[U-Boot] problem about PING error from PC to u-boot

[du zhenhuan]

I'm still struggling with my mpc8315e board , customized with a DP83848 
PHY chip.
after u-boot bootup , the LED of PHY link status is blinking,
When  I use ping PC  FORM u-boot , it's OK.

But when I ping u-boot FROM PC ,  it doesn't work and I just got timeout 
error etc.

I think the physical connection is OK, what could be the possible reason 
for this?
Hope someone can help me out. Thanks!
-