Automap

Do you mean for the SNAT mode? I can't say it any better than the LTM config guide:

 

 

"The SNAT automap feature automatically selects one of the systems self IP addresses (typically a floating self IP address of the egress VLAN), and maps it to the original IP address or addresses that you specify during SNAT creation. When you use this feature, you do not need to explicitly specify a translation address.

 

 

When automatically choosing a self IP address to map to the specified original IP address, the system gives preference to floating self IP addresses over static (non-floating) self IP addresses. This prevents any interruption in service when failover occurs. Note that if no floating self IP address is currently assigned to the egress VLAN, the system uses the floating IP address of a non-egress VLAN instead."

 

 

https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/LTM_config_guide_943/ltm_addrtrans.html1203505