ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP是Internet控制消息协议的缩写，是Internet协议套件（通常称为TCP/IP）的一个组成部分。它是网络设备用来诊断网络通信问题的网络层协议。IP的设计不是绝对可靠的。ICMP是对通信环境中的问题提供反馈，而不是制造IP可靠。一个ICMP数据报中最广为人知和最有用的消息之一是由于多种原因（包括无法到达网络、主机、aport或协议）而生成的目的地不可到达消息。
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
电子邮件系统中，发送邮件协议为SMTP协议，使用的端口号是（ ）。
可以通过电子邮件发送的文件类型有（ ）。
①视频文件②音频文件③图片文件④文本文件
下列关于ping命令的描述中，说法错误的是（ ）。
在Windows中，执行（ ）命令可以查看域名信息。
在Windows中，要查看到目标主机Alice的路径，可使用（ ）命令。
