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

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! -