2.4.4 Inheriting a LAN
HA Monitor inherits alias IP addresses.
An alias IP address is an alias assigned to an existing IP address. Alias IP addresses enable you to assign multiple IP addresses to a single interface. HA Monitor switches LANs by inheriting these alias IP addresses from the active system to the standby system during the hot standby operation.
- Stationary IP addresses and alias IP addresses
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A unique IP address must be assigned to each host for each LAN interface. This IP address is called a stationary IP address. Stationary IP addresses are not inherited by the remote system during the hot standby operation. Therefore, stationary IP addresses are used for servers that do not inherit IP addresses, communication for programs that are not subject to hot standby, and monitoring paths.
In addition to the stationary IP address, you can assign one or more additional IP addresses to a server. Such an IP address is called an alias IP address. HA Monitor inherits alias IP addresses. Therefore, alias IP addresses are used for servers that inherit IP addresses and communication for programs that are subject to the hot standby operation. If alias IP addresses are used, the client can use the same IP addresses for communication even after the hot standby operation has occurred. Note that for a TCP-base application, recovery processing such as reconnection is required because connection is released.
You can assign alias IP addresses only to an interface for which a stationary IP address has already been specified.
- Inheriting alias IP addresses
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An alias IP address assigned to a server is added to the LAN interface when the active server starts and is deleted from the LAN interface when the active server terminates. During the hot standby operation, an alias IP address is inherited by deleting the alias IP address from the active system and adding it to the standby system.
HA Monitor does not inherit MAC addresses. However, when inheriting alias IP addresses, HA Monitor executes a command for broadcasting an ARP request and reports a new mapping of IP addresses and MAC addresses.
The following figure shows an example of inheriting alias IP addresses.
Figure 2‒27: Example of inheriting alias IP addresses ![[Figure]](GRAPHICS/F0000042.GIF)
In this example, the IP addresses (a.b.c.d and e.f.g.h) assigned to the LAN adapter eth1 are stationary IP addresses. The IP addresses (s.t.u.v and w.x.y.z) assigned to the server are alias IP addresses. If hot standby switching occurs from host 1 to host 2, the alias IP addresses are inherited to host 2.