Intel Ethernet Controller Issue with PowerPC board

I have developed a PowerPC MPC7410 based processor board with Tsi107 as the Host bridge and intel 82551 the ethernet controller. We have ported u-boot-1.3.1 into it as its boot loader.

The issue is as follows:

When the board is powered on, i can ping to the host system through the ethernet port. I can do the tftp, i can do an nfs boot. But if I remain in uboot prompt for 90 minutes, then try to do a ping to the host machine, it says "Cannot reset the ethernet controller". The timing of this issue is about 90 minutes everytime. Is it something to do with the config of ethernet controller? Please advice.

regards,

Sandeep