This is the teardown of a Defzone 300sg network firewall. Firewalls are used to keep your internal network safe from external threats. This particular model was introduced around the year 2007. Interestingly, there is no information to be found about both the model and its manufacturer.


The case is a simple 19 inch 1U rack mount case. The case also has four rubber feet so that it can be put on any flat surface if not mounted in a 19 inch rack.

The front of the case has seven LEDs showing the status of Power, DIAG, DMZ, Wan 1, Wan 2, Wan 3, and Wan 4. There are 16 RJ-45 ports labeled 1 through 11, 12/Wan 4, 13/Wan 3, Wan 2, Wan 1, and DMZ. On the right side of the device sits a reset button. This button can only be pressed by a pointy object, like a small screwdriver.

Case: front view

The back of the case only has a IEC C14 power connector.

Case: rear view

Power supply

The PSU is an off-the-shelf part made by Seasonic (SSF-0251-2) and is capable of supplying 5A at 5V. The green and yellow wire was used to connect the mains ground coming in from the IEC C14 connector to the metal case.

Power Supply Unit

Main board

The first thing that stands out about the main board is the amount of empty space on it. The boards has a clear layout as a result of that. Most of the top copper layer is a ground plane which is completely stitched through with vias to connect it to the bottom copper layer of board.

Main board


The 5V from the power supply enters the main board via the white connector on the left. The voltage is stepped down to 3.3V by a Richtek RT9214 buck controller, together with a Tuofeng 4812 Dual N-channel MOSFET. The voltage is then stepped down again, from 3.3V to 1.8V. This is done with a Nikos L1085S3G linear regulator.

Main board: Power supply

Processor & memory

This firewall is based on the Intel PRIXP425ABD Network Processor. These processors were specifically designed to be used in network applications. These processors were based on the XScale mircoarchitecture which implemented the ARMv5 instruction set.

Above the processor are two Samsung K4S561632E-UC75 256Mb SDRAM chips. There are two unpopulated spots for more SRAM chips. On the right side of the processor sits a single Intel JS28F128 flash chip.

The 8-pin chip between the processor and its memory is a Pericom PI6C24. This is a clock buffer with five outputs. It is used to distribute the clock signal from the processor to the SDRAM and flash memory chips.

Another 8-pin chip can be seen just below the processor. This is a Cypress CY25100 spread spectrum clock generator. Its purpose is to reduce EMI emitted from the device.

Mostly out of view sits a Xilinx XC2C32A CPLD next to a few debug headers.

Main board: Processor & memory

Network chipset

The network connections are handled by a Realtek RTL8318P ethernet switch controller. It has two Realtek RTL8208B companion chips under the heatsinks. These chips are octal 10/100 base TX/RX PHY trancievers.

Main board: Network chipset

RJ-45 connectors

The RJ-45 connectors have their own separate ground plane. It is not connected to the ground plane covering most of the main board. This may have something to do with preventing ground loops. The inputs are filtered by Delta LFE8731 LAN filters.

Main board: RJ-45 connectors

LED drivers

Some Texas Intruments SNx4LV164A shift registers are used to as LED drivers for the status LEDs integrated in the RJ-45 connectors.

Main board: LED drivers

Real Time Clock

The main board has a 3V coin cell battery located on the lower right side. This battery powers a Ricoh RS5C372A RTC chip. The power from the battery passes through three zener diodes, each dropping the voltage 0.4V. This results in a 1.8V supply voltage for the RTC.

Main board: Real Time Clock