When you boot up the router, the router looks for a default file name-the PID of the router. For example, the Cisco 4000 Series Integrated Services Routers look for a file named isr 4451.cfg. The Cisco 4000 Series ISR looks for this file before finding the standard files-router-confg or the ciscortr.cfg.
The Cisco 4000 ISR looks for the isr4451.cfg file in the bootflash. If the file is not found in the bootflash, the router then looks for the standard files-router-confg and ciscortr.cfg. If none of the files are found, the router then checks for any inserted USB that may have stored these files in the same particular order.
If there is a configuration file with the PID as its name in an inserted USB, but one of the standard files are in bootflash, the system finds the standard file for use.
Use the show running-config command to view the initial configuration, as shown in the following example:
Router# show running-config Building configuration... Current configuration : 977 bytes ! version 15.3 service timestamps debug datetime msec service timestamps log datetime msec no platform punt-keepalive disable-kernel-core ! hostname Router ! boot-start-marker boot-end-marker ! ! vrf definition Mgmt-intf ! address-family ipv4 exit-address-family ! address-family ipv6 exit-address-family ! ! no aaa new-model ! ipv6 multicast rpf use-bgp ! ! multilink bundle-name authenticated ! ! redundancy mode none ! interface GigabitEthernet0/0/0 no ip address negotiation auto ! interface GigabitEthernet0/0/1 no ip address negotiation auto ! interface GigabitEthernet0/0/2 no ip address negotiation auto ! interface GigabitEthernet0/0/3 no ip address negotiation auto ! interface GigabitEthernet0 vrf forwarding Mgmt-intf no ip address negotiation auto ! ip forward-protocol nd ! no ip http server no ip http secure-server ! ! control-plane ! ! line con 0 stopbits 1 line vty 0 4 login ! ! end