Datasheet

63
OL-17436-01
Additional Configuration and Maintenance Tasks
into ROM monitor mode. Regardless of the setting of the Break enable bit in the software configuration
register, pressing the Break key during approximately the first 5 seconds of booting causes a return to
the ROM monitor.
Bit 9 is not used.
Bit 10 of the software configuration register controls the host portion of the IP broadcast address. Setting
bit 10 causes the processor to use all zeros in the host portion of the IP broadcast address; clearing bit
10 (the factory default) causes the processor to use all ones. Bit 10 interacts with bit 14, which controls
the network and subnet portions of the IP broadcast address.
Table 21 shows the combined effect of bits 10 and 14.
Bits 11 and 12 of the software configuration register determine the data transmission rate of the console
terminal. Table 22 shows the bit settings for the four available data transmission rates. The factory-set
default data transmission rate is 9600 bps.
Bit 13 of the software configuration register determines the response of the system to a bootload failure.
Setting bit 13 causes the system to load Cisco IOS software from Flash memory after five unsuccessful
attempts to load a boot file from the network TFTP server. Clearing bit 13 causes the system to continue
attempting to load a boot file from the network TFTP server indefinitely. Bit 13 in the software
configuration register is set to 0 as the default at the factory.
Understanding the Cisco IOS XR Software Configuration Register
The Cisco IOS XR Software configuration register (config-register) is a 16-bit, user-configurable value
that determines how the router functions during initialization. The configuration register can cause the
router to boot normally from the default startup configuration, or to enter ROM monitor mode during a
system reset. Typically, ROM monitor mode is used only for password recovery or for software
maintenance that cannot be performed in Exec mode or global configuration mode.
Table 21 Configuration Register Settings for Broadcast Address Destination
Bit 14 Bit 10 Address (<net> <host>)
Off Off <ones> <ones>
Off On <zeros> <zeros>
On On <net> <zeros>
On Off <net> <ones>
Table 22 System Console Terminal Data Transmission Rate Settings
Bit 12 Bit 11 Data Transmission Rate (bps)
0 0 9600
0 1 4800
1 0 1200
1 1 2400