JP2011259007A - Packet transfer method and packet transfer device with load balance function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate communication bias by simple processing while keeping an advantage that packets of an identical communication flow have an identical transfer destination in selection of a multi-pass transfer destination.SOLUTION: A transfer device comprises: a routing table 723; hash functions 727a to 727d; a hash function selection unit 726; and a transfer destination selection unit 730. The routing table 723 stores the transfer destination in association with a packet address. The hash functions 727a to 727d define a first field value used for identifying a packet flow as an input value, and output different output values against the identical input values. The hash function selection unit 726 selects one of the hash functions according to a second field value representing remaining number of times of transferring received packet. The transfer destination selection unit 730 selects the transfer destination based on the output value of the selected hash function which defines the first field value of the received packet as the input value, when there are two or more transfer destinations to which the received packet corresponds.

Description

  The present invention relates to a packet transfer apparatus having a load balance function, and particularly when there are two or more appropriate transfer destinations for a packet, by selecting one transfer destination from these transfer destinations, load balancing is achieved. The present invention relates to a transfer device that realizes a function.

  In an IP network, a routing table is prepared for a transfer device on the network. The routing table shows the correspondence between the destination address on the network and the forwarding destination that indicates the direction of the shortest path on the network to the device with the destination address when viewed from the forwarding device that holds the routing table. It is a table. When each transfer device receives a packet, it searches the routing table based on the destination address of the packet. Each transfer device transfers the packet to the transfer destination obtained by the search. By performing this processing in each transfer device, the packet finally arrives at the device at the destination address.

  The IP network is configured so that communication can be maintained even if a failure occurs in a transfer device or a line on the network by providing a transfer device and a line redundantly and appropriately arranged. When a failure occurs in the transfer device or the line, each transfer device detects the failure, and the communication is maintained by rewriting the routing table to the transfer destination indicating the direction of the route that bypasses the failure.

  Furthermore, by arranging redundant transfer devices and lines so that they can communicate with the same performance and function as normal communication paths, normal transfer devices and lines, redundant transfer devices and It is possible to communicate using both lines. As a result, even when there is no failure, a redundant transfer device or line can be used for packet transfer.

  In a network that uses both a normal transfer device and line and a redundant transfer device and line for communication, the normal transfer device and line as a transfer destination for a destination address in any transfer device on the network There are two or more transfer destinations: a transfer destination using a route (hereinafter referred to as “normal route”) and a transfer destination using a redundant transfer device and a line (hereinafter referred to as “redundant route”). In the transfer device, by distributing the packet to the transfer destination of the normal route and the transfer destination of the redundant route, the transfer load is distributed in the network. Note that “there are two or more transfer destinations corresponding to the destination address in the routing table” and “a set of two or more transfer destination entries and two or more transfer destinations” Is called “multipath”. Distributing a packet having a multipath destination address to a plurality of transfer destinations to distribute the transfer load is called “load balance”.

  As a method of realizing load balancing according to multipath, field values that can be used to identify communication flows are extracted from packets, values are obtained from the values using a hash function, and transfer destinations are determined from multipaths based on these values. A method of selecting is described in Non-Patent Document 1. A “hash function” is a function that uniquely assigns and outputs one of a finite number of output values to an input value, and outputs as many finite outputs as possible to various input values. This function determines the output value so that the values are evenly allocated.

  According to the load balancing method of Non-Patent Document 1, packets are distributed and transferred to each multipath transfer destination fairly due to the randomness of the hash function. Further, since the transfer destination is determined based on the value of the packet field, packets of the same communication flow take the same route. According to the load balancing method of Non-Patent Document 1, since it is not necessary to store the correspondence between the communication flow and the transfer destination, the design of the apparatus is simplified.

  However, in the method of Non-Patent Document 1, when all transfer devices have the same hash function in a network in which two or more transfer devices on the communication path are multipath, distribution to each transfer destination of the multipath is performed. Packets are not evenly distributed.

  As a method for solving this communication bias, there is a technique of Patent Document 1. In the technique of Patent Literature 1, a transfer destination determination method for a transfer device can be individually set for each transfer device by a network administrator. As a result, even if the transfer destination determination method in each transfer device uses a hash function, the load balancing function by multipath operates in the network.

  However, this technique places a heavy burden on the network administrator. In other words, the network administrator investigates whether there are two or more transfer devices that are multipaths on the communication path for communication between all terminals that should be able to generate communication. A transfer destination selection method that is as different as possible must be determined for each transfer device.

  Further, in the technique of Patent Document 1, a method is proposed in which communication is performed between adjacent transfer apparatuses and arbitration is performed so as to automatically select a different transfer destination determination method. According to this technique, even if the network administrator does not set a transfer destination determination method in the transfer device, the transfer destination selection method is automatically arbitrated between the transfer devices, and a protocol that uses a different transfer destination selection method is used. . As a result, multi-path load balancing is realized.

  However, in the above technique, it is necessary to prepare a protocol for selecting a transfer destination determination method, which complicates the configuration and processing of the transfer apparatus.

JP 2008-048010 A

“Multipath Issues in Unicast and Multicast Next-Hop Selection”, November 2000, RFC 2997.

  The problem to be solved by the present invention is to eliminate the bias of communication by simple processing while retaining the advantage that packets of the same communication flow have the same transfer destination in selecting a multipath transfer destination.

[Application Example 1]
A transfer device for transferring a packet received via a network to another device connected to the network via the network;
A routing table that stores one or more other devices as transfer destinations in association with packet destinations;
Two or more hash functions that use the value of the first field of the packet that can be used to identify the flow of the packet as input values, and that output different output values for the same input value When,
A hash function selection unit that selects one hash function of the two or more hash functions according to the value of the second field representing the number of times the received packet has been transferred so far or the remaining number of times that transfer is possible;
In the routing table, when there are two or more transfer destinations associated with the destination of the received packet, the value of the first field of the received packet is used as an input value. And a transfer destination selection unit that selects a transfer destination of the received packet from the two or more transfer destinations based on an output value.

  When a packet is transferred in the network, the value of the second field changes each time it is transferred. For this reason, when a packet is transferred in a network including a plurality of transfer devices having the above-described mode, the same hash function is used each time the packets are sequentially transferred by the plurality of transfer devices. Instead of determining the transfer destination, a different hash function is used to determine the transfer destination. For this reason, according to said aspect, the communication bias in a network can be eliminated automatically and with a simple process.

  On the other hand, in each transfer device, each hash function uses the value of the first field that can be used to identify the flow of the packet as an input value. For this reason, in a certain transfer device, as long as different packets of the same flow are packets that have been transferred through the same route, the same transfer destination is assigned to them. Therefore, the packets with the same communication flow have the same transfer destination.

  Note that “according to the value of the second field” means that the hash function selected when the value of the second field is the first value, and the value of the second field is the first value Means a selection method in which the first value and the second value exist such that the hash functions selected when they are different second values are different.

[Application Example 2]
A transfer device according to application example 1,
The transfer destination selection unit receives the received value from the two or more transfer destinations according to a remainder value when the output value is divided by the number of transfer destinations associated with the destination of the received packet. A transfer device that selects a packet transfer destination.

  According to such an aspect, a packet transfer destination can be determined using a hash function having an output value in an arbitrary range.

[Application Example 3]
A transfer device for transferring a packet received via a network to another device connected to the network via the network;
A routing table that stores one or more other devices as transfer destinations in association with packet destinations;
The value of the first field of the received packet that can be used for flow identification, and the second field of the received packet and the number of times the received packet has been transferred so far Or a hash function that outputs a hash value according to the value of the second field indicating the remaining transferable number of times,
In the routing table, when there are two or more transfer destinations associated with the destination of the received packet, transfer of the received packet from the two or more transfer destinations based on the output value of the hash function And a transfer destination selection unit that selects a destination.

  When a packet is transferred in the network, the value of the second field changes each time it is transferred. For this reason, when a packet is transferred in a network including a plurality of transfer apparatuses having the above-described mode, the same output value (hash value) is transmitted each time the packet is sequentially transferred by the plurality of transfer apparatuses. ), A different output value is used each time to determine the transfer destination. For this reason, according to said aspect, the communication bias in a network can be eliminated automatically and with a simple process.

  On the other hand, in each transfer device, the output value of the hash function includes the value of the first field that can be used to identify the flow of the packet, and the second value that represents the number of times the packet has been transferred so far or the remaining transferable number of times. It is uniquely determined according to the value of the field. For this reason, in a certain transfer device, as long as different packets of the same flow are packets that have been transferred through the same route, the same output value is obtained and transferred to the same transfer destination. Therefore, the packets with the same communication flow have the same transfer destination.

  Note that “output the hash value according to the value of the first field and the value of the second field” means the following selection method. That is, the hash value when the value of the first field is the value V11 and the value of the second field is the value V21, and the value of the second field where the value of the first field is V12 different from V11. There are a value V11 and a value V12 that are different from the hash value when the value is the value V21. Further, the hash value when the value of the first field is the value V11 and the value of the second field is the value V21, and the value of the first field is V11 and the value of the second field is V21. There are a value V21 and a value V22 that are different from the hash values when they are different V22.

[Application Example 4]
A transfer device according to application example 3,
The transfer destination selection unit receives the received value from the two or more transfer destinations according to a remainder value when the output value is divided by the number of transfer destinations associated with the destination of the received packet. A transfer device that determines the transfer destination of a packet.

  According to such an aspect, a packet transfer destination can be determined using a hash function having an output value in an arbitrary range.

Note that the present invention can be realized in various modes as described below.
(1) A packet transfer device.
(2) Packet transfer method.
(3) A network system including a packet transfer device.

The figure which shows the structural example of the network in which the multipath transfer apparatus has two stages. The block diagram which shows a TTL switching type load balance transfer apparatus. The routing table of the transfer apparatus 101. The routing table of the transfer apparatus 102. The routing table of the transfer apparatus 103. A table showing the flow. The table | surface which shows the packet transfer path | route for every flow at the time of using a TTL switching type load balance transfer apparatus. The block diagram which shows the load balance transfer apparatus of a reference example. The table | surface which shows the packet transfer path | route for every flow at the time of using the load balance transfer apparatus of a reference example. FIG. 5 is a block diagram illustrating a structure of a TTL mixed load balance transfer apparatus according to a second embodiment. The table | surface which shows the packet transfer path | route for every flow at the time of using a TTL mixed type load balance transfer apparatus.

A. Example 1:
A1. Configuration of load balance transfer device:
FIG. 1 is a diagram showing a network NT having two stages of multipath transfer apparatuses. The network in FIG. 1 is a network in which four terminals 111 to 114 are connected by transfer apparatuses 101 to 108 and lines 121 to 134.

  As shown in the upper part of FIG. 1, in the network NT, a terminal 111 having an address 10.0.0.1 and a terminal 112 having an address 10.0.0.2 are connected to the transfer apparatus 101. . Further, as shown in the lower part of FIG. 1, a terminal 113 having an address 20.0.0.1 and a terminal 114 having 20.0.0.2 are connected to the transfer apparatus 108. The transfer device 101 and the transfer device 108 are connected via transfer devices 102 to 107 and lines 123 to 132.

  The transfer apparatus 102 is connected to the transfer apparatus 108 via the line 125, the transfer apparatus 104, and the line 129. The transfer device 102 is connected to the transfer device 108 via a line 126, a transfer device 105, and a line 130. That is, the transfer device 102 and the transfer device 108 are connected by two paths.

  The transfer apparatus 103 is connected to the transfer apparatus 108 via a line 127, a transfer apparatus 106, and a line 131. The transfer device 103 is connected to the transfer device 108 via a line 128, a transfer device 107, and a line 132. That is, the transfer device 103 and the transfer device 108 are connected by two paths.

  The transfer device 101 is connected to the transfer device 102 via a line 123. Further, the transfer device 101 is connected to the transfer device 103 via a line 124. As a result, the transfer apparatus 101 and the transfer apparatus 108 are connected through four paths. The route from the transfer device 101 to the transfer device 108 passes through two transfer devices in any route. When receiving IP packets transmitted from the terminals 111 and 112 to the terminals 113 and 114, the transfer apparatuses 101 to 103 each have two transfer apparatuses as transfer destinations to which the IP packets can be transferred. is doing.

  FIG. 2 is a block diagram showing the TTL switching type load balance transfer device 701. In the first embodiment, the transfer apparatuses 101 to 108 in FIG. 1 are specifically the TTL switching load balance transfer apparatus 701 shown in FIG. The TTL switching load balance transfer apparatus 701 includes a packet transfer unit 710, a plurality of interfaces 711 to 714, and a transfer destination determination unit 720. The transfer destination determination unit 720 may be referred to as a “TTL switching transfer destination determination unit” in order to distinguish it from the transfer destination determination unit 720c of the reference example described later and the transfer destination determination unit 920 of the second embodiment.

  Packets arriving at the interfaces 711 to 714 are received by the packet transfer unit 710. The packet transfer unit 710 notifies the header part of the packet to the transfer destination determination unit 720 (see arrow Ah in FIG. 2). The transfer destination determination unit 720 determines the transfer destination of the packet based on the information of the packet header, and notifies the packet transfer unit 710 (see arrow Atr in FIG. 2). The packet transfer unit 710 subtracts 1 from the TTL field of the received packet and transmits the result to the transfer destination notified from the transfer destination determination unit 720.

  Note that “TTL (Time to live)” is an upper limit of the number of transfers by the transfer apparatus that can be performed before one packet is discarded. Each packet has a field (TTL field) that stores a TTL value. The terminal that first transmitted the packet sets a value corresponding to the purpose of the packet in the TTL field. Thereafter, each transfer device that has received the packet decrements the value of the TTL field by 1 each time the packet is transferred. In a transfer device, if the TTL field is 0, the packet is discarded. As a result, there is a routing loop on the network, and even when a packet circulates on the network, a situation where the packet circulates infinitely on the network is prevented. In the TTL switching type load balance transfer apparatus 701 of this embodiment, the packet transfer unit 710 subtracts the value of the TTL field. The TTL field corresponds to the “second field” in [Means for Solving the Problems].

  The transfer destination determination unit 720 includes a destination address extraction unit 721, a routing table search unit 722, a routing table 723, a flow identification field extraction unit 724, a TTL field extraction unit 725, a hash function selection unit 726, a plurality of hash functions 727a to 727d, And a transfer destination selection unit 730.

  The routing table 723 stores the number of transfer destinations associated with the destination address 211 and the transfer destination. The contents of the routing table 723 are different for each transfer device. The routing table 723 included in each transfer apparatus in FIG. 1 will be described later.

  The header portion of the packet notified by the packet transfer unit 710 is notified to the destination address extraction unit 721, the flow identification field extraction unit 724, and the TTL field extraction unit 725 (see arrow Ah in FIG. 2).

  The destination address extraction unit 721 extracts a destination address from the header portion of the notified packet and notifies the routing table search unit 722 (see arrow Aa in FIG. 2). The routing table search unit 722 searches the routing table 723 based on the notified destination address, and obtains a transfer destination and the number of transfer destinations as a search result. Then, the routing table search unit 722 notifies the transfer destination selection unit 730 of the transfer destination and the number of transfer destinations.

  The flow identification field extraction unit 724 extracts the field value used for flow identification from the header portion of the notified packet, and notifies the hash function selection unit 726 (see arrow Af in FIG. 2). In this embodiment, three fields of a source address, a destination address, and a protocol number are used for flow identification. Each packet includes fields of a source address represented by 4 bytes, a destination address represented by 4 bytes, and a protocol number represented by 1 byte.

  The TTL field extraction unit 725 extracts the value of the TTL field from the header portion of the notified packet, and notifies the hash function selection unit 726 (see arrow Att in FIG. 2).

  The hash function selection unit 726 selects one hash function from the four hash functions 727a to 727d based on the value of the TTL field notified from the TTL field extraction unit 725. Then, the values of the three fields of the transmission source address, the destination address, and the protocol notified from the flow identification field extraction unit 724 are notified to the selected hash function.

  More specifically, the hash function selection unit 726 divides the value of the TTL field notified from the TTL field extraction unit 725 by the remainder obtained by dividing the value of the hash function by the number of hash functions Nh = 4 Vs (Vs is An integer satisfying 1 ≦ Vs ≦ Nh) is calculated. When the value Vs is 1, the hash function 727a is selected. When the value Vs is 2, the hash function 727b is selected. When the value Vs is 3, the hash function 727c is selected. When the value Vs is 4, the hash function 727d is selected.

  When the hash function selection unit 726 is notified of the transmission source address, the destination address, and the protocol, the hash functions 727a to 727d calculate a hash value from the notified values and notify the transfer destination selection unit 730 of the calculation.

  The hash functions 727a to 727d are functions that generate a random hash value from the value of the flow identification field indicating the transmission source address, the destination address, and the protocol. The hash functions 727a to 727d are hash functions that obtain different hash values from the same flow identification field value.

The first hash function 727a is obtained by applying the generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to a byte string in which a total of 9 bytes including a transmission source address of 4 bytes, a destination address of 4 bytes, and a protocol number of 1 byte are arranged. , 8-bit CRC (Cyclic Redundancy Check) value is a hash function having a hash value.

The second hash function 727b applies the generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to a byte sequence in which a total of 9 bytes including a source address 4 bytes, a destination address 4 bytes, and a protocol number 1 byte are arranged. This is a hash function in which a value obtained by further rotating the 8-bit CRC value to the right by 2-bit rotation (cyclic shift without carry) is used as a hash value.

The third hash function 727c applies the generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to a byte sequence in which a total of 9 bytes including a source address of 4 bytes, a destination address of 4 bytes, and a protocol number of 1 byte are arranged. This is a hash function in which a value obtained by rotating the obtained 8-bit CRC value further 4 bits to the right is used as a hash value.

The fourth hash function 727d applies a generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to a byte sequence in which a total of 9 bytes of a source address 4 bytes, a destination address 4 bytes, and a protocol number 1 byte are arranged. This is a hash function in which a value obtained by rotating the obtained 8-bit CRC value further 6 bits to the right is used as a hash value.

  When there are a plurality of transfer destinations notified from the routing table search unit 722, the transfer destination selection unit 730 further transfers the hash value notified from any one of the hash functions 727a to 727d and the transfer notified from the routing table search unit 722. 1 is added to the remainder divided by the previous number Ntr to calculate a value Vtr (Vtr is an integer satisfying 1 ≦ Vtr ≦ Ntr). Then, the transfer destination selection unit 730 selects the transfer destination having the number represented by the value Vtr. For example, when the number of destinations Ntr is 2, the remainder is 0 or 1. If the remainder is 0, Vtr = 1 and the first transfer destination in the routing table entry is selected. When the remainder is 1, Vtr = 2 and the second transfer destination in the routing table entry is selected. By performing such processing, it is possible to select a transfer destination according to the number Ntr of transfer destinations using a hash function having an arbitrary output value range.

  The transfer destination selection unit 730 notifies the packet transfer unit 710 of the transfer device selected as the transfer destination (see arrow Atr in FIG. 2). If there is only one transfer destination notified from the routing table search unit 722, the transfer destination selection unit 730 notifies the packet transfer unit 710 of the transfer destination notified from the routing table search unit 722.

  FIG. 3 is a routing table 723 (see FIG. 2) of the transfer apparatus 101 shown in FIG. The routing table 723 stores the number 212 of transfer destinations associated with the destination address 211 and the transfer destinations 213 and 214. The transfer destination number 212 and the transfer destinations 213 and 214 define a transfer method corresponding to the destination address 211.

  The routing table of the transfer apparatus 101 shown in FIG. 3 has three entries. The entry 201 has an address 10.0.0.1 as a destination and a terminal 111 as a transfer destination associated with the destination. The address 10.0.0.1 is the address of the terminal 111 (see FIG. 1).

  The entry 202 has an address 10.0.0.2 as a destination and a terminal 112 as a transfer destination associated with the destination. The address 10.0.0.2 is the address of the terminal 112 (see FIG. 1).

  The entry 203 has an address 20.0.0.0/24 as a destination, that is, an address 20.0.0.0 to an address 20.0.0.255 and a transfer destination associated with these destinations. Transfer devices 102 and 103. That is, the entry 203 is a multipath having two transfer destinations. The address 20.0.0.0/24 (address 20.0.0.0 to address 20.0.0.255) includes the address 20.0.0.1 of the terminal 113 and the terminal 114. The address 20.0.0.2 is included (see FIG. 1).

  FIG. 4 is a routing table 723 (see FIG. 2) of the transfer apparatus 102 shown in FIG. The routing table of the transfer device 102 has two entries. The entry 301 has an address 10.0.0.0/24 as a destination, that is, an address 10.0.0.0 to an address 20.0.0.255, and a transfer destination associated with these destinations. Transfer device 101. Note that the address 10.0.0.0/24 (address 10.0.0.0 to address 10.0.0.255) includes the address 10.0.0.1 of the terminal 111 and the terminal 112. The address 10.0.0.2 is included (see FIG. 1).

  The entry 302 shown in FIG. 4 is associated with addresses 20.0.0.0/24 as destinations, that is, addresses 20.0.0.0 to 20.0.0.255, and these destinations. And transfer devices 104 and 105 as transfer destinations. That is, the entry 302 is a multipath having two transfer destinations. The address 20.0.0.0/24 (address 20.0.0.0 to address 20.0.0.255) includes the address 20.0.0.1 of the terminal 113 and the terminal 114. The address 20.0.0.2 is included (see FIG. 1).

  FIG. 5 is the routing table 723 of the transfer apparatus 103 shown in FIG. 1 (see FIG. 2). The routing table of the transfer device 103 has two entries. The entry 401 has addresses 10.0.0.0/24 as destinations, that is, addresses 10.0.0.0 to 20.0.0.255, and transfer destinations associated with these destinations. Transfer device 101. Note that the address 10.0.0.0/24 (address 10.0.0.0 to address 10.0.0.255) includes the address 10.0.0.1 of the terminal 111 and the terminal 112. The address 10.0.0.2 is included (see FIG. 1).

  The entry 402 shown in FIG. 5 is associated with addresses 20.0.0.0/24 as destinations, that is, addresses 20.0.0.0 to 20.0.0.255, and these destinations. And transfer devices 106 and 107 as transfer destinations. That is, the entry 402 is a multipath having two transfer destinations. The address 20.0.0.0/24 (address 20.0.0.0 to address 20.0.0.255) includes the address 20.0.0.1 of the terminal 113 and the terminal 114. The address 20.0.0.2 is included (see FIG. 1).

  Description of the contents of the routing table 723 of other transfer devices is omitted to facilitate understanding of the technology.

A2. Processing in the load balance transfer device:
Hereinafter, flow distribution when the TTL switching type load balance transfer device 701 is used will be described.

  FIG. 6 is a table Tf showing a flow for verifying the presence or absence of distribution bias on the network. In this embodiment, each flow is identified by a transmission source address, a destination address, and a protocol number. For this reason, in the table Tf, each flow is specified by the values in the columns of the source address 511, the destination address 512, and the protocol number 513. The packet of each flow stores these values in the field. The field storing the transmission source address, the destination address, and the protocol number corresponds to the “first field” in [Means for Solving the Problem].

  In the table Tf of FIG. 6, eight flows 501 to 508 are shown. The source address of each flow is either the address 10.0.0.1 of the terminal 111 or the address 10.0.0.2 of the terminal 112, as shown in the column 511. As shown in column 512, the destination address of each flow is either the address 200.0.0.1 of the terminal 113 or the address 20.0.0.2 of the terminal 114. As shown in a column 513, the protocol number of each flow is either 6 that is a TCP protocol number or 17 that is a UDP protocol number. As a result of the three fields each having two values, eight flows are shown in Table Tf.

  FIG. 7 shows a case where the TTL switching type load balance transfer device 701 shown in FIG. 2 is adopted for each transfer device in the network shown in FIG. 1, and packets of the flows 501 to 508 shown in FIG. Table Tp1 showing packet transfer paths (first hop, second hop, third hop). Note that the terminals 111 and 112 transmit packets with TTL set to 64 for packets of all flows.

  The table Tp1 in FIG. 7 includes, in addition to the contents of the table in FIG. 6, a column 814 indicating TTL when the source terminal transmits a packet, a column 815 corresponding to the first hop transfer device, and a second hop transfer. It has a column 819 corresponding to the device and a column 823 representing the third hop transfer device. A column 815 corresponding to the first hop transfer device includes a column 816 indicating the first hop transfer device, a column 817 indicating the TTL at the time when the first hop transfer device receives the packet, and a packet at the first hop. Column 818 representing the hash value corresponding to. A column 819 corresponding to the second hop transfer device includes a column 820 indicating the second hop transfer device, a column 821 indicating TTL at the time when the second hop transfer device receives the packet, and a packet at the second hop. 822 representing the hash value corresponding to.

  The process of determining the first hop to the third hop in the transfer destination determination unit 720 will be described using the flow 501 shown in the first row of the table Tp1 as an example. The source address of the flow 501 is 10.0.0.1. That is, the transmission source of the flow 501 is the terminal 111 (see FIG. 1). When transmitting the packet of the flow 501, the terminal 111 transmits the packet to the only transfer device 101 directly connected to the terminal 111 (see column 816). The terminal transmission TTL at the time when the terminal 111 transmits the packet is 64 (see column 814), and the first hop reception TTL is 64 (see column 817).

  The hash function selection unit 726 (FIG. 2) of the transfer apparatus 101 that is the first hop adds 1 to the remainder obtained by dividing the received TTL value 64 (see column 817 in FIG. 7) by the number of hash functions Nh = 4. The calculated value Vs is calculated. Here, since Vs = 1, the hash function selection unit 726 selects the hash function 727a corresponding to Vs = 1. Contents extracted by the flow identification field extraction unit 724 from the packet of the flow 501 (see the first row of the table Tf in FIG. 6), that is, the source address 10.0.0.1, the destination address 20.0.0. 1. Protocol number 6 is notified to the hash function 727a via the hash function selection unit 726 (see columns 511 to 513 in FIG. 7 and arrow Af in FIG. 2).

The hash function 727a applies the generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to the 9-byte byte sequence 0A00000111400106 in which three values of the source address, the destination address, and the protocol number are arranged, and the hash value of the first hop As 90 (see column 818 in FIG. 7).

  On the other hand, the destination address extraction unit 721 of the transfer apparatus 101 extracts the destination address 20.0.0.1 from the packet of the flow 501 and notifies the routing table search unit 722 (column 512 in FIG. 7 and FIG. 2). Arrow Aa).

  The routing table search unit 722 (see FIG. 2) searches the routing table 723 using the notified destination address 20.0.0.0.1. The routing table search unit 722 obtains the number of transfer destinations 2, the transfer device 102 as the transfer destination 1, and the transfer device 103 as the transfer destination 2 from the entry 203 of the routing table 723 of the transfer device 101 shown in FIG. This is notified to the transfer destination selection unit 730 (see FIG. 2).

  The transfer destination selection unit 730 receives the notification from the transfer function number 2 received from the routing table search unit 722, the transfer device 102 as the transfer destination 1, the transfer device 103 as the transfer destination 2, and the hash function 727a. Based on the hash value 90, the following processing is performed. That is, the transfer destination selection unit 730 obtains a value Vtr = 1 obtained by adding 1 to the remainder 0 obtained by dividing the hash value 90 by the transfer destination number Ntr = 2. Then, the transfer destination selection unit 730 selects the transfer destination with the number 1, that is, the transfer device 102 that is the transfer destination 1, and notifies this to the packet transfer unit 710 (see arrow Atr in FIG. 2).

  The packet transfer unit 710 subtracts 1 from the TTL of the packet to 63, and transfers the packet to the transfer device 102 that is the notified transfer destination.

  Thus, the transfer device 102 is selected as the second-hop transfer device for the flow 501 (see column 820 in FIG. 7). In addition, the TTL at the time when the transfer apparatus 102 receives is 63 (see column 821).

  The hash function selection unit 726 (see FIG. 2) of the transfer device 102 which is the second hop, adds 1 to the remainder obtained by dividing the received TTL value 63 (see column 821 in FIG. 7) by the number of hash functions Nh = 4. Calculate the added Vs. Since Vs = 4, the hash function selection unit 726 selects the corresponding hash function 727d. The contents extracted by the flow identification field extraction unit 724 from the packet of the flow 501, that is, the transmission source address 10.0.0.1, the destination address 20.0.0.1, and the protocol number 6 are stored in the hash function selection unit 726. Via the hash function 727d (see the first row of the table Tf in FIG. 6 and the arrow Af in FIG. 2).

The hash function 727d is obtained by applying a generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to a 9-byte byte sequence 0A00000111400106 in which three values of a source address, a destination address, and a protocol number are arranged to obtain a CRC value. Rotate the value 90 to the right by 6 bits to obtain 105 as the second hop hash value (see column 822 in FIG. 7).

  On the other hand, the destination address extraction unit 721 of the transfer apparatus 102 extracts the destination address 20.0.0.1 from the packet of the flow 501 and notifies the routing table search unit 722 (column 512 in FIG. 7 and FIG. 2). Arrow Aa).

  The routing table search unit 722 (see FIG. 2) searches the routing table 723 using the notified destination address 20.0.0.0.1. The routing table search unit 722 obtains the transfer destination number 2, the transfer device 104 as the transfer destination 1, and the transfer device 105 as the transfer destination 2 from the entry 302 of the routing table 723 of the transfer device 102 shown in FIG. This is notified to the transfer destination selection unit 730 (see FIG. 2).

  In the transfer destination selection unit 730, the number of transfer destinations notified from the routing table search unit 722, the transfer device 104 as the transfer destination 1, the transfer device 105 as the transfer destination 2, and the hash function 727d are received. Based on the hash value 105, the following processing is performed. That is, the transfer destination selection unit 730 obtains a value Vtr = 2 obtained by adding 1 to the remainder 1 obtained by dividing the hash value 105 by the transfer destination number Ntr = 2. Then, the transfer destination selection unit 730 selects the transfer destination with the number 2, that is, the transfer device 105 of the transfer destination 2, and notifies the packet transfer unit 710 (see arrow Atr in FIG. 2).

  The packet transfer unit 710 subtracts 1 from the TTL of the packet, and transfers the packet to the transfer device 105 that is the notified transfer destination.

  Thus, transfer device 105 is selected as the third hop transfer device for flow 501 (see column 823 in FIG. 7).

  FIG. 7 shows the results of obtaining the first hop, the second hop, and the third hop for the other flows 502 to 508 by the same method as described above.

  In FIG. 7, half of the 8 flows are assigned the transfer device 102 as the second hop, and the other half of the flows are assigned the transfer device 103 as the second hop (column 820). reference). That is, for the second hop, the flows are equally allocated to the transfer apparatuses 102 and 103. In FIG. 7, two quarters of the total of eight flows are equally allocated to the transfer device 104, the transfer device 105, the transfer device 106, and the transfer device 107 as the third hop (column 823). reference).

  As described above, when the TTL switching type load balance transfer device 701 according to the first embodiment is used, even when multipath transfer further occurs in the transfer device selected in multipath (the second hop in the above example), the packet is transmitted. It can be seen that it can be evenly distributed. For packet distribution, the network administrator does not need to set a transfer destination selection method and does not need to use a protocol for determining the transfer destination selection method.

A3. Effect of load balance transfer device:
In the first embodiment, a plurality of hash functions as a transfer destination selection method are prepared in the transfer device. Then, the value of the TTL field is extracted from the packet, the transfer destination selection method (hash function) corresponding to the value is selected for each packet, and the value of the field identifying the flow is applied to the selected transfer destination selection method. To determine the forwarding destination.

  In the transfer apparatus according to the first embodiment, since the hash function is used in the method of selecting the transfer destination from the multipath, it is not necessary to store the correspondence between the communication flow and the transfer destination.

  The value of the TTL field is decremented by 1 every time the transfer device transfers a packet. For this reason, (i) the value of the TTL field of a packet is different at each point in time at each transfer device to which the packet is transferred. On the other hand, for different packets of the same communication flow, the value of the TTL field at the time when the terminal first transmits is the same. Therefore, (ii) as long as the communication path is the same, the value of the TTL field at the time when the same transfer apparatus receives the same packet for any packet in the same flow.

  In the first embodiment, different packets of the same flow are transferred to the same transfer destination by the latter characteristic (ii) of the TTL field. Then, due to the former characteristic (i) of the TTL field, even if the packet is the same, the transfer destination is selected so as not to have the same selection tendency when it is in a different transfer device.

  The above effect is effectively exhibited in a network having two or more transfer devices that use a hash function as a method of selecting a transfer destination, which is a multipath transfer device. For this reason, it is not necessary for the network administrator to set a transfer destination selection method in order to distribute communication fairly in the network. Further, it is not necessary to provide a protocol for adopting as different a transfer destination selection method as possible for each transfer device. Here, the case where there are two transfer destinations in each transfer device has been described as an example (see FIG. 1), but the above effect is similarly applied to the case where there are three or more transfer destinations that can be transferred in the transfer device. Is obtained.

B. Reference example:
FIG. 8 is a block diagram illustrating a load balance transfer device 702 of a reference example. The load balance transfer device 702 of the reference example does not include a TTL field extraction unit 725, a hash function selection unit 726, and hash functions 727b to 727d (see FIGS. 2 and 8). Then, the flow identification field extraction unit 724 extracts the values of the source address, destination address, and protocol number fields (see FIG. 6) used for flow identification from the header portion of the packet, and notifies the hash function 727a. (See arrow Af in FIG. 8). Other points of the load balance transfer device 702 of the reference example are the same as those of the load balance transfer device 701 of the first embodiment.

  9 employs the load balance transfer device 702 of the reference example of FIG. 8 for each transfer device of the network NT of FIG. 1, and the packets of the flows 501 to 508 shown in FIG. This is a table Tpc showing packet transfer paths (first hop, second hop, third hop).

  However, the routing table 723 of the transfer apparatus 101 has the contents shown in FIG. 3, the routing table 723 of the transfer apparatus 102 has the contents shown in FIG. 4, and the routing table 723 of the transfer apparatus 103 is shown in FIG. It shall have the contents. The terminals 111 and 112 transmit packets with TTL set to 64 for all the flow packets.

  A flow 501 (see the first row in FIG. 7) shown in the first row of the table Tpc will be described as an example. The source address of the flow 501 is 10.0.0.1. That is, the transmission source of the flow 501 is the terminal 111 (see FIG. 1). When the terminal 111 transmits the packet of the flow 501, the terminal 111 transmits the packet to the transfer apparatus 101. Therefore, the first hop of the flow 501 is the transfer device 101 (see column 615 in FIG. 9).

  The source address 10.0.0.1, destination address 20.0.0.1, and protocol number 6 extracted by the flow identification field extraction unit 724 from the packet of the flow 501 are notified to the hash function 727a (FIG. 9). Column 511-513 and arrow Af in FIG. 8).

  The hash function 727a obtains 90 as the hash value of the first hop based on the transmission source address, the destination address, and the protocol number as in the case of the first embodiment (see the column 614 in FIG. 9).

  On the other hand, the destination address extraction unit 721 of the transfer apparatus 101 extracts the destination address 20.0.0.1 from the packet of the flow 501 and notifies the routing table search unit 722 (see arrow Aa in FIG. 2).

  The routing table search unit 722 searches the routing table 723 using the notified destination address 20.0.0.1 as in the first embodiment. Then, the routing table search unit 722 obtains the transfer destination number 2, the transfer device 102 as the transfer destination 1, and the transfer device 103 as the transfer destination 2, and notifies them to the transfer destination selection unit 730 (FIG. 3). Entry 203 and FIG. 8).

  The transfer destination selection unit 730 receives the notification from the transfer function number 2 received from the routing table search unit 722, the transfer device 102 as the transfer destination 1, the transfer device 103 as the transfer destination 2, and the hash function 727a. Based on the hash value 90, as in the case of the first embodiment, the transfer device 102 of the transfer destination 1 is selected and notified to the packet transfer unit 710 (column 616 in FIG. 9 and arrow Atr in FIG. 8). reference).

  The packet transfer unit 710 decrements the TTL of the packet by 1 to 63, and transfers the packet to the transfer device 102 that is the notified transfer destination.

  The flow identification field extraction unit 724 of the transfer device 102 that is the second hop extracts the source address 10.0.0.1, the destination address 20.0.0.1, and the protocol number 6 from the packet of the flow 501. And notifies the hash function 727a (see FIG. 8).

  The hash function 727a of the transfer device 102 that is the second hop is similar to the hash function 727a of the transfer device 101 that is the first hop, based on the source address, the destination address, and the protocol number. Get 90 as

  The routing table search unit 722 of the transfer device 102 that is the second hop uses the destination address 20.0.0.1 notified from the destination address extraction unit 721 to search the routing table of the transfer device 101 that is the first hop. Similarly to the unit 722, the routing table 723 is searched. Then, the routing table search unit 722 of the transfer device 102 which is the second hop obtains the transfer destination number 2, the transfer device 104 as the transfer destination 1, and the transfer device 105 as the transfer destination 2, and selects them as the transfer destination. Section 730 is notified (see entry 302 in FIG. 4 and FIG. 8).

  The transfer destination selection unit 730 receives the notification from the transfer function number 2 received from the routing table search unit 722, the transfer device 104 as the transfer destination 1, the transfer device 105 as the transfer destination 2, and the hash function 727a. Based on the hash value 90, the following processing is performed. That is, the transfer destination selection unit 730 obtains the value Vtr = 1 based on the hash value 90. Then, the transfer destination selection unit 730 selects the transfer device 104 of the transfer destination 1 and notifies the packet transfer unit 710 (see arrow Atr in FIG. 8).

  The packet transfer unit 710 subtracts 1 from the TTL of the packet to 63, and transfers the packet to the transfer device 104 that is the notified transfer destination.

  Thus, the transfer device 104 is selected as the transfer device of the third hop (see column 617 in FIG. 9).

  FIG. 9 shows the result of obtaining the first hop, the second hop, and the third hop for the other flows 502 to 508 by the same method as described above.

  Also in FIG. 9, as in FIG. 7 of the first embodiment, four of the eight flows are assigned to the transfer device 102 as the second hop, and the remaining half of the flows are transferred as the second hop. Device 103 is assigned (see column 616). That is, for the second hop, the flows are equally allocated to the transfer apparatuses 102 and 103.

  However, in FIG. 9, half of all eight flows are assigned the transfer device 104 as the third hop, and the other half of the flows are assigned the transfer device 107 as the third hop. (See column 617). That is, the transfer devices 105 and 106 are not selected as the third hop transfer device. In other words, the load balance does not function in the transfer apparatuses 102 and 103 as the second hop.

  The reason why the transfer destinations in the transfer apparatuses 102 and 103 are biased is that (i) the method of selecting a transfer destination uses a hash function that uses a field value usable for flow identification as an input value, and ( ii) The method is the same for all transfer devices.

  More specifically, in each of the packets transferred from the transfer device 101 to the transfer device 102, the transfer destination 1 is selected based on the value of the field representing the flow (that is, the hash value of the hash function 727a). 2 (the remainder of 2 is 0). For this reason, transfer destination 1 is also selected for those packets in transfer apparatus 102 which is the second hop. As a result, the third hop of those packets is the same forwarding device. Similarly, any of the packets transferred from the transfer apparatus 101 to the transfer apparatus 103 is a packet for which the transfer destination 2 is selected (that is, the remainder of 2 of the hash value of the hash function 727a is 1). For this reason, transfer destination 2 is selected for those packets in transfer apparatus 103 as the second hop. As a result, the third hop of those packets is the same forwarding device.

  As described above, the load balance transfer apparatus 702 of the reference example that does not include the plurality of hash functions 727b to 727d, the hash function selection unit 726, and the TTL field extraction unit 725 (see FIG. 2) When it is adopted as a transfer device for network NT, the load balance function cannot be fully exhibited.

  On the other hand, a plurality of hash functions 727b to 727d that output different hash values with respect to the same input value, a hash function selection unit 726 that selects those hash functions, and a hash function selection unit 726 that are different at each hop. The load balance transfer device 702 according to the first embodiment including the TTL field extraction unit 725 that gives an input value (see FIG. 2) has a sufficient load balance function when employed as the transfer device of the network NT in FIG. (See FIG. 7).

C. Example 2:
C1. Configuration of load balance transfer device:
FIG. 10 is a block diagram illustrating the structure of the TTL mixed load balance transfer apparatus 901 according to the second embodiment. The TTL mixed load balancer 901 does not include a hash function selection unit 726 and hash functions 727b to 727d (see FIGS. 2 and 10). The TTL mixed load balance transfer device 901 includes a TTL mixed hash function 926 instead. The flow identification field extraction unit 724 extracts the values of the source address, destination address, and protocol number fields (see FIG. 6) used for flow identification from the header portion of the packet, and notifies the TTL mixed hash function 926 of the values. (See arrow Af in FIG. 10). The TTL field extraction unit 725 extracts the value of the TTL field from the header portion of the packet and notifies the TTL mixed hash function 926 (see arrow Att in FIG. 10). The transfer destination determination unit having these configurations is referred to as a transfer destination determination unit 920 in order to distinguish it from the transfer destination determination unit 720 of the first embodiment. The transfer destination determination unit 920 may be referred to as a “TTL mixed transfer destination determination unit”.

  Other points of the TTL mixed load balance transfer device 901 of the second embodiment are the same as the TTL switching load balance transfer device 701 of the first embodiment.

  The TTL mixed hash function 926 calculates a hash value using the field value indicating the flow received from the flow identification field extraction unit 724 and the TTL value received from the TTL field extraction unit 725, and notifies the transfer destination selection unit 730. To do.

More specifically, the TTL mixed hash function 926 performs the following processing. That is, the TTL mixed hash function 926 calculates a remainder number Vr obtained by dividing TTL by 64. Then, a 72-bit string in which a total of 9 bytes including a transmission source address of 4 bytes, a destination address of 4 bytes, and a protocol number of 1 byte are arranged is bit-rotated to the right by Vr. An 8-bit CRC value obtained by applying the generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to the 72-bit string obtained as a result is set as a hash value as an output value.

  In the second embodiment, the TTL mixed hash function 926 as described above is adopted as an example, but a function having contents different from the above can be adopted as the function. For example, the number used when dividing the TTL to obtain the remainder number Vr can be a value other than 64. That is, the TTL mixed hash function may be a function that can generate a random value based on the value of the flow identification field and the TTL value. However, it is preferable that the number used when dividing the TTL to obtain the remainder number Vr is a value smaller than the number of digits of the number to be rotated and as large as possible. Further, it is preferably not a divisor of the number of digits of the number to be rotated.

  When there are a plurality of transfer destinations notified from the routing table search unit 722, the transfer destination selection unit 730 (see FIG. 10) is further notified of the hash value notified from the TTL mixed hash function 926 from the routing table search unit 722. The value Vtr (Vtr is an integer satisfying 1 ≦ Vtr ≦ Ntr) is calculated by adding 1 to the remainder divided by the transfer destination number Ntr. Then, the transfer destination selection unit 730 selects the transfer destination having the number represented by the value Vtr.

C2. Processing in the load balance transfer device:
FIG. 11 shows a case where the TTL mixed load balance transfer device 901 shown in FIG. 10 is adopted for each transfer device in the network shown in FIG. 1 and the packets of the flows 501 to 508 shown in FIG. Table Tp2 showing packet transfer paths. However, the routing table 723 of the transfer apparatus 101 has the contents shown in FIG. 3, the routing table 723 of the transfer apparatus 102 has the contents shown in FIG. 4, and the routing table 723 of the transfer apparatus 103 is shown in FIG. It shall have the contents. The terminals 111 and 112 transmit packets with TTL set to 64 for all the flow packets.

  Each column of the table Tp2 of FIG. 11 corresponds to each column of the table Tp1 of FIG. That is, column 1014 represents the TTL when the source terminal transmits a packet. Column 1015 corresponds to the first hop forwarding device. Column 1019 corresponds to the second hop forwarding device. Column 1023 represents a third hop forwarding device.

  A column 1015 corresponding to the first hop transfer device includes a column 1016 representing the first hop transfer device, a column 1017 representing the TTL at the time when the first hop transfer device received the packet, and a packet at the first hop. Column 1018 representing the hash value corresponding to. A column 1019 corresponding to the second hop transfer device includes a column 1020 representing the second hop transfer device, a column 1021 representing the TTL at the time when the second hop transfer device received the packet, and a packet at the second hop. 1022 representing the hash value corresponding to.

  The process of determining the first hop to the third hop in the transfer destination determination unit 920 will be described using the flow 501 shown in the first row of the table Tp2 as an example. As described in the first embodiment, the transmission source of the flow 501 is the terminal 111 (address 10.0.0.1) (see column 511 in FIG. 11). The first hop transfer device 1016 of the packet is the transfer device 101 (see column 1016 in FIG. 11 and FIG. 1). Further, the terminal transmission TTL 1014 at the time when the terminal 111 transmits the packet is 64 (see column 1014 in FIG. 11), and the first hop reception TTL 1017 is also 64 (see column 1017 in FIG. 11).

  In the transfer apparatus 101 that is the first hop, the flow identification field extraction unit 724 extracts the source address 10.0.0.1, the destination address 20.0.0.1, and the protocol number 6, and the TTL mixed hash function 926 (See arrow Af in FIG. 10). Also, the TTL field extraction unit 725 extracts the received TTL value 64 and similarly notifies the TTL mixed hash function 926 (see arrow Att in FIG. 10).

In the TTL mixed hash function 926, the number of remainders Vr = 0 obtained by dividing TTL by 64 is calculated. Then, the 9-byte byte sequence 0A0000011100000106 in which the notified source address, destination address, and protocol number are arranged is rotated to the right by Vr, that is, 0 bits. A CRC value 90 is obtained by applying the generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to the resulting value 0A000001100000106 to obtain 90 as the hash value of the first hop (see column 1018 in FIG. 11).

  On the other hand, the destination address extraction unit 721 of the transfer apparatus 101 extracts the destination address 20.0.0.1 from the packet of the flow 501 and notifies the routing table search unit 722 (see arrow Aa in FIG. 10).

  The routing table search unit 722 searches the routing table 723 using the notified destination address 20.0.0.1. Then, the routing table search unit 722 obtains the transfer destination number 2, the transfer device 102 as the transfer destination 1, and the transfer device 103 as the transfer destination 2 (see entry 203 in FIG. 3), and transfers them to the transfer destination selection unit. Notification to 730 (see FIG. 10).

  The transfer destination selection unit 730 receives a notification from the transfer destination number 2 received from the routing table search unit 722, the transfer device 102 as the transfer destination 1, the transfer device 103 as the transfer destination 2, and the TTL mixed hash function 926. Based on the received hash value 90, a value Vtr = 1 obtained by adding 1 to the remainder obtained by dividing the hash value 90 by the transfer destination number Ntr = 2 is obtained. Then, the transfer destination selection unit 730 selects the transfer destination with the number 1, that is, the transfer device 102 with the transfer destination 1, and notifies the packet transfer unit 710 (see FIG. 10).

  The packet transfer unit 710 decrements the TTL of the packet by 1 to 63, and transfers the packet to the transfer device 102 that is the notified transfer destination.

  Thus, the transfer device 102 is selected as the second-hop transfer device for the flow 501 (see column 1020 in FIG. 11). In addition, the TTL at the time when the transfer apparatus 102 receives is 63 (see column 1021 in FIG. 11).

  Also in the transfer apparatus 102 that is the second hop, the flow identification field extraction unit 724 similarly extracts the source address, the destination address, and the protocol number, and notifies the TTL mixed hash function 926 (see arrow Aa in FIG. 10). Also, the TTL field extraction unit 725 extracts the received TTL value 63 and notifies the TTL mixed hash function 926 (see arrow Att in FIG. 10).

The TTL mixed hash function 926 of the transfer apparatus 102 calculates the number of remainders Vr = 63 obtained by dividing TTL63 by 64. Then, the TTL mixed hash function 926 right-rotates the 9-byte byte sequence 0A0000011100000106 in which the notified source address, destination address, and protocol number are arranged by Vr, that is, 63 bits. By applying the generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 to the value 000002280000020C14 obtained as a result, the CRC value 41 is obtained, and 41 is obtained as the hash value of the second hop (see column 1022 in FIG. 11).

  On the other hand, the destination address extraction unit 721 of the transfer apparatus 102 extracts the destination address 20.0.0.1 from the packet of the flow 501 and notifies the routing table search unit 722 (see arrow Aa in FIG. 10).

  The routing table search unit 722 searches the routing table 723 (see FIG. 4) using the notified destination address 20.0.0.0.1. Then, the routing table search unit 722 obtains the transfer destination number 2, the transfer device 104 as the transfer destination 1, and the transfer device 105 as the transfer destination 2 (see entry 302 in FIG. 3), and transfers to the transfer destination selection unit 730. Notice.

  The transfer destination selection unit 730 receives the notifications from the transfer destination number 2 received from the routing table search unit 722, the transfer device 104 as the transfer destination 1, the transfer device 105 as the transfer destination 2, and the TTL mixed hash function 926. Based on the received hash value 41, the following processing is performed. That is, a value Vtr = 2 obtained by adding 1 to the remainder obtained by dividing the hash value 41 by the transfer destination number Ntr = 2 is obtained. Then, the transfer destination selection unit 730 selects the transfer destination number 2, that is, the transfer device 105 of the transfer destination 2 and notifies the packet transfer unit 710 of it.

  The packet transfer unit 710 decrements the TTL of the packet by 1, and transfers the packet to the transfer device 105 that is the notified transfer destination.

  Thus, the transfer device 105 is selected as the third hop transfer device for the flow 501 (see column 1023 in FIG. 11).

  FIG. 11 shows a result of obtaining the first hop, the second hop, and the third hop for the other flows 502 to 508 by the same method as described above.

  In FIG. 11, half of all eight flows are assigned the transfer device 102 as the second hop, and the other half of the flows are assigned the transfer device 103 as the second hop (sequence 1020). reference). That is, for the second hop, the flows are equally allocated to the transfer apparatuses 102 and 103. In FIG. 11, two-fourths of all eight flows are equally allocated to the transfer device 104, the transfer device 105, the transfer device 106, and the transfer device 107 as the third hop (column 1023). reference).

  As described above, even when the TTL mixed type load balance transfer device 901 of the second embodiment is used, even when the multipath transfer is further generated in the transfer device selected in the multipath (second hop in the above example), the packet It can be seen that can be evenly distributed. For packet distribution, the network administrator does not need to set a transfer destination selection method and does not need to use a protocol for determining the transfer destination selection method.

C3. Effect of load balance transfer device:
In the second embodiment, a transfer destination selection method (mixed hash function) that uses the value of the TTL field in addition to the value of the field that identifies the flow is prepared. Then, the TTL field and the field value for identifying the flow are extracted for each packet, and both are applied to the transfer destination selection method to determine the transfer destination.

  By using the property of the TTL field that the value of the TTL field of a packet is different at each point of time at each transfer device to which the packet is transferred, in this embodiment, the same packet is the same packet. However, when they are in different transfer apparatuses, the transfer destination is selected so as not to have the same selection tendency.

  In addition, as long as the communication path is the same, the TTL field characteristic that the value of the TTL field is the same at the time when the same transfer device receives the packet in the same flow is used in this embodiment. In, different packets of the same flow are transferred to the same transfer destination.

  As a result, also in the second embodiment, similar to the first embodiment, it is possible to obtain an effect superior to that of the reference example in packet transfer in the network.

D. Variations:
In addition, this invention is not restricted to said Example and embodiment, In the range which does not deviate from the summary, it is possible to implement in various aspects.

D1. Modification 1:
In the second to fourth hash functions 727b to 727d of the first embodiment, values obtained by further rotating the CRC value to the right by 2 bits, 4 bits, and 6 bits are used as hash values. However, the plurality of hash functions prepared in the TTL switching type load balance transfer device are not limited to these modes, and may be other modes. However, it is preferable that the value determined based on the field that can specify the flow is rotated by different bits. The number of bits to rotate is preferably not an integral multiple of the number of digits determined based on the field that can specify the flow.

D2. Modification 2:
In the above embodiment, the generator polynomial x ⁸ + x ⁷ + x ³ + x ² +1 is applied to the number obtained from the field that can specify the flow and the value obtained from the TTL field. However, the formula applied to the number obtained from each field may be another formula. However, the hash function is preferably a function that obtains a hash value by applying both a polynomial and a bit rotation to the input value. With such an aspect, the hash values can be made more uniform.

D3. Modification 3:
In the above embodiment, the transfer is selected using the function by switching the function using the value of the TTL field of the packet or by setting the value of the TTL field of the packet as one of the input values of the function. The point is changed. However, as the information used for changing the selected transfer destination, the value of a field other than the TTL field can be adopted. For example, if the packet has a field that stores the number of times that packet has been transferred, the value of that field can be used.

  That is, (1) the same communication flow received by the same transfer device has the same field value, and (2) the same flow packet received by a different transfer device If the field satisfies the condition that the field values are different, the transfer destination of the packet can be determined using the field.

  When a packet transfer destination is selected according to the value of the field as described above, according to the characteristic (1), in one transfer apparatus, packets of the same communication flow have the same transfer destination. Further, due to the characteristic (2), in different transfer apparatuses, the method of selecting a transfer destination is different even for packets of the same communication flow. As a result, packets in the same communication flow can eliminate communication bias in the network while retaining the advantage that the transfer destination is the same.

D4. Modification 4:
In the first embodiment, the hash function selection unit 726 has the hash function associated with the value of Vs according to the value Vs obtained by adding 1 to the remainder obtained by dividing the value of the TTL field by the number of hash functions Nh. Select. However, the selection of the hash function can be performed in other ways based on the value of a predetermined field. However, it is preferable that the method is to select one of the two or more hash functions according to the value of the field.

  Here, “select one hash function of two or more hash functions according to the value of the field” means that the hash function selected when the value of the field is the first value; It means a selection method in which the first value and the second value exist such that the hash function selected when the value of the field is a second value different from the first value is different. That is, the mode in which the same hash function is selected regardless of the value of the field is “a mode in which one hash function is selected from two or more hash functions according to the field value”. Is not included. On the other hand, in the aspect of “selecting one of the two or more hash functions according to the value of the field”, the hash function selected when the value of the field is the third value And a hash function selected when the field value is a fourth value different from the third value, even if there is a third value and a fourth value. Good.

D5. Modification 5
In the second embodiment, the TTL mixed hash function 926 bit-rotates the bit string obtained based on the value of the field that can specify the flow to the right by the remainder number Vr obtained by dividing TTL by 64. Then, a generator polynomial is applied to the value to obtain a hash value. However, the determination of the hash value can be performed by other methods based on the values of two predetermined fields. However, it is preferable that the method outputs a hash value according to the value of the first field and the value of the second field.

  Here, “output the hash value according to the value of the first field and the value of the second field” means the following selection method. That is, the hash value when the value of the first field is the value V11 and the value of the second field is the value V21, and the value of the second field where the value of the first field is V12 different from V11. There are a value V11, a value V12, and a value V21 that are different from the hash value when the value is the value V21. Further, the hash value when the value of the first field is the value V11 and the value of the second field is the value V21, and the value of the first field is V11 and the value of the second field is V21. There are a value V11, a value V21, and a value V22 that have different hash values when they are different V22.

  In other words, the same hash value is output as long as the value of the second field is the same regardless of the value of the first field. It is not included in the mode of outputting a hash value according to the value of the field 2. As long as the value of the first field is the same, the same hash value is output regardless of the value of the second field. It is not included in the mode of outputting the hash value according to the field value.

  On the other hand, in the aspect in which “the hash value is output according to the value of the first field and the value of the second field”, the value of the first field is the value V11 and the second field A hash value when the value of is the value V21 and a hash value when the value of the first field is V12 different from V11 and the value of the second field is the value V21 V11, value V12, and value V21 may exist. Further, the hash value when the value of the first field is the value V11 and the value of the second field is the value V21, and the value of the first field is V11 and the value of the second field is V21. There may be a value V11, a value V21, and a value V22 that have the same hash value when they are different V22.

D6. Modification 6
The functional units such as the destination address extraction unit 721, the hash functions 727a to 727d, and the TTL mixed hash function 926 in the above embodiment may be realized by executing software by the CPU or may be realized by hardware. .

101-108 ... transfer devices 111-114 ... terminals 121-134 ... lines 201-203 ... entries 211 in the routing table of the transfer device 101 ... column 212 for storing destination addresses ... column 213 for storing the number of transfer destinations ... transfer destination 1 Column 214 for storing transfer destinations 301-302 for storing transfer destination 2 entries 401-402 for routing table of transfer apparatus 102 ... entries 501-508 for routing table of transfer apparatus 103 ... communication flow 511 ... source of communication flow Column 512 indicating address ... Column 513 indicating destination address of communication flow ... Column 614 indicating protocol number of communication flow ... Column 615 indicating hash value obtained from packet of communication flow ... First transfer device of first hop of communication flow Column 616 indicating code ... Second-hop transfer device of communication flow Column 617 indicating code ... Column 701 indicating code of the third hop transfer device in the communication flow ... TTL switching load balance transfer device 710 ... Packet transfer unit 711-714 ... Interface 720 ... TTL switching type transfer destination determining unit 720c ... Transfer destination determination unit 721 ... Destination address extraction unit 722 ... Routing table search unit 723 ... Routing table 724 ... Flow identification field extraction unit 725 ... TTL field extraction unit 726 ... Hash function selection units 727a to 727d ... Hash function 730 ... Transfer destination selection Section 814 ... Column 815 indicating the TTL value at the time when the terminal of the communication flow transmitted the packet ... Column 816 indicating the contents of the first hop of the communication flow ... Column 817 indicating the code of the transfer device of the first hop of the communication flow ... The first-hop transfer device of the communication flow receives the packet A column 818 indicating the TTL value at the time point, a column 819 indicating a hash value obtained from the packet in the transfer device of the first hop of the communication flow, a column 820 indicating the content at the second hop of the communication flow, and a column 820 of the communication flow Column 821 indicating the code of the two-hop transfer device ... Column 822 indicating the TTL value at the time when the second hop transfer device of the communication flow received the packet. Obtained from the packet at the second hop transfer device of the communication flow Column 823 indicating a hash value ... Column 901 indicating a code of the third hop transfer device of the communication flow ... TTL mixed load balance transfer device 920 ... TTL mixed transfer destination determination unit 926 ... TTL mixed hash function 1014 ... of the communication flow Column 1015 indicating the TTL value at the time when the terminal transmitted the packet ... Column 1016 indicating the content of the first hop of the communication flow ... First column of the communication flow Column 1017 indicating the code of the transfer device in the network ... column 1018 indicating the TTL value at the time when the first hop transfer device of the communication flow received the packet, obtained from the packet in the transfer device in the first hop of the communication flow Column 1019 indicating the hash value ... Column 1020 indicating the content of the second hop of the communication flow ... Column 1021 indicating the code of the second hop transfer device of the communication flow ... The transfer device of the second hop of the communication flow receives the packet A column 1022 indicating the TTL value at the time of the transmission, a column 1023 indicating a hash value obtained from the packet in the second hop transfer device of the communication flow, a column Ah indicating a code of the third hop transfer device in the communication flow Arrow indicating notification of header part Atr ... Arrow indicating packet transfer destination notification NT ... Network Tf ... Table indicating flow Tp1 ... TTL switching type Table showing packet transfer path when adopting debalance transfer apparatus Tp2 ... Table showing packet transfer path when adopting TTL mixed load balance transfer apparatus Tpc ... Packet when adopting load balance transfer apparatus of reference example Table showing transfer route

Claims (4)

A transfer device for transferring a packet received via a network to another device connected to the network via the network;
A routing table that stores one or more other devices as transfer destinations in association with packet destinations;
Two or more hash functions that use the value of the first field of the packet that can be used to identify the flow of the packet as input values, and that output different output values for the same input value When,
A hash function selection unit that selects one hash function of the two or more hash functions according to the value of the second field representing the number of times the received packet has been transferred so far or the remaining number of times that transfer is possible;
In the routing table, when there are two or more transfer destinations associated with the destination of the received packet, the output of the selected hash function using the value of the first field of the received packet as an input value A transfer destination selecting unit that selects a transfer destination of the received packet from the two or more transfer destinations based on a value. The transfer device according to claim 1,
The transfer destination selection unit receives the received value from the two or more transfer destinations according to a remainder value when the output value is divided by the number of transfer destinations associated with the destination of the received packet. A transfer device that selects a packet transfer destination. A transfer device for transferring a packet received via a network to another device connected to the network via the network;
A routing table that stores one or more other devices as transfer destinations in association with packet destinations;
The value of the first field of the received packet that can be used for flow identification, and the second field of the received packet and the number of times the received packet has been transferred so far Or a hash function that outputs a hash value according to the value of the second field indicating the remaining transferable number of times,
In the routing table, when there are two or more transfer destinations associated with the destination of the received packet, transfer of the received packet from the two or more transfer destinations based on the output value of the hash function And a transfer destination selection unit that selects a destination. The transfer device according to claim 3,
The transfer destination selection unit receives the received value from the two or more transfer destinations according to a remainder value when the output value is divided by the number of transfer destinations associated with the destination of the received packet. A transfer device that determines the transfer destination of a packet.

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