How to clear Don't Fragment (DF) bit

when pmtu is disabled, bigip does not know what smallest mtu size is. so, bigip won't fragment packet when sending out and will receive icmp unreachable/fragmentation needed packet. this will increase number of packets sending back and forth in the network.

 

when ptumd is disabled, bigip will clear DF bit so when sending out packet to router.

 

does router handle fragmentation packet on their own and don't send ICMP fragmentation needed return to F5?

 

from tcpdump, I see F5 receive ICMP fragmentation needed packet but I didn't sure F5 resend smaller MTU.

 

thank you.