device=eth0, addr=a.b.c.253, mask=255.255.255.0, gw=a.b.c.1,
host=Sheeva, domain=, nis-domain=(none),
bootserver=a.b.c.1, rootserver=a.b.c.1, rootpath=
is a clear indication of kernel autoconfig function at work. So for your Debian Lenny on SD the network configuration is at issue. you can leave it as is right now let the kernel do the autoconfig. or may be copy the network configuration from NAND. it is my understand that Ubuntu
is a derivative from Debian
So I assume they work close enough for how network configuration.
I use Gentoo
as my Linux system although I am fluent in general how Linux system should work but I do not know how Debian based system initialize in detail. I suspect the ifup/ifdown
command may be checking some conditional indication file in system, instead checking the real network interface status. that is why you got ifup/ifdown
report not configured.