我配置虚拟IP地址的目的是为了实现高可用性，那是后话，先看看Ubuntu 12.04下如何设置虚拟IP地址。
首先看一下我的Ubuntu的IP：
chenshu@sloop2:~$ ifconfig eth0 Link encap:Ethernet HWaddr d0:67:e5:ef:5a:6e inet addr:10.112.18.158 Bcast:10.112.18.255 Mask:255.255.255.0 inet6 addr: fe80::d267:e5ff:feef:5a6e/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:341661 errors:0 dropped:0 overruns:0 frame:0 TX packets:242801 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:328287656 (328.2 MB) TX bytes:31858367 (31.8 MB) Interrupt:17 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:17904 errors:0 dropped:0 overruns:0 frame:0 TX packets:17904 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:2160236 (2.1 MB) TX bytes:2160236 (2.1 MB)
ping一下191,发现网络中没有，就用它做虚拟IP吧。sudo -s之后，执行下面的命令，
ifconfig eth0:0 10.112.18.191 netmask 255.255.255.0 up
确保虚拟IP地址和本机IP地址在一个网段。再来看一下是否成功：
ifconfig eth0 Link encap:Ethernet HWaddr d0:67:e5:ef:5a:6e inet addr:10.112.18.158 Bcast:10.112.18.255 Mask:255.255.255.0 inet6 addr: fe80::d267:e5ff:feef:5a6e/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:347634 errors:0 dropped:0 overruns:0 frame:0 TX packets:246488 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:335797145 (335.7 MB) TX bytes:32178089 (32.1 MB) Interrupt:17 eth0:0 Link encap:Ethernet HWaddr d0:67:e5:ef:5a:6e inet addr:10.112.18.191 Bcast:10.112.18.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Interrupt:17 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:17953 errors:0 dropped:0 overruns:0 frame:0 TX packets:17953 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:2164072 (2.1 MB) TX bytes:2164072 (2.1 MB)
本机测试：