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' asrivas.me www.asrivas.me mailserver.asrivas.me