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New Member

ISDN DDR IP design and static route settings

Hi all,

I am setting up a Cisco 1603 router configured to use ISDN BRI to dial to a NT RAS server for Internet Access. The IP address plan is as follow:

(Due to security reason I will not publish the public IP address, instead, I use private range. Assume all the IP address here are public)

Our corp network is

NT RAS server is on

Gateway to upstream ISP is

DHCP scope on NT RAS server is:



range - (30 addresses)

Now we want to cut a small portion of out IP to our branch office. The range will be

The branch office router (this Cisco 1603) has the following settings:


Ethernet IP:

And there will be some hosts under that network using the Cisco 1603 to firsly connect to our company network then access the Internet. The static route set on 1603 is:

! Using DDR

ip route dialer1

The 1603 router will actually connect to the NT RAS server and is able to ping the Internet hosts. However, none of the host behind the router can ping the Internet. They all receive request timeout error.

Could anyone please help me how to get the host behind the router to connect to the outside network? Thank you in advance.


Re: ISDN DDR IP design and static route settings

Sounds like a routing issue on the NT RAS server.

have you added a route back to the host's behind the 1603, if not then the NT RAS server wont know where to send the packets.

Check with netstat -r on the server, is it aware of network

To add the route on the NT server use the ROUTE ADD command from a command prompt, I cannot remember how you make it permanent though.

The 1603 can ping the Internet hosts because the ICMP packet will use the BRI IP address as its source, and the NT RAS will see that as directly connected.

New Member

Re: ISDN DDR IP design and static route settings

Thank you very much aacole. I think you got the point.

I will try to add a static route on the NT RAS server and see how it goes.