28-3
Figure 28-2
Work flow of automatic configuration
Start the device
without loading the
configuration file
The interface obtains
parameters through
DHCP
Is the TFTP server address
contained in the parameters?
Yes
No
Yes
No
Unicast a TFTP
request to obtain the
configuration file
Yes
Yes
Broadcast a TFTP
request to obtain the
configuration file
No
Remove the temporary
configurations and execute the
obtained configuration file
End
Is the TFTP server domain
name contained in the
parameters?
Resolve domain name
of the TFTP server
Succeeds
Fails
Fails
No
Remove the temporary
configurations and the device
starts with null configuration
Remove the temporary
configurations and the device
starts with null configuration
Succeeds
Obtaining the IP Address of an Interface and Related Information Through DHCP
Obtaining an IP address
When a device starts up without loading the configuration file, the system automatically configures the
first active interface (if an active Layer 2 Ethernet interface exists, this first interface is a virtual
interface corresponding with the default VLAN) of the device as obtaining its IP address through DHCP.
The device broadcasts a DHCP request through this interface. The Option 55 field specifies the
information (for example, the configuration file name, domain name and IP address of the TFTP server
and DNS server needed for obtaining the automatic configuration files) that the device can obtain from
the DHCP server.
Upon successfully obtaining its IP address through DHCP, the device resolves the Option 67 (or the file
field, configuration file name) field, Option 66 (domain name of the TFTP server) field, Option 150 (IP
address of the TFTP server) field and Option 6 (IP address of the DNS server) field. If failing to obtain
its IP address, the device removes the temporary configuration and starts up without loading the
configuration file.
