How to clear Don't Fragment (DF) bit

Now , I'm testing ICMP packet behavior from My computer to F5.

 

 

when I ping <1472 bytes to F5 ..I see ICMP request and ICMP reply is DF bit clear

 

 

when I ping >1472 bytes to F5 .. I see ICMP request and ICMP reply is DF bit clear too (more fragmented is set instead)

 

 

DF bit will set only when F5 send ping request to my computer.

 

 

but this issue .... F5 set DF bit in ICMP reply!! (so router drop it when ICMP reply payload is more than 1472 bytes , cause it's can't fragmented , and router send ICMP type 3 code 4 to tell F5 for Fragmented need) .... Is it strange or normal for DF bit is set in ICMP reply? Should I post tcpdump here or is it should to be secret for customer?

 

 

please correct me , thank you