HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 302

User Login with TACACS+ About Configuring TACACS+ User Login with TACACS+ When a user attempts a Password Authentication Protocol (PAP) login to a Cisco Nexus 5000 Series switch using TACACS+, the following actions occur: 1 When the Cisco Nexus 5000 Series switch establishes a connection, it contacts the TACACS+ daemon to obtain the username and password. Note TACACS+ allows an arbitrary conversation between the daemon and the user until the daemon receives enough information to authenticate the user. This action is usually done by prompting for a username and password combination, but may include prompts for other items, such as the user's mother's maiden name. 2 The Cisco Nexus 5000 Series switch will receive one of the following responses from the TACACS+ daemon: • ACCEPT-User authentication succeeds and service begins. If the Cisco Nexus 5000 Series switch requires user authorization, authorization begins. • REJECT-User authentication failed. The TACACS+ daemon either denies further access to the user or prompts the user to retry the login sequence. • ERROR-An error occurred at some time during authentication dither at the daemon or in the network connection between the daemon and the Cisco Nexus 5000 Series switch. If the Cisco Nexus 5000 Series switch receives an ERROR response, the switch tries to use an alternative method for authenticating the user. The user also undergoes an additional authorization phase, if authorization has been enabled on the Cisco Nexus 5000 Series switch. Users must first successfully complete TACACS+ authentication before proceeding to TACACS+ authorization. 3 If TACACS+ authorization is required, the Cisco Nexus 5000 Series switch again contacts the TACACS+ daemon and it returns an ACCEPT or REJECT authorization response. An ACCEPT response contains attributes that are used to direct the EXEC or NETWORK session for that user and determines the services that the user can access. Services include the following: • ◦ Telnet, rlogin, Point-to-Point Protocol (PPP), Serial Line Internet Protocol (SLIP), or EXEC services ◦ Connection parameters, including the host or client IP address (IPv4 or IPv6), access list, and user timeouts Default TACACS+ Server Encryption Type and Preshared Key You must configure the TACACS+ preshared key to authenticate the switch to the TACACS+ server. A preshared key is a secret text string shared between the Cisco Nexus 5000 Series switch and the TACACS+ server host. The length of the key is restricted to 63 characters and can include any printable ASCII characters (white spaces are not allowed). You can configure a global preshared secret key for all TACACS+ server configurations on the Cisco Nexus 5000 Series switch to use. You can override the global preshared key assignment by explicitly using the key option when configuring an individual TACACS+ server. Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 256 OL-16597-01