本章介绍一些常用网络命令。
ping
PING命令将数据包请求发送到指定地址，以测试两个节点之间的连接。
[kevin@localhost ~]$ ping www.qikegu.com
PING www.qikegu.com (121.199.13.249) 56(84) bytes of data.
64 bytes from 121.199.13.249 (121.199.13.249): icmp_seq=1 ttl=51 time=4.49 ms
64 bytes from 121.199.13.249 (121.199.13.249): icmp_seq=2 ttl=51 time=5.24 ms
64 bytes from 121.199.13.249 (121.199.13.249): icmp_seq=3 ttl=51 time=4.93 ms
^C
--- www.qikegu.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 4.497/4.892/5.241/0.305 ms
ping命令会一直执行，可使用-c选项指定执行次数。
[kevin@localhost ~]$ ping -c 3 www.qikegu.com
PING www.qikegu.com (121.199.13.249) 56(84) bytes of data.
64 bytes from 121.199.13.249 (121.199.13.249): icmp_seq=1 ttl=51 time=4.52 ms
64 bytes from 121.199.13.249 (121.199.13.249): icmp_seq=2 ttl=51 time=5.55 ms
64 bytes from 121.199.13.249 (121.199.13.249): icmp_seq=3 ttl=51 time=5.16 ms
--- www.qikegu.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2007ms
rtt min/avg/max/mdev = 4.522/5.080/5.551/0.428 ms
netstat
Netstat命令显示各种网络连接信息，信息包括套接字和路由表等。
[kevin@localhost ~]$ netstat
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 localhost.localdoma:ssh gateway:64763 ESTABLISHED
tcp 0 0 localhost.localdo:47130 59.111.0.251:http TIME_WAIT
tcp 0 0 localhost.localdoma:ssh gateway:64748 ESTABLISHED
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags Type State I-Node Path
unix 3 [ ] DGRAM 7442 /run/systemd/notify
unix 2 [ ] DGRAM 7444 /run/systemd/cgroups-agent
unix 5 [ ] DGRAM 7464 /run/systemd/journal/socket
unix 15 [ ] DGRAM 7466 /dev/log
...
添加选项-r显示路由表信息:
kevin@localhost ~]$ netstat -r
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
default gateway 0.0.0.0 UG 0 0 0 enp0s3
10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 enp0s3
ifconfig
ifconfig命令用于配置网络接口。
大多数情况下，我们使用这个命令查看主机IP地址。
[kevin@localhost ~]$ ifconfig -a
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.2.15 netmask 255.255.255.0 broadcast 10.0.2.255
inet6 fe80::a35f:b12e:1ef3:dd19 prefixlen 64 scopeid 0x20<link>
ether 08:00:27:9e:aa:23 txqueuelen 1000 (Ethernet)
RX packets 11875 bytes 9469332 (9.0 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 4535 bytes 1480350 (1.4 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 68 bytes 5896 (5.7 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 68 bytes 5896 (5.7 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
telnet
telnet连接目标主机: 如果连接建立，则通过telnet协议进行端口连接，这意味着两台主机之间的连接工作正常。
[kevin@localhost ~]$ telnet www.qikegu.com 443
Trying 121.199.13.249...
Connected to www.qikegu.com.
Escape character is '^]'.
nmap
黑客常用工具，功能强大，用于扫描服务器端口。
[kevin@localhost ~]$ nmap baidu.com
Starting Nmap 6.40 ( http://nmap.org ) at 2019-04-03 12:36 CST
Nmap scan report for baidu.com (220.181.57.216)
Host is up (0.035s latency).
Other addresses for baidu.com (not scanned): 123.125.114.144
Not shown: 998 filtered ports
PORT STATE SERVICE
80/tcp open http
443/tcp open https
Nmap done: 1 IP address (1 host up) scanned in 4.51 seconds
[kevin@localhost ~]$
scp
scp命令可以在目标主机与本地主机之间安全复制文件。
scp $filename user@targethost:/$path
启用/禁用网络接口
ifup/ifdown命令可以启用或禁用网络接口
启用：
# ifup eth0
禁用：
# ifdown eth0
nslookup
nslookup命令可以查询互联网域名服务器获取域名信息。
[kevin@localhost ~]$ nslookup www.qikegu.com
Server: 192.168.31.1
Address: 192.168.31.1#53
Non-authoritative answer:
Name: www.qikegu.com
Address: 121.199.13.249
tcpdump
tcpdump是一个嗅探器/抓包工具，用于抓取网络数据包。
tcpdump host 1.1.1.1
traceroute
traceroute跟踪到网络主机的路由。
[kevin@localhost ~]$ traceroute www.qikegu.com
traceroute to www.qikegu.com (121.199.13.249), 30 hops max, 60 byte packets
1 gateway (10.0.2.2) 0.191 ms 0.242 ms 0.114 ms
2 gateway (10.0.2.2) 2.995 ms 2.892 ms 2.790 ms
[kevin@localhost ~]$