[U-Boot] Regarding linux kernel booting.

Hi all, I am in bit of peculiar problem on booting linux kernel on my MPC7448-TSi108 based custom board. I am using u-boot 1.3.4 which was compiled on ELDK- 4.0. when i use bootp command to download the kernel image from the tftp server that was already working with other custom boards the kernel is not getting downloaded but if i am setting it to another environment variable i.e "> set ideboot bootp" and try to boot using "> run ideboot" this time the kernel image file is getting downloaded. kindly give me suggestion on this. i don't have any clue on what is happening ? The host system what ever i used for compilation is also same. Regards, T.