linux删除主ip,从ip自动被删除

1.eth0的30.1.1.0/24网段存在两个ip

一个主ip：30.1.1.1/24 从ip：30.1.1.2/24

[root@sangfor ~]# ip addr show eth0

371: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 500

link/ether 28:51:32:03:4a:ce brd ff:ff:ff:ff:ff:ff

inet 20.1.1.1/24 brd 20.1.1.255 scope global eth0

inet 30.1.1.1/24 brd 30.1.1.255 scope global eth0

inet 30.1.1.2/24 brd 30.1.1.255 scope global secondary eth0

inet6 fe80::2a51:32ff:fe03:4ace/64 scope link

valid_lft forever preferred_lft forever

2.删除主ip 30.1.1.1/24 后接口配置如下

[root@sangfor ~]# ip addr show eth0

379: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 500

link/ether 28:51:32:03:4a:ce brd ff:ff:ff:ff:ff:ff

inet 20.1.1.1/24 brd 20.1.1.255 scope global eth0

inet6 fe80::2a51:32ff:fe03:4ace/64 scope link

valid_lft forever preferred_lft forever

好神奇，从ip怎么也没了呢？？

原来是因为有一个内核参数控制这个：

down掉所属某个子网的primary ip的时候， 所有相关的secondary ip也会down掉。

设置一个内核参数， 当primary ip宕掉时可以将secondary ip提升为primary ip。

echo "1" > /proc/sys/net/ipv4/conf/all/promote_secondaries

接下来重复操作1、2两步，从ip就不会被删掉了：

[root@sangfor ~]# ip addr show eth0

371: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 500

link/ether 28:51:32:03:4a:ce brd ff:ff:ff:ff:ff:ff

inet 20.1.1.1/24 brd 20.1.1.255 scope global eth0

inet 30.1.1.1/24 brd 30.1.1.255 scope global eth0

inet 30.1.1.2/24 brd 30.1.1.255 scope global secondary eth0

inet6 fe80::2a51:32ff:fe03:4ace/64 scope link

valid_lft forever preferred_lft forever

[root@sangfor ~]# ip addr show eth0

371: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 500

link/ether 28:51:32:03:4a:ce brd ff:ff:ff:ff:ff:ff

inet 20.1.1.1/24 brd 20.1.1.255 scope global eth0

inet 30.1.1.2/24 brd 30.1.1.255 scope global eth0

inet6 fe80::2a51:32ff:fe03:4ace/64 scope link

valid_lft forever preferred_lft forever