trying to read flash content with dump_image command

Hi

I know that flash on my IXP425 board is located at 0x50000000 address

but found that

dump_image f1.bin 0x0 0x1000000

and

dump_image f2.bin 0x50000000 0x1000000

gives the same content of file

I started to play with mdb and found that it is not sensitive to high

area of address value - see same

mdb 0x0 10

0x00000000: 44 f0 9f e5 a5 78 00 eb 2b 76

mdb 0x50400000 10

0x50400000: 44 f0 9f e5 a5 78 00 eb 2b 76

mdb 0x50800000 10

0x50800000: 44 f0 9f e5 a5 78 00 eb 2b 76

So looks lilke any attempt to read high area of memory

maps me to 0x0 area

Any idea or explanation?