In nPath configuration, BIG-IP does not send ICMP reply to the L3 switch.

Hi KaiTT , 

> you should change your configuration little bit , use one of two scenarios :

1.  Change the default gateway for "20.20.20.1" instead of using Bigip self-ip as a gateway , and configure
   ( SNAT automap or SNAT pool ). 
   by this scenario , ICMP traffic should go through L3 swith without forward it to Big-ip
   All of this with respect to your routes.
2. Configure a fast layer 4 virtual server on your Big-ip and do not assign tcp profile to it , allow all protocols. 
   After creating it , go to virtual address and configure "echo-reply = disabled " not "always" 
   like below : 
   

in this scenario , ICMP traffic should go through Bigip to server 20.20.20.10 and return back to F5 big-ip " its gateway" 

> you only need to adjust your traffic flow , I recommend to do the first scenatio , using SNAT is very useful , so try it. 

Regards.