Information about virtual IP

[jmedinag]

Hi,

we are configuring a High Availability environment and we need to configure virtual IPs/hostnames. However, our knowledge about this issue is very limited and we need to start from the basic concepts. Is there any document or article describing the basic concepts and how to configure virtual IPs/hostnames?

Thanks in advance.

Jesus.

[jack challen_1]

A virtual IP address is nothing more than an additional IP address configured on an already-running interface. E.g. your interface lan0 might have the IP address 192.168.1.123 already, and you need it to respond to 192.168.1.100 as well.

You can configure an additional "virtual" interface "lan0:1" as 192.168.1.100, and it would work too. The name "virtual" is a bit of misnomer -- they're not virtual really, merely additional.

If they're used in HA applications, you will often find that this IP address is relocatable between machines -- either machine can use it, and the secondary node will take over if the primary fails. Serviceguard calls these IP addresses package IP address or relocatable IP addresses. They're also known as floating IP addresses.

Example:

node1 lan0: 192.168.1.123

node2 lan0: 192.168.1.124

package IP: 192.168.1.100

The package IP would be the IP address for the service, such as a webserver or database. It would run on either node1 or node2 (but not both), so if node1 is running the package, you'll find lan0:1 has the IP address 192.168.1.100 -- this would be taken down on node1 and started on node2 in the event of node1 failing.

You can configure quite a few of these additional IP addresses on any given interface (not sure what the limit is) so you might find a machine with lan0, lan0:1, lan0:2, lan0:3 and so on.

Does that make sense?