GoKawiilToday we are looking at the TP-Link TL-SG108, an 8 port Gigabit Ethernet plug-and-play desktop switch. It is a little less capable and cheaper than the usual fare here, but it does hide some interesting surprises!
Removing the two small screws on the bottom allows us to remove the top cover and see that the switch is based on the Realtek RTL8370N.
The RTL8370N is a low-cost Gigabit Ethernet switch chip first released in the mid 2010s and today is found in many low-cost 5 and 8 port gigabit switches. It may surprise you to learn that 5-8 port “web smart” managed switches are also using the RTL8370N. The feature difference is (mostly) a software limitation.
The RTL8370N has an embedded 8051 microcontroller, which for web managed switches is used to serve the web UI. Notably these switches do not offer cli access (telnet/ssh) as they lack the resources to run those services.
The Realtek description of the chip is very brief:
The RTL8370N-VB features low-power integrated 8-port Giga-PHYs that support 1000Base-T, 100Base-T, and 10Base-T.
Looking at the TL-SG108 switch and the box, there is no MAC address, no default IP address, and nothing to suggest that this switch would ever support more advanced features like VLAN tagging.
Luckily, the “Not for public release” datasheet on the RTL8370N can easily be found online.
The RTL8370N supports reading from an I2C EEPROM, or SPI flash after reset. The chip can operate with the 8051 core disabled, reading the configuration from directly from an I2C EEPROM into the chip registers. Which mode to operate in is determined at power-on by reading the value of pin straps:
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