ip alias and secondary ip address

孤陋寡闻了，以前一直以为ip别名（ip aliase）和辅助ip地址（secondary ip address）是一码事情。或者说是不知道还有secondary ip address一说。

今天偶然翻阅时，提到了这样一句话：

As of this writing, the Linux kernel supports both IP aliases and secondary IP addresses, though IP aliases are deprecated in favor of secondary IP addresses.

那也就意味着secondary ip address和ip aliase是不同的概念，首先问Google，Google没有给我好的答案。只好自己摸索了，于是目前只能得到下面的一些概念：

ip alias和secondary ip address是两种不同的实现方式，用来在Linux系统中给同一个物理网卡增加多个ip地址。

ip alias是由ifconfig程序来创建和维护的，而secondary ip address则是有ip程序来创建和维护的。ip addr add 创建的scondary ip address不能在ifconfig -a中看到，反过来，ifconfig创建的ethX:Y却能在ip addr show中看到。

ip alias大家比较熟悉，因此说说secondary ip address如何创建


[root@mlsx autostart]# ifconfig
eth1 Link encap:Ethernet HWaddr 00:13:77:00:7C:C6
inet addr:192.168.0.100 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:163438 errors:2515 dropped:0 overruns:0 frame:2515
TX packets:165217 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:96792997 (92.3 MiB) TX bytes:16356841 (15.5 MiB)

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:561 errors:0 dropped:0 overruns:0 frame:0
TX packets:561 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:119798 (116.9 KiB) TX bytes:119798 (116.9 KiB)

eth0被我用ifconfig eth0 down了。

[root@mlsx autostart]# ip addr sh
2: lo: mtu 16436 qdisc noqueue
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
4: eth0: mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:12:f0:1d:e8:c5 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.101/24 brd 192.168.1.255 scope global eth0
6: eth1: mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:13:77:00:7c:c6 brd ff:ff:ff:ff:ff:ff
inet 192.168.0.100/24 brd 192.168.0.255 scope global eth1

down下去的eth0在这里还是能体现出来的。

[root@mlsx autostart]# ip addr add 192.168.0.102/24 dev eth1
[root@mlsx autostart]# ip addr sh eth1
6: eth1: mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:13:77:00:7c:c6 brd ff:ff:ff:ff:ff:ff
inet 192.168.0.100/24 brd 192.168.0.255 scope global eth1
inet 192.168.0.102/24 scope global secondary eth1
[root@mlsx autostart]# ping 192.168.0.102
PING 192.168.0.102 (192.168.0.102) 56(84) bytes of data.
64 bytes from 192.168.0.102: icmp_seq=1 ttl=64 time=0.049 ms
64 bytes from 192.168.0.102: icmp_seq=2 ttl=64 time=0.043 ms

通过ip程序增加了一个secondar ip address，通过ip addr show也能看到，而且能ping通，但是ifconfig中却看不到。

[root@mlsx autostart]# ifconfig -a
eth1 Link encap:Ethernet HWaddr 00:13:77:00:7C:C6
inet addr:192.168.0.100 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:163888 errors:2515 dropped:0 overruns:0 frame:2515
TX packets:165696 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:96837439 (92.3 MiB) TX bytes:16426734 (15.6 MiB)

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:565 errors:0 dropped:0 overruns:0 frame:0
TX packets:565 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:120134 (117.3 KiB) TX bytes:120134 (117.3 KiB)

但是ip alias和secondary ip address在实际的使用过程中，会有什么差别呢？
大部分HA软件，包括开源的heartbeat都采用了ip alias的方式，为什么他们不采用secondary ip address方式呢？
或者说ip alias和secondary ip address比较起来，谁更优秀呢？

有人能告诉我吗？