KR19990061606A - How to prevent IP address theft in cable modem systems - Google Patents

Abstract

The present invention relates to a method for preventing IP address theft of a cable modem system. A plurality of subscribers are connected to a cable modem terminal system (CMTS, 30) through a cable network, respectively, using a cable modem, and the CMTS 30 and the cable modem. In a cable modem system that exchanges data using MPEG packets formed by adding headers to MAC frames, CMTS generates an entry table in the form of " user device number, Ethernet address, IP address > Recording the Ethernet address and IP address in the entry table, waiting for an IP packet transmitted from the cable modem, detecting the IP address, and transmitting the packet if the IP address exists in the entry table, Disposal step.

Therefore, the present invention compares the IP address of the IP packet transmitted from the cable modem with the IP address registered in the entry table to determine whether to transmit, thereby preventing the use of an invalid IP address and allowing an illegal user device connected to the cable modem to perform IP There is an effect that can prevent the theft of the address.

Description

Method of protecting a IP address peculation in a cable modem system

The present invention relates to a system constructed using a cable modem, and in particular, when the cable modem transmits a packet, the cable modem terminal system (CMTS) detects the IP address of the packet and delivers only a packet having a valid IP address. A method for preventing IP address theft of a modem system.

Cable modem network is a network system of remote access area such as Integrated Information Communication Network (ISDN) and Multi-Digital Subscriber Line (xDSL) .It is connected to the Internet and intranet to provide subscribers at home with high speed data transmission speed of Mbps. Provide various services such as search.

The concept of a cable modem network is similar to a cable TV network in data communication. In terms of using coaxial cable, cable TV connects an external coaxial cable to a set-top box and connects the TV to the set-top box. Cable modem networks, on the other hand, use a cable modem to connect a coaxial cable to a PC. At this time, there may be one PC or multiple PCs connected to the cable modem.

Cable modems are divided into workgroup, multiuser, and personal. Workgroup cable modems are designed for small groups with 4 or 8 ports for connecting PCs, and small LANs can be established through them. Multi-user cable modems are relatively large in libraries, schools, and factories. Is used in large places.

1 is a diagram illustrating a network constructed using a general cable modem, in which a plurality of cable modems (CM, 11-14, hereinafter referred to as 'CM') are connected to the cable network 20, and a cable modem 11-11. 14) PCs are connected to each other, and subscribers receive services such as the Internet from the backbone network 40, and the cable modem terminal system 30 (CMTS: Cable Modem Termination System (hereinafter referred to as 'CMTS')) is a headend. It is located in the role of providing an uplink channel and a downlink channel. The CMTS 30 transmits broadband data at a transmission rate of 500 kbps to 30 Mbps in a downlink channel by broadcasting, and each CM performs point-to-point narrowband query data at a rate of 96 kbps to 10 Mbps in an uplink channel. To transmit.

The protocol handled by the cable modem is the Internet Protocol (IP), and the cable modem system has a hierarchical structure as shown in Table 1 below for transparent transmission of IP messages.

Hierarchy Tier Network layer - Data connection layer Logical Link Control (LLC) sublayer Connection security sublayer Media access control (MAC) sublayer Physical Layer (PHY) Transmission Convergence (TC) Sublayer Physical Media Dependent (PMD) Sublayer

The hierarchical structure of the cable modem system is divided into vertical structures such as a network layer, a data connection layer, and a physical layer as shown in Table 1 above. The data link layer is divided into a logical link control (LLC) sublayer, a link-security sublayer, and a medium access control (MAC) sublayer. Is divided into a Transmission Convergence (TC) sublayer and a Physical Medium Dependent (PMD) sublayer.

In the above, the network layer transmits IP traffic as an Internet Protocol (IP) layer. The logical link control (LLC) sublayer of the data link layer establishes the Ethernet standard, the media access control (MAC) sublayer supports variable length PDUs, and the MAC protocol controls band allocation by CMTS, It divides streams into minislots at intervals of time and supports variable length packets to increase the efficiency of bandwidth allocation.

The transport convergence (TC) layer of the physical layer exists only in the downward case to provide additional services such as digital video, and defines a contiguous 188 byte MPEG packet. In addition, the Physical Media Dependent (PMD) sublayer supports functions such as 64QAM and 256QAM modulation schemes, error correction codes of Reed Solomon and Trellis in the downward direction, and QPSK and 16QAM modulation schemes, TDMA, and fixed slots in the upward direction. It supports length frames and variable length PDUs.

On the other hand, multiple user equipments (CPEs), such as PCs, may be connected to one cable modem. In this case, an illegal user device steals the IP address of a legitimate user device and transmits data to the CMTS through the cable network. It happens to send. However, in such a case, there is a problem that the CMTS does not determine this and accepts data as it is and delivers it to the backbone network.

Accordingly, the present invention has been made to solve the above problems, the IP of the cable modem system to deliver only packets having a valid IP address when transmitting a packet from the cable modem (CM) to the cable modem terminal system (CMTS). It is an object of the present invention to provide a method for preventing address theft.

In the method of the present invention for achieving the above object, a plurality of subscribers are each connected to a cable modem terminal system (CMTS) through a cable network using a cable modem, using a MAC frame between the CMTS and the cable modem In the cable modem system that transmits and receives data, the cable modem terminal system generates an entry table and registers an entry value through a modem initialization process, and filters the IP packet transmitted from the cable modem to determine whether to deliver the packet. Characterized in that comprises a step.

1 is a diagram illustrating a typical cable modem network and peripheral devices thereof;

2A is a flowchart illustrating a process of registering in an entry table according to an IP address theft prevention method of a cable modem system according to the present invention;

2B is a flowchart illustrating a process of filtering an IP packet according to the IP address theft prevention method of the cable modem system of the present invention.

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

First, the initialization process of the cable modem terminal system and the cable modem in order to help the understanding of the present invention will be described.

The cable modem terminal system (CMTS) can operate and reboot in stand-alone mode using configuration data during the initialization phase, and the cable modem (CM) sends packets if it is not a useful parameter. To prevent this from happening, no downstream messages, including sync, occur.

Looking at the initialization phase of the cable modem (CM), first, it scans the downstream channel and synchronizes it with the cable modem terminal system (CMTS) because the upstream channel cannot be used unless the cable modem is synchronized downstream. It then waits for an upstream channel descriptor (UCD) message that defines the characteristics of the upstream channel from the CMTS to obtain the transport parameters, if it is not a suitable channel upstream from the UCD message, it waits again for an available UCD message and from the transport parameters Once the upstream channel is found, the UCD extracts parameters and minislot timing for the upstream, and a MAP message regarding the band allocation of the selected channel. The parameter of the UCD message is defined in the form of type / length / value (TLV: type / length / value).

Subsequently, the cable modem performs a ranging and adjustment process, and then establishes an IP connection, current date and time, and security. The ranging is a process for obtaining a timing offset such that transmission of the cable modem is correctly aligned with the minislot boundary. Subsequently, the modem must download the parameter file using the Trivial File Transfer Protocol (TFTP). The TFTP is a file transfer protocol for downloading software and configuration information.

In the IP connection process, the cable modem must obtain a DHCP (Dynamic Host Configuration Protocol) to obtain parameters and IP addresses for establishing an IP connection. The DHCP is an internet protocol used for address assignment of a network layer, that is, an internet protocol (IP) layer. The DHCP request message that the cable modem sends to the DHCP side contains the hardware type that must be set for Ethernet, the hardware address of the cable modem to define the cable modem during DHCP processing, and the DHCP received from DHCP by the cable modem. The response message includes the IP address used by the cable modem, the name of the cable modem configuration file to be read from the TFTP server by the cable modem, and the IP address is provided from the DHCP response to the DHCP request.

In addition, for data transmission over the cable modem, the cable modem must obtain the Ethernet MAC address of the connected user device (CPE), which can only be obtained from the configuration file of the initialization process.

In the above initialization process, the cable modem terminal system (CMTS) uses a table of a customer premises equipment (CPE), an Ethernet address, and an IP address type, and the cable modem is a cable modem. When the packet is transmitted to the terminal system (CMTS), it is to compare the IP address of the packet with the IP address recorded in the table so as not to deliver a packet having an incorrect IP address.

2 is a flowchart illustrating a method for preventing IP address theft of a cable modem system according to the present invention.

FIG. 2A is a flowchart illustrating a process of registering a cable modem terminal system (CMTS) in an entry table. First, an entry table in the form of [user equipment (CPE) number], [Ethernet address], and [IP address] is shown. After creating (101), the Ethernet address is recorded in the entry table (102). The Ethernet address may be read from a configuration file obtained during the initialization of the modem. Subsequently, the cable modem enters a state waiting for a DHCP request message transmitted to DHCP (103) and determines whether a DHCP request message has been received (104). If the DHCP request message has not been received, the device stays in a waiting state, and if a DHCP request message is received, it enters into the DHCP response message waiting state that DHCP sends to the cable modem (105) and determines whether a DHCP response message has been received (106). . If the DHCP response message has not been received, the process branches to the fifth step 105 and remains in the waiting state for the response message. If the DHCP response message is received, the IP address is extracted from the DHCP message and recorded in the entry table (107).

FIG. 2B is a flowchart illustrating a process of filtering an IP packet transmitted from the cable modem to the CMTS. First, in operation 121, the IP packet is received and the IP packet is received. If it is determined that the IP packet has not been received, the packet continues waiting, and if the IP packet is received, the IP address of the received IP packet is detected (123). It is determined whether the detected IP address exists in the entry table (124). If the IP address exists in the entry table, the IP packet is transmitted (125). If the IP address does not exist in the entry table, the IP packet is discarded (126). .

As such, an IP packet transmitted from the cable modem (CM) through the cable modem terminal system (CMTS) to the backbone network, or from the cable modem (CM) through the cable modem terminal system (CMTS) to another cable modem (CM). In performing filtering on the transmitted IP packets, although not only valid IP addresses but also packets with incorrect IP addresses pass through the cable network, in the cable modem terminal system (CMTS), the IP layer, that is, the network layer, is used. As you go up and process the data, you filter the IP packets without too much overhead.

As described above, in the method of the present invention, a cable modem terminal system (CMTS) detects an IP address of an IP packet transmitted from a cable modem and compares it with an IP address registered in an entry table during modem initialization. This prevents use and prevents unauthorized user devices connected to the cable modem from stealing IP addresses.

Claims (3)

In the cable modem system, a plurality of subscribers are respectively connected to a cable modem terminal system (CMTS, 30) through a cable network using a cable modem, and exchanges data using a MAC frame between the CMTS 30 and the cable modem. , Generating, by the cable modem terminal system, an entry table and registering an entry value through a modem initialization process; And And filtering the IP packet transmitted from the cable modem to determine whether to forward the packet. The method of claim 1, wherein registering in the entry table Generating an entry table in the form of a user equipment (CPE) number, an Ethernet address, an IP address; Reading the Ethernet address from the configuration file and writing it to an entry table; Receiving a DHCP request and response message; And And extracting the IP address from the received DHCP message and recording the IP address in the entry table. The method of claim 1, wherein filtering the IP packet Receiving an IP packet to detect an IP address; Determining whether the detected IP address exists in the entry table; And Transmitting an IP packet if the IP address exists in the entry table, and discarding the IP packet if the IP address does not exist in the entry table.