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kridsana's avatar
kridsana
Icon for Cirrocumulus rankCirrocumulus
Dec 26, 2012

How to clear Don't Fragment (DF) bit

there is some virtual server that have a problem that     packet segment lost when MTU = 1500     so i want to clear DF bit to fix this problem , and how to clear it?     than...
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nitass's avatar
nitass
Icon for Employee rankEmployee
Jan 19, 2013
after F5 reassemble TCP , it send packet 1500 to client but checkpoint drop it and return ICMP fragmentation needed to F5 with MTU next hop 1476.don't you see bigip resend packet with lower length?

e.g.

in mt-0110-1000.pcap, packet 133 has 1460 tcp length. packet 136 and 137 have 1396 and 64 tcp length respectively. 1460 is 1396 + 64. 117.176.110.113 mac address belongs to f5. 

No.     Time                       Delta Time  Source                Src port Destination           Protocol Dst port Window     BiF        Vlan id Length Info
    133 2012-10-01 10:38:48.570136 0.000000    10.153.1.13           80       117.176.110.113       TCP      4394     6848       1460       109     1518   [TCP segment of a reassembled PDU]
    135 2012-10-01 10:38:48.570136 0.000000    10.151.25.1           80       10.153.1.13           ICMP     4394                           109     74     Destination unreachable (Fragmentation needed)
    136 2012-10-01 10:38:48.570136 0.000000    10.153.1.13           80       117.176.110.113       TCP      4394     6848       1621       109     1454   [TCP Out-Of-Order] 80 > 4394 [ACK] Seq=3441923333 Ack=2282044611 Win=6848 Len=1396
    137 2012-10-01 10:38:48.570136 0.000000    10.153.1.13           80       117.176.110.113       TCP      4394     6848       1621       109     122    [TCP Out-Of-Order] [TCP segment of a reassembled PDU]