you are in root's home directory not /
you can by the tilde ~
normally this is /root
so a cd sbin will not get you to /sbin but rather to /root/sbin if it exists. otherwise will result in an error.
cd /sbin will get you to where you want to go.
then typing ./ifconfig rather than ifconfig will execute the ifconfig file in /sbin
you could also just type /sbin/ifconfig
that would also execute ifconfig in /sbin
if that works root's $PATH is incorrect
to check type