my 2501 router's IOS version is 11.11
and vty can pass auth.the config is:
aaa new-model
aaa authentication login huateng radius
aaa authentication ppp huateng if-needed radius
ip radius source-interface Ethernet0
interface Async1
ip unnumbered Ethernet0
ip tcp header-compression passive
encapsulation ppp
bandwidth 38
async mode interactive
peer default ip address pool huateng_17
no cdp enable
ppp authentication chap huateng
ip local pool huateng_17 130.252.17.200 130.252.17.205
radius-server host 130.252.234.234
radius-server key ciscopix
line aux 0
autoselect during-login
autoselect ppp
modem InOut
login authentication huateng
modem autoconfigure discovery
transport input all
stopbits 1
rxspeed 38400
txspeed 38400
flowcontrol hardware
line vty 0 4
login authentication huateng
