по этой?
http://forum.dlink.ru/viewtopic.php?f=3&t=70046

Important: Any upgrades will be lost after a factory reset
It should be understood that a reset to factory defaults is exactly that. Any
NetDefendOS upgrades performed since the unit left the factory will be lost.
Reset Procedure for the NetDefend DFL-210, 260, 800 and 860
To reset the NetDefend DFL-210/260/800/860 models, hold down the reset button located at the
rear of the unit for 10-15 seconds while powering on the unit. After that, release the reset button and
the unit will continue to load and startup with its default factory settings.The IP address 192.168.1.1 will be assigned to the LAN interface.
Reset Procedure for the NetDefend DFL-1600, 1660, 2500, 2560 and 2560G
To reset the DFL-1600/1660/2500/2560/2560G models, press any key on the keypad when the
Press keypad to Enter Setup message appears on the front display. Now, select the Reset firewall
option and confirm by selecting Yes. Then wait for the reset process to complete after which the unit
will startup with its default factory settings.
The IP address 192.168.1.1 will be assigned to the default management interface LAN1 on the
DFL-1600 and DFL-2500 models. The management interface IP address for the DFL-1660,
DFL-2560 and DFL-2560G models will default to 192.168.10.1.
The default IP address factory setting for the default management interface is discussed further in
Section 2.1.3, “The Web Interface”.
Warning: Do NOT abort a reset to defaults
If the process of resetting to factory defaults is aborted before it finishes, the
NetDefend Firewall can then cease to function properly with the complete loss of all
stored user data.

Вопрос.

при этом сохранится ли конфигурация?
Если нет, то как можно ее сохранить?

Сбросится прошивка и конфигурация.
О сохранении конфигурации надо заботиться регулярно, загодя.