1.4 VPN Processing Principle and Communication Method

Combined revision comparison

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Fig. 1-4-1 Switching Hub and network adapter for Ethernet.

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AFig. 1-4-2 Ethernet frame (MAC frame).)

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The switching Hub used by Ethernet (layer 2 switch) constructs a network by Ethernet and is an important peripheral device for communication. Switching HubsHUBs have multiple ports (usually 8 ports, but can have from tens to hundreds. By connecting a compute to the Ethernet by network cable, etc., a physical network is connected between the switching Hub and computer's network adapter, thus enabling Ethernet communications by layer 2.

The ports of a switching Hub can also be connected to the ports of another switching Hub. Even though the connected switching HubsHUBs were originally separate Ethernet networks, by connecting them by network cable, they work like a single Ethernet network. This is called "cascade connection".

The computers connected to the switching HubsHUBs on the left and right in the following figure can communicate freely with each other.

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Fig. 1-4-3 Segment junction by cascade connection of switching hubs.HUBs

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Switching HubsHUBs constantly recognize in advance which computers with what sort of MAC address are connected to the respective ports and maintain the information in an internal database. This is called a "MAC address table".

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As was previously mentioned, the method of connecting two segments configured of two switching HubsHUBs and using as a single segment is called "cascade connection". Cascade connection can consist of an unlimited number of cascades provided the physical limit established for Ethernet is not exceeded. The fact that cascade connection can be accomplished easily is one of the greatest features of using Ethernet. By cascade connecting another switching Hub to one for which the number of ports has become insufficient, you can increase the number of available ports and increase the number of computers that can be connected to the network.

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Cascade connection and bridge connection are technically similar connection methods, but whereas cascade connection indicates connecting switching HubsHUBs to construct a single large segment from the beginning, bridge connection means connecting networks to be used as two segments that are physically separate and are administered separately.

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Virtual Hub is one of the most important functions of SoftEther VPN. Virtual Hub implements the same level of functions as the existing common layer 2 switching Hub as software. Virtual Hub has a MAC address learning function and frame exchange/delivery functions based on learning. Whereas conventional switching HubsHUBs used to handle this processing as hardware, with Virtual Hub of SoftEther VPN, the processing is handled as software.

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SoftEther VPN Server can create multiple Virtual HubsHUBs. You can create as many Virtual HubsHUBs as memory space, CPU speed and specifications will permit. Each respective Virtual Hub conducts MAC address learning for virtual Ethernet frames flowing through the VPN. As a result virtual layer 2 Ethernet segments are realized by sending Ethernet frames to computers participating in other VPNs.

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Connection between Virtual HubsFig. 1-4-4 Connection between Virtual HUBs or between Virtual Network Adapters.

Creation and Administration of Multiple Virtual HubsHUBs

If multiple Virtual HubsHUBs are created within a single VPN server, those Virtual HubsHUBs cannot communicate with each other. Consequently if multiple Virtual HubsHUBs are created, it means multiple Ethernet segments are formed within the VPN Server.

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Fig. 1-4-5 Segment separation by Virtual Hub within VPN Server.

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These setting contents are completely independent for each Virtual Hub, and administration is divided into units so each individual administrator can administrate separately. Administrators of VPN Servers at large can manage all Virtual HubsHUBs, but administrators granted authority concerning some Virtual HubsHUBs from the VPN Server administrator can manage only those Virtual HubsHUBs and are unable to manage other Virtual HubsHUBs.

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Method of Connecting Virtual HubsHUBs to each other

Virtual HubsHUBs can be cascade connected to Virtual HubsHUBs operating on the same VPN Server or VPN Server operating on another computer, and the cascade connected Virtual HubsHUBs that were originally separate segments are joined to work as a single segment.

For Virtual HubsHUBs operating on the same VPN Server, via virtual layer 3 switch by IP routing, network among Virtual HubsHUBs can be connected by layer 3.

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Fig. 1-4-6 SoftEther VPN Virtual Network Adapter recognized as a network adapter by the operating system.

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Fig. 1-4-7 Property window of Virtual Network Adapter  .

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With SoftEther VPN Server, you can create multiple Virtual HubsHUBs and operate them together. In the initial state however Virtual HubsHUBs have only independent layer 2 segments, and although computers connected to the same Virtual Hub can communicate freely, computers connected to separate Virtual HubsHUBs cannot communicate with each other.

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Using the virtual layer 3 switch function of SoftEther VPN Server enables IP routing among multiple Virtual HubsHUBs. If conducting IP routing among multiple Virtual HubsHUBs with the previous version of SoftEther 1.0, etc., you had to conduct IP routing with a physical layer 3 switch or special router by bridge connecting each respective Virtual Hub segment to a physical Ethernet segment. SoftEther VPN Server's support of virtual layer 3 switch function enables network administrators to easily realize communication among Virtual HubsHUBs by IP routing among multiple Virtual HubsHUBs.

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Fig. 1-4-8 IP routing among Virtual HubsHUBs by virtual layer 3 switch.

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By connecting Virtual Hub and physical existing LAN by multiple bases and by furthermore cascade connecting Virtual HubsHUBs existing physical LAN of multiple bases can be easily made a single segment via Internet to realize base-to-base VPN.

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Fig. 1-4-9 Example of base-to-base connection by SoftEther VPN  .

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Fig. 1-4-10 Computer-to-computer VPN  .

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Fig. 1-4-11 Remote access VPN  .

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Fig. 1-4-12 Base-to-base VPN of ordinary scale  .

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Fig. 1-4-13 Base-to-base VPN of large scale.

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