Linux 网络基础

本篇写一些关于linux网络相关的基础命令、配置等。

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hostname

1.查看主机名

[root@localhost ~]# hostname
localhost.localdomain

2.临时修改主机名

[root@localhost ~]# hostname server
[root@localhost ~]# bash
[root@server ~]# hostname
server
[root@server ~]# cat /etc/hostname
localhost.localdomain
[root@server ~]# hostnamectl status
   static hostname: localhost.localdomain
transient hostname: server
         icon name: computer-vm
           chassis: vm
        machine id: ec132d04a74d4b7e828b3905a6b83437
           boot id: 8d0046a6366944b08b3eb7e69b431f6b
    virtualization: vmware
  operating system: centos linux 7 (core)
       cpe os name: cpe:/o:centos:centos:7
            kernel: linux 3.10.0-693.el7.x86_64
      architecture: x86-64

3.永久修改主机名

[root@server ~]# hostnamectl set-hostname client
[root@server ~]# bash
[root@client ~]# hostname
client
[root@client ~]# cat /etc/hostname
client
[root@client ~]# hostnamectl status
   static hostname: client
         icon name: computer-vm
           chassis: vm
        machine id: ec132d04a74d4b7e828b3905a6b83437
           boot id: 8d0046a6366944b08b3eb7e69b431f6b
    virtualization: vmware
  operating system: centos linux 7 (core)
       cpe os name: cpe:/o:centos:centos:7
            kernel: linux 3.10.0-693.el7.x86_64
      architecture: x86-64

ifconfig

1.查看已启用的网络接口信息

[root@localhost ~]# ifconfig
ens33: flags=4163<up,broadcast,running,multicast>  mtu 1500
        inet 192.168.28.128  netmask 255.255.255.0  broadcast 192.168.28.255
        inet6 fe80::605e:3c48:bafd:e550  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:bc:ab:96  txqueuelen 1000  (ethernet)
        rx packets 471  bytes 520023 (507.8 kib)
        rx errors 0  dropped 0  overruns 0  frame 0
        tx packets 241  bytes 19798 (19.3 kib)
        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 1  (local loopback)
        rx packets 68  bytes 5916 (5.7 kib)
        rx errors 0  dropped 0  overruns 0  frame 0
        tx packets 68  bytes 5916 (5.7 kib)
        tx errors 0  dropped 0 overruns 0  carrier 0  collisions 0

virbr0: flags=4099<up,broadcast,multicast>  mtu 1500
        inet 192.168.122.1  netmask 255.255.255.0  broadcast 192.168.122.255
        ether 52:54:00:c3:55:5a  txqueuelen 1000  (ethernet)
        rx packets 0  bytes 0 (0.0 b)
        rx errors 0  dropped 0  overruns 0  frame 0
        tx packets 0  bytes 0 (0.0 b)
        tx errors 0  dropped 0 overruns 0  carrier 0  collisions 0

ens33：第一块以太网卡的名称。ens33中的en是ethernet的缩写，表示网卡类型为以太网，s表示热插拔插槽上的设备hot-plug slot，数字33表示插槽编号。

lo：回环网络接口，lo是loopback的缩写，它不代表真正的网络接口，而是一个虚拟的网络接口，其ip地址默认是127.0.0.1。回环地址通常仅用于对本机的网络测试。

virbr0：虚拟网桥的连接接口，默认为0号。其作用是连接主机上的虚机网卡提供外网的功能。

2.查看指定的网络接口信息

[root@localhost ~]# ifconfig ens33
ens33: flags=4163<up,broadcast,running,multicast>  mtu 1500
        inet 192.168.28.129  netmask 255.255.255.0  broadcast 192.168.28.255
        inet6 fe80::eb90:4805:2c20:18ac  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:5b:e0:09  txqueuelen 1000  (ethernet)
        rx packets 899  bytes 207777 (202.9 kib)
        rx errors 0  dropped 0  overruns 0  frame 0
        tx packets 205  bytes 26253 (25.6 kib)
        tx errors 0  dropped 0 overruns 0  carrier 0  collisions 0

inet：表示网络接口的ip地址。

netmask：表示网络接口的子网掩码。

broadcast：表示网络接口所在网络的广播地址。

ether：表示网络接口的mac地址。

3.设置网络接口的ip地址、子网掩码

• ifconfig 接口名 ip地址 [netmask 子网掩码]

• ifconfig 接口名 ip地址[/掩码长度]

[root@localhost ~]# ifconfig ens33 192.168.100.10 netmask 255.255.255.0
[root@localhost ~]# ifconfig ens33
ens33: flags=4163<up,broadcast,running,multicast>  mtu 1500
        inet 192.168.100.10  netmask 255.255.255.0  broadcast 192.168.100.255
        inet6 fe80::605e:3c48:bafd:e550  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:bc:ab:96  txqueuelen 1000  (ethernet)
        rx packets 626  bytes 562243 (549.0 kib)
        rx errors 0  dropped 0  overruns 0  frame 0
        tx packets 262  bytes 23344 (22.7 kib)
        tx errors 0  dropped 0 overruns 0  carrier 0  collisions 0

临时配置，重启失效。不指定子网掩码时，将使用ip地址所在分类的默认子网掩码。

4.临时禁用或者重新激活网卡

• ifconfig 接口名 down

[root@localhost ~]# ifconfig ens33 down
[root@localhost ~]# ifconfig ens33
ens33: flags=4098<broadcast,multicast>  mtu 1500
        ether 00:0c:29:bc:ab:96  txqueuelen 1000  (ethernet)
        rx packets 1067  bytes 667057 (651.4 kib)
        rx errors 0  dropped 0  overruns 0  frame 0
        tx packets 263  bytes 23404 (22.8 kib)
        tx errors 0  dropped 0 overruns 0  carrier 0  collisions 0

• ifconfig 接口名 up

[root@localhost ~]# ifconfig ens33 up
[root@localhost ~]# ifconfig ens33
ens33: flags=4163<up,broadcast,running,multicast>  mtu 1500
        inet 192.168.28.128  netmask 255.255.255.0  broadcast 192.168.28.255
        inet6 fe80::605e:3c48:bafd:e550  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:bc:ab:96  txqueuelen 1000  (ethernet)
        rx packets 1078  bytes 668954 (653.2 kib)
        rx errors 0  dropped 0  overruns 0  frame 0
        tx packets 285  bytes 26835 (26.2 kib)
        tx errors 0  dropped 0 overruns 0  carrier 0  collisions 0

5.设置虚拟网络接口

• ifconfig 接口名:序号 ip地址

[root@localhost ~]# ifconfig ens33:0 192.168.100.10
[root@localhost ~]# ifconfig ens33:0
ens33:0: flags=4163<up,broadcast,running,multicast>  mtu 1500
        inet 192.168.100.10  netmask 255.255.255.0  broadcast 192.168.100.255
        ether 00:0c:29:bc:ab:96  txqueuelen 1000  (ethernet)
[root@localhost ~]# ifconfig ens33:0 down

route

1.查看当前主机中的路由表信息

-n：将路由记录中的地址显示位数字形式

[root@localhost ~]# route
kernel ip routing table
destination     gateway         genmask         flags metric ref    use iface
default         promote.cache-d 0.0.0.0         ug    100    0        0 ens33
192.168.28.0    0.0.0.0         255.255.255.0   u     100    0        0 ens33
192.168.122.0   0.0.0.0         255.255.255.0   u     0      0        0 virbr0

[root@localhost ~]# route -n
kernel ip routing table
destination     gateway         genmask         flags metric ref    use iface
0.0.0.0         192.168.28.2    0.0.0.0         ug    100    0        0 ens33
192.168.28.0    0.0.0.0         255.255.255.0   u     100    0        0 ens33
192.168.122.0   0.0.0.0         255.255.255.0   u     0      0        0 virbr0

2.添加、删除到指定网段的路由记录

• route add -net 网段地址 gw ip地址

[root@localhost ~]# route add -net 192.168.100.0/24 gw 192.168.28.1
[root@localhost ~]# route -n
kernel ip routing table
destination     gateway         genmask         flags metric ref    use iface
0.0.0.0         192.168.28.2    0.0.0.0         ug    100    0        0 ens33
192.168.28.0    0.0.0.0         255.255.255.0   u     100    0        0 ens33
192.168.100.0   192.168.28.1    255.255.255.0   ug    0      0        0 ens33
192.168.122.0   0.0.0.0         255.255.255.0   u     0      0        0 virbr0

• route del -net 网段地址

[root@localhost ~]# route del -net 192.168.100.0/24
[root@localhost ~]# route -n
kernel ip routing table
destination     gateway         genmask         flags metric ref    use iface
0.0.0.0         192.168.28.2    0.0.0.0         ug    100    0        0 ens33
192.168.28.0    0.0.0.0         255.255.255.0   u     100    0        0 ens33
192.168.122.0   0.0.0.0         255.255.255.0   u     0      0        0 virbr0

3。添加、删除默认网关记录

• route add default gw ip地址

[root@localhost ~]# route add default gw 192.168.28.1
[root@localhost ~]# route -n
kernel ip routing table
destination     gateway         genmask         flags metric ref    use iface
0.0.0.0         192.168.28.1    0.0.0.0         ug    0      0        0 ens33
0.0.0.0         192.168.28.2    0.0.0.0         ug    100    0        0 ens33
192.168.28.0    0.0.0.0         255.255.255.0   u     100    0        0 ens33
192.168.122.0   0.0.0.0         255.255.255.0   u     0      0        0 virbr0

• route del default gw ip地址

[root@localhost ~]# route del default gw 192.168.28.1
[root@localhost ~]# route -n
kernel ip routing table
destination     gateway         genmask         flags metric ref    use iface
0.0.0.0         192.168.28.2    0.0.0.0         ug    100    0        0 ens33
192.168.28.0    0.0.0.0         255.255.255.0   u     100    0        0 ens33
192.168.122.0   0.0.0.0         255.255.255.0   u     0      0        0 virbr0

netstat

• 查看当前的网络连接状态、路由表、接口统计等信息。

-n：以数字的形式显示相关的主机地址、端口等信息。
-t：查看tcp传输控制协议相关的信息。
-u：显示udp用户数据报协议相关的信息。
-a：显示当前主机中所有活动的网络连接信息，包括监听、非监听状态的服务端口。
-l：显示处于监听listening状态的网络连接及端口信息。
-p：显示与网络连接相关联的进程号、进程名称信息，该选项需要root权限。
-r：显示路由表信息。

[root@localhost ~]# netstat -ntap
active internet connections (servers and established)
proto recv-q send-q local address           foreign address         state       pid/program name    
tcp        0      0 0.0.0.0:111             0.0.0.0:*               listen      1/systemd           
tcp        0      0 192.168.122.1:53        0.0.0.0:*               listen      1335/dnsmasq        
tcp        0      0 0.0.0.0:22              0.0.0.0:*               listen      1009/sshd           
tcp        0      0 127.0.0.1:631           0.0.0.0:*               listen      1012/cupsd          
tcp        0      0 127.0.0.1:25            0.0.0.0:*               listen      1306/master         
tcp6       0      0 :::111                  :::*                    listen      1/systemd           
tcp6       0      0 :::22                   :::*                    listen      1009/sshd           
tcp6       0      0 ::1:631                 :::*                    listen      1012/cupsd          
tcp6       0      0 ::1:25                  :::*                    listen      1306/master         

[root@localhost ~]# netstat -nuap
active internet connections (servers and established)
proto recv-q send-q local address           foreign address         state       pid/program name    
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           578/avahi-daemon: r 
udp        0      0 0.0.0.0:12162           0.0.0.0:*                           799/dhclient        
udp        0      0 192.168.122.1:53        0.0.0.0:*                           1335/dnsmasq        
udp        0      0 0.0.0.0:67              0.0.0.0:*                           1335/dnsmasq        
udp        0      0 0.0.0.0:68              0.0.0.0:*                           799/dhclient        
udp        0      0 127.0.0.1:323           0.0.0.0:*                           624/chronyd         
udp        0      0 0.0.0.0:51570           0.0.0.0:*                           578/avahi-daemon: r 
udp6       0      0 :::25751                :::*                                799/dhclient        
udp6       0      0 ::1:323                 :::*                                624/chronyd         

[root@localhost ~]# netstat -r
kernel ip routing table
destination     gateway         genmask         flags   mss window  irtt iface
default         promote.cache-d 0.0.0.0         ug        0 0          0 ens33
192.168.28.0    0.0.0.0         255.255.255.0   u         0 0          0 ens33
192.168.122.0   0.0.0.0         255.255.255.0   u         0 0          0 virbr0
[root@localhost ~]# netstat -rn
kernel ip routing table
destination     gateway         genmask         flags   mss window  irtt iface
0.0.0.0         192.168.28.2    0.0.0.0         ug        0 0          0 ens33
192.168.28.0    0.0.0.0         255.255.255.0   u         0 0          0 ens33
192.168.122.0   0.0.0.0         255.255.255.0   u         0 0          0 virbr0

ping

• 测试网络连通性

[root@localhost ~]# ping -c 4 127.0.0.1
ping 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.036 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.084 ms
64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.085 ms
64 bytes from 127.0.0.1: icmp_seq=4 ttl=64 time=0.096 ms

--- 127.0.0.1 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3009ms
rtt min/avg/max/mdev = 0.036/0.075/0.096/0.023 ms

traceroute

• 跟踪数据包的路由途径

[root@localhost ~]# traceroute 127.0.0.1
traceroute to 127.0.0.1 (127.0.0.1), 30 hops max, 60 byte packets
 1  localhost (127.0.0.1)  0.040 ms  0.010 ms  0.008 ms

traceroute命令能够比ping命令更加准确地定位网络连接的故障点，因此执行速度会比ping命令稍慢。在网络测试与排错过程中，通常会先使用ping命令测试与目的主机的网络连接，如果发现网络连接有故障，再使用traceroute命令跟踪查看是在哪个中间结点存在故障。

nslookup

• 测试 dns 域名解析

[root@localhost ~]# nslookup www.baidu.com
server:     192.168.28.2
address:    192.168.28.2#53

non-authoritative answer:
www.baidu.com   canonical name = www.a.shifen.com.
name:   www.a.shifen.com
address: 183.232.231.174
name:   www.a.shifen.com
address: 183.232.231.172

ifcfg-*

• 修改网络接口配置文件

[root@localhost ~]# vim /etc/sysconfig/network-scripts/ifcfg-ens33
type=ethernet
bootproto=static
device=ens33
onboot=yes
ipaddr=192.168.100.10
netmask=255.255.255.0
gateway=192.168.100.1

type：设置网卡类型，ethernet表示以太网。
bootproto：设置网络接口的配置方式，值为static时表示使用静态指定的ip地址，为dhcp时表示通过dhcp的方式动态获取地址。
device：设置网络接口的名称。
onboot：设置网络接口是否在linux操作系统启动时激活。
ipaddr：设置网络接口的ip地址。
netmask：设置网络接口的子网掩码。
gateway：设置网络接口的默认网关地址。

• 启用、禁用单个网络接口配置

[root@localhost ~]# ifdown ens33
device 'ens33' successfully disconnected.
[root@localhost ~]# ifup ens33
connection successfully activated (d-bus active path: /org/freedesktop/networkmanager/activeconnection/5)
[root@localhost ~]# ifconfig ens33
ens33: flags=4163<up,broadcast,running,multicast>  mtu 1500
        inet 192.168.100.10  netmask 255.255.255.0  broadcast 192.168.100.255
        inet6 fe80::20c:29ff:febc:ab96  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:bc:ab:96  txqueuelen 1000  (ethernet)
        rx packets 5640  bytes 1889047 (1.8 mib)
        rx errors 0  dropped 0  overruns 0  frame 0
        tx packets 410  bytes 37045 (36.1 kib)
        tx errors 0  dropped 0 overruns 0  carrier 0  collisions 0

• 重启网络服务（会先关闭所有的网络接口，再根据配置文件重新启用所有的网络接口）

[root@localhost ~]# service network restart
restarting network (via systemctl):                        [  ok  ]

[root@localhost ~]# systemctl restart network

/etc/hosts

• 本地主机映射文件

[root@localhost ~]# cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

当访问一个未知的域名时，先查找该文件中是否有相应的映射记录，如果找不到再去向dns服务器查询。

/etc/resolv.conf

• 指定为本机提供dns解析的服务器地址，最多可以指定3个，第3个后面的会被忽略。

[root@localhost ~]# cat /etc/resolv.conf
# generated by networkmanager
search localdomain
nameserver 192.168.28.2

search localdomain：设置默认的搜索域（域名扩展名）。

例如，当访问主机localhost时，就相当于访问localhost.localdomain。

scp

• 远程复制

本地 → 对方

[root@localhost ~]# scp /etc/hosts root@192.168.28.129:/etc/hosts
the authenticity of host '192.168.28.129 (192.168.28.129)' can't be established.
ecdsa key fingerprint is sha256:qmztjt0pibuskf9p3gfyf3ueogzbws08si7j0ebe/ci.
ecdsa key fingerprint is md5:ef:e6:06:22:8a:0f:24:00:f8:af:a5:59:5b:a2:b8:b1.
are you sure you want to continue connecting (yes/no)? yes
warning: permanently added '192.168.28.129' (ecdsa) to the list of known hosts.
root@192.168.28.129's password: 
hosts                                         100%  158   172.5kb/s   00:00    

对方 → 本地

[root@localhost ~]# scp root@192.168.28.129:/etc/hosts /etc/hosts
root@192.168.28.129's password: 
hosts                                         100%  158    90.5kb/s   00:00