Force 100Mbit ethernet speed on RTL-8152 USB ethernet adapter

After switching ISP providers I have replaced my trusty TP-LINK 1043ND running OpenWrt with Cisco EPC3928S which also has Gigabit Ethernet ports and 300Mbit WiFi I noticed problems with my RTL8152 based USB->Ethernet adapter which I was using with my gk802 device.

Everything works great with other devices but every 30 seconds or so I have packet loss on RTL8152 (10-30%). I have analyzed a problem and noticed that something might be wrong with auto-negotiation speeds since I noticed port light on EPC3928S was shutting down and re-initializing.

First install neccessary packages:

apt-get install ethtool net-tools

Use following commands to force eth0 device into 100Mbit speed:

mii-tool -F 100baseTx-FD

You can put this command into your /etc/rc.local file to make sure it gets executed on each reboot.

To switch back to negotiated speeds 100Mbit (full-duplex):

ethtool -s eth0 speed 100 duplex full

or simply reboot.

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