The Use Address for Server NAT check box is available in the Standard Options section of the Virtual Service modify screen. To access this screen, in the LoadMaster Web User Interface (WUI), go to Virtual Services > View/Modify Services and click Modify on the relevant Virtual Service.
By default, when the LoadMaster is being used to SNAT (Server Network Address Translate) Real Servers, the source IP address that is used on the internet is that of the LoadMaster. The Use Address for Server NAT option allows the Real Servers configured on the Virtual Service to use the Virtual Service as the source IP address instead.
This option is most useful for services such as SMTP when the LoadMaster is in a public domain and when the service requires a reverse DNS check to see if the source address sent from the LoadMaster is the same as the Mail Exchanger (MX) record of the sender.
If the Real Servers are configured on more than one Virtual Service which has this option set, only connections to destination port 443 will use this Virtual Service as the source IP address. The LoadMaster will try to match the port to the virtual service IP where possible.