i don't know why should i use snat and automap

Hello minkyu,

this question has been asked many times on this forum example :

https://devcentral.f5.com/questions/automap-configuration-53290

The AUTOMAP setting will replace the source IP address of the request. Precisely, it will modify "client IP addr" by the "BIG IP's Self IP addr". 

This allows backend servers (pool members) to respond directly to BIG-IP's self IP address. In this manner, both requests & responses pass through the BIG-IP. 

WITHOUT automap, if it is not explicitly configured on backend server or on routers, responses traffic will respond to the "client IP addr" which will cause asymmetric routing and client will deny traffic because request socket and response socket are not the same.

As said before, it is possible to set the "Source Address Translation" to "none", in this case you need to be sure that backend servers are configured to route responses to BIG IP's self IP addr. 

Regards

