IAS Telnet Access Catalyst 2950 (change authentication method)

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I use a Microsoft IAS to authenticate Users logging onto a Cisco Catalyst 2950 via telnet.
The problem is, that only pap authentication works. I tried to change the authentication method to md5 challenge, but there are no effects.

Quotet the notice from the event viewer:

User user was granted access.
Fully-Qualified-User-Name = test.rznur.de/Users/s
NAS-IP-Address = 192.168.15.1
NAS-Identifier = <not present>
Client-Friendly-Name = CiscoCatalyst2950
Client-IP-Address = 192.168.15.1
NAS-Port-Type = Virtual
NAS-Port = 2
Policy-Name = Zugriff
Authentication-Type = PAP
EAP-Type = <undetermined>


Heres the Switch' Configuration

aaa new-model
aaa authentication login default group radius enable
aaa authentication dot1x default group radius enable
enable password 7 0217115A0F140E2D
!
username hek password 7 0015060700490A0A
username bla password 7 0830594F0D0B041B

interface Vlan1
ip address 192.168.15.1 255.255.255.0
no ip route-cache
!
ip http server
radius-server host 192.168.15.16 auth-port 1612 acct-port 1813 key quadral
radius-server retransmit 3
radius-server key quadral
!
line con 0
line vty 0 3
password 7 131402130F1E0526
line vty 4
password 7 0015060700490A0A
line vty 5 15


Thanks in advance.