Cisco C921-4P User Manual

CHAPTER 4
ROM Monitor Overview and Basic Procedures
The ROM Monitor (ROMMON) is a bootstrap program that initializes the hardware and boots the Cisco 900
ISR when you power on or reload a router.
If your router does not find a valid system image to load when it is booting, the system enters the ROMMON
mode. ROMMON mode can also be accessed by interrupting the boot sequence during startup.
• ROM Monitor Overview, on page 33
ROM Monitor Overview
The ROM Monitor software is also known as ROMMON, boot software, boot image, or boot helper. Although
it is distributed with routers that use the Cisco IOS software, the ROMMON is a separate program from the
Cisco IOS software. During normal startup, ROMMON initializes the router, and then, the control passes to
the Cisco IOS software.
When you connect a terminal to the router that is in ROMMON mode, the ROMMON command-line interface
(CLI) prompt is displayed.
Access the ROMMON mode to perform these tasks:
• Specify config-register value to use for the next boot up
• Boot a valid IOS image
• Bypass NVRAM settings and config-register value for password recovery
After the Cisco IOS software boots up, ROMMON is no longer in use.
Note
Environmental Variables and the Configuration Register
Two primary connections exist between ROMMON and the Cisco IOS software: the ROMMON environment
variables and the configuration register.
The ROMMON environment variables define the location of the Cisco IOS software and describe how to
load it. After ROMMON has initialized the router, it uses the environment variables to locate and load the
Cisco IOS software.
Hardware Installation Guide for the Cisco 900 Series Integrated Services Router
33

Cisco C921-4P Specifications

General

Switch type	Managed
Quality of Service (QoS) support	Yes
USB 2.0 ports quantity	1
Basic switching RJ-45 Ethernet ports type	-
Basic switching RJ-45 Ethernet ports quantity	4
10G support	No
Networking standards	IEEE 802.1D
Product color	Black
Electromagnetic compatibility	47CFR, AS/NZS CISPR22 2, CISPR22, EN55022, ICES003, EN61000-3-2, KCC, EN55024, KN24
Flash memory	2048 MB
Internal memory	1024 MB
MAC address table	- entries
AC input voltage	100 - 240 V
AC input frequency	50 - 60 Hz
Storage temperature (T-T)	-40 - 70 °C
Operating temperature (T-T)	0 - 50 °C
Operating relative humidity (H-H)	5 - 95 %
Security algorithms	802.1x RADIUS
Harmonized System (HS) code	85176990

Weight and Dimensions

Depth	241.3 mm
Width	228.6 mm
Height	43.2 mm
Weight	1200 g