The default image of pureos that comes with the dev board have a default static ip configured (also with a default route). If you have a DHCP, to have access to your network, you have to, at least, remove (or change) the default route with:
ip route del default via 192.168.42.200 dev eth0
If you want to disable it permanently, you have to edit the file /etc/network/interfaces and comment out the lines after “auto eth0”. You can also change the static ip configuration to suits your needs.