"connection not visible or not available" after switch DSL to LAN

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http://askubuntu.com – I had a company computer(ubuntu 12.04LTS) taken home. My home use DSL and my company use LAN to connect to internet. The computer works well in my company, but I have to config it after taken home. I used pppoeconf to config the DSL successfully at home. and use pon dsl-provider to connect to internet. But after I take the computer back to company, I had to change back to LAN. After Google it, I modified the file /etc/network/interfaces auto lo iface lo inet loopback auto dsl-provider iface dsl-provider inet ppp pre-up /sbin/ifconfig eth0 up # line maintained by pppoeconf provider dsl-provid (HowTos)