Informix support for IPv6 addresses

On all platforms, IBM® Informix® recognizes Internet Protocol Version 6 (IPv6) addresses, which are 128 bits long, and Internet Protocol Version 4 (IPv4) addresses, which are 32 bits long.

Beginning with Informix 10.00.xC4 and Client SDK 2.90.xC4, the database server checks, on startup, whether IPv6 is supported in the underlying operating system. If IPv6 is supported it is used. If the underlying operating system does not support IPv6, the IPv4 address is used. Informix and Client SDK retrieve the IP address from the name service.

You can treat Informix that runs on a host with both IPv4 and IPv6 addresses the same way you treat a server running on a multi-homed host. You can configure Informix on a host with both IPv4 and IPv6 addresses in either of the following ways:

Create aliases (using the DBSERVERALIASES configuration parameter) and assign an IPv6 address to one of them and an IPv4 address to the other.
Instruct the Informix to listen on all the IP addresses configured on the host by using a wild-carded hostname in the sqlhosts file.
For example:
```
#dbservername   nettype    hostname   servicename   options
olserver1       onsoctcp   *myhost    onservice1
```
Starting with Informix Version 10.0, the host name entry in the SQLHOSTS file maps to an IPv6 address if the host has a configured IPv6 address. If the host does not have a configured IPv6 address, the hostname entry maps to an IPv4 address.

Disabling IPv6 Support

Informix also provides a way to disable IPv6 support when working in IPv4 environments.

To disable IPv6 support for all database instances and client applications:

Create an empty file $INFORMIXDIR/etc/IFX_DISABLE_IPV6.

The file must have read permission for user informix. The file is not read from or written to, and is not required to contain any data.

To disable IPv6 support for a single database instance or for a single client application:

On the database server instance, or on the workstation on which applications are run, create an environment variable named IFX_DISABLE_IPV6 and set its value to yes, as in:
```
IFX_DISABLE_IPV6=yes
```