Abstract:
Disclosed are an apparatus and a method for performing state transition of a backup router in a router redundancy system comprising a master router and at least one backup router for routing hosts. The method includes the steps of determining if a master router has a fault, and shifting the backup router into a master state if the master router has a fault and replacing a address of the backup router with a address of the master router in such a manner that the backup router operates with the replaced addresses.

Description:
CROSS-REFERENCE TO RELETED APPLICATION  
       [0001]     This application claims the benefit under 35 U.S.C. 119(a) of Korean Patent Application entitled “Apparatus And Method For Performing State Transition Of Backup Router In Router Redundancy System” filed in Korean Intellectual Property Office on Jun. 1, 2004 and assigned Serial No. 2004-39849, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a wireless local area network (WLAN). More particularly, the present invention relates to an apparatus and a method for dualizing a default router of hosts in a router redundancy system.  
         [0004]     2. Description of the Related Art  
         [0005]     A conventional local area network (LAN) is connected to other LANs through at least one router, so that hosts of the conventional LAN, such as personal computers (PCs) or relay entities, can communicate with other hosts provided in the other LANs. The routers receive data packets having destination addresses and transfer the data packets to the destination addresses through a predetermined route capable of fast transferring the data packets to the destination addresses.  
         [0006]     In a LAN environment, each host recognizes only one default router in order to communicate with other hosts through external networks. When a host transmits data packets to predetermined destination addresses, the host transfers the data packets to the default router. However, the router may malfunction in the event of a fault such as a power loss, reset, or scheduled maintenance. If such a malfunction occurs in the default router, the host does not communicate with other hosts through the external networks.  
         [0007]     In order to solve the above problem, a virtual routing redundancy protocol (VRRP) presented in a request for comments (RFC)  2338  and a hot standby router protocol (HSRP) presented in RFC  2281  allow the hosts to connect to a master router and at least one backup router when the hosts use the default router. The backup routers are called a “backup group” and a router selected from the backup group can be used by the host.  
         [0008]     The master router periodically sends a broadcast message to the backup routers in order to notify the backup routers of the available state of the master router. Thus, the backup routers may recognize the available state of the master router based on the broadcast message. If the master router does not send the broadcast message to the backup routers due to an error occurring in the master router, the selected backup router determines that the master router has a fault, so the backup router plays the role of the master router.  
         [0009]     For instance, if the backup router does not receive the broadcast message from the master router until three transmission periods has elapsed, the backup router determines that the master router has the fault.  
         [0010]      FIG. 1  is a diagram illustrating a network for operating a router redundancy protocol. As shown in  FIG. 1 , a plurality of hosts  140  through  146  are connected to a master router  120  and a backup router  122  through a LAN  130 . Network elements, which access the LAN  130 , are connected to an external network through the master router  120  or the backup router  122 . For instance, the network elements are connected to an Internet  110  in such a manner that the network elements can communicate with other network elements of the Internet  110 .  
         [0011]     The master router  120  and the backup router  122  have the same virtual internet protocol (IP) addresses (a.b.c.d) and media access control (MAC) addresses (00:00:5E:00:01:01) and act as routers for the hosts  140  through  146 . The hosts  140  through  146  establish the virtual IP address (a.b.c.d) as an IP address of the default router (that is, a default gateway) in order to transfer the packets through the master router  120  if the master router  120  has no fault. If the master router  120  has a fault, the backup router  122  detects the fault of the master router  120  and acts as the default router for the hosts  140  through  146 , instead of the master router  120 .  
         [0012]     As shown in  FIG. 1 , the master router  120  and the backup router  122  establish virtual IP addresses and MAC addresses based on the same virtual identification (ID)s separately from the IP addresses and MAC addresses. In addition, the hosts  140  through  146  establish the virtual IP address as the IP address of the default gateway. At this time, although data of the hosts are transmitted to the master router  120  and the backup router  122  having the same virtual IDs and virtual IP addresses, only the master router  120  may transmit the data.  
         [0013]     As mentioned above, according to the conventional router redundancy protocol, the virtual IDs, virtual IP addresses and MAC addresses must be established with respect to the master router and the backup router, making the structure of the conventional router redundancy protocol complicated. In addition, a virtual IP address field must be formed in a keepalive message, so the size of the keepalive message may increase.  
         [0014]     In order to solve the problems occurring in the conventional router redundancy protocol using the virtual IP address of the router, an apparatus and a method are needed that are capable of improving efficiency of the router by minimizing down time without separately establishing the virtual IP address and MAC address when the backup router is operated due to a malfunction of the master router.  
       SUMMARY OF THE INVENTION  
       [0015]     Accordingly, the present invention is to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide an apparatus and a method for performing state transition of a backup router to a master router when the master router has the fault in a router redundancy system.  
         [0016]     Another object of the present invention is to provide an apparatus and a method for operating a backup router by using an internet protocol (IP) address and a media access control (MAC) address of a master router when the master router has the fault in a router redundancy system.  
         [0017]     To accomplish these objects, according to an aspect of the present invention, a method for performing state transition of a backup router in a router redundancy system comprising a master router and at least one backup router for routing hosts is provided. The method comprises the steps of determining if a broadcast message is periodically transmitted to the backup router from the master router within a predetermined time, and shifting the backup router into a master state if the broadcast message is not periodically transmitted to the backup router from the master router and replacing an IP address and a hardware address of the backup router with an IP address and a hardware address of the master router in such a manner that the backup router operates with the replaced addresses.  
         [0018]     According to another aspect of the present invention, an apparatus for dualizing a default router of hosts in a router redundancy system is provided. The apparatus comprises a first router, which is a master router, for periodically transmitting a broadcast message based on an IP address and a hardware address thereof in order to indicate an available state of the first router, and a second router, which is a backup router, for receiving the broadcast message from the first router and determining if the broadcast message is periodically transmitted thereto from the first router within a predetermined time, wherein the second router is shifted into a master state if the broadcast message is not periodically transmitted to the second router from the first router and replaces an IP address and a hardware address of the backup router with an IP address and a hardware address of the first router in such a manner that the second router operates with the replaced addresses. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0020]      FIG. 1  is a diagram illustrating a structure of a network for operating a conventional router redundancy protocol;  
         [0021]      FIG. 2  is a diagram illustrating a structure of a network for operating a router redundancy protocol according to an exemplary embodiment of the present invention; and  
         [0022]      FIG. 3  is a flowchart illustrating an operational procedure of a backup router according to an exemplary embodiment of the present invention.  
         [0023]     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features and structures. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0024]     Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In the following detailed description, a detailed description of known functions and configurations incorporated herein will be omitted for clarity and conciseness. In addition, terms used in the following detailed description are defined by taking functions of elements used in the present invention into consideration, so they may vary depending on users, intentions of operators or the practices thereof. Thus, definitions of the terms used in the following description may be determined based on the full context of the present invention.  
         [0025]     According to the router redundancy protocol of the present invention, a master router periodically sends a broadcast message to a backup router in order to notify the backup router of the available state of the master router. The broadcast message has a destination address in the form of a multicast address so that all of network elements provided in a local area network (LAN) can receive the broadcast message. At an initial stage, the master router and the backup router are selected based on a priority thereof. That is, a router having a higher priority is selected as the master router. A user can determine the priority for the routers when establishing the routers. If a router has a priority higher than the other router, that router becomes the master router. In addition, if a router has a priority lower than the other router, that router becomes the backup router.  
         [0026]     The backup router can determine whether the master router has a fault based on the broadcast message transmitted thereto from the master router. If the backup router does not receive the broadcast message from the master router for a predetermined period of time (for instance, three transmission periods), the backup router determines that the master router has the fault, so the backup router serves as the master router.  
         [0027]      FIG. 2  is a diagram illustrating a structure of a network for operating a router redundancy protocol according to an exemplary embodiment of the present invention.  
         [0028]     A master router  120  and a backup router  122  have mutually different internet protocol (IP) addresses and media access control (MAC) addresses. The master router  120  serves as a default router for hosts  140  through  146 . The hosts  140  through  146  establish the IP address (a.a.a.a) of the master router  120  as an IP address of the default router, which is a default gateway, in order to transfer the packets through the master router  120  if the master router  120  has no fault.  
         [0029]     If the backup router  122  is selected as the master router due to the fault of the master router  120 , the backup router  122  replaces its IP address and MAC address with the IP address and MAC address of the master router  120 . In addition, the backup router  122  periodically sends the broadcast message while establishing a source address of the broadcast message based on the replaced IP address and MAC address. If the backup router  122  receives an address resolution protocol (ARP) request message from the hosts  140  through  146 , the master-state backup router  122  transmits an ARP reply packet to the hosts  140  through  146  while establishing the source address of the ARP reply packet based on the replaced IP address (a.a.a.a).  
         [0030]     That is, the backup router currently acting as a master router (i.e., master-state backup router  122 ) replaces the source IP address and MAC address with the IP address and MAC address of the master router  120 , so that the hosts may operate in relation to the master-state backup router  122  while recognizing the master-state backup router  122  as the default router.  
         [0031]     Even if the original master router  120  is recovered while the master-state backup router  122  is performing the routing procedure, the master-state backup router  122  continuously performs the routing procedure as the default router. However, if the master-state backup router  122  has a fault while performing the routing procedure, the original master router  120  again serves as the default router instead of the backup router  122 .  
         [0032]      FIG. 3  is a flowchart illustrating an operational procedure of the backup router according to an exemplary embodiment of the present invention.  
         [0033]     Referring to  FIG. 3 , the backup router sets a timer for receiving the broadcast message from the master router at step  302 . Then, the backup router waits for a predetermined period of time until the timer expires at step  304 . After that, the backup router determines whether the broadcast message is transmitted thereto from the master router before the timer has expired at step  306 . If it is determined at step  306  that the backup router has received the broadcast message, the backup router stores the IP address and MAC address of the master router included in the broadcast message at step  308 . After that, the backup router resets the timer while maintaining the backup state and repeats steps  304  through  308 . However, if it is determined at step  306  that the backup router has not received the broadcast message until the timer has expired, the backup router is shifted into the master state at step  310 .  
         [0034]     Then, the master-state backup router replaces its IP address and MAC address with the stored IP address and MAC address of the master router at step  312 . After that, the master-state backup router waits for a predetermined period of time until the timer expires in order to receive the broadcast message at step  314 . If it is determined at step  314  that the timer has not expired, step  318  is performed. In addition, if it is determined at step  314  that the timer has expired, the master-state backup router transmits the broadcast message to a network element though the network while establishing the source address of the broadcast message based on the replaced IP address and MAC address at step  316 .  
         [0035]     If the master-state backup router receives the ARP request packet from the hosts at step  318 , the master-state backup router transmits the ARP replay packet while establishing the source address of the ARP replay packet based on the replaced address at step  320  and performs a packet transmission service at step  322 . However, if the master-state backup router does not receive the ARP request packet from the hosts at step  318 , step  322  is performed to provide the packet transmission service.  
         [0036]     As described above, according to a method for dualizing the default router of the hosts provided in the LAN embodied in the present invention, the backup router plays the role of the master router by using the IP address and MAC address of the master router. In addition, the present invention does not require additional virtual IP/MAC addresses for the routers, so the structure of the router redundancy protocol can be simplified. In addition, since it is not necessary to form the virtual IP address field in the broadcast message, a size of the broadcast message may be reduced, so that the efficiency of the router system can be improved.  
         [0037]     While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.