You could use tar to back up files. There is an option to create a snapshot file. Then you can create incremental backups in the future.
During a `--create' operation, specifies that the archive that
`tar' creates is a new GNU-format incremental backup, using
SNAPSHOT-FILE to determine which files to backup. With other
operations, informs `tar' that the archive is in incremental
format. *Note Incremental Dumps::.
My favorite backup program is "kdar". It is used to create backups in slices that you can burn to CD or DVD.
Im not sure what your question about obtaining IP address means. Maybe you are referring to using DHCP to obtain an ip address automatically for you interface. If you want to find out the IP address of a domain on the web, you could use the "host" or "dig" commands.