centos8平台使用ip命令代替ifconfig管理网络

一，为什么建议使用ip命令代替ifconfig？

1，ifconfig所属的net-tools包已经不再被维护了

     虽然可以用，但会发生看不到部分ip等情况，

[root@centos8 liuhongdi]# whereis ifconfig
ifconfig: /usr/sbin/ifconfig /usr/share/man/man8/ifconfig.8.gz

[root@centos8 liuhongdi]# rpm -qf /usr/sbin/ifconfig 
net-tools-2.0-0.51.20160912git.el8.x86_64

2，ip命令属于iproute这个包，是linux重点推荐的命令

大家过去用ifconfig成习惯的，还是要转到ip这个命令上来

[root@centos8 liuhongdi]# whereis ip
ip: /usr/sbin/ip /usr/share/man/man7/ip.7.gz /usr/share/man/man8/ip.8.gz

[root@centos8 liuhongdi]# rpm -qf /usr/sbin/ip
iproute-4.18.0-15.el8.x86_64

如果找不到ip命令，可以用dnf安装

[root@centos8 liuhongdi]# dnf install iproute

3，ip命令的操作并未写入到磁盘中，当服务器重启时，这些配置会丢失，

     所以大家如果是需要永久性保存的配置，建议使用nmcli做配置

     请移动这一篇:

https://www.cnblogs.com/architectforest/p/12612562.html

说明：刘宏缔的架构森林是一个专注架构的博客，地址：https://www.cnblogs.com/architectforest

         对应的源码可以访问这里获取： https://github.com/liuhongdi/

 说明：作者:刘宏缔 邮箱: 371125307@qq.com

二，查看ip命令的版本和帮助:

1,查看版本

[root@centos8 liuhongdi]# ip -V
ip utility, iproute2-ss180813

2,查看帮助:

[root@centos8 liuhongdi]# ip -help 

3,查看手册

[root@centos8 liuhongdi]# man ip

三，ip命令之link(网络设备)管理

link指network device,网络设备

1,列出所有的link

[root@centos8 liuhongdi]# ip link

2,只看指定的link设备

[root@centos8 liuhongdi]# ip link show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

3,查看指定link设备的收发包统计信息

# -s: 显示statistics

[root@centos8 liuhongdi]# ip -s link show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast   
    11593445   60054    0       0       0       0       
    TX: bytes  packets  errors  dropped carrier collsns 
    164314     2331     0       0       0       0 

4，只显示当前激活的网络设备

[root@centos8 liuhongdi]# ip link show up

5,停用一个网络设备

[root@centos8 liuhongdi]# ip link set ens33 down
[root@centos8 liuhongdi]# ip link show ens33
2: ens33: <BROADCAST,MULTICAST> mtu 1500 qdisc fq_codel state DOWN mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

注意 state是 DOWN

6，启用一个网络设备

[root@centos8 liuhongdi]# ip link set ens33 up
[root@centos8 liuhongdi]# ip link show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

注意 state已恢复为UP

7,查看针对link可以做的操作:

[root@centos8 liuhongdi]# ip link set help

可以做的操作很多

比较常用的应该是修改mtu

8,关闭打开link的多播(multicast)功能:

[root@centos8 liuhongdi]# ip link set ens33 multicast off
[root@centos8 liuhongdi]# ip link show ens33
2: ens33: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

可以看到MULTICAST已经被关闭了

[root@centos8 liuhongdi]# ip link set ens33 multicast on
[root@centos8 liuhongdi]# ip link show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

可以看到MULTICAST已经被再次打开

9，配置link的mtu的大小

[root@centos8 liuhongdi]# ip link set ens33 mtu 1000
[root@centos8 liuhongdi]# ip link show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1000 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

可以看到mtu已经被改成了1000

[root@centos8 liuhongdi]# ip link set ens33 mtu 1500
[root@centos8 liuhongdi]# ip link show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

可以看到mtu已经被改回了1500

说明：什么是mtu?

Maximum Transmission Unit 最大传输单元，就是数据包封包的最大值，

超过这个值就需要拆分成多个包发送

mtu过大或过小有什么影响？

1、本地MTU值大于网络MTU值时，本地传输的数据包过大导致网络会拆包后传输，不但产生额外的数据包，而且消耗了“拆包、组包”的时间。

2、本地MTU值小于网络MTU值时，本地传输的数据包可以直接传输，但是未能完全利用网络给予的数据包传输尺寸的上限值，传输能力不能完全发挥

可见过大或过小会带来网络的不稳定(丢包)或网速过慢

 建议：就使用默认值1500就很安全，当网络有不正常现象时，

我们可以查看mtu是否被人为修改过以致产生网络异常

10,修改link的名字

说明：网卡运行时不能改名：

[root@centos8 liuhongdi]# ip link set ens33 name ens33link
RTNETLINK answers: Device or resource busy

先停用

[root@centos8 liuhongdi]# ip link set ens33 down
[root@centos8 liuhongdi]# ip link set ens33 name ens33link

改名完成后再激活

[root@centos8 liuhongdi]# ip link set ens33link up
[root@centos8 liuhongdi]# ip link show ens33link
2: ens33link: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

11,修改link的mac地址:

[root@centos8 liuhongdi]# ip link show ens33link
2: ens33link: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

可以看到 mac地址是:00:0c:29:bb:c5:a6

[root@centos8 liuhongdi]# ip link set ens33link down
[root@centos8 liuhongdi]# ip link set ens33link address 00:0c:29:bb:c5:a7

[root@centos8 liuhongdi]# ip link set ens33link up
[root@centos8 liuhongdi]# ip link show ens33link 
2: ens33link: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a7 brd ff:ff:ff:ff:ff:ff

说明：可以看到网卡地址已被修改成了00:0c:29:bb:c5:a7

四，ip命令之address(ip地址)管理

1，查看所有的ip地址:

# a,address,addr: 都是ip地址

[liuhongdi@centos8 ~]$ ip a

2,查看指定设备的ip

[root@centos8 liuhongdi]# ip a show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.14/24 brd 192.168.3.255 scope global dynamic noprefixroute ens33
       valid_lft 83751sec preferred_lft 83751sec
    inet 192.168.3.13/24 brd 192.168.3.255 scope global secondary noprefixroute ens33
       valid_lft forever preferred_lft forever
    inet6 fe80::2785:9624:cea4:c935/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

3，分别查看设备的ipv4地址和ipv6地址

#-4 :显示ipv4地址

[root@centos8 liuhongdi]# ip -4 a show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    inet 192.168.3.35/24 brd 192.168.3.255 scope global dynamic noprefixroute ens33
       valid_lft 85737sec preferred_lft 85737sec
    inet 192.168.3.13/24 brd 192.168.3.255 scope global secondary noprefixroute ens33
       valid_lft forever preferred_lft forever

#-6 :显示ipv6地址

[root@centos8 liuhongdi]# ip -6 a show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 fe80::2785:9624:cea4:c935/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

4,添加ip

[root@centos8 liuhongdi]# ip a add 192.168.5.15/24 dev ens33link 
[root@centos8 liuhongdi]# ip a show ens33link 
2: ens33link: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:bb:c5:a7 brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.37/24 brd 192.168.3.255 scope global dynamic noprefixroute ens33link
       valid_lft 85844sec preferred_lft 85844sec
    inet 192.168.5.15/24 scope global ens33link
       valid_lft forever preferred_lft forever
    inet 192.168.3.13/24 brd 192.168.3.255 scope global secondary noprefixroute ens33link
       valid_lft forever preferred_lft forever
    inet6 fe80::20c:29ff:febb:c5a7/64 scope link 
       valid_lft forever preferred_lft forever

可以看到ip已添加成功

5,删除ip

[root@centos8 liuhongdi]# ip a show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff
    inet 192.168.5.8/24 brd 192.168.5.255 scope global noprefixroute ens33
       valid_lft forever preferred_lft forever
    inet 192.168.3.35/24 brd 192.168.3.255 scope global dynamic noprefixroute ens33
       valid_lft 86144sec preferred_lft 86144sec
    inet 192.168.3.13/24 brd 192.168.3.255 scope global secondary noprefixroute ens33
       valid_lft forever preferred_lft forever
    inet6 fe80::2785:9624:cea4:c935/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

192.168.5.8/24是我们要删除的ip

[root@centos8 liuhongdi]# ip a del 192.168.5.8/24 dev ens33 
[root@centos8 liuhongdi]# ip a show ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.35/24 brd 192.168.3.255 scope global dynamic noprefixroute ens33
       valid_lft 86019sec preferred_lft 86019sec
    inet 192.168.3.13/24 brd 192.168.3.255 scope global secondary noprefixroute ens33
       valid_lft forever preferred_lft forever
    inet6 fe80::2785:9624:cea4:c935/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

删除成功了

6,清除ip:指定ip

#flush: 清除ip

[root@centos8 liuhongdi]# ip a add 192.168.5.15/24 dev ens33
[root@centos8 liuhongdi]# ip a ls dev ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.35/24 brd 192.168.3.255 scope global dynamic noprefixroute ens33
       valid_lft 80454sec preferred_lft 80454sec
    inet 192.168.5.15/24 scope global ens33
       valid_lft forever preferred_lft forever
    inet 192.168.3.13/24 brd 192.168.3.255 scope global secondary noprefixroute ens33
       valid_lft forever preferred_lft forever
    inet6 fe80::2785:9624:cea4:c935/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

[root@centos8 liuhongdi]# ip a flush to 192.168.5.15/24
[root@centos8 liuhongdi]# ip a ls dev ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.35/24 brd 192.168.3.255 scope global dynamic noprefixroute ens33
       valid_lft 80398sec preferred_lft 80398sec
    inet 192.168.3.13/24 brd 192.168.3.255 scope global secondary noprefixroute ens33
       valid_lft forever preferred_lft forever
    inet6 fe80::2785:9624:cea4:c935/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

7,清除ip: 指定设备:

[root@centos8 liuhongdi]# ip a flush dev ens33
[root@centos8 liuhongdi]# ip a ls dev ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff

可见ens33这个设备上已经没有ip了

五, ip命令使用例子之route管理

1，查看路由表

#ip r 等于 ip route,查看路由

[root@centos8 liuhongdi]# ip r
default via 192.168.3.1 dev ens33 proto static metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.13 metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.14 metric 100 
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown 

2,添加默认路由

[root@centos8 liuhongdi]# ip route add default via 192.168.5.2 dev ens33
[root@centos8 liuhongdi]# ip r
default via 192.168.5.2 dev ens33 
default via 192.168.3.1 dev ens33 proto static metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.13 metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.35 metric 100 
192.168.5.0/24 dev ens33 proto kernel scope link src 192.168.5.8 metric 100 
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown 

3，删除默认路由

[root@centos8 liuhongdi]# ip route del default via 192.168.5.2 dev ens33
[root@centos8 liuhongdi]# ip r
default via 192.168.3.1 dev ens33 proto static metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.13 metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.35 metric 100 
192.168.5.0/24 dev ens33 proto kernel scope link src 192.168.5.8 metric 100 
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown 

4,修改默认路由

[root@centos8 liuhongdi]# ip route add default via 192.168.5.2 dev ens33
[root@centos8 liuhongdi]# ip r
default via 192.168.5.2 dev ens33 
default via 192.168.3.1 dev ens33 proto static metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.13 metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.35 metric 100 
192.168.5.0/24 dev ens33 proto kernel scope link src 192.168.5.8 metric 100 
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown 
[root@centos8 liuhongdi]# ip route replace default via 192.168.5.4 dev ens33
[root@centos8 liuhongdi]# ip r
default via 192.168.5.4 dev ens33 
default via 192.168.3.1 dev ens33 proto static metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.13 metric 100 
192.168.3.0/24 dev ens33 proto kernel scope link src 192.168.3.35 metric 100 
192.168.5.0/24 dev ens33 proto kernel scope link src 192.168.5.8 metric 100 
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown 

5，设置到网络49.7.40/24的路由经过网关192.168.5.8

[root@centos8 liuhongdi]# ip route add 49.7.40/24 via 192.168.5.8
[root@centos8 liuhongdi]# ip r
default via 192.168.3.1 dev ens33 proto static metric 100 
49.7.40.0/24 via 192.168.5.8 dev ens33

6,从路由表中删除一条记录:

[root@centos8 liuhongdi]# ip route del 49.7.40.0/24 via 192.168.5.8 dev ens33

六,ip命令使用例子之统计信息

# -s :统计信息

[root@centos8 liuhongdi]# ip -s link ls ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast   
    3635277    17405    0       0       0       0       
    TX: bytes  packets  errors  dropped carrier collsns 
    24862      301      0       0       0       0   

# -s -s :统计信息,增加了 tx rx的错误信息    

[root@centos8 liuhongdi]# ip -s -s link ls ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 00:0c:29:bb:c5:a6 brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast   
    3638862    17421    0       0       0       0       
    RX errors: length   crc     frame   fifo    missed
               0        0       0       0       0       
    TX: bytes  packets  errors  dropped carrier collsns 
    24862      301      0       0       0       0       
    TX errors: aborted  fifo   window heartbeat transns
               0        0       0       0       2 

七, ip命令使用例子之arp

1,查看mac地址的arp表

[root@centos8 liuhongdi]# ip neigh 
192.168.3.1 dev ens33 lladdr fc:94:35:07:73:77 STALE
192.168.5.4 dev ens33  FAILED

2，添加一个mac和ip的对应项

[root@centos8 liuhongdi]# ip neigh add 192.168.1.100 lladdr 00:0c:29:c0:5a:ef dev ens33
[root@centos8 liuhongdi]# ip neigh 
192.168.3.1 dev ens33 lladdr fc:94:35:07:73:77 STALE
192.168.1.100 dev ens33 lladdr 00:0c:29:c0:5a:ef PERMANENT
192.168.5.4 dev ens33  FAILED

添加已成功

3,删除一个mac和ip的对应项

[root@centos8 liuhongdi]# ip neigh del 192.168.1.100 lladdr 00:0c:29:c0:5a:ef dev ens33
[root@centos8 liuhongdi]# ip neigh 
192.168.3.1 dev ens33 lladdr fc:94:35:07:73:77 STALE
192.168.5.4 dev ens33  FAILED

删除成功

 八，查看centos版本

[root@centos8 conf]# cat /etc/redhat-release 
CentOS Linux release 8.1.1911 (Core)