Hello Sanghee,
the method is a short way to tell how the ip address has been given to the interface:
nvram -> saved config
manual -> configured after last reload
unset -> simply not configured
there should also an option for when you set the ip address using the initial setup dialog on a device with an empty or skipped configuration.
see command reference
http://www.cisco.com/en/US/partner/docs/ios/ipaddr/command/reference/iad_ip.html#wp1027146
or
http://www.cisco.com/en/US/docs/ios/ipaddr/command/reference/iad_ip.html#wp1027146
Table 30 provides the following list
The Method field has the following possible values:
•RARP or SLARP-Reverse Address Resolution Protocol (RARP) or Serial Line Address Resolution Protocol (SLARP) request.
•BOOTP-Bootstrap protocol.
•TFTP-Configuration file obtained from the TFTP server.
•manual-Manually changed by CLI command.
•NVRAM-Configuration file in NVRAM.
•IPCP-ip address negotiated command.
•DHCP-ip address dhcp command.
•unassigned-No IP address.
•unset-Unset.
•other-Unknown.
Hope to help
Giuseppe
