Cisco C921-4P User Manual

The configuration register is a software setting that controls how a router starts up. One of the primary uses
of the configuration register setting is to control whether the router starts in ROMMON mode or Administration
EXEC mode. The configuration register is set in either ROMMON mode or Administration EXEC mode as
needed. You can set the configuration register using the Cisco IOS software prompt when you need to use
ROMMON mode. When maintenance in ROMMODE mode is complete, change the configuration register
back so that the router reboots with the Cisco IOS software.
Access ROMMON Mode with a Terminal Connection
When the router is in ROMMON mode, you can access the ROMMODE software only from a terminal
connected directly to the console port of the card. Because the Cisco IOS software (EXEC mode) is in operation,
the nonmanagement interfaces are not accessible. Therefore, all Cisco IOS software resources are unavailable.
Network Management Access and ROMMON Mode
ROMMON mode is a router mode, not a mode within the Cisco IOS software. The ROMMON software and
the Cisco IOS software are two separate programs that run on the same router. At any given time, the router
is running one of these programs, but it never runs both at the same time.
One area that can be confusing when using ROMMON and the Cisco IOS software is the area that defines
the IP configuration for the Management Ethernet interface. Most users are comfortable with configuring the
Management Ethernet interface in the Cisco IOS software. When the router is in ROMMON mode, however,
the router is not running the Cisco IOS software, therefore, Management Ethernet interface configuration is
not available.
When you want to access other devices, such as a TFTP server, while in ROMMON mode on the router, you
must configure the ROMMON variables with IP access information.
For more information on ROMMON and Basic Procedures, see Cisco ISR 900 Software Configuration Guide.
Hardware Installation Guide for the Cisco 900 Series Integrated Services Router
34
ROM Monitor Overview and Basic Procedures
ROM Monitor Overview

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