This document explains how privilege levels affect a user's ability to perform certain commands on a router.
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When access to the router is configured by privilege levels, a common issue is that the show running or write terminal commands are configured at or below the user's privilege level. When the user executes the command, the configuration appears to be blank. This is actually by design for these reasons:
The write terminal / show running-config command shows a blank configuration. This command displays all of the commands that the current user is able to modify (in other words, all the commands at or below the user's current privilege level). The command should not display commands above the user's current privilege level because of security considerations. If so, commands such as snmp-server community could be used to modify the current configuration of the router and gain complete access to the router.
The show config / show start-up config command displays a full configuration, but does not truly show the actual configuration. Instead, the command simply prints out the contents of NVRAM, which happens to be the configuration of the router at the time the user does a write memory.
To enable a privileged user to view the entire configuration in memory, the user needs to modify privileges for all commands that are configured on the router. For example:
aaa new-model aaa authentication login default local aaa authorization exec default local username john privilege 9 password 0 doe username six privilege 6 password 0 six username poweruser privilege 15 password poweruser username inout password inout username inout privilege 15 autocommand show running privilege configure level 8 snmp-server community privilege exec level 6 show running privilege exec level 8 configure terminal
To understand this example, it is necessary to understand privilege levels. By default, there are three command levels on the router:
privilege level 0 — Includes the disable, enable, exit, help, and logout commands.
privilege level 1 — Normal level on Telnet; includes all user-level commands at the router> prompt.
privilege level 15 — Includes all enable-level commands at the router# prompt.
Commands available at a particular level in a particular router can be found by typing a ? at the router prompt. Commands may be moved between privilege levels by using the privilege command, as illustrated in the example. While this example shows local authentication and authorization, the commands work similarly for TACACS+ or RADIUS authentication and exec authorization (more granularity in control of the router may be achieved with implementation of TACACS+ command authorization with a server.)
Additional details on the users and privilege levels presented in the example:
User six is able to Telnet in and execute the show run command, but the resulting configuration is virtually blank because this user cannot configure anything (configure terminal is at level 8, not at level 6). The user is not permitted to see usernames and passwords of the other users, or to see Simple Network Management Protocol (SNMP) information.
User john is able to Telnet in and execute the show run command, but only sees commands that he can configure (the snmp-server community part of the router configuration, since this user is our network management administrator). He can configure snmp-server community because configure terminal is at level 8 (at or below level 9), and snmp-server community is a level 8 command. The user is not permitted to see usernames and passwords of the other users, but he is trusted with the SNMP configuration.
User inout is able to Telnet in, and, by virtue of being configured for autocommand show running, sees the configuration displayed but is disconnected thereafter.
User poweruser is able to to Telnet in and execute the show run command. This user is at level 15, and is able to see all commands. All commands are at or below level 15; users at this level can also view and control usernames and passwords.
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