If you are familiar with Cisco routers and switches, then you might have noticed that the Cisco ASA doesn’t offer the
erase startup-configuration command. Of course, we can erase our startup configuration, but there are some other commands to achieve this.
This is the most simple option:
ciscoasa# write erase
Erase configuration in flash memory? [confirm]
write erase to remove the startup configuration and reboot your firewall. The other option is to use the factory default method:
ciscoasa(config)# configure factory-default 192.168.1.1 255.255.255.0
Based on the management IP address and mask, the DHCP address
pool size is reduced to 253 from the platform limit 256
WARNING: The boot system configuration will be cleared.
The first image found in disk0:/ will be used to boot the
system on the next reload.
Verify there is a valid image on disk0:/ or the system will
Begin to apply factory-default configuration:
Clear all configuration
Executing command: interface management0/0
Executing command: nameif management
INFO: Security level for "management" set to 0 by default.
Executing command: ip address 192.168.1.1 255.255.255.0
Executing command: security-level 100
Executing command: no shutdown
Executing command: exit
Executing command: http server enable
Executing command: http 192.168.1.0 255.255.255.0 management
Executing command: dhcpd address 192.168.1.2-192.168.1.254 management
Executing command: dhcpd enable management
Executing command: logging asdm informational
Factory-default configuration is completed
As you can see above, this clears the configuration and enables the management interface with the IP address we specified. It also enables the DHCP server and HTTP server so that we can connect through ASDM.