This option can be used to have virtual servers created for this reseller use an IPv6 address other than the system's default, which is typically shared by all name-based virtual websites. This can be useful for 'branding' servers created by different resellers, by have each reseller's IPv4 address resolve to a different hostname.

The IP you enter must already be active on the system, which can be done in Webmin's Network Configuration module. The IP will not be used for virtual servers with their own private IPs, as each always gets a distinct address.