I had to edit my ifup file to get dhcp to work with my cable modem.
My ISP is @home I added the
"-h myhostname"
below for PUMPARGS= ,
put in the cc-xxx name that they use to identify you.
if [ -n "${DYNCONFIG}" ]; then
PUMPARGS="-h myhostname"
DHCPCDARGS=
if [ -n "${DHCP_HOSTNAME}" ]; then
PUMPARGS="-h ${DHCP_HOSTNAME}"
DHCPCDARGS="-h ${DHCP_HOSTNAME}"
fi
if [ -n "${NEEDHOSTNAME}" ]; then
PUMPARGS="${PUMPARGS} --lookup-hostname"
DHCPCDARGS="${DHCPCDARGS} -H"
fi
if [ "${PEERDNS}" = "no" ]; then
PUMPARGS="${PUMPARGS} -d"
DHCPCDARGS="${DHCPCDARGS} -R"
fi