I followed this guide from that step is enough 5 DDNS Client Software - Linux DDclient (step 5 in content) I edited ddclient.conf this way
Code:
use=vigor-2200usb, fw=192.168.1.1:80
fw-login=user,  fw-password=yourrouter_pass

login= my_username_for_freedns.afraid.org                       # default login
password=my_pass_for_freedns.afraid.org
protocol=freedns                                
#proxy=fasthttp.sympatico.ca:80                 # default proxy
server=freedns.afraid.org                       # 
#server=members.dyndns.org:8245                 # default server (bypassing proxies)
robertobalu.com.crabdance.com            # domains must go after those login, use staff
robertobalu.com.chickenkiller.com
#mx=r.balejik@robertobalu.com.chickenkiller.com
you've to put it in that order otherwise you'll get message like invalid login ......