一般来说，ICMP 报文具有类似的结构。接下来的一系列图是 Wireshark 对同一个 ICMP 数据包的观察，每个图都指出了不同的方面。ICMP echo 请求是 IP 数据包的有效载荷，包含在数据字段中。ICMP 没有 TCP 或 UDP 报头。展开 IP 报头后，我们会发现 ICMP 的 IP 数据包有效载荷类型是 01。图 6-2 中突出显示了这一点。
图 6-2. IP 有效载荷类型 ICMP ...
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