I use ddclient to update my dynamic IP address which is assigned by Comcast. This is the gist for the ddclient configuration:
# Configuration file for ddclient generated by debconf
#
# /etc/ddclient.conf
daemon=5m
syslog=yes
use=if, if=eth0
ssl=yes
use=web, web=myip.dnsomatic.com
protocol=freedns
login=abcd
password='CENSORED'
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www.asrivas.me
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