what is TTL？
正确答案:Time to Live （TTL） is an eight-bit field that will be set with a certain number when the packet is first generated. As the packet is passed from router to router， each router will decrement this number. If the number reaches zero， the packet will be discarded and an error message （ICMP time exceeded message） will be sent to the source. This process prevents "lost" packets from wandering endlessly through a network.
答案解析:有
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