On the Cisco ASR 1000 Series Routers, IP addresses can be configured in ROMmon (the IP_ADDRESS= and IP_SUBNET_MASK= commands) and through the use of the IOS command-line interface (the ip address command in interface configuration mode).
Assuming the IOS process has not begun running on the Cisco ASR 1000 Series Router, the IP address that was set in ROMmon
acts as the IP address of the Management Ethernet interface. In cases where the IOS process is running and has taken control
of the Management Ethernet interface, the IP address specified when configuring the Gigabit Ethernet 0 interface in the IOS
CLI becomes the IP address of the Management Ethernet interface. The ROMmon-defined IP address is only used as the interface
address when the IOS process is inactive.
For this reason, the IP addresses specified in ROMmon and in the IOS CLI can be identical and the Management Ethernet interface
will function properly in single RP configurations.
In dual RP configurations, however, users should never configure the IP address in the ROMmon on either RP0 or RP1 to match
each other or the IP address as defined by the IOS CLI. Configuring matching IP addresses introduces the possibility for an
active and standby Management Ethernet interface having the same IP address with different MAC addresses, which will lead
to unpredictable traffic treatment.