1-22) The first hop (the Layer 3 device that first receives the packet) responds by sending a TTL-expiredICMP message to the source, with its IP address encapsulated. In this way, the source device canget the address of the first Layer 3 device.3) The source device sends a packet with a TTL value of 2 to the destination device.4) The second hop responds with a TTL-expired ICMP message, which gives the source device theaddress of the second Layer 3 device.5) The above process continues until the ultimate destination device is reached. In this way, thesource device can trace the addresses of all the Layer 3 devices involved to get to the destinationdevice.Introduction to System DebuggingThe device provides various debugging functions. For the majority of protocols and features supported,the system provides corresponding debugging information to help users diagnose errors.The following two switches control the display of debugging information:z Protocol debugging switch, which controls protocol-specific debugging information.z Screen output switch, which controls whether to display the debugging information on a certainscreen.As Figure 1-1 illustrates, suppose the device can provide debugging for the three modules 1, 2, and 3.Only when both the protocol debugging switch and the screen output switch are turned on candebugging information be output on a terminal.Figure 1-1 The relationship between the protocol and screen debugging switchDebugginginformationProtocoldebuggingswitchswitchScreen outputOFF ONOFFON131 2 3OFF ONON131 2 313ONDebugginginformationswitchScreen outputProtocolswitchdebuggingOutputting debugging information to a terminal is most commonly used. You can also configure tooutput debugging information to other directions. For detailed configuration, refer to Information CenterConfiguration in the System Volume.
