Chapter 3 Installing the Router
Cisco IOS User Interface
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Cisco 12006 and Cisco 12406 Router Installation and Configuration Guide
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Global Configuration Mode
Global configuration commands apply to features that affect the system as a
whole, rather than just one protocol or interface. Use the configure terminal
privileged EXEC command to enter global configuration mode. Commands to
enable a particular routing or bridging function are global configuration
commands.
Interface Configuration Mode
Many features are enabled on a per-interface basis. Interface configuration
commands modify the operation of an interface, such as Ethernet, FDDI, or serial
port. Interface configuration commands always follow an interface global
configuration command, which defines the interface type.
For details on interface configuration commands that affect general interface
parameters, such as bandwidth or clock rate, refer to the “Interface Commands”
chapter in the Configuration Fundamentals Command Reference. For
protocol-specific commands, see the appropriate Cisco IOS software command
reference.
Subinterface Configuration Mode
You can configure multiple virtual interfaces (called subinterfaces) on a single
physical interface. Subinterfaces appear to be distinct physical interfaces to the
various protocols. For detailed information on how to configure subinterfaces, see
the appropriate module for a specific protocol in the Cisco IOS software
documentation.
ROM Monitor Mode
If your router does not find a valid system image, or if you interrupt the boot
sequence, the system might enter read-only memory (ROM) monitor mode. From
ROM monitor mode, you can boot the system or perform diagnostic tests. You
also can enter ROM monitor mode by entering the reload EXEC command and
then pressing the Break key during the first 60 seconds of startup.