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New Member

IP Address Pools

We are working on a remote access dial up solution Users dial into a bank of modems hosted by a trusted 3rd party network provider. The 3rd party network is terminated on a Cisco 3640 router installed in the client premises. The 3640 router is configured with a local IP address pool from which it assigns an IP address to the dial up client.

A PPP connection is set up between the dial up client/remote laptop and the 3640 router. The client then undergoes a 2 step authentication process. Firstly, the user must authenticate themselves with an authentication server using the RADIUS protocol using a token card for password generation and a user ID. RADIUS packets are sent by the 3640 RADIUS client to the RADIUS authentication server. User details (password and ID) are verified and an authentication PASS message returned to the RADIUS client. At this point the remote laptop should be assigned an available IP address from the IP address pool on the router. The laptop now has an IP address to allow it to communicate with the Win2000 authentication server, step 2 in the authentication process.

We are experiencing problems in our development. The laptop is not being assigned an IP address by the router following successful verification of RADIUS password and RADIUS ID. Our development environment is as follows:

W2K Laptop->analogue telephone exchange simulator->external modem connected over serial connection to Cisco 2500 router->RADIUS server over switched and routed network

Has anybody successfully configured IP address pools locally on a Cisco router. We have tested a PPP connection between laptop and router without RADIUS authentication and have successful access to the router and receive the router prompt as you would with a hyperterminal session. However the laptop is still not assigned an IP address.

Any comments/suggestions on experiences with IP Address pools very welcome.


New Member

Re: IP Address Pools

As your development environment is utilizing a 2501 this may or may not be very useful. We have

a 3661 with a PRI attached to a bank of internal modems (async interfaces on the router). A

remote user dials the lead number on our PRI and is connected to one of the internal modems (line 97-120 below). After the handshake the user's ID and password information are authenticated on a AAA server using Radius. Upon authentication the router assigns an ip address from the pool listed below. Hopefully some form of this configuration will work for your 3640 series as it is essentially the same platform as our 3661.

interface Loopback0

ip address

no ip directed-broadcast


interface Serial2/0:23

no ip address

no ip directed-broadcast

encapsulation ppp

dialer-group 1

isdn switch-type primary-ni

isdn incoming-voice modem

fair-queue 64 256 0


interface Group-Async0

ip unnumbered Loopback0

no ip directed-broadcast

encapsulation ppp

keepalive 10

dialer in-band

dialer idle-timeout 900

dialer-group 1

async default routing

async mode interactive

peer default ip address pool dialup

ppp authentication chap pap

group-range 97 120


ip local pool dialup


line 97 120

autoselect during-login

autoselect ppp

modem Dialin

modem autoconfigure type 2730

transport input all

flowcontrol hardware

hope that helps

-Bruce McDougall