Hi dpreviti,
I don’t seem to have this issue in my network environment, I have my ESPRESSObin connected to the Ethernet through its wan port and power it up. Then under the buildroot prompt if do ifconfig eth0 up then dhclient wan, in about 8 seconds the dhclient wan returns with valid IP address acquired from the DHCP server. See my log below:
Starting NFS services: done
Starting NFS daemon: done
Starting NFS mountd: done
Starting vsftpd: OK
Starting HPA’s tftpd:
Welcome to Buildroot
buildroot login: root
# ifconfig eth0 up
# [ 16.087887] mvneta d0030000.ethernet eth0: Link is Up – 1Gbps/Full – flow control off
# dhclient wan
[ 29.060437] dsa dsa@0 wan: Link is Down
[ 32.077210] dsa dsa@0 wan: Link is Up – 1Gbps/Full – flow control rx/tx
# ifconfig
eth0 Link encap:Ethernet HWaddr F0:AD:4E:03:69:30
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:43 errors:0 dropped:0 overruns:0 frame:0
TX packets:2 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:532
RX bytes:7164 (6.9 KiB) TX bytes:700 (700.0 B)
Interrupt:9
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:2 errors:0 dropped:0 overruns:0 frame:0
TX packets:2 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1
RX bytes:140 (140.0 B) TX bytes:140 (140.0 B)
wan Link encap:Ethernet HWaddr F0:AD:4E:03:69:30
inet addr:10.82.40.149 Bcast:10.82.43.255 Mask:255.255.252.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:43 errors:0 dropped:0 overruns:0 frame:0
TX packets:2 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:6218 (6.0 KiB) TX bytes:684 (684.0 B)
#
If you may post your full log here, we maybe find some clues.