ASA ping and trace configuration

ASA ping and trace configuration The 
 
external network cannot ping and tracer the internal network. The internal network can ping and trace the external network: 
1. Write acl to allow trace traffic returned from the external port: 
    access-list ping extended permit icmp any any time-exceeded  
    access -list ping extended permit icmp any any unreachable  
    access-group ping in interface outside  

2. Release ping globally:  
    policy-map global_policy  
    class inspection_default    
    inspect icmp   

3: Set decrement-ttl so that ping does not display "*"
    policy-map global_policy  
    class class-default 
    set connection decrement-ttl 
   
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icmp deny any outside outside interface prohibits ping