tailieunhanh - Nortel Guide to VPN Routing for Security and VoIP phần 9

Địa chỉ Nghị quyết Protocol (ARP) cung cấp một cách để tìm địa chỉ MAC của một nút khi chỉ có địa chỉ IP được biết đến. Cách ARP công trình đơn giản. Một nút gửi sẽ gửi một phát sóng thông qua mạng với địa chỉ IP của các nút mà nó đang cố gắng để xác định vị trí. | Troubleshooting Overview 581 ARP The Address Resolution Protocol ARP provides a way to find a node s MAC address when only the IP address is known. The way ARP works is simple. A sending node will send a broadcast through the network with the IP address of the node that it is trying to locate. Once a node recognizes an IP address in an ARP broadcast it will respond to the originating node with the MAC address that matches the IP address. ARP entries are stored in a cache known as the ARP table. ARP is limited to the nodes within the network that support broadcasting and will accept a broadcast packet. Other nodes will ignore the broadcasts. Sometimes a node may be moved or for some other reason a node may no longer be able to locate another node within the network. When this occurs you might want to try to force the node to relearn where the destination node may reside. The Arp section of the Tools screen provides access to the ARP table and some options that can be used to assist in troubleshooting. This section is located at the bottom of the Tools screen see Figure 12-38 . Within the Arp section is one field that allows you to specify the IP address of a node that you would like to have removed from the ARP cache so the device will resend the ARP broadcast packets. You can enter the IP address and then press the Arp delete button that is in this section. Two other buttons can be chosen within the Arp section. The first button is the Show Arp Table button. By clicking this button you will receive an output of the ARP table which lists the entries contained in the VPN Router s ARP cache. Figure 12-39 shows an example of an ARP table. The other button provides an option to clear the entire ARP table. Figure 12-38 The Arp section of the System Tools screen 582 Chapter 12 Figure 12-39 The ARP table Packet Capture Previously in this chapter we discussed the use of sniffers as a helpful tool in troubleshooting data connection issues within a network. Often however a .