In order to assign specific users the same address, first thing you have to make sure is that those addresses are not part of the default pool which is defined on the router.
Depends whether you want to assign the static ip address from the router itself or thru Radius...
1) When using thru the router it will again depend whether you have dialer profiles or legacy DDR.
When using Dialer profile (dialer pool commands used), you will need to create a dialer profile for each customer that you want to assign a particular user an ip address to which will match on their ppp username, then on the dialer profile, you can do a "peer default ip address " and that way you can assign them an ip address.
However if you start creating multiple dialer profiles, you are going to run into an issue of default binding, which is when the router will try to match on a dialer profile but if it does not match it will drop the call and therefore you will need to create a virtual-template for all other calls that do not match a dialer profile.
Below is some relevant links and sample configs which may come in handy.
Per User Configuration
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/dial_c/dcperusr.htm
Configuring Virtual Profiles
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/dial_c/dcvprof.htm#3866
Configuring Peer-to-Peer Dialer profiles
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fdial_c/fnsprt5/dcdiprof.htm
Typical Scenarios and Configurations
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fdial_c/fnsprt12/dafntrpr.ht
m#xtocid1843813
When using legacy DDR:
interface Group-Async 1
dialer map ip x.x.x.x name USERNAME (where x.x.x.x is the static ip address that you want to assign to the particular user)
2)When using Radius:
The static assignment will be taken care by the Radius server, this would be using a AAA server to assing particular users an ip address and all other users an ip address out of a pool.. You need to offload authorization to the Radius for this purpose using the following command:
aaa authorization network default radius local
Radius Profile
user password = xxxxx
service-type = framed
framed-protocol = ppp
framed-ip-address = x.x.x.x
Thanks, Mak.
