JP4981829B2 - MRC file creation device, MRC file creation method and program thereof - Google Patents

Description

  The present invention relates to a routing technique in a packet switching network such as an IP (Internet Protocol) network.

  It is important for network operators to perform failure recovery by quickly switching paths and maintain transfer quality in response to the occurrence of node or link failures. As a failure recovery method in an IP network, there is a failure recovery method using a routing protocol such as OSPF (Open Shortest Path First) (see Non-Patent Document 1). In this OSPF, a node that detects a failure calculates a detour route based on topology database information excluding the failure portion from all nodes, and automatically switches the transfer route. However, in OSPF, since the node calculates a detour path after the failure occurs, there is a problem that it takes time to recover from the failure.

  As a method for solving such a problem, an MRC (Multiple Routing Configurations) method has been proposed that realizes high-speed failure recovery by calculating a detour route in advance. In this MRC method, a detour information storage file (hereinafter referred to as an MRC file) is prepared in advance, and when a failure occurs, the transfer path is switched based on the MRC file corresponding to the failure.

  Here, the MRC file will be described with reference to FIG. The MRC file is a file indicating detour information at the time of failure by a combination of a normal node, an isolated node, a normal link, an isolated link, and a restricted link for a given topology. An isolated link indicates a failure link, and an isolated node indicates a failure node. The restricted link is a link that can be used only as the last hop to the isolated node.

  For example, the MRC file # 1 in the state indicated by reference numeral 102 in FIG. 11 is an MRC file having a topology including nodes N1 to N6 as indicated by reference numeral 101. In this MRC file # 1, (1) when the link between the nodes N2 and N3 fails, (2) when the node N2 fails, (3) when the node N6 fails, and (4) the node N1, A detour route when the link between N6 fails is shown. Here, the detour route uses a normal link, but a restricted link can also be used if it is the last hop to the isolated node. Actually, by setting a very large cost (for example, the maximum value “65535” defined by OSPF) to the isolated link of this MRC file, the link is made unusable. That is, in OSPF, since a link with a link cost as low as possible is selected, a link with such a very large link cost is not selected. Also, the restricted link is set to a sufficiently large value (for example, the total cost of all normal links) although it is lower than this isolated link, so that it is used only at the last hop.

  The reason why the restricted link is provided in the MRC file as described above is that the cause of the inability to communicate between nodes may be both a link failure and a node failure. For example, in the topology indicated by reference numeral 101, the causes of communication failure between the nodes N3 and N2 are (1) a link failure between the nodes N3 and N2, (2) a node failure at the node N2, and the like. Here, if the cause of the communication failure between the nodes is (1) a link failure between the nodes N3 and N2, for example, the path from the node N4 to the node N1 is via the node N3, It may be via the node N2. However, if the cause of the communication failure between the nodes N3 and N2 is (2) the node failure of the node N2, the link between the nodes N4 and N2 and between the nodes N2 and N1 is actually incapable of communication. This link cannot be used as a detour route. Therefore, for example, like the MRC file # 1 indicated by reference numeral 102, by providing a restricted link in which a sufficiently large link cost value is set for at least one link of the node N2, which is an isolated node, communication is disabled. The reachability to the node N2 can be ensured when the cause is a simple link failure. Further, when the cause of the communication failure is a node failure of the node N2, it is possible to select as few routes as possible through the node N2.

In order to create such an MRC file, the following conditions must be satisfied.
(Condition 1) In the MRC file, links excluding isolated links (that is, normal links and restricted links) must be connected graphs. This is to ensure the route reachability of the route constituted by links other than the isolated link.
(Condition 2) The union of isolated nodes and isolated links in all MRC files must match the original topology. This is because node failures and link failures that may occur in the topology need to be covered by all MRC files.
(Condition 3) At least one restricted link is connected to the isolated node, and the other links need to be isolated links. The opposite node of the restricted link is the normal node. This is because, as described above, it is necessary to consider both the case where communication is not possible due to a link failure and the case where communication is not possible due to a node failure when creating a detour path in the MRC file.

  Here, the creation algorithm of the MRC file according to the prior art will be described with reference to FIG. Here, a case where the number of MRC files = 4 is designated for the topology indicated by reference numeral 101 will be described as an example. First, an MRC file composed of normal links and normal nodes is created for all links having the topology indicated by reference numeral 101. Then, an arbitrary node is selected from this MRC file. For example, the node N1 is selected. Next, one link among the links connected to the selected node N1 is set as a restricted link. Other links are isolated links. At this time, it is randomly determined which link is a restricted link. By the above processing, all the links of this node N1 become isolated links or restricted links, so that this node N1 becomes an isolated node. In this way, MRC file # 0 is created (S1). Hereinafter, the process from selecting a node from the topology to setting the node as an isolated node will be referred to as a basic process.

  Next, the process proceeds to creation of MRC file # 1. Here, basic processing is performed on the opposite node of a link that has not been made an isolated link in the MRC file # 0 (for example, a link that has been restricted link). That is, the link between the nodes N1 and N6 is an isolated link, and the link between the nodes N5 and N6 is a restricted link. Then, the MRC file # 1 is created with the node N6 as an isolated node (S2). Such basic processing is executed on the node N5 which is the opposite node of the restricted link of the node N6 to create the MRC file # 2 (S3), and is executed on the node N4 which is the opposite node of the restricted link of the node N5. MRC file # 3 is created (S4).

  Here, the fourth MRC file (MRC file # 3) has been created, but all the nodes of the topology indicated by reference numeral 101 have not been selected as isolated nodes. Therefore, basic processing is performed on the MRC file # 0 created in S1. That is, basic processing is performed on the node N3 that is the opposite node of the restricted link of the node N4 in the MRC file # 3, and the node is updated to the MRC file # 0 indicated by reference numeral 103 (S5). Furthermore, since all the nodes indicated by reference numeral 101 have not been selected as isolated nodes, basic processing is performed on the MRC file # 1. That is, basic processing is performed on the node N2 that is the opposite node of the restricted link of the node N3, and the MRC file # 1 indicated by reference numeral 102 is updated (S6). As a result of the above processing, all the nodes in the topology have become isolated nodes, and the processing ends. Then, the MRC file # 0 indicated by reference numeral 103, the MRC file # 1 indicated by reference numeral 102, the MRC file # 2 created by S3, and the MRC file # 3 created by S4 are output.

  According to such an algorithm, since a link that could not be an isolated link in the previous MRC file is an isolated link in the next MRC file, all nodes in the topology are isolated nodes, and all links are isolated. It can be a link. Also, the basic processing is sequentially performed on a predetermined number of MRC files, and even if the basic processing is performed up to the last MRC file, if all the nodes are not yet isolated nodes, the process returns to the first created MRC file. The basic processing is executed, and the results of the basic processing (isolated link, restricted link, and isolated node) are added to the MRC file. Accordingly, since a detour path when a plurality of failures (failed nodes and failed links) occurs can be stored in one MRC file, it is not always necessary to prepare an MRC file for each failure.

IETF RFC2328 “OSPF Version 2”, April 1999 A. Kyalbein, et.al “FAST IP NETWORK RECOVERY USING multiple routing configurations” in proceeding of infocom, April 2006

  However, the above-described technique is mainly intended to cover all the detour paths for a single failure (a single node failure and a single link failure), and a failure pattern (isolated) per MRC file. The aggregation efficiency of nodes and isolated links is not necessarily high. Therefore, there may be a large number of MRC files that the router should store. For example, in the example described with reference to FIG. 11, a total of four MRC files are created for the topology indicated by reference numeral 101. However, the MRC file group covering all the detour paths of all the failure patterns of the topology indicated by reference numeral 101 is not limited to these four MRC files. For example, the three MRC files (MRC files # 0 to ##) shown in FIG. 2) is also conceivable. Accordingly, an object of the present invention is to solve the above-described problems and reduce the number of MRC files that a router should hold.

  In order to solve the above-described problem, the invention described in claim 1 is an MRC file creation device that creates an MRC (Multiple Routing Configurations) file indicating a detour path when a node failure and a link failure occur in a network. Then, topology information indicating the topology of the network, and MRC file creation management information indicating the node that has become an isolated node and the link that has become an isolated link in the MRC file created so far for the topology are stored. A storage unit, a link cost initial value creation unit that generates an initial value W0, which is a set of initial values of link costs of each link in the topology, using a random number, and a topology by the Kruskal method using the generated initial value W0 A spanning tree creation unit that deletes at least some of the links and creates a spanning tree of the topology , Referring to the topology, the terminal node in the spanning tree created by the spanning tree creation unit is set as an isolated node in the MRC file, and the link connected to this terminal node is defined as a restricted link, which is deleted when creating the spanning tree. An MRC file creation unit that creates an MRC file of the topology using the isolated link as an isolated link, and records the node that has become the isolated node and the link that has become the isolated link in the MRC file management information in the created MRC file; After the MRC file is created by the MRC file creation unit, N new sets of link costs W ′ are created by adding random values to the link cost values of links other than the isolated link in the MRC file. Link cost value change unit, spanning tree creation unit, MRC file creation unit, A repetitive control unit that controls the cost value changing unit, and an output unit that outputs the MRC file group created by the MRC file creating unit, and the repetitive control unit includes (1) a new link to the spanning tree creating unit When a spanning tree is created using the link cost values of the cost sets W′1 to W′N and an MRC file is created from the created spanning tree, the MRC file management information includes A process for selecting a spanning tree having the largest number of newly isolated nodes and isolated links for the MRC files created so far, and (2) the MRC file creation unit using the selected spanning tree Processing to create an MRC file, (3) The link cost value changing unit randomly selects a link cost value for a link other than an isolated link in the MRC file. In the MRC file creation management information, a process for creating a new set of link costs W ′ by adding values W ′ is performed until all nodes indicated in the topology become isolated nodes and all links become isolated links. It is made to perform.

  The invention according to claim 6 creates an MRC file indicating a detour route when a node failure and a link failure occur in the network, and creates topology information indicating the network topology and the topology so far. An MRC file creation device having a storage unit for storing a node that has become an isolated node and an MRC file creation management information that indicates a link that has become an isolated link in the generated MRC file uses a random number for each link in the topology. Using the step of generating an initial value W0, which is a set of link cost values, and the initial value W0 of the set of link costs, at least a part of the topology links is deleted by the Kruskal method, and a topology spanning tree is created. In the spanning tree created by the spanning tree creation unit with reference to the step and topology Create an MRC file of the topology with the end node as the isolated node in the MRC file, the link connecting to this end node as the restricted link, and the link deleted in creating the spanning tree as the isolated link. In the MRC file, the step of recording the node that became the isolated node and the link that became the isolated link in the MRC file management information, and the link cost of the link other than the isolated link in the MRC file after the MRC file is created The step of creating N new sets of link costs W ′ obtained by adding a random value to the value of and the step of outputting the created MRC file group are executed. Using the link cost value of each of the new link cost sets W′1 to W′N When N spanning trees are created and an MRC file is created by using the spanning tree among the created spanning trees, the MRC file created so far indicated in the MRC file management information becomes a new isolated node. Selecting a spanning tree having the largest number and the number of isolated links; (2) creating an MRC file from the selected spanning tree; and (3) link costs of links other than isolated links in the MRC file. Creating a new link cost set W ′ by adding a random value to the value, and in the MRC file creation management information, all nodes indicated in the topology are isolated nodes and all links The MRC file creation method is characterized in that the process is executed until “I” becomes an isolated link.

  Such an MRC file creation apparatus first creates a spanning tree of the topology and creates an MRC file based on this spanning tree. In other words, a topology in which the number of links is reduced as much as possible while creating the route reachability of each node in the topology in the MRC file is created. As a result, the number of failure patterns collected in one MRC file can be increased as much as possible. Thereafter, the MRC file creation apparatus sequentially creates MRC files that cover all failure patterns in the topology. When creating the next MRC file after creating one MRC file, the MRC file management information is used. Referring to the MRC file created so far, a spanning tree having the largest number of new isolated nodes and isolated links is created, and an MRC file is created using the spanning tree. By doing so, when the MRC file creation apparatus creates the MRC file group, it is possible to create an MRC file group with as few fault patterns as possible between the MRC files. Therefore, the MRC file creation device can reduce the number of MRC files for the topology. Note that the Kruskal method used for creating spanning trees in this MRC file creation apparatus creates spanning trees by removing links with relatively high link cost values. Therefore, using this property, when the link cost set creation unit creates a new link cost set, the link cost values of links other than isolated links in the MRC file are randomly increased. By creating the set W ′, it becomes easier to create a spanning tree different from the spanning tree created last time. In addition, since N sets (N patterns) of link cost sets W ′ are created, a wide range of spanning trees can be created. Therefore, the MRC file created by the MRC file creation apparatus is also rich in variations, and it becomes easy to find an MRC file in which the number of new isolated nodes and isolated links is greatly increased. Therefore, the MRC file creation apparatus can easily find an MRC file group that minimizes the number of MRC file groups that cover all failure patterns in the topology for a given topology.

  In the invention described in claim 2, the link cost value changing unit in the MRC file creation device described in claim 1 adds (1) a random value to each link cost of links other than the isolated link in the MRC file. After creating N new link cost sets W ′, (2) link costs of links connected to nodes other than isolated nodes in the MRC file for each of the created N new link cost sets W ′. 1 is selected, the selected link cost is changed to the minimum value that can be set in OSPF (Open Shortest Path First), and the link cost of the link connected to a node other than the isolated node is other than the selected link cost. The link cost of this link is changed to the maximum value that can be set in OSPF.

  By doing so, the MRC file creation device can easily find an MRC file in which the number of new isolated nodes and isolated links greatly increases. Therefore, the MRC file creation apparatus can easily find an MRC file group that minimizes the number of MRC file groups that cover all failure patterns in the topology for a given topology.

  According to a third aspect of the present invention, the link cost initial value creating unit in the MRC file creating device according to the first or second aspect generates a plurality of initial values WO using random numbers, and the repetitive control unit Based on the generated initial value W0, the process of creating MRC file groups by the spanning tree creating unit, the MRC file creating unit, and the link cost value changing unit is executed by the number of generated initial values W0, and the created MRC The MRC file group having the smallest number of files is selected from the file group, and the output unit outputs the selected MRC file group.

  By doing so, the MRC file creation device creates various MRC file groups and selects the MRC file group having the smallest number of files from among them, so that it is easy to find the MRC file group having the smaller number of MRC files. Become.

  In the invention according to claim 4, the iterative control unit in the MRC file creation device according to claim 1 or 2 provides (1) a random value for each link cost of a link other than an isolated link in the MRC file. When a spanning tree is created based on a set of N new link costs W ′ created by addition, and an MRC file is created based on the created spanning tree, When it is determined that an MRC file that increases the number of newly isolated nodes could not be created with respect to the MRC file created so far indicated in the MRC file creation management information, (2) the created N For each new set of link costs W ′, the link cost of a link connected to a node other than the isolated node in the MRC file is The selected link cost is changed to the minimum value that can be set in OSPF, and the link cost of the link other than the selected link cost among the link costs of the links connected to the nodes other than the isolated node is changed to OSPF. A process of changing to a maximum value that can be set in is executed.

  Also by doing in this way, the MRC file creation device can make the newly created MRC file an MRC file including a new isolated node that is not covered by the MRC file created so far. Here, when the MRC file creation apparatus determines that an MRC file that increases a new isolated node cannot be created by any of the N link cost sets W ′ obtained by randomly increasing the link cost value. Then, the process shown in (2) is executed. Therefore, the MRC file creation device does not need to execute the process shown in (2) more than necessary.

  According to the fifth aspect of the present invention, when an MRC file group created by the MRC file creation device according to any one of the first to fourth aspects is used, a node failure or link failure occurs in the network. The route control device performs route control.

  In this way, the number of MRC files held by the path control device can be reduced.

  The invention according to claim 7 is a program for causing a computer to execute the MRC file creation method according to claim 6.

  According to such a program, it is possible to cause a general computer (for example, a router) to execute the MRC file creation method according to claim 6.

  According to the present invention, the number of MRC files that the router should hold can be reduced.

It is the figure explaining the outline | summary of the MRC file creation method of this Embodiment. It is the figure explaining the outline | summary of the MRC file creation method of this Embodiment. It is a functional block of the router of this Embodiment. It is the flowchart which showed the outline | summary of the processing procedure of the router of FIG. It is the flowchart which showed the detail of the process of S11 of FIG. It is the flowchart which showed the detail of the process of S11 of FIG. (A) is the figure which illustrated the initial value W0 of the set of link costs in this Embodiment. (B) is the figure which demonstrated notionally the increase in the value of the link cost set W1-WN in this Embodiment. (C) is the figure which showed notionally the selection process of the spanning tree GX in this Embodiment. (A) is the figure explaining the MRC file creation method used as a comparative example. FIG. 6B is a diagram illustrating an MRC file group created by the router of FIG. It is the figure quoted in order to demonstrate the effect of the MRC file creation apparatus of this Embodiment. It is a functional block diagram of the failure recovery apparatus of the present embodiment. It is a figure explaining the MRC file creation method used as a comparative example. It is the figure which illustrated the MRC file.

  Hereinafter, modes for carrying out the present invention will be described. First, the outline of the processing procedure of the MRC file according to the present embodiment will be described with reference to FIGS. Here, a case where an MRC file of topology 301 in FIG. 1 is created will be described as an example. Assume that an initial value of a link cost generated by a random number is given to each link constituting this topology 301. The MRC file creation apparatus creates a spanning tree 302 based on this topology 301. Note that the spanning tree is a tree topology composed of a minimum number of links that can remove a part of links between nodes and ensure route reachability. In this spanning tree 302, a node (a leaf node) at the end is set as an isolated node (failed node). In addition, a link connected to the leaf node is a restricted link (a link used only at the last hop). Then, the link deleted when creating the spanning tree 302 is set as an isolated link (failure link), and an MRC file # 0 as shown in FIG. 1 is created. According to such a method, the above-described MRC file creation conditions, that is, the link except for the isolated link in the above (Condition 1) MRC file becomes a connected graph, and (Condition 3) an isolated node It is possible to create an MRC file satisfying that at least one restricted link is connected to and other links are isolated links.

  Here, since the MRC file creation apparatus creates an MRC file based on the spanning tree of the topology, one MRC file can cover the detour paths of a number of failure patterns while ensuring route reachability. When one MRC file is created in this way, the MRC file creation device changes the link cost value of each link in the topology and creates another spanning tree. Note that the Kruskal method is used as a spanning tree creation method used in the present embodiment (see Kiyoshi Ishihata, “Algorithms and Data Structures” p280-283, Iwanami Shoten, 1991). In this Kruskal method, a spanning tree is created by removing links preferentially from those having a high link cost value. Therefore, different spanning trees can be created by changing the value of the link cost of each link in the topology. Then, the MRC file creation device creates an MRC file based on the created spanning tree. Such processing is repeated until the above-described MRC file creation conditions, (Condition 3), satisfy the condition that the union of isolated nodes and isolated nodes in all MRC files matches the original topology.

  That is, as shown in FIG. 2, the MRC file creation apparatus first creates (2) spanning trees for (1) input topology. The creation of the spanning tree here is performed based on the initial value of the link cost of the input topology generated by random numbers. (3) Create an MRC file (MRC file # 0) based on the created spanning tree. Then, the information of the created MRC file is recorded in (A) MRC file creation management information. Here, (A) the MRC file creation management information includes links that are not yet isolated links and nodes that are not isolated nodes. Therefore, the MRC file creation device changes the link cost value by adding a random value to the link cost value of the link that has not become an isolated link in (3). Then, (4) a spanning tree is created using the changed link cost value, and (5) an MRC file (MRC file # 1) is created based on the created spanning tree. The information of the created MRC file is recorded in (B) MRC file creation management information.

  Here, (B) the MRC file creation management information includes a link that is not yet an isolated link and a node that is not an isolated node. Therefore, the MRC file creation apparatus further changes the link cost value by adding a random value to the link cost value of the link that has not become an isolated link in (5). Then, (6) a spanning tree is created using the changed link cost value, and (7) an MRC file (MRC file # 2) is created based on the created spanning tree. Information on the created MRC file is recorded in (C) MRC file creation management information. Here, when it is confirmed that all the links in the MRC file creation management information are isolated links and all the nodes are isolated nodes, the process is terminated. Thereafter, random numbers are generated again to set the initial value of the link cost for each link, and spanning tree creation and MRC file creation processing based on the created spanning tree are repeated a predetermined number of times. Then, the MRC file creation device outputs the MRC file group having the smallest number of files among the MRC file groups created by the above processing. By doing so, the MRC file creation device can find a combination of MRC file groups having as few files as possible with respect to the input topology.

<Configuration>
Next, the configuration of such an MRC file creation apparatus will be described with reference to FIG. Here, a case where the MRC file creation device is realized by a router (route control device) that performs route control in the network will be described as an example.

  As shown in FIG. 3, the function of the router 10 is roughly divided into an input / output unit 11, a processing unit 12, and a storage unit 13. The input / output unit 11 controls input / output of data that is the basis of topology information 131 (described later) and path information 134 with other routers 10 and packets with other routers 10. The processing unit 12 performs MRC file creation processing, path control based on the created MRC file, and the like. The storage unit 13 stores topology information 131 and route information 134 necessary for creating an MRC file. Such an input / output unit 11 includes a communication interface for transmitting and receiving packets via a network and an input / output interface. The processing unit 12 is realized by a program execution process by a CPU (Central Processing Unit) included in the router 10 or a dedicated circuit. Further, the storage unit 13 includes a storage medium such as a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), and a flash memory. When the router 10 is realized by program execution processing, the storage unit 13 stores a program for realizing the function of the router 10.

  The processing unit 12 includes an MRC file creation processing unit 121 that creates an MRC file, and a route control unit 128 that performs route control of received packets.

  This MRC file creation processing unit 121 includes a link cost initial value creation unit 122, a spanning tree creation unit 123, an MRC file creation unit 124, a link cost value change unit 125, an iterative control unit 126, and an MRC file group output. And a processing unit 127.

Among these, the link cost initial value creation unit 122 generates a random number to generate an initial value W0 (WO = {w ₀₁ , w ₀₂ , w) which is a set of link cost values for each link of the network indicated in the topology information 131. w ₀₃ ,..., w _0X,. The link cost initial value creating unit 122 creates a plurality (M) of initial values W0.

The spanning tree creation unit 123 creates a spanning tree of the topology indicated in the topology information 131 by the Kruskal method using the given link cost set value. The spanning tree creation process by the Kruskal method is performed according to the following procedure.
(1) When a graph (topology) is given, a flag “0” is assigned to all links.
(2) From this graph, the link with the lowest link cost is selected, and the flag of the link is set to “1”.
(3) The edge with the minimum cost is extracted from the remaining links with the flag “0”.
(4) When the flag of the link selected in (3) is set to “1”, when a cycle (loop) is made by all the links of the flag “1”, this link is deleted from the graph. When the cycle is not possible, the flag of this link is set to “1”.
(5) If there is no link that can be set to the flag “1” in the graph, a spanning tree is created by the link of the flag “1” and all the nodes. If there is a link that can set the flag “1” in the graph, return to (3).
Through the above processing, spanning tree creation unit 123 can create a spanning tree of the topology indicated in the topology information. This Kruskal method has a characteristic that a link with a high link cost value is easily removed.

  In addition, when the spanning tree creation unit 123 receives input of a plurality of link cost sets W′1 to W′N, it creates N spanning trees using the respective values.

The MRC file creation unit 124 creates an MRC file by comparing the network topology indicated by the topology information 131 with the spanning tree created by the spanning tree creation unit 123. The procedure for creating this MRC file is as follows (see FIG. 1).
(1) A leaf of a spanning tree, that is, a node at the end of the spanning tree is an isolated node. For example, in the spanning tree 302 in FIG. 1, since the leaves are nodes N3, N5, and N6, these nodes are set as isolated nodes.
(2) A link connected to a leaf of a spanning tree is a restricted link. That is, since there is one link connected to the leaf, this link is designated as a restricted link. For example, in the spanning tree 302 in FIG. 1, since the leaves are nodes N3, N5, and N6, links connected to these nodes are referred to as restricted links.
(3) A link deleted from the topology by creating a spanning tree is set as an isolated link. For example, the topology 301 and the spanning tree 302 are compared, and the link between the nodes N2 and N3, the link between the nodes N3 and N4, and the link between the nodes N5 and N6 are deleted. Let the link be an isolated link.

  Further, whenever the MRC file is created, the MRC file creation unit 124 of FIG. 3 shows the MRC file creation management information 133 (details will be described later) as the node that became the isolated node and the link that became the isolated link in the MRC file. To record. By referring to such MRC file creation management information 133, it can be understood from the MRC file (MRC file group) created so far which node is an isolated node and which link is an isolated link.

  The link cost value changing unit 125 creates N new link cost sets W ′ in which Wopt (the set of link costs used for the previous spanning tree creation) has been changed. Here, the link cost value changing unit 125 (1) randomly increases the link cost value of the non-isolated link among the link costs indicated in Wopt, and (2) randomly selects from among the non-isolated nodes. For one node, the link cost value of one of the links connected to that node is set as the minimum value, and the link cost value of the remaining links connected to that node is set as the maximum value.

  That is, (1) When the link cost value changing unit 125 reads the link cost set Wopt used for the previous spanning tree creation, the link cost value changing unit 125 copies N of these values. Then, a random value (wmin to wmax) is added to the link cost value of the link that has become an isolated link in the previously created MRC file among the set of N link costs that have been copied (W1 to WN). (See FIG. 7B described later). Here, the link cost value of the non-isolated link is increased because a link with a high link cost value is easily removed in the above-described Kruskal method. That is, when the link is removed, the link becomes an isolated link in the MRC file, so that the isolated link can be increased. Further, (2) the link cost value changing unit 125 selects one link connected to a node other than the isolated node (non-isolated node) in the MRC file for each of the N new link cost sets W ′. . The link cost of the selected link is set to the minimum value (for example, “1”) that can be set in OSPF (Open Shortest Path First). Further, among the links connected to the non-isolated node, the link cost other than the link for which the minimum value is set is set as the maximum value (for example, “65535”) that can be set in OSPF.

  That is, when the spanning tree creation unit 123 creates a spanning tree based on this link cost, the link cost value changing unit 125 changes the link cost so that at least one non-isolated node becomes a leaf. That is, the link cost value changing unit 125 changes the link cost so that the isolated node increases in the MRC file created by the MRC file creating unit 124.

  The iterative control unit 126 keeps the link cost value changing unit 125 on the link cost value until the condition 2 (the union of the isolated node and the isolated link in the MRC file matches the topology shown in the topology information 131) is satisfied. The change processing is executed, the spanning tree creation unit 123 is caused to execute spanning tree creation processing, and the MRC file creation unit 124 is caused to execute MRC file creation processing.

  Specifically, the iterative control unit 126 causes the spanning tree creation unit 123 to create N spanning trees using the link cost values of the new link cost sets W′1 to W′N. From the spanning tree, the spanning tree having the largest number of isolated nodes and the number of isolated links when the MRC file is created by the spanning tree is selected. Then, the repetition control unit 126 causes the MRC file creation unit 124 to create an MRC file using the selected spanning tree. Here, the reason why the spanning tree having the largest number of isolated nodes and the largest number of isolated links is selected is to create an MRC file including information on the detour paths of as many fault patterns as possible per file. It is. The iterative control unit 126 then changes the link cost value to the link cost value changing unit 125, the spanning tree creating unit 123, and the MRC file creating unit 124 until there is no non-isolated link and non-isolated node in the MRC file creation management information 133. Processing, spanning tree creation processing, and MRC file creation processing are executed. That is, if a non-isolated link or non-isolated node remains in the MRC file creation management information 133, the iterative control unit 126 causes the link cost value change unit 125 to change the link cost value again, and causes the spanning tree creation unit 123 to change this link cost value. A spanning tree is created based on the link cost value after the change, and the MRC file creation unit 124 creates an MRC file. The iterative control unit 126 executes such processing for the number of initial values WO of the set of link costs created by the link cost initial value creation unit 122 (for example, M times). Then, the repetitive control unit 126 selects an MRC file group (a set of MRC files) having the smallest number of files among the MRC file groups created as a result. Details of the processing procedure of the repetitive control unit 126 will be described later using a flowchart.

  The MRC file group output processing unit (output unit) 127 outputs the MRC file group selected by the repetition control unit 126 to the storage unit 13.

  Next, the route control unit 128 will be described. The route control unit 128 includes a route calculation unit 129 and a packet transfer unit 130. The route calculation unit 129 calculates a transfer route based on the topology information 131 and the MRC file group 132, and creates route information 134 (described later) and detour route information 135 (described later) for each failure pattern. For example, the route information 134 is information indicating an interface for outputting the packet for each destination address of the packet. The detour route information 135 is information indicating an interface for outputting the packet for each destination address of the packet when a failure of the failure pattern occurs for each failure pattern.

  The packet transfer unit 130 refers to the route information 134 or the detour route information 135 based on the destination address of the received packet, selects an output interface of the packet, and outputs the packet from the selected output interface. Here, when a failure occurs, the packet transfer unit 130 refers to the detour route information 135 and selects an output interface of the packet. Which detour route information 135 should be used depends on the failure information input to the router 10. Judgment based on.

  Next, the storage unit 13 will be described. The storage unit 13 stores topology information 131, an MRC file group 132, MRC file creation management information 133, route information 134, and detour route information 135.

  The topology information 131 is information indicating the identification information of each node (router) in the network, the link to which each node is connected, and the like. The topology information 131 is, for example, information as shown in the topology 301 in FIG. The topology information 131 is referred to when creating a spanning tree or an MRC file.

  The MRC file group 132 is an MRC file group output by the MRC file group output processing unit 127. This MRC file group is used to create the detour route information 135.

  The MRC file creation management information 133 is information in which links that have become isolated links and nodes that have become isolated nodes are recorded in the MRC file created by the MRC file creation unit 124 ((A) to (C) in FIG. 2). (Refer to MRC file creation management information). The iterative control unit 126 can determine whether or not an MRC file group that covers all node failures and link failures can be created for a given topology by referring to the MRC file creation management information 133. .

  The route information 134 is information indicating an interface for outputting the packet for each destination address of the packet. The detour route information 135 is information indicating an interface for outputting the packet for each destination address of the packet when a failure of the failure pattern occurs for each failure pattern.

<Processing procedure>
The outline of the MRC file creation processing by the router 10 will be described with reference to FIG. First, when the link cost initial value creation unit 122 creates M (M patterns) link cost initial values W0, the router 10 in FIG. 3 selects initial values selected from the created M initial values WO. An MRC file group is created using W0 (S11). Then, the created MRC file group is recorded in the storage unit 13 (S12). Details of the MRC file group creation process in S11 will be described later. Next, the iterative control unit 126 of the router 10 determines whether or not the MRC file group creation processing shown in S11 has been executed M times (S13). That is, when it is determined whether the MRC file group has been created for all the created M initial values W0, and when it is determined that the MRC file group has been created for all the created M initial values W0 (Yes in S13), Among the created MRC file groups, the MRC file group (set of MRC file groups) with the smallest number of files is selected and output to the storage unit 13 (S14). On the other hand, when the iterative control unit 126 determines that the MRC file group creation process has not been executed M times (No in S13), the process returns to S11 to execute the MRC file group creation process.

  Thus, since the router 10 creates MRC file groups for each of the initial values W0 of the set of M (M patterns) link costs, various MRC file groups can be created. Therefore, the router 10 can easily find an MRC file group (a set of MRC files) having as few files as possible.

  Next, the details of the process of S11 of FIG. 4 will be described using FIG. 5 and FIG. 6 with reference to FIG. First, the link cost initial value creating unit 122 of the router 10 in FIG. 3 generates a random number and generates an initial value W0 of a set of link costs (S21). Then, the initial value W0 is substituted into Wopt (S22), and the management variable i = 0 of the MRC file is set (S23).

  Next, the spanning tree creation unit 123 of the router 10 creates a spanning tree based on the value of Wopt, and the MRC file creation unit 124 creates an MRC file from the spanning tree (S24), and the value of the management variable i Is increased by 1 (S25). The created MRC file is stored in a predetermined area of the storage unit 13. In addition, the node that has become an isolated node and the link that has become an isolated link by the created MRC file are recorded in the MRC file creation management information 133 (see FIGS. 2A to 2C). Here, the iterative control unit 126 refers to the MRC file creation management information 133 and creates G ′ = (V ′, E ′), which is a set of non-isolated node V ′ and non-isolated nodes in all MRC files. (S26). If G ′ is an empty set (Yes in S27), the MRC file group output processing unit 127 outputs all MRC files (MRC file groups) (S30).

  On the other hand, if this G ′ is not an empty set in S27 (No in S27), the iterative control unit 126 creates one MRC file with the nodes and links included in this G ′ as isolated nodes and isolated links, respectively. It is determined whether or not it is possible (S28). If one MRC file can be created (Yes in S28), the MRC file creation unit 124 creates an MRC file (S29), and the MRC file group output processing unit 127 creates all the MRC files (MRC file). Group) is output (S30).

  On the other hand, if one MRC file cannot be created in S28 (No in S28), the process proceeds to S31 in FIG. The link cost value changing unit 125 in FIG. 3 first creates a set of N link costs W1 to WN obtained by copying the value of Wopt (S31). Then, the link cost value changing unit 125 executes the following processing on the link cost set W selected from the link cost sets W1 to WN. That is, the link cost value changing unit 125 randomly increases the link cost value of the non-isolated link in the link cost set W in the range of wmin to wmax (S32).

For example, as shown in FIG. 7A, when the initial value W0 is {w ₀₁ , w ₀₂ , w ₀₃ ,..., W _0X,. First, N initial values WO are copied to create W1 to WN. Then, the target W of the current process is selected from the W1 to WN, and the value of wmin to wmin is added to the link cost of the non-isolated link among the link costs of the selected W. For example, when w ₀₂ and w _0X are link costs of non-isolated links, values (wa, wc) randomly selected from wmin to wmax are added to the values of w ₀₂ and w _0X in W1.

  Returning to the description of FIG. When the link cost value changing unit 125 increases the value of the link cost at the initial value W0 in this way, the link cost value changing unit 125 then refers to the MRC file creation management information 133 to determine the non-isolated node. Select. Then, for the link connected to the selected non-isolated node, one link sets the minimum link cost (for example, “1”) that can be set by OSPF, and the maximum link that can be set for the remaining links. Set the cost (for example, “65535”). Thus, when the spanning tree creation unit 123 creates a spanning tree based on this link cost, the selected non-isolated node becomes a leaf of the spanning tree (see the spanning tree 302 in FIG. 1). In other words, when an MRC file is created based on this spanning tree, this node becomes an isolated node, so the MRC file creation unit 124 can create an MRC file that increases the number of new isolated nodes.

  Here, when the iterative control unit 126 determines that the processing has been completed for the link cost sets W1 to WN created in S31 (Yes in S34), the spanning tree creation unit 123 performs the processing in S32 and S33. The spanning trees G1 to GN are created using the link cost sets W1 to WN (S35). On the other hand, in S34, if the processing has not been completed for the link cost sets W1 to WN (No in S34), the process returns to S32. After S35, the iterative control unit 126 refers to the MRC file creation management information 133, and selects the spanning tree GX having the largest number of isolated nodes and isolated links from the spanning trees G1 to GN ( S36).

  For example, as shown in FIG. 7B, the spanning tree creation unit 123 creates spanning trees G1 to GN based on the link cost sets W1 to WN. Then, as shown in (c), the iterative control unit 126 creates new isolated links and isolated nodes when the MRC file is created based on the MRC file creation management information 133 and the spanning trees G1 to GN. The most spanning tree GX is selected (S36). Then, the iterative control unit 126 substitutes the set WX of link costs, which is the basis for creating this spanning tree GX, into Wopt (S37). Then, the process returns to S24 in FIG.

  By performing the above processing, the router 10 can increase the number of failure patterns that can be collected per MRC file as much as possible. Therefore, the number of MRC files for the input topology can be reduced as much as possible.

  Moreover, according to the router 10 of this Embodiment, the following effects which are not in the prior art can be obtained. For example, in the topology as shown in FIG. 8A, if three MRC files are created by the conventional technique, there are cases where the MRC files cannot be created. That is, the link between the nodes N1 and N6 is a restricted link, the other link connected to the node N1 is an isolated link, and the node N1 is an isolated node (S81). Further, the link between the nodes N6 and N5 is set as a restricted link, and the link between the nodes N1 and N6 is set as an isolated node (S82). Then, the link between the nodes N5 and N4 is set as a restricted link, and the link between the nodes N6 and N5 is set as an isolated node (S83). Here, all nodes are not yet isolated nodes and all links are not isolated links. Since the target number of MRC files is “3”, the process returns to the MRC file # 0 created in S81 and the processing is continued. However, if the link between the nodes N5 and N4 is removed from the MRC file # 0, that is, if it is an isolated link, connectivity (route reachability) cannot be ensured, so this link cannot be an isolated link. That is, if the link between the nodes N5 and N4 is removed, the link between the nodes N6 and N5 is isolated. Therefore, in the above (Condition 1), the link excluding the isolated link needs to be a connected graph. It cannot satisfy the condition that Therefore, an MRC file for a given topology cannot be created.

  On the other hand, according to the router 10 of the present embodiment, as shown in FIG. 8B, three MRC files (MRC files # 0 to # 2) satisfying (condition 1) to (condition 3) are created. be able to. That is, for example, when an MRC file is created by a conventional technique for a topology having no symmetry as shown in FIGS. 8A and 8B, aggregation of failure patterns (detour route patterns due to failures) is inefficient. become. Therefore, the target number of MRC files may not be able to cover all failure patterns. On the other hand, according to the router 10 of the present embodiment, (1) a topology in which a fault is removed in the MRC file is created by a spanning tree, and (2) an MRC file that newly increases isolated nodes and isolated links as much as possible. MRC file that covers as many fault patterns as possible with a small number of MRC files, even if the topology is not symmetric. Groups can be created.

  In the above-described embodiment, the link cost value changing unit 125 of the router 10 in FIG. 3 randomly increases the link cost values of W1 to WN to create new link cost sets W1 ′ to WN ′. After the creation, the iterative control unit 126 creates a spanning tree based on the set of N new link costs W ′ and creates an MRC file, and determines that there is a node that becomes a new isolated node. Then, the process shown in S33 of FIG. 6 may be omitted. That is, the router 10 may not perform the process shown in S33 if it is known that a new isolated node can be surely increased only by increasing the link cost value at random. In addition, the link cost value changing unit 125 skips the process shown in S32 of FIG. 6 and executes the process shown in S33. However, the link cost value changing unit 125 executes the process shown in S33. When the number is smaller than a predetermined threshold, the process shown in S32 may be executed.

  Note that the MRC file creation apparatus of the present embodiment may be realized as the failure recovery apparatus 40 shown in FIG. Constituent elements similar to those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted. The failure recovery device 40 monitors a failure of a link connecting the router 20 and the router 20 in the network by the network information acquisition device 50, and when a failure occurs, the router 20 in the network is bypassed based on the MRC file. Instructs a route change to the route. Such a system includes a failure recovery device 40, a network information acquisition device 50, and a network composed of a plurality of routers 20. The failure recovery apparatus 40 is a computer that instructs the router 20 to perform path control, and is realized by, for example, a PCE (Path Computation Element). When the network information acquisition device 50 detects a failure or the like of the router 20 in the network or a link connecting the routers 20, the network information acquisition device 50 notifies the failure recovery device 40 of the router 20 or the link in which this failure has occurred. The router 20 is an IP router that performs path control based on an instruction from the failure recovery apparatus 40.

  The function of the failure recovery apparatus 40 is roughly divided into an input / output unit 41, a processing unit 42, and a storage unit 43 as shown in FIG. The input / output unit 41 includes a communication interface for communicating with the router 20 in the network and an input / output interface. The processing unit 42 is realized by a program execution process by a CPU provided in the failure recovery device 40, a dedicated circuit, or the like. Furthermore, the storage unit 43 includes a storage medium such as a RAM, a ROM, an HDD, and a flash memory. When the function of the failure recovery apparatus 40 is realized by program execution processing, the storage unit 43 stores a program for realizing the function of the failure recovery apparatus 40.

  The processing unit 42 includes a route control unit 428 that gives a route control instruction to the router 20 in the network, instead of the route control unit 128 of the router 10 in FIG. 3. The route control unit 428 includes a route calculation unit 129 and a route control instruction unit 430. The route control instruction unit 430 instructs the router 20 to perform route control based on the route information indicated by the route information 134 before the failure occurs. On the other hand, when the failure information is received via the network information acquisition device 50 of FIG. 9, the bypass route information 135 is referred to and the router 20 is instructed to avoid the failed router 20 and the link. Note that which detour route information 135 should be used when this failure occurs is determined based on the failure information input to the failure recovery device 40. By providing such an MRC file creation unit 124, the number of MRC files and detour path information held by the failure recovery apparatus 40 can be reduced as much as possible.

  The program for realizing the router 10 and the failure recovery apparatus 40 according to the present embodiment can be provided by being stored in a computer-readable recording medium (such as a CD-ROM). It is also possible to provide the program through a network such as the Internet.

10, 20 Router 11, 41 Input / output unit 12, 42 Processing unit 13, 43 Storage unit 40 Failure recovery device 50 Network information acquisition device 121 MRC file creation processing unit 122 Link cost initial value creation unit 123 Spanning tree creation unit 124 MRC file Creation unit 125 Link cost value change unit 126 Repetition control unit 127 MRC file group output processing unit 128,428 Path control unit 129 Route calculation unit 130 Packet transfer unit 131 Topology information 132 MRC file group 133 MRC file creation management information 134 Path information 135 Detour route information 430 Route control instruction unit

Claims (7)

An MRC file creation device for creating an MRC (Multiple Routing Configurations) file indicating a detour path when a node failure occurs and a link failure occurs in a network,
Storage for storing topology information indicating the topology of the network and MRC file creation management information indicating a node that has become an isolated node and a link that has become an isolated link in the MRC file that has been created so far. And
A link cost initial value creating unit that generates an initial value W0, which is a set of initial values of link costs of each link in the topology, using a random number;
Using the generated initial value W0, at least a part of the link of the topology is deleted by the Kruskal method, and a spanning tree creating unit that creates the spanning tree of the topology;
With reference to the topology, a terminal node in the spanning tree created by the spanning tree creation unit is set as an isolated node in the MRC file, a link connected to the terminal node is defined as a restricted link, and the spanning tree is created. The MRC file of the topology is created with the link deleted in step 1 as an isolated link, and the node that became the isolated node and the link that became the isolated link in the created MRC file are recorded in the MRC file management information. An MRC file creation unit;
After the MRC file is created by the MRC file creation unit, N sets of new link cost sets W ′ obtained by adding random values to the link cost values of links other than isolated links in the MRC file A link cost value change section to be created;
An iterative control unit that controls the spanning tree creation unit, the MRC file creation unit, and the link cost value change unit;
An output unit for outputting the MRC file group created by the MRC file creation unit,
The iterative control unit includes:
(1) The spanning tree creating unit creates a spanning tree using the link cost values of the new link cost sets W′1 to W′N, and among the created spanning trees, the spanning tree When an MRC file is created with a tree, a process of selecting a spanning tree having the largest number of isolated nodes and the number of isolated links for the MRC file created so far indicated in the MRC file management information. ,
(2) processing for causing the MRC file creation unit to create an MRC file from the selected spanning tree;
(3) A process of causing the link cost value changing unit to create N new link cost sets W ′ obtained by adding random values to the link cost values of links other than the isolated link in the MRC file. In the MRC file creation management information, the MRC file creation apparatus is executed until all nodes indicated in the topology become isolated nodes and all links become isolated links. The link cost value changing unit
(1) After creating a new set of link costs W ′ by adding a random value to each link cost of links other than the isolated link in the MRC file,
(2) For each of the created N new link cost sets W ′, one link cost of a link connected to a node other than the isolated node in the MRC file is selected, and the selected link cost is designated as OSPF. (Open Shortest Path First) is changed to the minimum value that can be set, and link costs of links other than the selected link cost among links costs connected to nodes other than the isolated node can be set in OSPF 2. The MRC file creation device according to claim 1, wherein the MRC file creation device is changed to a maximum value. The link cost initial value creating unit
A plurality of initial values WO are generated using random numbers,
The iterative control unit includes:
Based on the generated initial value W0, a process for creating MRC file groups by the spanning tree creating unit, the MRC file creating unit, and the link cost value changing unit is executed for the number of the generated initial values W0. ,
From the created MRC file group, select the MRC file group having the smallest number of files,
The MRC file creation apparatus according to claim 1, wherein the output unit outputs the selected MRC file group. The iterative control unit includes:
(1) Create a spanning tree based on a set W ′ of N new link costs created by adding a random value to each link cost of links other than isolated links in the MRC file. When an MRC file is created based on the spanning tree that has been created, the MRC that increases the number of nodes that become newly isolated nodes with respect to the MRC file created so far indicated by the MRC file creation management information by any spanning tree. When it is determined that the file could not be created,
(2) The link cost value changing unit selects one link cost of a link connected to a node other than the isolated node in the MRC file for each of the created N new link cost sets W ′. The selected link cost is changed to the minimum value that can be set in the OSPF, and the link cost of the link other than the selected link cost is set in the OSPF among the link costs of the links connected to the nodes other than the isolated node. 3. The MRC file creation apparatus according to claim 1, wherein a process of changing to a maximum possible value is executed.   A path control device that performs path control when a node failure or link failure occurs in the network, using the MRC file group created by the MRC file creation device according to any one of claims 1 to 4. An MRC file indicating a detour path when a node failure and a link failure occur in the network is created, topology information indicating the topology of the network, and an isolated node in the MRC file created so far for the topology. An MRC file creation device comprising a storage unit for storing the node and the MRC file creation management information indicating the isolated link;
Generating an initial value W0, which is a set of link cost values for each link in the topology, using random numbers;
Using the initial value W0 of the set of link costs to delete at least a part of the links of the topology by the Kruskal method and creating a spanning tree of the topology;
With reference to the topology, a terminal node in the spanning tree created by the spanning tree creation unit is an isolated node in the MRC file, a link connected to the terminal node is a restricted link, and the spanning tree is created The MRC file of the topology is created with the link deleted in step 1 as an isolated link, and the node that became the isolated node and the link that became the isolated link in the created MRC file are recorded in the MRC file management information. Steps,
After the MRC file is created, creating N new sets of link costs W ′ obtained by adding random values to the link cost values of links other than isolated links in the MRC file;
Outputting the created MRC file group,
The MRC file creation device includes:
(1) N spanning trees are created using the link cost values of the new link cost sets W′1 to W′N, and an MRC file is created by the spanning tree among the created spanning trees. Selecting a spanning tree having the largest number of isolated nodes and the number of isolated links for the MRC file created so far indicated in the MRC file management information when created,
(2) creating an MRC file from the selected spanning tree;
(3) creating N new sets of link costs W ′ obtained by adding random values to the values of link costs of links other than isolated links in the MRC file;
The MRC file creation management information is executed until all nodes indicated in the topology are isolated nodes and all links are isolated links in the MRC file creation management information.   A program for causing a computer to execute the MRC file creation method according to claim 6.

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