KR100509920B1 - Method and system for mobile ip assignment in wireless lan - Google Patents

Abstract

In the present invention, in assigning a mobile IP address to a user terminal, a foreign agent performs a DHCP process, allocates a local IP address to the user terminal, and then performs a mobile IP address assignment process using the local IP address. The present invention relates to a method and system for efficiently providing mobile IP between subnets in a wireless LAN, to reduce unnecessary broadcast packets for mobile IP allocation in a network, and to allow a foreign agent to use a user. There is no need to maintain a MAC table for the terminal.

Description

Method and system for providing efficient mobile IP between subnets in wireless LAN {METHOD AND SYSTEM FOR MOBILE IP ASSIGNMENT IN WIRELESS LAN}

The present invention relates to a method and system for efficiently providing a mobile IP between subnets in a WLAN, and to reduce unnecessary broadcast packets for mobile IP allocation and to accommodate a DHCP (Dynamic Host Configuration Protocol) process in a user terminal. The present invention relates to a method and system for providing efficient mobile IP between subnets in a WLAN.

Due to the development of technology and the improvement of the economic level, the number of Internet users is increasing rapidly every year.

Network devices such as user terminals and set-top boxes connected to the Internet each have a unique TCP / IP address (Transmission Control Protocol / Internet Protocol). Internet service can be used by accessing network equipment. TCP / IP, adopted as the standard protocol of the Internet, is a collection of protocols that allows data to be exchanged between different network equipment. Software that performs network services includes Explorer and Netscape. Specifically, the IP address is composed of four parts (for example, 211.203.81.245) for identifying a network and a network device, and is configured differently for each network device, which is managed by a network information center (NIC).

In addition, the IP address of each network device can be divided into a static IP address (Dynamic IP Address) and a dynamic IP address (Dynamic IP Address).

The static IP address has the advantage of being able to access the network equipment by entering the static IP address anywhere since the IP address does not change, but the IP address fee is relatively expensive.

In contrast, the dynamic IP address refers to an IP address assigned to be available for a certain period of time from a Dynamic Host Configuration Protocol (DHCP) server that allocates a dynamic IP. Network equipment using a dynamic IP address is given a valid IP address from a DHCP server after a certain period of time. Dynamic IP addresses have the disadvantage of having variable IP addresses, but they have the advantage of being able to use the network without paying a lower fee than static IP addresses. As such, static IP addresses and dynamic IP addresses have their advantages and disadvantages. Both types of IP addresses are currently in use.

In the past, the construction of a wire-based infrastructure such as a dedicated line installation and a telephone line was considered as a prerequisite for the use of the Internet. However, in recent years, mobility in wireless LAN based on wireless and CDMA wireless data service The use of the Internet to guarantee security is in the spotlight. WLAN has the advantage of using high-speed data, but has the disadvantage that the area to receive the service is limited. Therefore, to compensate for this, a method of using a wireless LAN in a service area and a data service of a CDMA in an area other than the service area has been proposed. In addition, a method using a mobile IP address is most commonly used to provide roaming of heterogeneous data networks. Mobile IP (Mobile IP) is a fixed IP that is currently assigned and used without changing the initial assigned IP regardless of where a mobile user terminal such as a laptop or personal digital assistant (PDA) moves. Also, the concept of continuing to receive the corresponding service is applied.

The conventional method used to guarantee mobility between different subnets in a wireless LAN using a mobile IP is that the user terminal, which is one of the network equipments, undergoes an authentication process and then bills the agent to a foreign agent (FA). A method of transmitting a message (Agent Solicitation Message, which is a type of Address Resolution Protocol (ARP)) to start a mobile IP allocation procedure. However, the conventional method described above uses a broadcast packet to allow a user terminal to use a broadcast packet. Signaling such as an Agent Solicitation Message and a Mobile IP Request Message should be performed. Therefore, unnecessary traffic (traffic) between the same subnet increases, the problem that the external agent (FA) has to perform an unnecessary call processing process for mobile IP allocation.

Accordingly, an object of the present invention is to provide an efficient mobile IP providing method and system between subnets in a wireless LAN capable of presenting an efficient mobile IP allocation method and interworking heterogeneous data networks between different subnets in a wireless LAN.

Another object of the present invention is to allow the user terminal to accommodate a Dynamic Host Configuration Protocol (DHCP) process, thereby reducing unnecessary broadcast packets for mobile IP allocation in the network, and the external agent (FA) is a user The present invention provides an efficient mobile IP providing method between subnets in a WLAN that does not need to maintain a MAC table for the terminal 105.

Another object of the present invention is to provide efficient mobile IP processing in a foreign agent (FA), and to use it in a wireless LAN that can be universally used for roaming of heterogeneous networks as well as roaming between different subnets. It is to provide an efficient mobile IP providing method and system between subnets.

In order to achieve the above objects, according to an aspect of the present invention, in the method for the foreign agent (Foreign Agent) to be assigned a mobile IP address (Mobile IP Address) to the user terminal, the MAC authentication request received from the user terminal Correspondingly performing MAC authentication, assigning a local IP address to the user terminal, and using the assigned local IP address, a mobile IP address to the user terminal. A mobile IP address allocation method is provided, the system, apparatus, and a recording medium for enabling the mobile IP address allocation method to be performed. In one preferred embodiment of the present invention, According to the present invention, a method for allowing a foreign agent to allocate a mobile IP address to a user terminal may include: Performing MAC authentication in response to a MAC authentication request received from the device, receiving a static IP address from the user terminal, and if the static IP address is valid, Setting a static IP address to a local IP address corresponding to the user terminal, and using the local IP address, a mobile IP address to the user terminal. A mobile IP address allocation method is provided, the method comprising: assigning an IP address, and a system, apparatus, and a recording medium for enabling the mobile IP address allocation method are provided.

In addition, the method for allocating a mobile IP address according to the present invention further includes assigning an arbitrary local IP address to the user terminal when the received static IP address is invalid. can do.

According to another preferred embodiment of the present invention, in a method for allowing a foreign agent to be assigned a mobile IP address to a user terminal, receiving a server discovery message (DHCP Discover Message) from the user terminal And transmitting a DHCP Offer Message corresponding to the server discovery message to the user terminal, and receiving an DHCP Request Message from the user terminal. And transmitting an IP allocation response message (DHCP ACK) corresponding to the IP allocation request message (DHCP ACK) to the user terminal, wherein the IP allocation response message (DHCP ACK) is at least a local IP address (Local). IP address) and a mobile IP address assigned to the user terminal using the local IP address. A mobile IP address allocation method is provided, and a system, apparatus, and a recording medium for enabling the mobile IP address allocation method to be performed are provided. The mobile IP address allocation according to the present invention is also provided. In the method, the user terminal may use a Mobile IP Agent Solicitation message and a MIP registration request message for assigning the Mobile IP address using the Local IP Address. Request message).

According to another preferred embodiment of the present invention, in a method in which a foreign agent assigns a mobile IP address to a user terminal, a DHCP request message is received from the user terminal. Receiving, wherein the DHCP request message includes at least a static IP address pre-allocated to the user terminal; and the static IP address is valid. Checking whether or not the mobile station has been configured, and if the static IP address is valid, transmitting an IP allocation response message (DHCP ACK) including the static IP address to the user terminal; If the static IP address is not valid, performing a process of allocating a local IP address for the user terminal, and the static IP address. A mobile IP address allocation method is provided, comprising: assigning a mobile IP address to the user terminal using an address or a local IP address. A system, an apparatus, and a recording medium are provided to enable an address allocation method. The step of performing a local IP address allocation process for the user terminal may include an IP allocation error message (DHCP NACK) sent to the user terminal. Transmitting, receiving a server discovery message (DHCP Discover Message) from the user terminal, and transmitting an IP Offer Message (DHCP Offer Message) corresponding to the server discovery message (DHCP Discover Message) to the user terminal. And receiving an IP request message from the user terminal (DHCP Request Message), and receiving the IP request message (DHCP R). sending an IP allocation response message (DHCP ACK) corresponding to an equest message to the user terminal, wherein the IP allocation response message (DHCP ACK) includes at least a local IP address; can do.

The user terminal registers a MIP agent solicitation message and a MIP for assigning the mobile IP address using the valid fixed IP address or the local IP address. A request message (Mobile IP Registration Request Message) may be transmitted.

According to another aspect of the present invention, in a foreign agent for assigning a mobile IP address to a user terminal, a server discovery message (DHCP Discover Message), an IP allocation request message (DHCP) from the user terminal A request message, a mobile IP agent solicitation message, a mobile IP registration request message, and a MIP registration request message from a home agent corresponding to the user terminal. Means for receiving a Mobile IP Registration Response message corresponding to a Mobile IP Registration Request message, an IP Offer Message corresponding to the DHCP Discover Message, and an IP assignment. IP ACK response message (DHCP ACK) corresponding to the request message (DHCP Request Message), the MIP agent request message (Mobile) The MIP agent notification message and the MIP registration response message corresponding to the IP agent solicitation message are transmitted to the user terminal, and the MIP registration request message is transmitted. Means for transmitting a Message to the Home Agent, wherein the IP ACK response message (DHCP ACK) includes at least a Local IP Address; and the IP Assignment Request message (DHCP Request). And a means for allocating a local IP address to the user terminal in response to a message). In addition, an external agent according to the present invention is provided with the DHCP request message. If the user terminal includes a pre-allocated static IP address, check whether the static IP address is valid. It may further comprise means.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a data flow diagram illustrating a mobile IP address allocation procedure in a wireless LAN according to the prior art.

In a conventional wireless LAN, a mobile IP network includes a user terminal 105, an access point (AP) (not shown), a foreign agent (FA) 110, and a home agent (HA). A home agent 115, an AAA server (not shown), and the like.

An access point (AP) is a device that converts the data of the wired LAN into a radio wave of 2.4 GHz and transmits it to the wireless LAN card, which may correspond to a base station of a mobile communication service system.

The external agent (FA) 110 is a gateway located in an external network (ie, a visitor network) to which the user terminal 105 is connected. However, since the function and use of the external agent (FA) 115 is well known to those skilled in the art, a detailed description thereof will be omitted.

The home agent (HA) 115 is a device that manages current location information, subscriber information, and the like of the user terminal 105. The function and use of the home agent (HA) 120 is also well known to those skilled in the art, so a detailed description thereof will be omitted.

The AAA server performs measurements of network usage to authenticate whether a wireless Internet user is a legitimate user (Authentication), to authorize and validate a subscriber's authorization level (Authorization), to accounting and to plan resources. An apparatus for assigning IP and transmitting / receiving data of a mobile IP network in a WLAN according to the prior art will now be described with reference to FIG. 1.

However, before the step shown in FIG. 1, a MAC process (Message authentication code Authentication) is performed between the user terminal 105 and the AAA server via an access point and an external agent (FA) 110. Omit.

Referring to FIG. 1, in step 130, the user terminal 105 transmits a mobile IP agent solicitation message to an external agent (FA) 110 via an access point (AP). The Mobile IP Agent Solicitation Message is when the user terminal 105 requests a response without waiting for an Advertisement sent from an external agent (FA) 110 (eg, an Advertisement). Is a long period of time). The external agent (FA) 110 sends a MIP Agent Advertisement Message to the user terminal 105 in step 135. The Mobile IP Agent Advertisement Message (MIP Agent Advertisement Message) is a message used when the external agent (FA) 110 declares its own capacity (Capability), the user terminal 105 is a foreign agent (FA) In order to be able to discover the 110 or the home agent (HA) 115, it is periodically transmitted in a multicast or broadcast manner. The MIP agent advertisement message may allow the user terminal 105 to identify whether the currently connected network is a home network or a visitor network, and the user terminal 105. ) Provides a Care-of Address (COA) that can be assigned. The COA is then the same as the address of the foreign agent (FA) 110.

In other words, step 130 and step 135 are agent discovery steps, and the existence of the user terminal 105 and the external agent (FA) 110 is determined by an agent discovery message, that is, a MIP agent billing message (Mobile). This step is notified through an IP Agent Solicitation Message and a MIP Agent Advertisement Message.

In step 140, the user terminal transmits a Mobile IP Registration Request message to an external agent (FA) 110 via an access point (AP). Then, in step 145, the external agent (FA) 110 relays a MIP registration request message to the home agent HA, thereby allowing the home agent HA to user. Determine whether or not to provide a service to the terminal 105. The Mobile IP Registration Request message includes a request for generation and update of a mobility binding list of the home agent (HA) 115. The home agent (HA) 115 includes a user terminal (A). After registering a Care-of Address (COA) corresponding to 105 (storing mobility information of the user terminal 105), in step 150 a MIP Registration Response message (Mobile IP Registration Response Message) is sent to an external agent (FA) 110. To send).

The external agent (FA) 110 stores the information in a cache (Visited List) indicating that the user terminal 105 is connected to its network and is to be provided with a service, and then responds with a MIP registration through step 155. A message (Mobile IP Registration Response Message) is transmitted to the user terminal 105. Through this procedure, the user terminal 105 is provided with an environment in which a service can be provided from any host (not shown).

In other words, steps 140 to 155 are performed as a registration process when a point-of-attachment of the user terminal 105 is changed, and the home agent (HA) 115 transmits the COA of the user terminal 105 to the home agent (HA) 115. It can be said that the process.

In the above-described mobile IP allocation scheme according to the related art, when the user terminal 105 transmits a MIP registration request message or the like, an IP broadcast packet should be used, and an external agent (FA) 110 must have a table that binds the MAC address. In addition, in the above-described method, since the user terminal 105 performs MAC authentication and then performs a mobile IP registration process immediately without going through a Dynamic Host Configuration Protocol (DHCP) process, unnecessary traffic increases. In addition, the external agent (FA) 110 may be referred to as a kind of router that processes an IP layer which is a layer 3, but according to the above-described method, the user terminal (MA) in the MAC layer of the layer 2 may be a layer 2. 105) there is a problem in that unnecessary burden because it must be managed.

2 is a data flow diagram illustrating a mobile IP address allocation procedure according to an embodiment of the present invention.

As described above with reference to FIG. 1, before the step shown in FIG. 2, a MAC process (Message authentication code Authentication) is performed between the user terminal 105 and the AAA server via an access point and an external agent (FA) 110. However, this is a general matter and will be omitted here.

In general, after the MAC authentication, the user terminal 105 is assigned a local IP address through a dynamic host configuration protocol (DHCP) allocation process. That is, each user terminal 105 must have a unique IP address in order to access the Internet, and DHCP (Dynamic Host Configuration Protocol) is a communication protocol that controls to automate the assignment of Internet Protocol (IP) addresses. (That is, address automatic acquisition protocol). DHCP dynamically allocates IP addresses during the operation of the user terminal 105 to solve operational problems caused by the setting of addresses, and not only the IP address but also various types of information, such as models and sites, can be notified to clients. To make it possible.

Dynamically assigning IP addresses is the same as Bootstrap protocol (BOOTP), but the address value itself is also dynamically determined and can be used to save the address if the number of user terminals 105 is greater than the number of available IP addresses. Has

If there is no DHCP, the IP address must be manually entered at each user terminal 105, and a new IP address will have to be newly entered if the user terminal 105 is moved to another place. That is, DHCP supervises each user terminal 105 and instructs to distribute IP addresses at a central location and also automatically provides a new IP address when the user terminal 105 moves to another location.

However, as in the conventional mobile IP allocation procedure described with reference to FIG. 1, it is a heavy burden in software to immediately proceed to the mobile IP allocation process without going through a DHCP process. By suggesting an external agent (FA) 110 that can perform the functions of the foreign agent of the agent and the function of the DHCP server, the status of the user terminal 105 by the local IP address (Local IP Address) Provide ways to manage it.

Hereinafter, a method of allocating a local IP address and then a mobile IP address according to the present invention will be described with reference to FIG. 2. Referring to FIG. The user terminal 105 transmits a server discover message (DHCP Discover Message) to the external agent (FA) (110).

In step 215, the external agent (FA) 110 transmits an IP Offer Message (DHCP Offer Message) to the user terminal 105 in response to the server discovery message received from the user terminal 105. At 220, the user terminal 105 transmits an IP allocation request message (DHCP Request Message) to an external agent (FA) 110.

In step 225, the external agent (FA) 110 assigns an IP including a local IP address and IP allocation time information in response to a DHCP request message received from the user terminal 105. The response message (DHCP ACK) is transmitted to the user terminal 105. That is, the external agent (FA) 110 extracts (or generates) a local IP address for the user terminal 105, and then includes the IP address in an IP assignment response message (DHCP ACK). Will be sent.

Thereafter, the user terminal 105 starts a mobile IP allocation process using a local IP address allocated from the external agent (FA) 110. Steps 230 to 255, which are mobile IP allocation processes, are the same as steps 130 to 155 of FIG. 1, which will be omitted.

However, the mobile IP allocation process according to the present invention differs from the above description of FIG. 1 by using an IP broadcast packet, a MIP agent solicitation message, a MIP registration request message, and a mobile IP. Rather than sending a Registration Request Message, etc., the message is sent to an assigned Local IP Address. Therefore, unnecessary traffic of the same subnet can be reduced, and the external agent (FA) 110 has an advantage of not having to maintain a MAC table for the user terminal 105.

3A is a data flow diagram illustrating a mobile IP address assignment procedure according to another preferred embodiment of the present invention, and FIG. 3B is a mobile IP address assignment according to another preferred embodiment of the present invention. 3A and 3B are diagrams illustrating a process of allocating a mobile IP address when a static IP address is assigned to the user terminal 105.

However, as described above with reference to FIG. 1, before the steps illustrated in FIGS. 3A and 3B, MAC authentication is performed between the user terminal 105 and the AAA server via an access point and an external agent (FA) 110. ) Process is performed, but this is general and will be omitted here. In addition, when the steps shown in FIGS. 3A and 3B are the same as those of FIG. 2 described above, the same reference numerals will be used.

Referring to FIG. 3A, in step 310, the user terminal 105 transmits a DHCP request message to a foreign agent (FA) 110 using a static IP address that is already assigned. In step 320, the external agent (FA) 110, if the IP request message (DHCP Request Message) received from the user terminal 105 is a valid static IP address (Static IP Address), the static IP An IP assignment response message (DHCP ACK) including an address (static IP address) is transmitted to the user terminal 105. In addition, when the static IP address is not valid, the processing procedure of the foreign agent (FA) 110 will be described later with reference to FIG. 3B.

Thereafter, the user terminal 105 transmits an agent solicitation message, a mobile IP request message, and the like to an external agent using a static IP address as described above with reference to FIG. 2. (FA) 110, the external agent (FA) 110 receives a MIP registration response message (Mobile IP Registration Response Message) from the home agent (HA) 115 and transmits to the user terminal 105 Done. However, since the processes of steps 230 to 255 for allocating a mobile IP address to the user terminal 105 have already been described above with reference to FIGS. 1 and 2, duplicate description thereof will be omitted. 3B illustrates a processing procedure when a static IP address is assigned to the user terminal 105, but the static IP address is determined to be invalid.

Referring to FIG. 3B, in step 350, the user terminal 105 transmits a DHCP request message to the external agent (FA) 110 using a static IP address that is already assigned. do.

If the external agent (FA) 110 receives an IP allocation request message (DHCP Request Message) received from the user terminal 105 due to an invalid static IP address, the user agent through step 355. In step 105, an IP allocation error message (DHCP NACK) is transmitted. When the external agent (FA) 110 determines that the static IP address is invalid, the static IP address is used by another user terminal 105 in the same subnet. And an IP address that cannot be assigned in the subnet.

Thereafter, the user terminal 105 transmits a server discovery message (DHCP Discover Message) and an IP allocation request message (DHCP Request Message) to an external agent (FA) 110 to receive a local IP address. do. The user terminal 105 sends an agent solicitation message, a MIP request message, and the like to an external agent (FA) 110 by using the assigned local IP address. In addition, the external agent (FA) 110 receives a MIP registration response message (Mobile IP Registration Response Message) from the home agent (HA) 115 and transmits it to the user terminal 105. However, steps 210 to 255 for allocating a local IP address and a mobile IP address to the user terminal 105 have been described above with reference to FIGS. 1 and 2. In this way, the duplicate description will be omitted. As described above, after MAC authentication, the user terminal 105 proposes a pre-assigned static IP address to the external agent (FA) 110 in the DHCP process and the external agent (FA). If it is approved by 110, it proceeds to the mobile IP address assignment process. However, if the external agent (FA) 110 cannot assign the IP address proposed by the user terminal 105 (for example, the user terminal 105 may have already assigned the proposed IP address to another user terminal 105 of the same subnet). If a different IP address is used, or an IP address that cannot be assigned in the same subnet is proposed), a different IP address is assigned.

Accordingly, even through the method illustrated in FIGS. 3A and 3B, the foreign agent (FA) 110 may call the user terminal 105 using the local IP address (or a static IP address) as in the case of FIG. 2 described above. Can be managed, and as a result, unnecessary broadcast packets can be reduced.

The present invention is not limited to the above embodiments, and many variations are possible by those skilled in the art within the spirit of the present invention.

As described above, the method and system for providing efficient mobile IP between subnets in a WLAN according to the present invention may provide an efficient mobile IP allocation method and interworking between heterogeneous data networks in different wireless LANs.

In addition, the present invention allows the user terminal to accommodate the Dynamic Host Configuration Protocol (DHCP) process, thereby reducing unnecessary broadcast packets for mobile IP allocation in the network, the external agent (FA) There is no need to maintain a MAC table for the user terminal 105. The present invention also enables efficient mobile IP processing in a foreign agent (FA), and only roaming between different subnets. It can also be used universally for roaming heterogeneous networks.

1 is a data flow diagram illustrating a mobile IP address allocation procedure in a wireless LAN according to the prior art.

2 is a data flow diagram illustrating a procedure for allocating a Mobile IP Address according to an embodiment of the present invention.

3A is a data flow diagram illustrating a Mobile IP Address assignment procedure according to another preferred embodiment of the present invention.

FIG. 3B is a data flow diagram illustrating a mobile IP address allocation procedure according to another preferred embodiment of the present invention. FIG.

<Explanation of symbols for the main parts of the drawings>

105: user terminal

110: foreign agent (FA)

115: home agent (HA)

Claims (12)

A method for allowing a foreign agent to allocate a mobile IP address to a user terminal, Performing MAC authentication in response to a MAC authentication request received from the user terminal; Assigning a local IP address to the user terminal; Assigning a mobile IP address to the user terminal using the assigned local IP address; Mobile IP address allocation method comprising a. A method for allowing a foreign agent to allocate a mobile IP address to a user terminal, Performing MAC authentication in response to a MAC authentication request received from the user terminal; Receiving a static IP address (Static IP Address) from the user terminal; If the static IP address (Static IP Address) is valid, the static IP address (Static IP Address) corresponding to the local IP address ( Local IP Address); Allocating a mobile IP address to the user terminal using the local IP address; Mobile IP address allocation method comprising a. The method of claim 2, If the received static IP address (Static IP Address) is not valid, assigning any local IP address (Local IP Address) to the user terminal Mobile IP address assignment method further comprises. A method for allowing a foreign agent to allocate a mobile IP address to a user terminal, Receiving a server discovery message (DHCP Discover Message) from a user terminal; Transmitting an IP Offer Message (DHCP Offer Message) corresponding to the Server Discover Message to the user terminal; Receiving a DHCP Request Message from the user terminal; Transmitting an IP allocation response message (DHCP ACK) corresponding to the DHCP request message (DHCP ACK) to the user terminal, wherein the IP allocation response message (DHCP ACK) is at least a local IP address (Local IP Address); Assigning a mobile IP address to the user terminal using the local IP address; Mobile IP address allocation method comprising a. The method of claim 4, wherein The user terminal uses a MIP agent solicitation message and a MIP registration request message for assigning the mobile IP address using the local IP address. To send) Mobile IP address allocation method, characterized in that. A method for allowing a foreign agent to allocate a mobile IP address to a user terminal, Receiving a DHCP Request Message from a user terminal, wherein the DHCP Request Message includes at least a static IP address pre-assigned to the user terminal; ; Checking whether the static IP address is valid; If the static IP address is valid, transmitting an IP allocation response message (DHCP ACK) including the static IP address to the user terminal; the static IP address Is invalid, performing a local IP address allocation process for the user terminal; And assigning a mobile IP address to the user terminal by using the static IP address or the local IP address. . The method of claim 6, Performing a local IP address assignment process for the user terminal, Transmitting an IP allocation error message (DHCP NACK) to the user terminal; Receiving a server discovery message (DHCP Discover Message) from a user terminal; transmitting a DHCP Offer Message corresponding to the server discovery message (DHCP Offer Message) to the user terminal; Receiving a DHCP Request Message from the user terminal; Transmitting an IP allocation response message (DHCP ACK) corresponding to the DHCP request message (DHCP ACK) to the user terminal, wherein the IP allocation response message (DHCP ACK) is at least a local IP address (Local IP Address); Mobile IP address assignment method comprising; The method of claim 7, wherein The user terminal uses a valid IP address or a local IP address (Local IP Address) MIP agent request message (Mobile IP Agent Solicitation Message) and MIP registration request message for assigning the Mobile IP Address (Mobile IP Address) (Mobile IP Registration Request Message) characterized in that the mobile IP address allocation method. In a foreign agent that allows a mobile IP address to be assigned to a user terminal, Receiving a server discovery message (DHCP Discover Message), an IP allocation request message (DHCP Request Message), a Mobile IP Agent Solicitation message, and a Mobile IP Registration Request message from the user terminal; Means for receiving a MIP registration response message corresponding to the MIP registration request message from a home agent corresponding to a user terminal; the server confirmation message (DHCP Discover) Corresponding to the IP Offer Message (DHCP Offer Message), the IP Assignment Response Message (DHCP ACK) corresponding to the DHCP Request Message, and the MIP Agent Solicitation Message. MIP agent notification message (Mobile IP Agent Advertisement message) and the MIP registration response message (Mobile IP Registrati) means for transmitting an on response message to the user terminal and for transmitting the mobile IP registration request message to the home agent, wherein the IP allocation response message (DHCP ACK) is at least Includes a Local IP Address; Means for allocating a local IP address to the user terminal in correspondence with the DHCP request message; External agent comprising a. The method of claim 9, Means for checking the validity of the fixed IP address when the DHCP request message includes a static IP address pre-allocated to the user terminal. External agent. A program of instructions that can be executed by an external agent is tangibly implemented to perform a mobile IP address allocation method, and in a recording medium that can be read by the external agent, Receiving a server discovery message (DHCP Discover Message) from a user terminal; Transmitting an IP Offer Message (DHCP Offer Message) corresponding to the Server Discover Message to the user terminal; Receiving a DHCP Request Message from the user terminal; Transmitting an IP allocation response message (DHCP ACK) corresponding to the DHCP request message (DHCP ACK) to the user terminal, wherein the IP allocation response message (DHCP ACK) is at least a local IP address (Local IP Address); Allocating a mobile IP address to the user terminal using the static IP address or the local IP address; Recording medium that records a program that can run. A program of instructions that can be executed by an external agent is tangibly implemented to perform a mobile IP address allocation method, and in a recording medium that can be read by the external agent, Receiving a DHCP Request Message from a user terminal, wherein the DHCP Request Message includes at least a static IP address pre-assigned to the user terminal; ; Checking whether the static IP address is valid; If the static IP address is valid, transmitting an IP allocation response message (DHCP ACK) including the static IP address to the user terminal; the static IP address Is invalid, performing a local IP address allocation process for the user terminal; And a program for executing a step of assigning a mobile IP address to the user terminal using the static IP address or the local IP address.