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Nortel Guide to VPN Routing for Security and VoIP phần 6

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các vấn đề giấy chứng nhận với những cái tên thay thế. Ví dụ, trong khi sử dụng Entrust PKI, các kết nối VPN có thể cấp giấy chứng nhận với Email, DNS tên hoặc địa chỉ IP là tên thay thế. Identity Server Certificate địa phương trình đơn thả xuống hiển thị | 350 Chapter 8 Media Access Control MAC Addressing A MAC address is a hardware physical address that identifies the node to the other nodes on the network. MAC addressing is used by layer 2 nodes to identify the device and formulate data traffic paths to that device. Every node in a network has a MAC address. Figure 8-13 shows an example of MAC addressing of nodes within a LAN segment. Not all networking protocols will use the MAC address but on broadcast networks the MAC address allows all of the nodes in the network to be identified and allows delivery of frames intended for a specific destination. MAC addresses are permanently attached to a device and are assigned by product manufacturers. MAC addressing is administered by the IEEE. The IEEE ensures that there is no duplication of MAC addresses so all Network Interface Cards NICs have a unique MAC address that is assigned to it by the manufacturer. Because of this the end user can install a NIC anywhere within a network and not be concerned about duplication of MAC addresses. MAC addresses are 48 bits long. The first 24 bits are known as the Organization Unique Identifier OUI and they identify the manufacturer of the device. The remaining 24 bits make up a unique number that is assigned by the manufacturer to identify the individual component. NOTE You can determine the manufacturer s OUI code by searching on the IEEE Web site. MAC 00-00-75-00-00-02 Figure 8-13 MAC addressing Overview of Ethernet LANs and Network Routing 351 Internet Protocol IP Addressing An IP address is a unique number that is used by layer 3 nodes to communicate with one another in a network. An IP address is assigned to each host interface within a network. To route data between subnets the IP address of the sending and the receiving nodes must be known. Figure 8-14 shows an example of three subnets connected with a router and therefore capable of communicating with IP addressing. An IP address may be permanently assigned to a node. This .