KR101641799B1 - Failover system and method for restoring a TCP session - Google Patents

Abstract

When a failure is detected, a failover callback function is called. When a failover callback function is called, a simulated SYN packet is generated using the stored session information and transmitted to the TCP block of the backup server. In the TCP block, The present invention relates to a fail-over system and method for recovering a TCP session when a failure occurs by generating a simulated ACK packet using the stored session information and transmitting the simulated ACK packet to a TCP block.

Description

[0001] The present invention relates to a failover system and method for restoring a TCP session,

And more particularly, to a technique for providing a seamless service to a user using a backup server even when a failure occurs in a master server in a fault tolerant system that provides redundant communication.

A fault tolerant system is a system that can perform normal or partial functions even if a fault or failure occurs in a part of the components constituting the system.

Fault tolerance systems are used in safety-critical and mission-critical embedded systems where accidents occur that cause damage to people or property if they occur in the event of a fault. Specifically, it is used in embedded systems in various fields such as nuclear power, power generation, energy, defense, aviation, space, automobile, railroad, shipbuilding, plant,

Among the methods of restoring the fault in the fault tolerant system, the redundant system is typically operated in the following three ways.

First, a replication method is a method in which a plurality of identical systems are prepared and executed in parallel, and a result satisfying a majority is applied as a correct result.

Second, the redundancy method is a method of preparing a plurality of the same system and switching to the auxiliary system when a failure occurs.

Third, the diversity scheme is based on the precondition that a plurality of systems do not cause the same failure, and a plurality of different hardware systems are prepared in the same specification and operated as duplication.

In the duplicated communication system using the multiplexing method, when a failure occurs in the master server, there is a risk of packet loss when restoring to a method in which all the TCP packets exchanged at the master server are directly synchronized with the client at the backup server, Information synchronization takes a lot of time.

In addition, when restoration is performed in the same manner as the established TCP session in the present system, a synchronization routine for each TCP parameter must be implemented.

Therefore, there is a need for a technique for restoring a TCP session while minimizing direct synchronization with the client and many modifications of the kernel.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art.

Specifically, the present invention aims to provide a failover system and method for restoring a TCP session.

It is another object of the present invention to provide a seamless service to a user by using a backup server even if a failure occurs in a master server in a fault tolerant system for providing redundant communication.

The present invention also provides a method for restoring TCP session information from a backup server when a failure occurs during TCP-based communication in a master server, maintaining a session with a connected communication partner, and providing a seamless service to a user The purpose.

In order to achieve the above object, a failover system for restoring a TCP session when a failure occurs according to an embodiment of the present invention stores session information with all clients that a master server establishes a TCP connection Session store block; An application wrapper block that calls a failover callback function if a failure is detected; And a session handling block for generating a simulated SYN packet using the session information stored in the session storage block and transmitting the simulated SYN packet to a TCP block of the backup server, Upon receipt of the packet, an ACK request function is called. When the ACK request function is called, the session handling block generates a simulated ACK packet using the stored session information.

Wherein the failover system transfers session information for the TCP connection to the session storage block when the master server establishes a TCP connection with the client, Further comprising a session synchronization block for communicating information to the session handling block

At this time, the session synchronization block may transmit a beep signal to the master server at a predetermined cycle to determine the failure of the master server.

At this time, the stored session information may include a source port number, a destination port number, and a sequence number.

The stored session information may further include at least one of an acknowledgment number and window size information.

In this case, the session handling block writes the client port number of the session to be restored in the source port number field of the simulated SYN packet using the stored session information, and updates the destination port number of the simulated SYN packet and a value obtained by subtracting 1 from the stored sequence number included in the stored session information is written in the sequence number field of the simulated SYN packet, The simulated SYN packet can be generated by setting a flag bit for notifying and a flag bit for indicating that the packet is a SYN packet.

In this case, the session handling block writes the client port number of the session to be restored in the source port number field of the simulated ACK packet using the stored session information, and updates the destination port number of the simulated ACK packet a sequence number field of the mock ACK packet is recorded in the field number field, and a stored sequence number contained in the stored session information is described in a field number field of the mock ACK packet. bit) and a flag bit indicating that the packet is an ACK packet, thereby generating the simulated ACK packet.

A method for restoring a TCP session when a failure occurs in a failover system according to another embodiment of the present invention includes: calling a failover callback function when a failure is detected; Generating a simulated SYN packet using the stored session information when the failover callback function is called; Transmitting the simulated SYN packet to a TCP block of a backup server; Calling an ACK request function in the TCP block; Generating a simulated ACK packet using the stored session information when the ACK request function is called; And transmitting the simulated ACK packet to the TCP block.

A method of restoring a TCP session when a failure occurs includes the steps of storing session information for the TCP connection when the master server establishes a TCP connection with a client before the failure is detected, A step of deleting the corresponding session information.

The generating of the simulated SYN packet may include writing the client port number of the session to be restored in the source port number field of the simulated SYN packet using the stored session information, The backup server port number is written in the destination port number field and a value obtained by subtracting 1 from the stored sequence number included in the stored session information is written in the sequence number field of the simulated SYN packet , The simulated SYN packet can be generated by setting a flag bit indicating that the packet is a simulation packet and a flag bit indicating that the packet is a SYN packet.

The calling of the ACK request function in the TCP block may include checking a flag bit indicating a mock packet included in the simulated SYN packet and a flag bit indicating a SYN packet in the TCP block, It is possible to call the ACK request function without transmitting the SYN / ACK packet.

The generating of the mock ACK packet includes writing the client port number of the session to be restored in a source port number field of the mock ACK packet using the stored session information, The backup server port number in the destination port number field, the stored sequence number contained in the stored session information in the sequence number field of the simulated ACK packet, The simulated ACK packet can be generated by setting a flag bit and a flag bit indicating that the packet is an ACK packet.

At this time, the step of calling the ACK request function in the TCP block may generate a simulated SYN / ACK packet without sending the ACK request function and transmit the simulated SYN / ACK packet to the session handling block.

The present invention can be applied to an application and a routing protocol using a TCP connection in a fault tolerant system that provides high availability through redundancy with a master server and a backup server, thereby providing a stable network environment even in the event of a failure.

In addition, it is a recovery method that utilizes a 3-way handshake connection method, which is a TCP session connection method. Thus, stable TCP session restoration is possible, and recovery time can be shortened due to minimization of session information required for synchronization. It is possible to use the socket API (Application Programming Interface) of the present invention as it is.

1 is a diagram illustrating a configuration of a fail-over system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a format of a TCP packet transmitted in a fail-over system according to an embodiment of the present invention.
FIG. 3 is a schematic view illustrating a process of performing a failover according to an exemplary embodiment of the present invention. Referring to FIG.
4 is a flowchart illustrating a process of restoring a TCP session through a backup server in a failover system according to an embodiment of the present invention.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

However, the present invention is not limited to or limited by the embodiments. Like reference symbols in the drawings denote like elements.

Hereinafter, a failover system and method for restoring a TCP (Transport Control Protocol) session according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 4. FIG.

1 is a diagram illustrating a configuration of a fail-over system according to an embodiment of the present invention.

1, the failover system includes an application block 110, a session synchronization block 120, a session storage block 130, an application wrapper block 140, a session handling block 150, and a TCP block 160 .

The session synchronization block 120 transmits a beep signal to the master server in a predetermined cycle to determine a failure of the master server.

When the master server establishes a TCP connection with the client, the session synchronization block 120 delivers the session information for the TCP connection to the session storage block 130, and stores the session information in the session storage block 130 at the request of the session handling block 150. [ And transfers the session information to the session handling block 150.

The session storage block 130 stores session information with all clients established by the master server in the TCP connection.

At this time, the stored session information includes a source port number, a destination port number, and a sequence number, and includes an acknowledgment number and window size information .

The application wrapper block 140 provides an API (Application Programming Interface) that can utilize the TCP session recovery function.

The application wrapper block 140 temporarily suspends the TCP session update until the application block 110 processes the TCP data for synchronization at the time of receiving a TCP based packet and temporarily stores the flush generated after the data processing at the application block 110. [ And then notifies the session synchronization block 120 to store the session information in the session storage block 130 after receiving the message.

The application wrapper block 140 temporarily suspends data processing at the time of transmitting a TCP-based packet, and after completing a processing procedure of storing a transmission packet in the session storage block 130 through the session handling block 150, Packets are processed.

The application wrapper block 140 calls a failover callback function when a failure is detected and a TCP session restoration request is received from the application block 110.

When the application wrapper block 140 receives the simulated SYN packet from the TCP block, it calls the ACK request function without transmitting the SYN / ACK packet.

At this time, the confirmation of the simulation SYN packet can be confirmed by confirming the flag bit indicating that it is a simulation packet included in the packet and the flag bit indicating that it is a SYN packet.

Alternatively, the application wrapper block 140 may generate a simulated SYN / ACK packet and send it to the session handling block 150, instead of calling the ACK request function.

The session handling block 150 operates in the kernel space and manages the TCP session and the packet information and transmits the updated TCP session and packet information to the session storage block 130 through the session synchronization block 120 do.

The session handling block 150 communicates with the session synchronization block 120 in the user space above the kernel space using the system internal communication function by the internally defined stack in the session handling block 150.

The session handling block 150 generates a simulated SYN packet using the session information stored in the session storage block 130 and transmits the simulated SYN packet to the TCP block 160 of the backup server.

When the ACK request function is called, the session handling block 150 generates a simulated ACK packet using the stored session information.

The session handling block 150 receives the session information stored in the session store block 130 through the session synchronization block 120 and restores the TCP session when the TCP session is restored. If there is a send packet that does not receive the ACK And retransmits it.

The simulated SYN packet and the simulated ACK packet generated by the session handling block 150 will be described below with reference to FIG.

FIG. 2 is a diagram illustrating a format of a TCP packet transmitted in a fail-over system according to an embodiment of the present invention.

2, the TCP header of the simulated packet includes a source port number field, a destination port number field, a sequence number field, an offset field, A TCP field, a Reserve field, a TCP flags field, a Window field, a Checksum field, an Urgent Pointer field, and a TCP option field.

The source port number field indicates the port number of the source port. In the case of the mock packet of the present invention, the source port number field indicates the client port number of the session to be recovered.

The destination port number field indicates the port number of the destination. In the case of the simulated packet of the present invention, the destination port number field indicates the port number of the master server / backup server of the session to be recovered.

The sequence number field indicates a sequence number for identifying the divided data.

The offest field is used to inform the length of the header or the beginning of the data.

A reserved field is a reserved bit. In the present invention, the reserved field is used as a flag bit to check whether a packet is a simulated packet by using one bit of a reserved field.

The TCP flags field indicates a set of flag bits for TCP control, and includes a flag bit indicating that the packet is a SYN packet and a flag bit indicating that the packet is an ACK packet.

The Window field is used to provide the opponent of the communication with its buffer free capacity size for TCP flow control.

The Checksum field is used to check whether an error has occurred using the sum.

The Urgent Pointer field indicates the serial number of the last byte of the emergency data contained in the TCP segment.

The TCP Options field can contain up to 40 bytes of optional data.

Returning to FIG. 1, the session handling block 150 records the client port number of the session to be restored in the source port number field of the simulated SYN packet using the stored session information, A backup server port number is written in the destination port number field, a value obtained by subtracting 1 from the stored sequence number contained in the session information stored in the sequence number field of the simulated SYN packet is written, And a flag bit indicating that the packet is a SYN packet, thereby generating a simulated SYN packet.

When generating a simulated SYN packet, the reason for subtracting 1 from the sequence number is

Since 1 is added to the sequence number in the normal 3-way handshake process, 1 should be subtracted to assign the same sequence number in the simulation 3-way handshake process.

The session handling block 150 records the client port number of the session to be restored in the source port number field of the simulated ACK packet using the stored session information and outputs the destination port number of the simulated ACK packet, Field, a backup server port number, a stored sequence number contained in the session information stored in the sequence number field of the simulated ACK packet, a flag bit indicating that the packet is a simulated packet, and an ACK packet And sets a flag bit to generate a simulated ACK packet.

FIG. 3 is a schematic view illustrating a process of performing a failover according to an exemplary embodiment of the present invention. Referring to FIG.

3, the master server 320 includes a 3-way handshake for transmitting and receiving a SYN packet 341, a SYN / ACK packet 342, and an ACK packet 343 with the client 310 And then transmits / receives data (344).

If the master server 320 establishes a TCP session with the client 310 and a failure occurs while communicating data 345, the failover system 330 may detect the failure 350

The TCP session that was being connected to the backup server 332 by the master server 320 must be restored in order to resume communication with the client 310 via the backup server 332. [

The backup server 332 calls the failover callback function with the session handling block 334. [

Thereafter, the backup server 332 performs a simulated three-way handshake with the session handling block 334. [ The simulated three way handshake sends a simulated SYN packet to the backup server 332 in the session handling block 334 and calls the ACK request function without sending the SYN / ACK packet at the backup server 332, And sends a simulated ACK packet to the backup server 332 at block 334. FIG.

Then, the session handling block 334 transmits the transmission message to the backup server 332 (355), and the backup server 332 transmits the transmission message to the client 310 (360).

Thereafter, the client 310 resumes communication with the backup server 332 (361)

On the other hand, the backup server 332 calls a failover callback function and discards all packets received before the recovery of the TCP session is completed. This is because if another TCP packet is processed during TCP session recovery, an error may occur.

Hereinafter, a method for restoring a TCP session when a failure occurs in the fail-over system according to the present invention will be described with reference to the drawings.

4 is a flowchart illustrating a process of restoring a TCP session through a backup server in a failover system according to an embodiment of the present invention.

4, when the master server establishes a TCP connection with the client, the failover system stores the session information for the TCP connection, deletes the corresponding session information when the TCP connection is released, And manages all the set session information (410).

If the failover system detects a failure (412), it calls the failover callback function (414).

When the failover callback function is called, the failover system generates a simulated SYN packet using the stored session information (416).

The failover system uses the stored session information to describe the client port number of the session to be restored in the source port number field of the simulated SYN packet and to backup the destination port number field of the simulated SYN packet A server port number, a value obtained by subtracting 1 from the stored sequence number included in the session information stored in the sequence number field of the simulated SYN packet, and a flag bit indicating that the packet is a simulated packet and a SYN packet A simulated SYN packet can be generated.

The failover system sends the simulated SYN packet to the backup server's TCP block (418).

When the simulated SYN packet is received from the TCP block, the SYN / ACK packet is not transmitted and the ACK request function is called (420).

When the ACK request function is called, the failover system generates a mock ACK packet using the stored session information (422).

The failover system records the client port number of the session to be restored in the source port number field of the simulated ACK packet using the stored session information, and stores the backup port number in the destination port number field of the simulated ACK packet The server port number, the stored sequence number included in the session information stored in the sequence number field of the simulated ACK packet, and a flag bit indicating that the packet is a simulated packet and a flag bit indicating that the packet is an ACK packet It is possible to generate a simulated ACK packet.

The failover system sends a simulated ACK packet to the TCP block (424).

The backup server restores the TCP session through the mock three-way handshake and resumes communication with the client (426).

A failover system and method for restoring a TCP session according to an embodiment of the present invention may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

110; Application block
120; Session synchronization block
130; Session store block
140; Application wrapper block
150; Session handling block
160; TCP block

Claims (14)

A session storage block for storing session information with all the clients connected to the TCP connection by the master server;
An application wrapper block that calls a failover callback function if a failure is detected; And
And a session handling block for restoring a TCP session using session information stored in the session storage block,
The session handling block includes:
The client port number of the session to be restored is described in the source port number field of the simulated SYN packet using the stored session information,
A backup server port number is written in a destination port number field of the simulated SYN packet,
A value obtained by subtracting 1 from a stored sequence number included in the stored session information is written in a sequence number field of the simulated SYN packet,
Generates a simulated SYN packet by setting a flag bit indicating that the packet is a simulated packet and a flag bit indicating that the packet is a SYN packet, and transmits the simulated SYN packet to the TCP block
Upon receipt of the simulated SYN packet from the TCP block, if a simulated SYN packet is generated after the TCP session is generated, an ACK request function is called instead of transmitting a SYN / ACK packet
When the ACK request function is called, the client port number of the session to be restored is written in the source port number field of the mock ACK packet using the stored session information,
The backup server port number is written in a destination port number field of the simulated ACK packet,
A sequence number field of the mock ACK packet is stored in the stored sequence information included in the stored session information,
Generates a simulated ACK packet by setting a flag bit indicating that the packet is a simulated packet and a flag bit indicating that the packet is an ACK packet, and transmits the generated simulated ACK packet to the TCP block
Upon receiving the simulated ACK packet, the TCP block completes the recovery procedure for the session generated by the simulated SYN and transmits the recovered session information through the application wrapper block
Failover system that restores TCP sessions on failure.
The method according to claim 1,
When the master server establishes a TCP connection with the client, transfers the session information for the TCP connection to the session storage block, and stores the stored session information stored in the session storage block in the session handling block, Further comprising a session synchronization block
Failover system that restores TCP sessions on failure.
3. The method of claim 2,
Wherein the session synchronization block comprises:
Transmits a beep signal to the master server at a predetermined cycle to determine the failure of the master server
Failover system that restores TCP sessions on failure.
The method according to claim 1,
Wherein the stored session information comprises:
A source port number, a destination port number, and a sequence number.
Failover system that restores TCP sessions on failure.
5. The method of claim 4,
Wherein the stored session information comprises:
An acknowledgment number, and window size information.
Failover system that restores TCP sessions on failure.

delete delete Calling a failover callback function if a failure of the master server is detected in the backup server;
Generating a simulated SYN packet using the stored session information when the failover callback function is called;
Transmitting the simulated SYN packet to a TCP block;
Calling an ACK request function in the TCP block;
Generating a simulated ACK packet using the stored session information when the ACK request function is called;
Transmitting the simulated ACK packet to the TCP block; And
And delivering the session through the session recovery and application wrapper block in the TCP block,
Wherein the generating the simulated SYN packet comprises:
The client port number of the session to be restored is described in the source port number field of the simulated SYN packet using the stored session information,
The backup server port number is written in a destination port number field of the simulated SYN packet,
A value obtained by subtracting 1 from a stored sequence number included in the stored session information is written in a sequence number field of the simulated SYN packet,
Generates a simulated SYN packet by setting a flag bit indicating that the packet is a simulation packet and a flag bit indicating that the packet is a SYN packet,
The step of calling an ACK request function in the TCP block comprises:
Upon receipt of the simulated SYN packet in the TCP block, if the SYN packet is a simulated SYN packet after the TCP session is created, an ACK request function is called instead of transmitting a SYN / ACK packet,
Wherein the generating the simulated ACK packet comprises:
A client port number of a session to be restored is written in a source port number field of the simulated ACK packet using the stored session information,
The backup server port number is written in a destination port number field of the simulated ACK packet,
A sequence number field of the simulated ACK packet is stored in the stored sequence information,
Generates a simulated ACK packet by setting a flag bit indicating that the packet is a simulated packet and a flag bit indicating that the packet is an ACK packet,
Wherein the step of restoring the session in the TCP block and delivering the session through the application wrapper block comprises:
Upon receiving the simulated ACK packet from the TCP block, the recovery process for the session generated by the simulated SYN packet is completed and the recovered session information is delivered through the application wrapper block
How to restore TCP sessions on failover systems.
9. The method of claim 8,
Before the failure is detected,
When the master server establishes a TCP connection with a client, storing the session information for the TCP connection, and deleting the session information when the TCP connection is released
How to restore TCP sessions on failover systems.
delete 9. The method of claim 8,
The step of calling an ACK request function in the TCP block comprises:
The TCP block checks a flag bit indicating that the packet is a simulated packet included in the simulated SYN packet and a flag bit indicating that it is a SYN packet and confirms that the packet is the simulated SYN packet. If the SYN / ACK packet is not transmitted, Calling the request function
How to restore TCP sessions on failover systems.
delete 9. The method of claim 8,
The step of calling an ACK request function in the TCP block comprises:
Generates a simulated SYN / ACK packet without invoking the ACK request function, and transmits the simulated SYN / ACK packet to the session handling block
How to restore TCP sessions on failover systems.
A computer-readable recording medium having recorded thereon a program for executing the method according to any one of claims 8, 9, 11 and 13.

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