Failed to restart TFTP issue

[richard_chen]

NiKiZe, thanks for your reply,
1.we use the server2012 for DHCP&iPXE, so we haven't found the logs for TFTP service
2.I checked wireshark packets of onboard LAN and USB LAN, no exception information was found.
3.we checked the packets of wireshark for normal boot iPXE NB, we found after NB show "Contacting server 100.110.3.4 .", it will start to get boot\undionly.kpxe by TFTP, there have only two types packets(DHCP request,ACK), and only need about 1 second it will start to get undiony.kpxe. But for fail boot iPXE NB, it always show dot with "Contacting server 100.110.3.4", and after about one minutes, it will show TFTP error, i checked the packets of wireshark during show "Contacting server 100.110.3.4.....................", there only have DHCP request and ACK, no any others packets, also have no packets for starting TFTP boot\undionly.kpxe. I am very puzzled that why it can get boot\x86\wdsnbp.com by TFTP at first, and it show TFTP error after "Contacting server 100.110.3.4...............", what is it doing during "Contacting server 100.110.3.4........"