is connected to the first node is allocated to one of ports of the first node that is connected to the connected node.

Description:
CLAIM OF PRIORITY 
     The present application claims priorities from Japanese patent application P2007-118360 filed on Apr. 27, 2007, and Japanese patent application P2007-339630 filed on Dec. 28, 2007, the content of which are hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     This invention relates to a management computer for network management and, more particularly, to a management computer that automatically sets switches constituting a network. 
     The networking of business operations (including mission-critical applications) in a corporation has lately become increasingly common, which has created a demand for improved network availability. 
     In a conventional network, a failure in a network device such as a switch or a router is dealt with by the administrator of the network by manually replacing the failed network device. This lowers the availability of the network significantly since communication cannot be held over the network until the failed network device is replaced with a functioning one. 
     There has been known a protocol called spanning tree protocol (STP). The STP is for controlling switches that constitute a network such that the network recovers automatically from a failure. When a failure occurs in the network, the switches autonomously execute processing of recovering from the network failure using the STP. The STP, with which failure recovery processing is automatically executed upon failure in a network, improves the network availability, compared to manual recovery from a network failure by a network administrator. 
     A virtual router redundancy protocol (VRRP) and a gigabit switch redundancy protocol (GSRP) are protocols that can improve the network availability even more. The extent to which these protocols are effective for recovery from a failure is limited to adjacent (interconnected) network devices. The VRRP and GSRP are control protocols for redundancy switches formed of an active switch and a standby switch. The VRRP and GSRP win hereinafter be referred to as redundant system control protocols. 
     With redundant system control protocols whose failure recovery extent is limited to adjacent network appliances, a network can recover from a failure more quickly than when the STP is employed. 
     To apply a redundant system control protocol, the administrator of a network connects both switches that constitute redundancy switches to other switches in the network. The network administrator then sets an active path which runs through one of the switches constituting the redundancy switches and a standby path which runs through the other switch constituting the redundancy switches. Of the two switches constituting the redundancy switches, the one through which the active path runs is called an active switch and the one through which the standby path runs is called a standby switch. 
     The network administrator activates the redundant system control protocol between the active switch and the standby switch. The active switch uses the redundant system control protocol to monitor the operation state of the standby switch while the standby switch uses the redundant system control protocol to monitor the operation state of the active switch. 
     One of ports that the standby switch has is connected to the active switch and the rest of the ports are set to a standby state in which communication is stopped until a failure occurs in the active switch. The ports in the standby state are subjects of automatic recovery processing which is executed with the use of the redundant system control protocol. 
     In the case where the redundant system control protocol is the GSRP, the network administrator sets one of ports of the active switch that is connected to the standby switch and the port of the standby switch that is connected to the active switch as ports that are used in mutual switch monitoring communication according to the GSRP. 
     SUMMARY OF THE INVENTION 
     The network administrator logically partitions the network to build a plurality of virtual LANs (VLAN: Virtual Local Area Network) within the network constituted of switches. The network administrator controls access to the VLANs from user terminals by specifying (defining) for each switch which port accesses which VLAN. A port that is connected to a switch transfers packets of a plurality of VLANs in a multiplexed fashion, and the network administrator therefore must assign a plurality of VLANs to a port that is connected to a switch. 
     To apply a redundant system control protocol to a network that is constituted of switches to which VLANs are assigned, the administrator of the network sets, for every VLAN that is to be provided redundancy, two switches constituting redundancy switches and a plurality of switches connected to the redundancy switches. The network administrator needs to set the ports such that ports on the active path and ports on the standby path are allocated to the same VLAN in order to ensure that the same VLAN is accessed either via the active path or via the standby path. 
     In installing a new switch to a network, the administrator of the network has to set the connection relation between the new switch to be introduced and existing switches, and VLANs to be allocated to ports of the new switch as well as ports of the existing switches. The network administrator also needs to design the network configuration such that two switches constituting redundancy switches are connected directly in the case where the GSRP is employed as a redundant system control protocol. 
     To change an existing network that does not have a redundancy configuration into a redundancy configuration network by adding a new switch to the existing network, the administrator of the network has to change the settings of an existing switch that is to be provided redundancy, the settings of the new switch, and the settings of all switches that are to be connected to the existing switch to be provided redundancy and to the new switch. 
     Specifically, the network administrator has to set the inter-switch connection relation and VLANs for all of the above switches. This means that the larger the network scale, the more switches need settings change by the network administrator. An increase in network scale therefore increases the workload of the network administrator, who will find it difficult to change the settings of switches correctly and timely. 
     This invention has been made in view of the above, and it is a first object of this invention to facilitate the introduction of a redundancy configuration to a large-scale network by reducing the workload of the administrator of the network that is required to change the settings of switches. 
     In a large-scale network where the administrator of the network has a greater workload in changing the settings of switches, the probability that the network administrator makes mistakes in setting switches is higher than in networks of smaller scale. Setting switches erroneously is a factor in the lowering of network availability. 
     It is a second object of this invention to reduce switch setting errors in a large-scale network when the network configuration is changed by reducing the workload of the administrator of the network that is required to change the settings of switches. 
     According to one embodiment of the invention, there is therefore provided a management computer connected to a plurality of nodes each having a plurality of ports, comprising: a transmission module for sending a configuration definition to each of the plurality of nodes; an input module for receiving an input of network configuration information containing free port information of each of the plurality of nodes and information on a VLAN set between at least two of the plurality of nodes; and a display module for using graphics representing the plurality of nodes and connection relations between the plurality of nodes to display latest network configuration information reflecting the network configuration information received as the input, wherein the input module further receives a selection of one of a node and a connection relation that is selected, out of the plurality of nodes and the connection relations, to be provided redundancy, wherein the display module further displays the network configuration information including a redundancy configuration with the use of graphics representing the plurality of nodes, the node that has been provided redundancy, the connection relations, and the connection relation that has been provided redundancy, wherein the input module further receives an input of a confirmation of the network configuration information, and wherein, based on the input of the confirmation, the transmission module sends, to each of the plurality of nodes, respective configuration definitions of the plurality of nodes in a network configuration with the redundancy configuration. 
     According to a mode of this invention, less workload is required of the administrator of a network to set switches when the network is changed into a network that has redundancy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be appreciated by the description which follows in conjunction with the following figures, wherein: 
         FIG. 1  is a diagram showing the configuration of a computer system according to the first embodiment of this invention; 
         FIG. 2  is a diagram showing the configuration of the network according to the first embodiment of this invention; 
         FIG. 3  is a diagram showing the configuration of the management server according to the first embodiment of this invention; 
         FIG. 4  is a sequence diagram for network designing through the management server according to the first embodiment of this invention; 
         FIG. 5  is a diagram illustrating the network configuration input screen according to the first embodiment of this invention; 
         FIG. 6  is a diagram showing the configuration of a port information management table which is created for the switch after a network configuration is entered by the administrator according to the first embodiment of this invention; 
         FIG. 7  is a diagram showing the configuration of a port information management table which is created for the switch after a network configuration is entered by the administrator according to the first embodiment of this invention; 
         FIG. 8  is a diagram showing the configuration of a port information management table which is created for the switch after a network configuration is entered by the administrator according to the first embodiment of this invention; 
         FIG. 9  is a diagram showing the configuration of a port information management table which is created for the switch after a network configuration is entered by the administrator according to the first embodiment of this invention; 
         FIG. 10  is a diagram showing the configuration of a VLAN information management table which is created for the switch after a network configuration is entered by the administrator according to the first embodiment of this invention; 
         FIG. 11  is a diagram showing the configuration of a VLAN information management table which is created for the switch after a network configuration is entered by the administrator according to the first embodiment of this invention; 
         FIG. 12  is a diagram showing the configuration of a VLAN information management table which is created for the switch after a network configuration is entered by the administrator according to the first embodiment of this invention; 
         FIG. 13  is a diagram showing the configuration of a VLAN information management table which is created for the switch after a network configuration is entered by the administrator according to the first embodiment of this invention; 
         FIG. 14  is a diagram illustrating the redundancy switch specifying screen for specifying which switch is to be provided redundancy according to the first embodiment of this invention; 
         FIG. 15  is a flow chart of redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 16  is a flow chart of redundant link creating processing according to the first embodiment of this invention; 
         FIG. 17  is a diagram showing a redundant system display screen, which is used to check the network after the redundancy configuration creating processing is executed according to the first embodiment of this invention; 
         FIG. 18  is a diagram showing the port information management table for the switch to be provided redundancy that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 19  is a diagram showing the port information management table for the switch that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 20  is a diagram showing the port information management table for the switch that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 21  is a diagram showing the port information management table for the switch that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 22  is a diagram showing the port information management table for the switch that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 23  is a diagram showing the VLAN information management table for the switch that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 24  is a diagram showing the VLAN information management table  2123  for the switch that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 25  is a diagram showing the VLAN information management table for the switch that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 26  is a diagram showing the VLAN information management table for the switch to be provided redundancy that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 27  is a diagram showing a VLAN information management table  2125  for the new switch that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 28  is a diagram showing the redundant system management table that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention; 
         FIG. 29  is a diagram illustrating an update message  2051  for updating the settings of the switch according to the first embodiment of this invention; 
         FIG. 30  is a diagram illustrating an update message  2052  for updating the settings of the switch according to the first embodiment of this invention; 
         FIG. 31  is a diagram illustrating an update message  2053  for updating the settings of the switch according to the first embodiment of this invention; 
         FIG. 32  is a diagram illustrating an update message for updating the settings of the switch according to the first embodiment of this invention; 
         FIG. 33  is a diagram illustrating an update message  2055  for updating the settings of the switch according to the first embodiment of this invention; 
         FIG. 34  is a sequence diagram of network designing in the management server when two of the switches constituting a network are selected as the switches that serve as redundancy switches according to the second embodiment of this invention; 
         FIG. 35  is a flow chart showing redundancy condition judging processing according to the second embodiment of this invention; 
         FIG. 36  is a sequence diagram of network designing in the management server according to the third embodiment of this invention; 
         FIG. 37  is a sequence diagram of network designing in the management server according to the fourth embodiment of this invention; and, 
         FIG. 38  is a flow chart of redundancy pair search processing according to the fourth embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment of this invention will be described below with reference to  FIGS. 1 to 33 . 
       FIG. 1  is a diagram showing the configuration of a computer system according to the first embodiment of this invention. 
     This computer system contains a management server  2  and a network  4 , which is managed by the management server  2 . 
     An administrator  1  of the network  4  can know the configuration of the network  4  through an input/output device of the management server  2 , on which the configuration of the network  4  is displayed. The administrator  1  can also enter an instruction for providing the network  4  redundancy to the input/output device of the management server  2 . 
     The management server  2  is connected to the network  4  to receive link information, which indicates the connection relation between network devices  3 . The management server  2  sets the settings of the network devices  3  using a protocol for setting the network devices  3 . The network devices  3  are, for example, routers, switches, and user terminals. 
       FIG. 2  is a diagram showing the configuration of the network  4  according to the first embodiment of this invention. 
     The network  4  includes the management server  2 , switches  301  to  305 , and user terminals  341  to  344 . The switches  301  to  305  will collectively be referred to as switches  300 , and the user terminals  341  to  344  will collectively be referred to as user terminals  340 . 
     The switch  301  and the switch  305  are the most upstream switches of the network  4 , and are called core switches  351  which are positioned at the center of the network  4 . The switches  301  and  305  are connected directly to each other. 
     The switches  302  to  304  are floor switches which directly accommodate other devices than the switches  300  (in this embodiment, the management server  2  and the user terminals  341  and  342 ). The switches  302  to  304  are directly connected to both of the core switches: the switches  301  and  305 . This provides redundancy to the switches  301  and  305  which are core switches and, when a failure occurs in one of the switches  301  and  305 , the switches  302  to  304  which are floor switches can communicate with either the switch  301  or the switch  305  that is not suffering from the failure. 
     The management server  2 , shown as element  331 , is connected to the switch  302  and belongs to a VLAN  99 . The user terminals  341  and  342  are connected to the switch  303 , and the user terminal  341  belongs to a VLAN  10  whereas the user terminal  342  belongs to a VLAN  20 . The user terminals  343  and  344  are connected to the switch  304 , and the user terminal  343  belongs to the VLAN  20  whereas the user terminal  344  belongs to the VLAN  10 . 
       FIG. 3  is a diagram showing the configuration of the management server  2  according to the first embodiment of this invention. 
     The management server  2  has a memory  20 , an input/output interface (I/F)  21 , a network interface (I/F)  22 , and a CPU  24 . 
     The management server  2  connects with an input/output device  23  via the input/output I/F  21 . The input/output device  23  includes, for example, a display, a keyboard, and a mouse. The management server  2  connects with the network  4  via the network I/F  22 . 
     The memory  20  contains an OS  203 , an device setting program  204 , a redundancy configuration settings creating program  211 , an device settings information database  205 , a VLAN information management table  212 , a port information management table  213 , and a redundant system management table  214 . The CPU  24  executes various programs loaded onto the memory  20 . 
     The device setting program  204  is run on the OS  203 , sets a VLAN to each switch  300 , and sets ports that connect the switch  301  and the switch  305  as GSRP ports. The device setting program  204  uses a command line interface, Net.conf, or the like to set the switches  300 . The device settings information database  205  holds the settings of the switches  300  in the form of data readable and writable through the OS  203 . 
     The redundancy configuration settings creating program  211  is run on the OS  203  and creates settings for the switches  300  that are necessary to provide redundancy to the network  4 . 
     The VLAN information management table  212  is used to manage VLANs set to the respective switches  300  in the form of data readable and writable through the OS  203  and sorted by switch  300 . Details of the VLAN information management table  212  will be described with reference to  FIGS. 10 to 13 . 
     The port information management table  213  is used to manage the utilization state of ports of the respective switches  300  in the form of data readable and writable through the OS  203 . Details of the port information management table  213  will be described with reference to  FIGS. 6 to 9 . 
     The redundant system management table  214  is used to manage the connection relation between two switches that constitute redundancy switches in the form of data readable and writable through the OS  203 . Details of the redundant system management table  214  will be described with reference to  FIG. 28 . 
       FIG. 4  is a sequence diagram for network designing through the management server  2  according to the first embodiment of this invention. 
     First, the administrator  1  enters a network configuration to the management server  2  via a network configuration input screen  230 , which is displayed on the input/output device  23  (S 701 ). Details of the network configuration input screen  230  will be described with reference to  FIG. 5 . 
     Based on the entered network configuration, the management server  2  updates network information managed in the VLAN information management table  212 , the port information management table  213 , and the redundant system management table  214  (S 702 ). 
     The management server  2  then makes the entered network configuration reflected on the network configuration input screen  230  to display the network configuration on the input/output device  23  (S 703 ). 
     Next, the administrator  1  specifies which switch  300  is to be provided redundancy via a redundancy switch specifying screen  234 , which is shown in  FIG. 14 , and via the network configuration input screen  230  (S 704 ). 
     The management server  2  creates a network configuration necessary to give the specified switch  300  redundancy (S 705 ). Based on the created network configuration, the management server  2  updates network information managed in the VLAN information management table  212 , the port information management table  213 , and the redundant system management table  214  (S 706 ). The management server  2  makes the updated network configuration reflected on the network configuration input screen  230  to display the network configuration on the input/output device  23  (S 707 ). 
     The administrator  1  checks whether the network configuration that is displayed by the input/output device  23  in the network configuration input screen  230  matches the actual configuration of the network  4  (S 708 ). When the network configuration that is displayed by the input/output device  23  in the network configuration input screen  230  matches the actual configuration of the network  4 , the administrator  1  instructs the management server  2  via the input/output device  23  to update the settings of the switches  300  (S 709 ). 
     Receiving this instruction, the management server  2  sends an instruction to update the settings to the switches  300  (S 710 ). Each switch  300  that has received the instruction from the management server  2  updates its settings (S 711 ). 
     The management server  2  thus automatically creates settings for the respective switches  300  that are necessary to give the network  4  redundancy and updates the settings of the respective switches  300 , thereby reducing the workload of the administrator  1 . 
       FIG. 5  is a diagram illustrating the network configuration input screen  230  according to the first embodiment of this invention. 
     The network configuration input screen  230  contains an edit window  231 , an edit palette  232 , and an edit canvas  233 . 
     The edit window  231  is a window used by the administrator  1  to edit the network configuration. The edit palette  232  contains icons representing the switches  300 , icons indicating connections between network devices, icons representing the user terminals  340 , and the like. Displayed on the edit canvas  233  is a drawing of a network designed by the administrator  1 . 
     The administrator  1  picks up one of the icons in the edit palette  232  and drag-and-drops the icon to place it on the edit canvas  233 . The management server  2  newly displays the placed icon on the edit canvas  233 . The administrator  1  informs the management server  2  of a new network configuration by operating icons that indicate connections between network devices displayed on the edit canvas  233  in a manner that connects the network devices to one another. 
       FIGS. 6 to 9  are diagrams showing the configuration of the port information management table  213  according to the first embodiment of this invention. 
     The port information management table  213  is created for each switch  300  managed by the management server  2 . 
     The port information management table  213  contains in each entry a port identifier  21301 , a connected node identifier  21302 , a connected port identifier  21303 , and a VLAN identifier  21304 . 
     Registered as the port identifier  21301  is an identifier unique to each port of the switch  300  for which the port information management table  213  in question is created. 
     Registered as the connected node identifier  21302  is an identifier unique to a specific network device that is connected to the port of the switch  300  corresponding to the port information management table  213 . When one port of this switch  300  is connected with another switch  300 , an identifier unique to the another switch  300  is registered as the connected node identifier  21302 . When one port of this switch  300  is connected with one of the user terminals  340  or with the management server  2 , a uniform identifier indicating that the connected device is none of the switches  300  is registered as the connected node identifier  21302 . The identifier indicating that the connected device is none of the switches  300  is “ 999 ” in this embodiment. 
     Registered as the connected port identifier  21303  is an identifier unique to a specific port of the connected switch  300  that is connected to the port identified by the port identifier  21301 . When the connected node is an device other than the switches  300 , nothing is registered as the connected port identifier  21303 . 
     Registered as the VLAN identifier  21304  is an identifier unique to a VLAN that is allocated to a specific port of the switch  300  corresponding to the port information management table  213 . 
       FIG. 6  is a diagram showing the configuration of a port information management table  2131  which is created for the switch  301  after a network configuration is entered by the administrator  1  according to the first embodiment of this invention. 
     The port information management table  2131  shows that a port “ 0 ” of the switch  301  is connected to a port “ 6 ” of the switch  302 , a port “ 1 ” of the switch  301  is connected to a port “ 6 ” of the switch  303 , and a port “ 2 ” of the switch  301  is connected to a port “ 6 ” of the switch  304 . 
     The port information management table  2131  also shows that the VLAN  99  is allocated to the port “ 0 ” of the switch  301 , the VLAN  10 , the VLAN  20 , and the VLAN  99  are allocated to the port “ 1 ” of the switch  301 , and the VLAN  10 , the VLAN  20 , and the VLAN  99  are allocated to the port “ 2 ” of the switch  301 . 
       FIG. 7  is a diagram showing the configuration of a port information management table  2132  which is created for the switch  302  after a network configuration is entered by the administrator  1  according to the first embodiment of this invention. 
     The port information management table  2132  shows that a port “ 0 ” of the switch  302  is connected to an device other than the switch  300 , and a port “ 6 ” of the switch  302  is connected to a port “ 0 ” of the switch  301 . 
     The port information management table  2132  also shows that the VLAN  99  is allocated to the port “ 0 ” of the switch  302 , and the VLAN  99  is allocated to the port “ 6 ” of the switch  302 . 
     Since the VLAN  99  is a VLAN for management, the management server  2  is connected to the port “ 0 ”. 
       FIG. 8  is a diagram showing the configuration of a port information management table  2133  which is created for the switch  303  after a network configuration is entered by the administrator  1  according to the first embodiment of this invention. 
     The port information management table  2133  shows that a port “ 0 ” of the switch  303  is connected to an device other than the switch  300 , a port “ 1 ” of the switch  303  is connected to an device other than the switch  300 , and a port “ 6 ” of the switch  303  is connected to a port “ 1 ” of the switch  301 . 
     The port information management table  2133  also shows that the VLAN  10  is allocated to the port “ 0 ” of the switch  303 , the VLAN  20  is allocated to the port “ 1 ” of the switch  303 , and the VLAN  10 , the VLAN  20 , and the VLAN  99  are allocated to the port “ 6 ” of the switch  303 . 
     The fact that the VLAN  99  is not allocated to the ports “ 0 ” and “ 1 ” indicates that the user terminals  340  are connected to the ports “ 0 ” and “ 1 ”. 
       FIG. 9  is a diagram showing the configuration of a port information management table  2134  which is created for the switch  304  after a network configuration is entered by the administrator  1  according to the first embodiment of this invention. 
     The port information management table  2134  shows that a port “ 0 ” of the switch  304  is connected to an device other than the switch  300 , a port “ 1 ” of the switch  304  is connected to an device other than the switch  300 , and a port “ 6 ” of the switch  304  is connected to a port “ 2 ” of the switch  301 . 
     The port information management table  2134  also shows that the VLAN  20  is allocated to the port “ 0 ” of the switch  304 , the VLAN  10  is allocated to the port “ 1 ” of the switch  304 , and the VLAN  10 , the VLAN  20 , and the VLAN  99  are allocated to the port “ 6 ” of the switch  304 . 
     The fact that the VLAN  99  is not allocated to the ports “ 0 ” and “ 1 ” indicates that the user terminals  340  are connected to the ports “ 0 ” and “ 1 ”. 
       FIGS. 10 to 13  are diagrams showing the configuration of the VLAN information management table  212  according to the first embodiment of this invention. 
     The VLAN information management table  212  is created for each switch  300  managed by the management server  2 . 
     The VLAN information management table  212  contains in each entry a VLAN identifier  21201 , a port identifier  21202 , and an IP address  21203 . 
     Registered as the VLAN identifier  21201  is an identifier unique to each VLAN that is defined to be allocated to the switch  300  for which the VLAN information management table  212  in question is created. Registered as the port identifier  21202  is an identifier unique to a port that is allocated a VLAN identified by the VLAN identifier  21201  of the same entry. Registered as the IP address  21203  is an IP address at which the switch  300  of this VLAN information management table  212  is accessed over a VLAN identified by the VLAN identifier  21201  of the same entry. 
       FIG. 10  is a diagram showing the configuration of a VLAN information management table  2121  which is created for the switch  301  after a network configuration is entered by the administrator  1  according to the first embodiment of this invention. 
     The VLAN information management table  2121  shows that the VLAN  10 , the VLAN  20 , and the VLAN  99  are defined to be allocated to the switch  301 . According to the VLAN information management table  2121 , the VLAN  10  is allocated to the port “ 1 ” and the port “ 2 ”, the VLAN  20  is allocated to the port “ 1 ” and the port “ 2 ”, and the VLAN  99  is allocated to the port “ 0 ”, the port “ 1 ”, and the port “ 2 ”. The VLAN information management table  2121  also shows that the IP address of the switch  301  in the VLAN  10  is “192. 168. 10. 201”, the IP address of the switch  301  in the VLAN  20  is “192. 168. 20. 201”, and the IP address of the switch  301  in the VLAN  99  is “192. 168. 99. 1”. 
       FIG. 11  is a diagram showing the configuration of a VLAN information management table  2122  which is created for the switch  302  after a network configuration is entered by the administrator  1  according to the first embodiment of this invention. 
     The VLAN information management table  2122  shows that the VLAN  99  is defined to be allocated to the switch  302 . According to the VLAN information management table  2122 , the VLAN  99  is allocated to the port “ 0 ” and the port “ 6 ”. The VLAN information management table  2122  also shows that the IP address of the switch  302  in the VLAN  99  is “192. 168. 99. 2”. 
       FIG. 12  is a diagram showing the configuration of a VLAN information management table  2123  which is created for the switch  303  after a network configuration is entered by the administrator  1  according to the first embodiment of this invention. 
     The VLAN information management table  2123  shows that the VLAN  10 , the VLAN  20 , and the VLAN  99  are defined to be allocated to the switch  303 . According to the VLAN information management table  2123 , the VLAN  10  is allocated to the port “ 0 ” and the port “ 6 ”, the VLAN  20  is allocated to the port “ 1 ” and the port “ 6 ”, and the VLAN  99  is allocated to the port “ 6 ”. The VLAN information management table  2123  also shows that the IP address of the switch  303  in the VLAN  10  is “192. 168. 10. 203”, the IP address of the switch  303  in the VLAN  20  is “192. 168. 20. 203”, and the IP address of the switch  303  in the VLAN  99  is “192. 168. 99. 3”. 
       FIG. 13  is a diagram showing the configuration of a VLAN information management table  2124  which is created for the switch  304  after a network configuration is entered by the administrator  1  according to the first embodiment of this invention. 
     The VLAN information management table  2124  shows that the VLAN  10 , the VLAN  20 , and the VLAN  99  are defined to be allocated to the switch  304 . According to the VLAN information management table  2124 , the VLAN  10  is allocated to the port “ 1 ” and the port “ 6 ”, the VLAN  20  is allocated to the port “ 0 ” and the port “ 6 ”, and the VLAN  99  is allocated to the port “ 6 ”. The VLAN information management table  2124  also shows that the IP address of the switch  304  in the VLAN  10  is “192. 168. 10. 204”, the IP address of the switch  304  in the VLAN  20  is “192. 168. 20. 204”, and the IP address of the switch  304  in the VLAN  99  is “192. 168. 99. 4”. 
     In  FIGS. 9 to 13 , the VLAN  99  is defined to be allocated to all of the switches  301  to  304  and IP addresses in the VLAN  99  are defined for all of the switches  301  to  304 . This enables the management server  2  to access the switches  301  to  304  all. 
       FIG. 14  is a diagram illustrating the redundancy switch specifying screen  234  for specifying which switch  300  is to be provided redundancy according to the first embodiment of this invention. 
     The redundancy switch specifying screen  234  contains an edit window  231 , an edit canvas  233 , and a sub-menu  235 . 
     The redundancy switch specifying screen  234  is the network configuration input screen  230  that is displayed as a result of the processing of S 703  after the administrator  1  enters a network configuration, and is used by the administrator  1  to specify which switch  300  is to be provided redundancy. 
     The edit window  231  and the edit canvas  233  are the same as the window and the canvas in the network configuration input screen  230  of  FIG. 5 , and their descriptions are omitted here. 
     In the edit canvas  233 , a network configuration entered by the administrator  1  in S 701  is displayed. 
     The sub-menu  235  is displayed when the administrator  1  selects an icon of one switch  300  with a mouse. The sub-menu  235  includes “redundancy”, “copy”, “delete”, and “property”. 
     When the administrator  1  selects one switch  300 , the icon of the selected switch  300  is displayed in an enhanced manner. Examples of how to display the icon of the selected switch  300  in an enhanced manner include drawing a dotted line or the like around the icon of the switch  300 . 
     The sub-menu  235  is displayed near the icon of the switch  300  displayed in an enhanced manner. When the administrator  1  selects “redundancy”, the switch  300  represented by this icon is chosen as the switch  300  that is to be provided redundancy. 
     The management server  2  searches for an identifier unique to the switch  300  chosen as the switch  300  that is to be provided redundancy. 
     In this embodiment, the switch  300  that is to be provided redundancy is selected with a mouse. Alternatively, the administrator  1  may enter the identifier of the switch  300  that is to be provided redundancy with a keyboard. 
     With a user interface put between the server and the administrator such as this redundancy switch specifying screen, this invention makes it possible to design a redundancy configuration network by selecting which switch in the network is to be provided redundancy on the screen, instead of requiring the administrator to set individual switches as in prior art. This invention accordingly has an effect of reducing errors made by the administrator in designing a redundancy configuration network and thus enhancing the reliability of redundancy configuration network designing. More specifically, this invention has an effect of reducing design errors by displaying a network to be designed on the screen with the use of graphics and thus enabling the administrator to intuitively select a switch that is to be provided redundancy. 
       FIG. 15  is a flow chart of redundancy configuration creating processing according to the first embodiment of this invention. 
     The redundancy configuration creating processing is executed by the CPU  24  by running the redundancy configuration creating program  211 . The redundancy configuration creating processing is the processing of S 703  shown in  FIG. 4 . 
     First, the administrator  1  specifies which switch  300  is to be provided redundancy through the redundancy switch specifying screen  234 . The CPU  24  obtains the identifier of the switch  300  specified as a switch to be provided redundancy (S 1801 ). The CPU  24  keeps the identifier of the switch  300  that is obtained in S 1801  as S 0 . 
     The CPU  24  then creates, in the memory  20 , the port information management table  213  and the VLAN information management table  212  for a new switch  300  (S) which constitutes redundancy switches together with the switch  300  (S 0 ) to be provided redundancy (S 1802 ). 
     The CPU  24  next chooses, from the port information management table  213  for the switch  300  (S 0 ) to be provided redundancy, one connected switch  300  which is connected to the switch  300  (S 0 ) to be provided redundancy, and obtains the identifier of the connected switch  300  as well as the identifier of one of ports of the connected switch  300  that is connected to the switch  300  (S 0 ) to be provided redundancy (S 1803 ). The CPU  24  keeps the switch identifier obtained in S 1802  as S 1 , and keeps the port identifier obtained in S 1802  as P 1 . The connection between the switch  300  (S 0 ) to be provided redundancy and the connected switch  300  (S 1 ) is called a valid link. Therefore, the connection between the switch  300  (S 0 ) to be provided redundancy and the user terminals  340  is not a valid link. 
     Specifically, the CPU  24  chooses, from entries of the port information management table  213  for the switch  300  (S 0 ) to be provided redundancy, one entry in which the identifier of another switch  300  is registered as the connected node identifier  21302 . The CPU  24  obtains the switch identifier registered as the connected node identifier  21302  in the chosen entry and a port identifier registered as the connected port identifier  21303  in the chosen entry. 
     The CPU  24  refers to the identifier S 1  of the switch  300  and the port identifier P 1  which are obtained in S 1803 , executes redundant link creating processing shown in  FIG. 16  (S 1804 ), and updates the port information management table  213  and VLAN information management table  212  of the connected switch  300  (S 1 ) as well as the port information management table  213  and VLAN information management table  212  of the new switch  300  (S). 
     The CPU  24  next judges whether or not the redundant link creating processing has been executed for every valid link of the switch  300  (S 0 ) to be provided redundancy (S 1805 ). 
     When it is judged in S 1805  that not all of the valid links of the switch  300  (S 0 ) to be provided redundancy have finished the redundant link creating processing, the CPU  24  returns to S 1803  to choose one link out of the valid links for which the redundant link creating processing has not been executed yet. 
     When it is judged in S 1805  that all of the valid links of the switch  300  (S 0 ) to be provided redundancy have received the redundant link creating processing, the CPU  24  creates settings of a redundant system control protocol. 
     First, the CPU  24  refers to the port information management table  213  for the switch  300  (S 0 ) to be provided redundancy to choose one free port which is not connected to any network device out of the ports of the switch  300  (S 0 ) to be provided redundancy, and obtains the identifier of the chosen free port. The CPU  24  also refers to the port information management table  213  for the new switch  300  (S) to choose one free port which is not connected to any device out of the ports of the new switch  300  (S), and obtains the identifier of the chosen free port (S 1806 ). The CPU  24  keeps the identifier of the free port of the switch  300  (S 0 ) to be provided redundancy as P 4  and keeps the identifier of the free port of the new switch  300  (S) as P 5 . 
     In obtaining a free port of the new switch  300  (S), the CPU  24  chooses a port that shares the same identifier with the obtained free port of the switch  300  (S 0 ) to be provided redundancy, if there is such a port. 
     This makes the identifier of the port of the new switch  300  (S) that is connected to the switch  300  (S 0 ) to be provided redundancy the same as the identifier of the port of the switch  300  (S 0 ) to be provided redundancy that is connected to the new switch  300  (S). The administrator  1  can thus easily understand the connection relation between the connected switch  300  (S 1 ) and the switches  300  that constitute redundancy switches (the switch  300  (S 0 ) to be provided redundancy and the new switch  300  (S)). 
     Next, the CPU  24  sets, as ports to which the redundant system control protocol is applied, the port of the switch  300  (S 0 ) to be provided redundancy that is identified by the port identifier obtained in S 1806  (the port P 4 ) and the port of the new switch  300  (S) that is identified by the port identifier obtained in S 1806  (the port P 5 ) (S 1807 ). 
     Specifically, the CPU  24  registers the identifier of a VLAN for redundant system control protocol communication as the VLAN identifier  21304  in an entry of the port information management table  213  for the switch  300  (S 0 ) to be provided redundancy whose port identifier  21301  matches the free port identifier (P 4 ) obtained in S 1806 . The CPU  24  also registers the identifier of the VLAN for redundant system control protocol communication as the VLAN identifier  21304  in an entry of the port information management table  213  for the new switch  300  (S) whose port identifier  21301  matches the free port identifier (P 5 ) obtained in S 1806 . 
     The CPU  24  then adds an entry holding the identifier of the redundant system control protocol communication VLAN as the VLAN identifier  21201  to the VLAN information management table  212  for the switch  300  (S 0 ) to be provided redundancy. In the added entry, the CPU  24  registers as the port identifier  21202  the free port identifier (P 4 ) obtained in S 1806  and, as the IP address  21203 , an IP address unique to the switch  300  (S 0 ) to be provided redundancy in the redundant system control protocol communication VLAN. 
     The CPU  24  also adds an entry holding the identifier of the redundant system control protocol communication VLAN as the VLAN identifier  21201  to the VLAN information management table  212  for the new switch  300  (S). In the added entry, the CPU  24  registers as the port identifier  21202  the free port identifier (P 5 ) obtained in S 1806  and, as the IP address  21203 , an IP address unique to the new switch  300  (S) in the redundant system control protocol communication VLAN. 
     The CPU  24  subsequently updates the redundant system management table  214  shown in  FIG. 28 . Specifically, the CPU  24  registers an identifier unique to a redundancy pair that is formed of the switch  300  (S 0 ) to be provided redundancy and the new switch  300  (S) as a pair identifier  21401 . As a first node identifier  21402  and a first port identifier  21403 , the CPU  24  registers the identifier of one of the switches  300  constituting the redundancy pair and the identifier of one of ports of the switch  300  identified by the first node identifier  21402  that is connected to the other switch  300  constituting the redundancy pair, respectively. As a second node identifier  21404  and a second port identifier  21405 , the CPU  24  registers the identifier of the other switch  300  constituting the redundancy pair and the identifier of one of ports of the switch  300  identified by the second node identifier  21404  that is connected to the switch  300  identified by the first node identifier  21402 , respectively. 
     The CPU  24  next updates the port information management table  213  for the switch  300  (S 0 ) to be provided redundancy (S 1808 ). Specifically, the CPU  24  chooses an entry of the port information management table  213  for the switch  300  (S 0 ) to be provided redundancy whose port identifier  21301  matches the port identifier (P 4 ) of the switch  300  (S 0 ) to be provided redundancy which has been obtained in S 1806 . In the chosen entry, the CPU  24  registers the identifier of the new switch  300  (S) as the connected node identifier  21302 , and the free port identifier (P 5 ) of the new switch  300  (S) as the connected port identifier  21303 . 
     The CPU  24  also updates the port information management table  213  for the new switch  300  (S) (S 1809 ). Specifically, the CPU  24  chooses an entry of the port information management table  213  for the new switch  300  (S) whose port identifier  21301  matches the port identifier (P 5 ) of the new switch  300  (S) which has been obtained in S 1806 . In the chosen entry, the CPU  24  registers the identifier of the switch  300  (S 0 ) to be provided redundancy as the connected node identifier  21302 , and the free port identifier (P 4 ) of the switch  300  (S 0 ) to be provided redundancy as the connected port identifier  21303 . 
     The CPU  24  ends the redundancy configuration creating processing after executing S 1809 . 
       FIG. 16  is a flow chart of redundant link creating processing according to the first embodiment of this invention. 
     The redundant link creating processing is executed by the CPU  24  by running the redundancy configuration settings creating program  211 . The redundant link creating processing is the processing of S 1804  shown in  FIG. 15 . 
     The CPU  24  executes S 1901  to S 1904  to set the connection relation between the connected switch  300  (S 1 ) and the new switch  300  (S) in the port information management table  213  for the connected switch  300  (S 1 ) and the port information management table  213  for the new switch  300  (S). 
     First, the CPU  24  chooses one free port which is not connected to any network device out of the ports of the connected switch  300  (S 1 ), and obtains the identifier of the chosen free port (S 1901 ). The CPU  24  keeps the identifier of the free port of the connected switch  300  (S 1 ) as P 2 . 
     The following describes how the CPU  24  obtains a free port of the connected switch  300  (S 1 ) specifically. 
     The CPU  24  first judges whether or not a port of the connected switch  300  (S 1 ) is a free port. The identifier of this port has the number immediately preceding or following the port identifier (P 1 ) of the port that has been chosen as one connected to the switch  300  (S 0 ) to be provided redundancy in S 1803  of the redundancy configuration creating processing shown in  FIG. 15 . 
     When the port whose identifier has the number immediately preceding or following the port identifier (P 1 ) is a free port, the CPU  24  obtains the identifier of this port. 
     When the port whose identifier has the number immediately preceding or following the port identifier (P 1 ) is not a free port, the CPU  24  judges whether or not another port is a free port. 
     This way, when the port whose identifier has the number immediately preceding or following the port identifier (P 1 ) is a free port, the identifier of the port (P 1 ) of the connected switch  300  (S 1 ) that is connected to the switch  300  (S 0 ) to be provided redundancy has the number immediately preceding or following the identifier of the port (P 2 ) of the connected switch  300  (S 1 ) that is connected to the new switch  300  (S). The administrator  1  can thus easily understand the connection relation between the connected switch  300  (S 1 ) and the switches  300  that constitute redundancy switches (the switch  300  (S 0 ) to be provided redundancy and the new switch  300  (S)). 
     The CPU  24  next chooses one free port which is not connected to any network device out of the ports of the new switch  300  (S), and obtains the identifier of the chosen free port (S 1902 ). The CPU  24  keeps the identifier of the free port of the new switch  300  (S) as P 3 . 
     The following describes how the CPU  24  obtains a free port of the new switch  300  (S) specifically. 
     The CPU  24  first judges whether or not a port of the new switch  300  (S) is a free port. This port shares the same port identifier with the port of the switch  300  (S 0 ) to be provided redundancy that is connected to the connected switch  300  (S 1 ). 
     When the port that shares the same port identifier with the port connected to the connected switch  300  (S 1 ) is a free port, the CPU  24  obtains the identifier of this port. 
     When the port that shares the same port identifier with the port connected to the connected switch  300  (S 1 ) is not a free port, the CPU  24  judges whether or not another port is a free port. 
     This way, when a free port of the new switch  300  (S) is identified by the same port identifier as the port of the switch  300  (S 0 ) to be provided redundancy that is connected to the connected switch  300  (S 1 ), the port of the new switch  300  (S) that is connected to the connected switch  300  (S 1 ) and the port of the switch  300  (S 0 ) to be provided redundancy that is connected to the connected switch  300  (S 1 ) share the same identifier. The administrator  1  can thus easily understand the connection relation between the connected switch  300  (S 1 ) and the switches  300  that constitute redundancy switches (the switch  300  (S 0 ) to be provided redundancy and the new switch  300  (S)). 
     The CPU  24  next chooses an entry of the port information management table  213  for the connected switch  300  (S 1 ) whose port identifier  21301  matches the port identifier (P 2 ) obtained in S 1901 . In the chosen entry, the CPU  24  registers the identifier of the new switch  300  (S) as the connected node identifier  21302  and the port identifier (P 3 ) obtained in S 1902  as the connected port identifier  21303  (S 1903 ). 
     The CPU  24  chooses an entry of the port information management table  213  for the new switch  300  (S) whose port identifier  21301  matches the port identifier (P 3 ) obtained in S 1902 . In the chosen entry, the CPU  24  registers the identifier of the connected switch  300  (S 1 ) as the connected node identifier  21302  and the port identifier (P 2 ) obtained in S 1901  as the connected port identifier  21303  (S 1904 ). 
     Processing of setting a VLAN to the new switch  300  (S) and the connected switch  300  (S 1 ) will be described next. 
     First, the CPU  24  refers to the port information management table  213  for the connected switch  300  (S 1 ) to choose one VLAN identifier from among the identifiers of VLANs that are allocated to the port (P 1 ) chosen in S 1803  (S 1905 ). The CPU  24  keeps the identifier of the chosen VLAN as V 1 . 
     The CPU  24  executes S 1906  and S 1907  in order to allocate, to the port (P 2 ) of the connected switch  300  (S 1 ) that is connected to the new switch  300  (S), a VLAN allocated to a port of the connected switch  300  (S 1 ) that is connected to the switch  300  that is connected to the switch  300  (S 0 ) to be provided redundancy. The CPU  24  thereby updates the port information management table  213  for the connected switch  300  (S 1 ) and the VLAN information management table  212  for the connected switch  300  (S 1 ). 
     The CPU  24  chooses an entry of the port information management table  213  for the connected switch  300  (S 1 ) whose port identifier  21301  matches the port identifier (P 2 ) obtained in S 1901 . In the chosen entry, the CPU  24  registers the VLAN identifier (V 1 ) obtained in S 1905  as the VLAN identifier  21304 . 
     The CPU  24  then chooses from the VLAN information management table  212  for the connected switch  300  (S 1 ) an entry whose VLAN identifier  21201  matches the VLAN identifier (V 1 ) obtained in S 1905 . In the chosen entry, the CPU  24  registers the port identifier (P 2 ) obtained in S 1901  as the port identifier  21202 . 
     The CPU  24  next executes S 1908  and S 1909  in order to allocate, to the port (P 3 ) of the new switch  300  (S) that is connected to the connected switch  300  (S 1 ), a VLAN allocated to a port of the connected switch  300  (S 1 ) that is connected to the switch  300  that is connected to the switch  300  (S 0 ) to be provided redundancy. The CPU  24  thereby updates the port information management table  213  for the new switch  300  (S) and the VLAN information management table  212  for the new switch  300  (S). 
     The CPU  24  chooses an entry of the port information management table  213  for the new switch  300  (S) whose port identifier  21301  matches the port identifier (P 3 ) obtained in S 1902 . In the chosen entry, the CPU  24  registers the VLAN identifier (V 1 ) obtained in S 1905  as the VLAN identifier  21304  (S 1908 ). 
     The CPU  24  then chooses from the VLAN information management table  212  for the new switch  300  (S) an entry whose VLAN identifier  21201  matches the VLAN identifier (V 1 ) obtained in S 1905 . In the chosen entry, the CPU  24  registers the port identifier (P 3 ) obtained in S 1902  as the port identifier  21202  (S 1909 ). 
     In the case where the VLAN information management table  212  for the new switch  300  (S) does not have an entry whose VLAN identifier  21201  matches the VLAN identifier (V 1 ) obtained in S 1905 , the CPU  24  adds an entry that holds as the VLAN identifier  21201  the VLAN identifier (V 1 ) obtained in S 1905 . The CPU  24  registers, in the added entry, as the port identifier  21202 , the port identifier (P 3 ) obtained in S 1902 . 
     The CPU  24  next judges whether or not S 1906  to S 1909  have been executed for every VLAN identifier allocated to the port (P 1 ) chosen in S 1803  (S 1910 ). 
     When it is judged that S 1906  to S 1909  have been executed for every VLAN identifier allocated to the port (P 1 ) chosen in S 1803 , the CPU  24  ends the redundant link creating processing and moves on to S 1805  shown in  FIG. 15 . 
     When it is judged that not all of the VLAN identifiers that are allocated to the port (P 1 ) chosen in S 1803  have finished S 1906  to S 1909 , the CPU  24  returns to S 1905  to obtain another VLAN identifier. 
       FIG. 17  is a diagram showing a redundant system display screen  236 , which is used to check the network after the redundancy configuration creating processing is executed according to the first embodiment of this invention. 
     The redundant system display screen  236  contains an edit window  231  and an edit canvas  233 . 
     The redundant system display screen  236  is a screen displayed based on the updated port information management table  213  and VLAN information management table  212  after the redundancy configuration creating processing shown in  FIG. 4  is executed. 
     On the redundant system display screen  236 , an icon of the new switch  300 , which has been newly added to constitute one of redundancy switches, is displayed by a dotted line. Links of the new switch  300  to other switches  300  are also displayed by dotted lines. This enables the administrator  1  to easily understand a change brought by the addition of the new switch  300 . 
     This invention thus has an effect of helping the administrator grasp design details intuitively by displaying the finished network configuration design on the redundant system display screen. Accordingly, the administrator can easily understand whether design details fit the design concept, which means that checking the final design details is easy and design errors are reduced. 
     Described next with reference to  FIGS. 18 to 28  are the port information management tables  213  and VLAN information management tables  212  for the switches  301  to  305  and the redundant system management table  214  that have been updated as a result of the CPU  24  executing the redundancy configuration creating processing when the administrator  1  designates the switch  301  as the switch  300  to be provided redundancy and the switch  305  as the new switch  300  in  FIG. 2 . The switch  300  to be provided redundancy will be referred to as the switch  301  to be provided redundancy and the new switch  300  will be referred to as the new switch  305 . 
     The port information management table  2131  and VLAN information management table  2121  for the switch  301  to be provided redundancy that have been updated through the redundancy configuration creating processing will be described first with reference to  FIGS. 18 and 26 . 
       FIG. 18  is a diagram showing the port information management table  2131  for the switch  301  to be provided redundancy that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     The port information management table  2131  for the switch  301  to be provided redundancy is updated in S 1807  and S 1808 . 
     Specifically, in S 1808 , an identifier “ 305 ” of the new switch  305  is registered as the connected node identifier  21302  in an entry whose port identifier  21301  is “ 7 ”. As the connected port identifier  21303  of this entry, “ 7 ” is registered which is the identifier of the port of the new switch  305  that is connected to the switch  301  to be provided redundancy. In S 1807 , an identifier “ 200 ” of the redundant system control protocol communication VLAN is registered as the VLAN identifier  21304  of this entry. 
       FIG. 26  is a diagram showing the VLAN information management table  2121  for the switch  301  to be provided redundancy that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     The VLAN information management table  2121  for the switch  301  to be provided redundancy is updated in S 1807 . 
     Specifically, S 1807  adds an entry whose VLAN identifier  21201  is the identifier “ 200 ” of the redundant system control protocol communication VLAN. In this entry, the identifier “ 7 ” of the port of the switch  301  to be provided redundancy that is connected to the new switch  305  is registered as the port identifier  21202 , and an IP address “192. 168. 200. 1” unique to the switch  301  to be provided redundancy in the VLAN “ 200 ” is registered as the IP address  21203 . 
     A port information management table  2132  and VLAN information management table  2122  for the switch  302  that have been updated through the redundancy configuration creating processing will be described next with reference to  FIGS. 19 and 23 . 
       FIG. 19  is a diagram showing the port information management table  2132  for the switch  302  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     The switch  302  is the connected switch  300  that is connected to the switch  301  to be provided redundancy. With the switch  302  being the connected switch  300 , an identifier “ 302 ” of the switch  302  and an identifier “ 6 ” of the port of the switch  302  that is connected to the switch  301  to be provided redundancy are chosen in S 1803  of  FIG. 15 . 
     In S 1901  of  FIG. 16 , a port identifier “ 7 ” immediately following the identifier “ 6 ” of the port of the switch  302  that is connected to the switch  301  to be provided redundancy is obtained as a free port identifier. In S 1903 , the identifier “ 305 ” of the new switch  305  is registered as the connected node identifier  21302  and an identifier “ 0 ” of a port of the new switch  305  which is obtained as a free port in S 1902  is registered as the connected port identifier  21303  in an entry of the port information management table  2132  whose port identifier  21301  is “ 7 ”. 
     The CPU  24  obtains, in S 1902 , as a free port, a port of the new switch  305  that is identified by the port identifier “ 0 ”, the same as the port identifier “ 0 ” of the port of the switch  301  to be provided redundancy that is connected to the switch  302 . In other words, a port of the new switch  305  that is identified by the port identifier “ 0 ” is connected to the switch  302 . 
     Therefore, the identifier “ 0 ” of the port of the new switch  305  is registered as the connected port identifier  21303  in the port information management table  2132  for the switch  302 . 
     In S 1905  of  FIG. 16 , the CPU  24  obtains the identifier “ 99 ” of the VLAN allocated to the port “ 6 ” of the switch  302  that is connected to the switch  301  to be provided redundancy. 
     In S 1906 , the VLAN identifier “ 99 ” obtained in S 1905  is registered as the VLAN identifier  21304  in an entry of the port information management table  2132  whose port identifier  21301  is “ 7 ”. 
       FIG. 23  is a diagram showing the VLAN information management table  2122  for the switch  302  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     In S 1907  of  FIG. 16 , the identifier “ 7 ” of the port obtained in S 1902  as a free port of the new switch  305  is registered as the port identifier  21202  in an entry of the VLAN information management table  2122  whose VLAN identifier  21201  matches the VLAN identifier “ 99 ” obtained in S 1905 . 
     Through the above steps, the connection relation between the switch  302  and the new switch  305  is registered in the port information management table  2132  for the switch  302 . Also, a VLAN allocated to the port “ 6 ” of the switch  302  which is connected to the switch  301  to be provided redundancy is allocated to the port “ 7 ” of the switch  302  which is connected to the new switch  305  in the port information management table  2132  and VLAN information management table  2122  for the switch  302 . 
     A port information management table  2133  and VLAN information management table  2123  for the switch  303  that have been updated through the redundancy configuration creating processing will be described next with reference to  FIGS. 20 and 24 . 
       FIG. 20  is a diagram showing the port information management table  2133  for the switch  303  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     The switch  303  is the connected switch  300  that is connected to the switch  301  to be provided redundancy. With the switch  303  being the connected switch  300 , an identifier “ 303 ” of the switch  303  and an identifier “ 6 ” of the port of the switch  303  that is connected to the switch  301  to be provided redundancy are chosen in S 1803  of  FIG. 15 . 
     As in  FIG. 19 , in S 1903  of  FIG. 16 , the CPU  24  registers the identifier “ 305 ” of the new switch  305  as the connected node identifier  21302  and an identifier “ 1 ” of a port of the new switch  305  which is obtained as a free port in S 1902  is registered as the connected port identifier  21303  in an entry of the port information management table  2133  whose port identifier  21301  is “ 7 ”. 
     In S 1906 , as the VLAN identifier  21304  of this entry, the CPU  24  registers the identifiers “ 10 ”, “ 20 ”, and “ 99 ” of the VLANs that are allocated to the port “ 6 ” obtained in S 1905 . 
       FIG. 24  is a diagram showing the VLAN information management table  2123  for the switch  303  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     In S 1907  of  FIG. 16 , the CPU  24  registers the port identifier “ 7 ” obtained in S 1902  as the port identifier  21202  in every entry of the VLAN information management table  2123  whose VLAN identifier  21201  matches any one of the VLAN identifiers “ 10 ”, “ 20 ”, and “ 99 ” obtained in S 1905 . 
     Through the above steps, the connection relation between the switch  303  and the new switch  305  is registered in the port information management table  2133  for the switch  303 . Also, a VLAN allocated to the port “ 6 ” of the switch  303  which is connected to the switch  301  to be provided redundancy is allocated to the port “ 7 ” of the switch  303  which is connected to the new switch  305  in the port information management table  2133  and VLAN information management table  2123  for the switch  303 . 
     A port information management table  2134  and VLAN information management table  2124  for the switch  304  that have been updated through the redundancy configuration creating processing will be described next with reference to  FIGS. 21 and 25 . 
       FIG. 21  is a diagram showing the port information management table  2134  for the switch  304  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     The switch  304  is the connected switch  300  that is connected to the switch  301  to be provided redundancy. With the switch  304  being the connected switch  300 , an identifier “ 304 ” of the switch  304  and an identifier “ 6 ” of the port of the switch  304  that is connected to the switch  301  to be provided redundancy are chosen in S 1803  of  FIG. 15 . 
     As in  FIG. 19 , in S 1903  of  FIG. 16 , the CPU  24  registers the identifier “ 305 ” of the new switch  305  as the connected node identifier  21302  and an identifier “ 2 ” of a port of the new switch  305  which is obtained as a free port in S 1902  is registered as the connected port identifier  21303  in an entry of the port information management table  2134  whose port identifier  21301  is “ 7 ”. 
     In S 1906 , as the VLAN identifier  21304  of this entry, the CPU  24  registers the identifiers “ 10 ”, “ 20 ”, and “ 99 ” of the VLANs that are allocated to the port “ 6 ” obtained in S 1905 . 
       FIG. 25  is a diagram showing the VLAN information management table  2124  for the switch  304  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     In S 1907  of  FIG. 16 , the CPU  24  registers the port identifier “ 7 ” obtained in S 1902  as the port identifier  21202  in every entry of the VLAN information management table  2124  whose VLAN identifier  21201  matches any one of the VLAN identifiers “ 10 ”, “ 20 ”, and “ 99 ” obtained in S 1905 . 
     Through the above steps, the connection relation between the switch  304  and the new switch  305  is registered in the port information management table  2134  for the switch  304 . Also, a VLAN allocated to the port “ 6 ” of the switch  304  which is connected to the switch  301  to be provided redundancy is allocated to the port “ 7 ” of the switch  304  which is connected to the new switch  305  in the port information management table  2134  and VLAN information management table  2124  for the switch  304 . 
     A port information management table  2135  and VLAN information management table  2125  for the switch  305  that have been updated through the redundancy configuration creating processing will be described next with reference to  FIGS. 22 and 27 . 
       FIG. 22  is a diagram showing the port information management table  2135  for the switch  305  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     In S 1904  of  FIG. 16 , the identifiers of the switches  302 ,  303 , and  304  connected to the switch  301  to be provided redundancy, and the identifiers of the ports of the switches  302 ,  303 , and  304  that are connected to the switch  301  to be provided redundancy are registered as the connected node identifier  21302  and the connected port identifier  21303 , respectively. 
     The ports of the switches  302 ,  303 , and  304  that are connected to the new switch  305  are, as described with reference to  FIGS. 19 to 22 , the ports “ 7 ” immediately following the ports “ 6 ” of the switches  302 ,  303 , and  304  that are connected to the switch  301  to be provided redundancy. 
     The port of the new switch  305  that is connected to the switch  302  is, as described with reference to  FIG. 19 , the port “ 0 ”, the same as the port “ 0 ” of the switch  301  to be provided redundancy that is connected to the switch  302 . 
     Similarly, the port of the new switch  305  that is connected to the switch  303  is the port “ 1 ” and the port of the new switch  305  that is connected to the switch  304  is the port “ 2 ”. 
     The identifier “ 302 ” of the switch  302  and the port identifier “ 7 ” of the switch  302  are therefore registered as the connected node identifier  21302  and the connected port identifier  21303 , respectively, in an entry of the port information management table  2135  whose port identifier  21301  is “ 0 ”. 
     Similarly, the identifier “ 303 ” of the switch  303  and the port identifier “ 7 ” of the switch  303  are registered as the connected node identifier  21302  and the connected port identifier  21303 , respectively, in an entry whose port identifier  21301  is “ 1 ”. In an entry whose port identifier  21301  is “ 2 ”, the identifier “ 304 ” of the switch  304  and the port identifier “ 7 ” of the switch  304  are registered as the connected node identifier  21302  and the connected port identifier  21303 , respectively. 
     The CPU  24  next registers, as the VLAN identifier  21304 , the identifiers of VLANs allocated to the ports “ 6 ” of the switches  302  to  304  which are connected to the switch  301  to be provided redundancy. 
     Specifically, “ 99 ” is registered as the VLAN identifier  21304  in an entry of the port information management table  2135  whose port identifier  21301  is “ 0 ”. “ 10 ”, “ 20 ”, and “ 99 ” are registered as the VLAN identifier  21304  in an entry whose port identifier  21301  is “ 1 ”. “ 10 ”, “ 20 ”, and “ 99 ” are registered as the VLAN identifier  21304  in an entry whose port identifier  21301  is “ 2 ”. 
     In S 1807  and S 1809 , the CPU  24  registers the identifier “ 301 ” of the switch  301  to be provided redundancy as the connected node identifier  21302 , the port identifier “ 7 ” of the port of the switch  301  to be provided redundancy that is connected to the new switch  305  as the connected port identifier  21303 , and the identifier “ 200 ” of the redundant system control protocol communication VLAN as the VLAN identifier  21304  in an entry of the port information management table  2135  whose port identifier  21301  is “ 7 ”. 
       FIG. 27  is a diagram showing a VLAN information management table  2125  for the new switch  305  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     The VLAN information management table  2125  holds no values when created for the new switch  305  in S 1802 . In S 1909 , entries are added to register as the VLAN identifier  21201  the identifiers “ 10 ”, “ 20 ”, and “ 99 ” of the VLANs allocated to the ports “ 6 ” of the switches  302  to  304  which are connected to the switch  301  to be provided redundancy. 
     In the entry that has “ 10 ” as the VLAN identifier  21201 , the identifiers “ 1 ” and “ 2 ” of the ports allocated the VLAN “ 10 ” are registered as the port identifier  21202 . As the IP address  21203  of this entry, the CPU  24  registers an IP address “192.168.10.205” unique to the new switch  305  in the VLAN “ 10 ”. 
     The entries that have respectively “ 20 ” and “ 99 ” as the VLAN identifier  21201  are set in a similar manner, and the description is therefore omitted. 
     The VLAN information management table  2125  is updated further in S 1807 . 
     Specifically, in S 1807 , the CPU  24  adds an entry whose VLAN identifier  21201  is the identifier “ 200 ” of the redundant system control protocol communication VLAN. In the added entry, the port identifier “ 7 ” of the port of the new switch  305  that is connected to the switch  301  to be provided redundancy is registered as the port identifier  21202 , and an IP address “192.168.200.5” unique to the new switch  305  in the VLAN “ 200 ” is registered as the IP address  21203 . 
       FIG. 28  is a diagram showing the redundant system management table  214  that has been updated through the redundancy configuration creating processing according to the first embodiment of this invention. 
     The redundant system management table  214  contains in each entry a pair identifier  21401 , a first node identifier  21402 , a first port identifier  21403 , a second node identifier  21404 , and a second port identifier  21405 . 
     Registered as the pair identifier  21401  is an identifier unique throughout the network  4  to a specific combination of the switches  300  constituting redundancy switches. 
     Registered as the first node identifier  21402  is an identifier unique to one of the switches  300  constituting the redundancy switches. 
     Registered as the first port identifier  21403  is an identifier unique to a port of the one switch  300  constituting the redundancy switches that is connected to the other switch  300  constituting the redundancy switches. 
     Registered as the second node identifier  21404  is an identifier unique to the other of the switches  300  constituting the redundancy switches. 
     Registered as the second port identifier  21405  is an identifier unique to a port of the other switch  300  constituting the redundancy switches that is connected to the one switch  300  constituting the redundancy switches. 
     The identifier of either of two switches constituting redundancy switches can be registered as the first node identifier  21402  and the second node identifier  21404 . 
     In S 1807 , the CPU  24  registers the identifier “ 301 ” of the switch  301  to be provided redundancy as the first node identifier  21402  and, as the first port identifier  21403 , the port identifier “ 7 ” of the port of the switch  301  to be provided redundancy that is connected to the new switch  305 . As the second node identifier  21404  and the second port identifier  21405 , the CPU  24  registers the identifier “ 305 ” of the new switch  305  and the port identifier “ 7 ” of the port of the new switch  305  that is connected to the switch  301  to be provided redundancy, respectively. 
     The CPU  24  registers, as the pair identifier  21401 , an identifier “ 1 ” unique to the redundancy switch pair formed of the switch  301  to be provided redundancy and the new switch  305 . 
     The description given next with reference to  FIGS. 29 to 33  is about update messages sent by the management server  2  to update the respective settings of the switches  301  to  305 . 
       FIG. 29  is a diagram illustrating an update message  2051  for updating the settings of the switch  301  according to the first embodiment of this invention. 
     The update message  2051  is a message written in XML to deliver an instruction to allocate the VLAN “ 200 ” to the port of the switch  301  that is identified by the port identifier “ 7 ”. 
       FIG. 30  is a diagram illustrating an update message  2052  for updating the settings of the switch  302  according to the first embodiment of this invention. 
     The update message  2052  is a message written in XML to deliver an instruction to allocate the VLAN “ 99 ” to the port of the switch  302  that is identified by the port identifier “ 7 ”. 
       FIG. 31  is a diagram illustrating an update message  2053  for updating the settings of the switch  303  according to the first embodiment of this invention. 
     The update message  2053  is a message written in XML to deliver an instruction to allocate the VLAN “ 10 ”, “ 20 ”, and “ 99 ” to the port of the switch  303  that is identified by the port identifier “ 7 ”. 
       FIG. 32  is a diagram illustrating an update message  2054  for updating the settings of the switch  304  according to the first embodiment of this invention. 
     The update message  2054  is a message written in XML to deliver an instruction to allocate the VLAN “ 10 ”, “ 20 ”, and “ 99 ” to the port of the switch  304  that is identified by the port identifier “ 7 ”. 
       FIG. 33  is a diagram illustrating an update message  2055  for updating the settings of the switch  305  according to the first embodiment of this invention. 
     The update message  2055  is a message written in XML to deliver an instruction to allocate the VLAN “ 99 ” to the port of the switch  305  that is identified by the port identifier “ 0 ”, to allocate the VLANs “ 10 ”, “ 20 ”, and “ 99 ” to the port of the switch  305  that is identified by the port identifier “ 1 ”, to allocate the VLANs “ 10 ”, “ 20 ”, and “ 99 ” to the port of the switch  305  that is identified by the port identifier “ 2 ”, and to allocate the VLAN “ 200 ” to the port of the switch  305  that is identified by the port identifier “ 7 ”. 
     In the manner described above, the management server  2  updates the port information management table  213  and VLAN information management table  212  of each switch  300  based on an instruction given by the administrator  1  via the input/output device. The management server  2  thus automatically designs the connection relation between the new switch  300  and the existing switches  300 , thereby making it unnecessary for the administrator  1  to design the connection relation between the new switch  300  and the existing switches  300 . 
     The administrator  1  can update, via the management server  2 , the automatically designed settings of the switches  301  to  305 . 
     Second Embodiment 
     A second embodiment of this invention describes how the management server  2  designs the settings of the switches  300  automatically in the case where the administrator  1  selects two of the switches  300  constituting a network as the switches  300  that serve as redundancy switches. 
     The second embodiment will be described with reference to  FIGS. 34 and 35 . 
       FIG. 34  is a sequence diagram of network designing in the management server  2  when two of the switches  300  constituting a network are selected as the switches  300  that serve as redundancy switches according to the second embodiment of this invention. 
     First, as in S 701  of  FIG. 4 , the administrator  1  enters a network configuration to the management server  2  (S 3701 ). 
     Subsequently, as in S 702  of  FIG. 4 , based on the entered network configuration, the management server  2  updates network information managed in the VLAN information management table  212 , the port information management table  213 , and the redundant system management table  214  (S 3702 ). 
     As in S 703  of  FIG. 4 , the management server  2  then displays the entered network configuration on the input/output device  23  (S 3703 ). 
     The administrator  1  next designates two of the switches  300  constituting the network that is displayed in S 3703  as redundancy switches (S 3704 ). 
     In the first embodiment where the administrator  1  only designates the switch  300  to be provided redundancy, the switch  300  that constitutes redundancy switches together with the switch  300  to be provided redundancy is newly added to the network  4  as the new switch  300 . In the second embodiment, on the other hand, the administrator  1  selects both of two switches  300  that constitute redundancy switches. 
     Next, the management server  2  judges whether or not the two switches  300  designated as redundancy switches meet a redundancy condition, which has to be fulfilled by the switches  300  to be capable of serving as redundancy switches (S 3712 ). Details of this redundancy condition judging processing will be described with reference to  FIG. 35 . 
     When it is judged in S 3712  that the two switches  300  designated as redundancy switches do not meet the redundancy condition, the management server  2  displays a message on the input/output device  23  to the effect that the designated two switches  300  cannot serve as redundancy switches. 
     When it is judged in S 3712  that the two switches  300  designated as redundancy switches meet the redundancy condition, the management server  2  creates a network configuration necessary to apply the designated redundancy switches to the network (S 3705 ). 
     Specifically, the CPU  24  executes the redundancy configuration creating processing shown in  FIG. 15 . In this embodiment, S 1802  to S 1805  of the redundancy configuration creating processing are not executed since the second embodiment does not need to set, in one of the switches  300  constituting redundancy switches, the connection relation between the other switch  300  constituting the redundancy switches and the connected switch  300  which is connected to the other switch  300 . 
     In S 1801 , the CPU  24  obtains the identifiers of the two designated switches  300 . The CPU  24  keeps the obtained identifier of one of the two switches  300  as S 0  and the obtained identifier of the other switch  300  as S. 
     S 1806  to S 1809  in the second embodiment are the same as in the first embodiment, and the description is omitted here. 
     As in S 706  of  FIG. 4 , the management server  2  updates network information managed in the VLAN information management table  212 , the port information management table  213 , and the redundant system management table  214  (S 3706 ). As in S 707  of  FIG. 4 , the management server  2  displays the updated network configuration on the input/output device  23  (S 3707 ). 
     As in S 708  of  FIG. 4 , the administrator  1  checks whether the network configuration that is displayed by the input/output device  23  matches the actual configuration of the network  4  (S 3708 ). 
     As in S 709  of  FIG. 4 , when the network configuration that is displayed by the input/output device  23  matches the actual configuration of the network  4 , the administrator  1  instructs the management server  2  to update the settings of the respective switches  300  (S 3709 ). 
     As in S 710  of  FIG. 4 , receiving this instruction, the management server  2  sends an instruction to change the settings to the respective switches  300  (S 3710 ). Each switch  300  that has received the instruction from the management server  2  updates its settings (S 3711 ). 
     In this embodiment, a network configuration is entered to the management server  2  in S 3701 . Alternatively, the management server  2  may obtain network configuration information from the switches  300  constituting the network  4  to update network information managed in the VLAN information management table  212 , the port information management table  213 , and the redundant system management table  214 . 
       FIG. 35  is a flow chart showing redundancy condition judging processing according to the second embodiment of this invention. 
     The redundancy condition judging processing is executed by the CPU  24  by running the redundancy configuration settings creating program  211 . 
     First, at S 3801 , the CPU  24  obtains the identifiers of the two switches  300  specified in S 3704 . The CPU  24  keeps the identifier of one of the two specified switches  300  as S 1  and keeps the identifier of the other switch  300  as S 2 . 
     The CPU  24  searches the port information management tables  213  of the two specified switches (S 1  and S 2 ) for the connected switch  300  that is connected to the switch  300  (S 1 ) and the connected switch  300  that is connected to the switch  300  (S 2 ) (S 3802 ). 
     The CPU  24  judges whether or not the switch  300  (S 1 ) and the switch  300  (S 2 ) are each connected to three or more connected switches  300  (S 3803 ). 
     To elaborate, the CPU  24  judges whether or not the switch  300  (S 1 ) is connected to two switches  300  excluding the switch  300  (S 2 ), and whether or not the switch  300  (S 2 ) is connected to two switches  300  excluding the switch  300  (S 1 ). 
     When it is judged in S 3803  that at least one of the switch  300  (S 1 ) and the switch  300  (S 2 ) is connected to less than three connected switches  300 , the CPU  24  determines that these two specified switches  300  do not meet the redundancy condition, and then ends the redundancy condition judging processing (S 3806 ). 
     When it is judged in S 3803  that the count of the connected switches  300  that are connected to the switch  300  (S 1 ) and the count of the connected switches  300  that are connected to the switch  300  (S 2 ) are each equal to or higher than three, the CPU  24  judges whether or not all the connected switches  300  that are connected to the switch  300  (S 1 ) share the same identifiers with all the connected switches  300  that are connected to the switch  300  (S 2 ) (S 3804 ). 
     When it is judged in S 3804  that at least one of the connected switches  300  that are connected to the switch  300  (S 1 ) and one of the connected switches  300  that are connected to the switch  300  (S 2 ) do not share the same identifier with each other, the CPU  24  determines that these two specified switches  300  do not meet the redundancy condition, and then ends the redundancy condition judging processing (S 3806 ). 
     When it is judged in S 3804  that all of the connected switches  300  that are connected to the switch  300  (S 1 ) share the same identifiers with all of the connected switches  300  that are connected to the switch  300  (S 2 ), the CPU  24  determines that these two specified switches  300  meet the redundancy condition, and then ends the redundancy condition judging processing (S 3805 ). 
     In this way, a message to the effect that two switches  300  specified by the administrator  1  do not meet a redundancy condition is displayed on the input/output device  23  when at least one of the two specified switches  300  is connected to less than three connected switches  300 , or when not all of the connected switches  300  that are connected to one of the two specified switches  300  share the same identifiers with the connected switches  300  that are connected to the other specified switch  300 . The administrator  1  is thus prevented from setting wrong switches as redundancy switches. 
     Third Embodiment 
     A third embodiment of this invention will be described next with reference to  FIG. 36 . 
     In the third embodiment, the management server  2  creates redundancy switch settings based on link information that is sent from the new switch  300  when the new switch  300  is newly added to the network  4 . 
       FIG. 36  is a sequence diagram of network designing in the management server  2  according to the third embodiment of this invention. 
     S 3901  to S 3903  and S 3905  to S 3912  are the same as S 3701  to S 3703  and S 3705  to S 3712  described in the second embodiment with reference to the flow chart of  FIG. 34 , and the description will not be repeated. 
     In S 3904 , the new switch  300  sends link information to the management server  2  when connected to another switch  300 . The switch  300  to which the new switch  300  is connected will be referred to as a connected switch  300 . 
     The link information contains the identifier of the new switch  300 , the identifier of one of the ports of the new switch  300  that is connected to the connected switch  300 , the identifier of the connected switch  300 , and the identifier of one of the ports of the connected switch  300  that is connected to the new switch  300 . 
     The CPU  24  receives the link information. Based on the received link information, the CPU  24  updates the port information management table  213  for the new switch  300  and the port information management table  213  for the connected switch  300  to which the new switch  300  is connected. 
     Specifically, the CPU  24  registers the identifier of the connected switch  300  that is contained in the link information as the connected node identifier  21302  in an entry of the port information management table  213  for the new switch  300  whose port identifier  21301  matches the identifier of the port that is connected to the connected switch  300 . As the connected port identifier  21303  of this entry, the CPU  24  registers the port identifier of the connected switch  300  that is contained in the link information as the identifier of a port connected to the new switch  300 . 
     The CPU  24  next registers the identifier of the new switch  300  contained in the link information as the connected node identifier  21302  in an entry of the port information management table  213  for the connected switch  300  whose port identifier  21301  matches the identifier of the port that is connected to the new switch  300 . As the connected port identifier  21303  of this entry, the CPU  24  registers the identifier of the new switch  300  that is contained in the link information. As the connected port identifier  21303  of this entry, the CPU  24  registers the port identifier of the new switch  300  that is contained in the link information as the identifier of a port connected to the connected switch  300 . 
     The CPU  24  then executes the redundancy condition judging processing shown in  FIG. 35  on the pair of the new switch  300  and the connected switch  300  (S 3912 ). 
     When it is judged in S 3912  that the new switch  300  and the connected switch  300  meet the redundancy condition, the CPU  24  proceeds to S 3905 . When it is judged in S 3912  that at least one of the new switch  300  and the connected switch  300  does not meet the redundancy condition, the CPU  24  notifies the administrator  1  of this fact. 
     The following is a detailed description of S 3905 . 
     The CPU  24  executes the redundancy configuration creating processing shown in  FIG. 15 . In this embodiment where two switches  300  constituting redundancy switches are the new switch  300  and the connected switch  300  that is connected to the new switch  300 , there is no need to set, in one of the switches  300  constituting redundancy switches, the connection relation between the other switch  300  constituting the redundancy switches and the connected switch  300  that is connected to the other switch  300 . Accordingly, S 1802  to S 1805  of the redundancy configuration creating processing are not executed in this embodiment. 
     In S 1801 , the CPU  24  obtains the identifier of the new switch  300  and the identifier of the connected switch  300  connected to the new switch  300  from the received link information. The CPU  24  keeps the obtained identifier of one of the switches  300  as S 0  and keeps the obtained identifier of the other switch  300  as S. 
     S 1806  to S 1809  in the third embodiment are the same as in the first embodiment, and the description is omitted here. 
     According to the third embodiment of this invention, when the administrator  1  connects a new standby switch to an existing network that is constituted of switches, a network in which redundant system control is in effect between an existing active switch and the newly installed standby switch is automatically designed. The third embodiment of this invention thus has effects of shortening the time required to build a redundancy configuration network, and reducing errors in setting VLANs to switches. 
     Fourth Embodiment 
     A fourth embodiment of this invention will be described next with reference to  FIGS. 37 and 38 . 
     In the fourth embodiment, the management server  2  creates redundancy switch settings by searching the switches  300  which are components of the network  4  for two switches  300  constituting redundancy switches (a redundancy pair) when an instruction to give the network  4  redundancy is received from the administrator  1 . 
       FIG. 37  is a sequence diagram of network designing in the management server  2  according to the fourth embodiment of this invention. 
     S 4001  to S 4003  and S 4005  to S 4011  are the same as S 3701  to S 3703  and S 3705  to S 3711  described in the second embodiment with reference to the flow chart of  FIG. 34 , and the description will not be repeated. 
     The administrator  1  inputs an instruction to find a redundancy pair from among the switches  300  constituting the network  4  to the management server  2  (S 4004 ). 
     The CPU  24  receives the input redundancy instruction and searches for a redundancy pair (S 4012 ). Details of the redundancy pair search processing will be described with reference to  FIG. 38 . 
     The CPU  24  executes the redundancy configuration creating processing on two switches  300  found as a redundancy pair (S 4005 ). 
     Specifically, the CPU  24  executes the redundancy configuration creating processing shown in  FIG. 15 . In this embodiment where two switches  300  constituting redundancy switches are the two switches  300  searched for as a redundancy pair, there is no need to set, in one of the switches  300  constituting redundancy switches, the connection relation between the other switch  300  constituting the redundancy switches and the connected switch  300  that is connected to the other switch  300 . Accordingly, S 1802  to S 1805  of the redundancy configuration creating processing are not executed in this embodiment. 
     In S 1801 , the CPU  24  obtains the identifier of one of the switches  300  found as a redundancy pair and the identifier of the other switch  300  found as the redundancy pair. The CPU  24  keeps the obtained identifier of one of the switches  300  found as a redundancy pair as S 0  and keeps the obtained identifier of the other switch  300  found as the redundancy pair as S. 
     S 1806  to S 1809  in the fourth embodiment are the same as in the first embodiment, and the description is omitted here. 
       FIG. 38  is a flow chart of redundancy pair search processing according to the fourth embodiment of this invention. 
     First, the CPU  24  obtains the identifiers of two switches  300  out of the switches  300  constituting the network  4  (S 4101 ). The CPU  24  keeps the obtained identifier of one of the two switches  300  as S 1  and keeps the obtained identifier of the other switch  300  as S 2 . 
     Next, the CPU  24  searches the port information management tables  213  of the switches  300  that are identified by the obtained two identifiers (S 1  and S 2 ) (S 4102 ). 
     The CPU  24  judges whether or not the switches  300  identified by the obtained identifiers (S 1  and S 2 ) meet the redundancy condition shown in  FIG. 35  (S 4103 ). 
     When it is judged in S 4103  that the switches  300  identified by the obtained identifiers (S 1  and S 2 ) meet the redundancy condition, the CPU  24  determines that the redundancy pair search processing has been successful, and ends the redundancy pair search processing. 
     When it is judged in S 4103  that the switches  300  identified by the obtained identifiers (S 1  and S 2 ) do not meet the redundancy condition, the CPU  24  judges whether or not there are other switches  300  that are candidates for a redundancy pair (S 4104 ). 
     Specifically, the CPU  24  judges whether or not S 4103  has been executed for every pair that is obtained by pairing two of the switches  300  constituting the network  4 . 
     When it is judged in S 4104  that there are other switches  300  that are candidates for a redundancy pair, the CPU  24  obtains the identifiers of two switches  300  that are a different pair from the pair of the two switches  300  whose identifiers have been obtained in S 4101  (S 4105 ). The CPU  24  keeps the newly obtained identifier of one of the two switches  300  as S 1  and keeps the newly obtained identifier of the other switch  300  as S 2 . 
     The CPU  24  then executes S 4103  for the switches  300  that are identified by the identifiers (S 1  and S 2 ) obtained in S 4105 . 
     This way, the administrator  1  only needs to input an instruction to find a redundancy pair to the management server  2 , which searches for a redundancy pair, automatically creates settings necessary to give the network  4  redundancy for the respective switches  300 , and updates the settings of the switches  300 . The workload of the administrator  1  is thus reduced. 
     In this embodiment, S 4103  is executed for every pair of the switches  300  constituting the network  4 . The CPU  24  may instead execute S 4103  for a pair of directly connected switches  300 . 
     Specifically, in S 4101  and S 4105 , the CPU  24  selects one switch  300  as a half of a pair and picks up the switch  300  that is connected directly to the former switch  300 . The CPU  24  obtains the identifiers of the two selected switches  300 . 
     The CPU  24  then judges in S 4104  whether or not S 4103  has been executed for every pair of directly connected switches  300 . 
     This way, S 4102  to S 4107  are executed only for directly connected switches  300  instead of executing S 4102  to S 4107  to all the switches  300 . The processing load of the CPU  24  is thus reduced. 
     This invention is applicable to management servers for managing networks, in particular, management servers for managing networks that have redundancy. 
     While the present invention has been described in detail and pictorially in the accompanying drawings, the present invention is not limited to such detail but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims.