When the password is entered, the administrator can change any part of the router’s configuration. The parser a part of the EXEC process responsible for command processing is switched into the configuration context, using the configure command, which is usually given an optional parameter specifying the source of configuration. You can see the list of parameters for the configure command below:

R1#configure ?
  memory             Configure from NV memory
  network            Configure from a TFTP network host
  overwrite-network  Overwrite NV memory from TFTP network host
  terminal           Configure from the terminal

R1#configure

The terminal keyword specifies that the parser should use the current terminal session as input and output streams for command processing.

Commands entered by the administrator are instantly processed and applied to the running software modules, as shown in listing about making dynamic changes to a router’s configuration such as below, where there is an interface is dynamically shut down and brought up.

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R1#configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#int s0

R1(config-if)#shutdown

R1(config-if)#

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed state to

down

R1(config-if)#

%LINK-5-CHANGED: Interface Serial0, changed state to administratively down

R1(config-if)#no shutdown

R1(config-if)#

%LINK-3-UPDOWN: Interface Serial0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed state to up

R1(config-if)#^Z

R1#

The configure terminal command is the method of using manually entered commands to change a router’s configuration online via a terminal session. If the memory keyword is specified for the configure command, the router reads the backed-up copy of the configuration from NVRAM and passes it to the parser. This is exactly what routers do on start-up. NVRAM is used to store the configuration, which is used the next time the router is reloaded. Usually, the configure memory command is used to restore the router’s configuration after some or all its current settings have been reset.