help!!! cisco 1841 with dyndns behind NAT

[chuang123]

hi all,

my ISP provide me a NAT modem, it's not replaceble! so I can only connect to the LAN of the Vodafone modem. therefore, my cisco 1841's WAN interface got a private IP.

topology:

actual LAN switch---->cisco 1841(NAT)<-->Vodafone modem(NAT)<--->internet

modem LAN: 172.16.1.0

1841 WAN IP: 172.16.1.2

1841 LAN IP: 10.2.1.0/24 (this is actual LAN )

I search solution on the web but no luck. everyone only show a method which router must use public IP on WAN

or it is a limitation on cisco device? I had a ZyXEL router before, which can easily accomplish this task.

can anyone help?

partial config-------------------------------

ip ddns update method DYNDNS

HTTP

  add http://username:pw@members.dyndns.org/nic/updatesystem=dyndns&hostname=pw@members.dyndns.org/nic/updatesystem=dyndns&hostname=<h>&myip=<a>

interval maximum 0 0 3 0

interface FastEthernet0/0

ip ddns update hostname chuang123.dyndns.org

ip ddns update DYNDNS

ip address dhcp

------------------------------------------------

fa0/0 is my WAN, it's behind NAT got private IP of 172.16.1.2

[paolo bevilacqua]

Just remove the 'myip' parameter from the query, and dyndns will use the public address the request comes from.

Note however, that since ISP use central PAT, there is no guarantee that you will be able to reach the router from outside their network, using a public address.