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      本章主要讲述如何进行网络诊断。

操作系统：

CentOS Stream 9

操作步骤·：

操作指令 ping：   测试网络连接的连通性和延迟。

[root@localhost ~]# ping 192.168.80.111
PING 192.168.80.111 (192.168.80.111) 56(84) 比特的数据。
64 比特，来自 192.168.80.111: icmp_seq=1 ttl=64 时间=0.041 毫秒
64 比特，来自 192.168.80.111: icmp_seq=2 ttl=64 时间=0.048 毫秒
64 比特，来自 192.168.80.111: icmp_seq=3 ttl=64 时间=0.042 毫秒
64 比特，来自 192.168.80.111: icmp_seq=4 ttl=64 时间=0.034 毫秒
^C
--- 192.168.80.111 ping 统计 ---
已发送 4 个包， 已接收 4 个包, 0% packet loss, time 3082ms
rtt min/avg/max/mdev = 0.034/0.041/0.048/0.005 ms
[root@localhost ~]# ping 192.168.80.1
PING 192.168.80.1 (192.168.80.1) 56(84) 比特的数据。
64 比特，来自 192.168.80.1: icmp_seq=1 ttl=64 时间=0.776 毫秒
64 比特，来自 192.168.80.1: icmp_seq=2 ttl=64 时间=0.692 毫秒
64 比特，来自 192.168.80.1: icmp_seq=3 ttl=64 时间=0.687 毫秒
^C
--- 192.168.80.1 ping 统计 ---
已发送 3 个包， 已接收 3 个包, 0% packet loss, time 2044ms
rtt min/avg/max/mdev = 0.687/0.718/0.776/0.040 ms
[root@localhost ~]# ping jd.com
PING jd.com (211.144.27.126) 56(84) 比特的数据。
64 比特，来自 211.144.27.126 (211.144.27.126): icmp_seq=1 ttl=49 时间=14.5 毫秒
64 比特，来自 211.144.27.126 (211.144.27.126): icmp_seq=2 ttl=49 时间=14.1 毫秒
64 比特，来自 211.144.27.126 (211.144.27.126): icmp_seq=3 ttl=49 时间=14.4 毫秒
64 比特，来自 211.144.27.126 (211.144.27.126): icmp_seq=4 ttl=49 时间=14.5 毫秒
64 比特，来自 211.144.27.126 (211.144.27.126): icmp_seq=5 ttl=49 时间=14.8 毫秒
^C
--- jd.com ping 统计 ---
已发送 5 个包， 已接收 5 个包, 0% packet loss, time 4002ms
rtt min/avg/max/mdev = 14.075/14.448/14.773/0.227 ms
[root@localhost ~]# 

指令tcpdump: 抓包工具，用于分析网络流量，诊断网络问题

下载 yum install tcpdump -y

[root@localhost ~]# tcpdump host 192.168.80.111
dropped privs to tcpdump
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on ens160, link-type EN10MB (Ethernet), snapshot length 262144 bytes
17:18:59.828458 IP 192.168.80.97.62142 > localhost.localdomain.ssh: Flags [.], ack 2087800729, win 8208, length 0
17:18:59.829371 IP localhost.localdomain.ssh > 192.168.80.97.62142: Flags [P.], seq 1:221, ack 0, win 249, length 220
17:18:59.870734 IP 192.168.80.97.62142 > localhost.localdomain.ssh: Flags [.], ack 221, win 8208, length 0
17:18:59.891741 IP localhost.localdomain.55556 > dns.google.domain: 47703+ PTR? 111.80.168.192.in-addr.arpa. (45)
17:18:59.962110 IP dns.google.domain > localhost.localdomain.55556: 47703 NXDomain 0/0/0 (45)
17:18:59.962476 IP localhost.localdomain.41280 > dns.google.domain: 24390+ PTR? 97.80.168.192.in-addr.arpa. (44)
17:19:00.015187 IP dns.google.domain > localhost.localdomain.41280: 24390 NXDomain 0/0/0 (44)
17:19:00.015460 IP localhost.localdomain.43924 > dns.google.domain: 45008+ PTR? 8.8.8.8.in-addr.arpa. (38)
17:19:00.015533 IP localhost.localdomain.ssh > 192.168.80.97.62142: Flags [P.], seq 221:601, ack 0, win 249, length 380
17:19:00.056273 IP 192.168.80.97.62142 > localhost.localdomain.ssh: Flags [.], ack 601, win 8212, length 0
17:19:00.056870 IP dns.google.domain > localhost.localdomain.43924: 45008 1/0/0 PTR dns.google. (62)
17:19:00.057159 IP localhost.localdomain.ssh > 192.168.80.97.62142: Flags [P.], seq 601:965, ack 0, win 249, length 364
17:19:00.099179 IP 192.168.80.97.62142 > localhost.localdomain.ssh: Flags [.], ack 965, win 8211, length 0
17:19:00.100256 IP localhost.localdomain.ssh > 192.168.80.97.62142: Flags [P.], seq 965:1769, ack 0, win 249, length 804
17:19:00.141658 IP 192.168.80.97.62142 > localhost.localdomain.ssh: Flags [.], ack 1769, win 8207, length 0
17:19:00.203538 IP localhost.localdomain.ssh > 192.168.80.97.62142: Flags [P.], seq 1769:2037, ack 0, win 249, length 268
17:19:00.243835 IP 192.168.80.97.62142 > localhost.localdomain.ssh: Flags [.], ack 2037, win 8206, length 0

指令traceroute ：显示数据包到目标主机经过的路由器路径

下载  yum -y install traceroute

[root@localhost a]# traceroute 192.168.80.111
traceroute to 192.168.80.111 (192.168.80.111), 30 hops max, 60 byte packets1  localhost.localdomain (192.168.80.111)  0.219 ms  0.191 ms  0.180 ms
[root@localhost a]#