Unstable ethernet/fiber pc to pc connection Windows

by user2323470   Last Updated August 25, 2017 13:00 PM

We have two Windows 7 PCs (64 bit) connected to each other directly, i.e. without a router in between, using a fiber connection with two ethernet-to-fiber converters. PC1 uses a Realtek PCIe GBE Family Controller, PC2 uses an Intel Gigabit CT Desktop Adapter, the media converters are Digitus Gigabit Ethernet Media Converter DN-82121-1. The connections are running with gigabit speed.

PC1 and PC2 have been configured with static IP addresses and respectively. Apart from the IP address, only the subnet mask ( is set, other fields such as gateway are left blank.

The connection works normally most of the time, but sometimes it suffers from packet loss which usually keeps increasing until the connection becomes completely unusable. This seems to happen totally at random about once a day. Occassionally, it doesn't happen for more than a day. We have the machines constantly ping each other to monitor the situation.

We have no idea what the cause of this is. We don't even know if it's a hardware or a software issue. During the degradation of the connection, all LEDs on the media converters indicate normal operations. Windows doesn't notice anything about the connection, it still sees it as connected, just some and eventually all packets are lost.

Re-plugging the ethernet cables during an "attack" seems to have no effect. After a while, though, the connection starts working again on its own.

Because the problem doesn't occur that often and we have no way of provoking it, it's really hard to debug. ANY ideas are welcome.

One thing that is odd, I don't know if it has anything to do with the problem: when sending TCP packets with random data (for testing) from the Realtek (PC1) to the Intel (PC2), the transfer rate is around 30 MiB/s, but in the other direction is around 60 MiB/s. After disabling Energy Efficient Ethernet and Green Ethernet on the Realtek (we thought it might have something to do with the connection problems), the send speed fluctuates between 30 and 45 MiB/s.

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