To update IP record on dyndns.com i use ddclient package
how to install:
sudo apt-get install ssh libio-socket-ssl-perl ddclient
myconfig (example)
cat /etc/ddclient.conf
# Configuration file for ddclient generated by debconf
#
# /etc/ddclient.conf
daemon=3600
use=web, web=checkip.dyndns.com, web-skip='IP Address'
server=members.dyndns.org
login=MYDDNSLOGIN
password='MYDDNSPASS'
MYHOST.dyndns-server.com