Ethernet Interface Link Up too slow

Following is my system log:

Initializing random number generator… done.
Starting network…
udhcpc (v1.24.2) started
Sending discover…
Sending discover…
Sending discover…
No lease, failing
Starting dropbear sshd: OK

Welcome to Buildroot
buildroot login: [ 13.958319] macb 10090000.ethernet eth0: link up (100/Full)
root
Password:
# udhcpc
udhcpc (v1.24.2) started
Sending discover…
Sending select for 192.168.0.126…
Lease of 192.168.0.126 obtained, lease time 86400
deleting routers
adding dns 192.168.0.1

I found that the LED of the ethernet turns yellow always after it asks me to log in, which means udhcpc in boot stage will never get a ip address until I log in and run udhcpc by myself.
Do you have this problem ?