A multi-connection system MCS configured to connect a client and a server in a multi-connection manner for a service using an Internet protocol, the MCS comprising: a plurality of proxies; an MCS client, when the client transmits a forward packet to the server, configured to receive the forward packet, generate the forward MCS packets by adding a forward MCS sequence identification ID identifying the packet to the forward packet, and sequentially and respectively transmit the forward MCS packets to the plurality of proxies connected via a network, wherein a number of MCS packets corresponds to a number of pieces of proxy access information connected to the plurality of proxies or a set number of pieces of proxy access information, and when the server transmits a backward MCS packet to the client, configured to respectively receive the backward MCS packets from the plurality of proxies, extract the MCS sequence IDs from the backward MCS packets, compare the extracted backward MCS sequence IDs with MCS sequence IDs stored beforehand, store the extracted backward MCS sequence IDs, generate client-receivable packets from the backward MCS packets, and transmit the client-receivable packets to the client when the extracted backward MCS sequence IDs are not identical to the stored backward MCS sequence IDs, and block the backward MCS packets received from the plurality of proxies from being transmitted to the client when the extracted backward MCS sequence IDs are identical to the stored backward MCS sequence IDs; and an MCS server, when the client transmits a forward MCS packet to the server, configured to respectively receive the forward MCS packets from the plurality of proxies, extract the forward MCS sequence IDs from the forward MCS packets, compare the extracted forward MCS sequence IDs with forward MCS sequence IDs stored beforehand; store the extracted forward MCS sequence IDs, generate server-receivable packets from the forward MCS packets, and transmit the server-receivable packets to the server when the extracted forward MCS sequence IDs are not identical to the stored forward MCS sequence IDs; and block the forward MCS packets from being transmitted to the server when the extracted forward MCS sequence IDs are identical to the stored MCS sequence IDs, and when the server transmits a backward packet to the client, configured to receive the backward packet from the server, generate backward MCS packets by adding a backward MCS sequence identification ID identifying the backward packet to the packet, and sequentially and respectively transmit the backward MCS packets to the plurality of proxies connected via a network, wherein a number of backward MCS packets corresponds to a number of pieces of proxy access information connected to the plurality of proxies or a set number of pieces of proxy access information. a plurality of proxies; an MCS client, when the client transmits a forward packet to the server, configured to receive the forward packet, generate the forward MCS packets by adding a forward MCS sequence identification ID identifying the packet to the forward packet, and sequentially and respectively transmit the forward MCS packets to the plurality of proxies connected via a network, wherein a number of MCS packets corresponds to a number of pieces of proxy access information connected to the plurality of proxies or a set number of pieces of proxy access information, and when the server transmits a backward MCS packet to the client, configured to respectively receive the backward MCS packets from the plurality of proxies, extract the MCS sequence IDs from the backward MCS packets, compare the extracted backward MCS sequence IDs with MCS sequence IDs stored beforehand, store the extracted backward MCS sequence IDs, generate client-receivable packets from the backward MCS packets, and transmit the client-receivable packets to the client when the extracted backward MCS sequence IDs are not identical to the stored backward MCS sequence IDs, and block the backward MCS packets received from the plurality of proxies from being transmitted to the client when the extracted backward MCS sequence IDs are identical to the stored backward MCS sequence IDs; and an MCS server, when the client transmits a forward MCS packet to the server, configured to respectively receive the forward MCS packets from the plurality of proxies, extract the forward MCS sequence IDs from the forward MCS packets, compare the extracted forward MCS sequence IDs with forward MCS sequence IDs stored beforehand; store the extracted forward MCS sequence IDs, generate server-receivable packets from the forward MCS packets, and transmit the server-receivable packets to the server when the extracted forward MCS sequence IDs are not identical to the stored forward MCS sequence IDs; and block the forward MCS packets from being transmitted to the server when the extracted forward MCS sequence IDs are identical to the stored MCS sequence IDs, and when the server transmits a backward packet to the client, configured to receive the backward packet from the server, generate backward MCS packets by adding a backward MCS sequence identification ID identifying the backward packet to the packet, and