ifconfig in particular is usually in /usr/sbin or /sbin and that directory's not going to be in the vanilla PATH for normal users. Most likely is that your PATH is altered by a shell startup file (say .bash_profile) which isn't being sourced by the shell that you're getting when you connect this way. You'd probably get similar results if you tried to run the command via "ssh otherhost ifconfig -a". Check the bash manual page for the exact set of startup files it sources under different circumstances.