R1 must authenticate Telnet via Cisco ISE at 192.168.1.5 with shared secret Cisco123. R1 currently has radius server ISE1 and an AAA group defined as tacacs+ RAD-SERV, and aaa authentication login default group RAD-SERV. Which configuration change fixes Telnet authentication against ISE?

The correct answer is aaa group server radius RAD-SERV server name ISE1. This command creates a new AAA server group named RAD-SERV of type radius and associates it with the existing ISE1 server definition. Since the aaa authentication login default group RAD-SERV command is already configured, this new group will be used for Telnet authentication. The incorrect option line vty 0 4 login authentication RAD-SERV is wrong because RAD-SERV is currently a TACACS+ group, and the question specifies authentication via Cisco ISE, which uses RADIUS. The option aaa group server tacacs+ ISE1 server name RAD-SERV is incorrect because it defines a TACACS+ group, not a RADIUS group, which is required for Cisco ISE. The option line vty 0 4 login authentication default is incorrect because it would use the existing default authentication method, which is currently configured to use the TACACS+ group RAD-SERV, not the desired RADIUS server.