You are concerned that you cannot trust some users on VLAN_25. Configure the interfaces for R1 and R5 to authenticate the routing protocol updates through the LAN with the best authentication method.
Configure R3, R5, and R6 to authenticate any routing updates on the IS-IS running on VLAN_22. Make this configuration on the interface level.
Configure Sw2 to permit only Telnet access from R3 with source address of 160.10.3.3. Also make sure that both successful and failed Telnet connections are logged.
