208 Configuring Authentication, Authorization, and A ccounting
Each service is configured using method lists. The method lists define how
each service is to be performed by specifying the methods available to
perform a service. The first method in a list is tried first. If the first method
returns an error, the next method in the list is tried. This continues until all
methods in the list have been attempted. If no method can perform the
service, then the service fails. A method may return an error due to lack of
network access, misconfiguration of a server, and other reasons. If there is no
error, the method returns success if the user is allowed access to the service
and failure if the user is not.
AAA gives the user flexibility in configuration by allowing different method
lists to be assigned to different access l ines. In this way, it is possible to
configure different security requirements for the serial console than for
Telnet, for example.
Methods
A method performs the configured service. Not every method is available for
every service. Some methods require a username and password and other
methods only require a password. Table10-1 summarizes the various
methods:
Table 10-1. AAA Methods
Method Username? Password? Can Return an Error?
enable no yes yes
ias yes yes no
line no yes yes
local yes yes yes
none no no no
radius yes yes yes
tacacs yes yes yes