Boot from network

I’m triyng to installa OpenWRT on this routerboard but get stuck at first step:

RouterBOOT booter 3.34

RouterBoard 953GS-5HnT

CPU frequency: 720 MHz
 Memory speed: 300 MHz
  Memory size: 128 MiB
    NAND size: 128 MiB

Press any key within 2 seconds to enter setup..
writing settings to flash... OK
Please, check ethernet cable...
Ethernet link absent...
trying dhcp protocol................................................................................................................................................................................................................................................................................................................................................................................................................... failed
kernel loading failed

My DHCP server is a RB951 the TFTP servert is up, but the dhcp protocol always fail, tried also to change from eth1 to eth2 , still the same.
If I boot the RouterOS, it gets the dhcp address.
What am I missing?
Thank, BR