I am running Windows 7 with a WiFi connection to my router, and I'm connecting a Raspberry Pi via an Ethernet cable. Network sharing is turned on, and to some extent this setup works. I can ping any location (e.g. bing.com) from the Pi. I can open a web browser on the Pi to google.com. However, the web brower won't connect to most sites, most of the time. I set up a packet sniffer on the PC and found that in each case that's because the PC is receiving packets of 1500 bytes, and does not pass them on to the PI over the Ethernet cable. It sends back an ICMP Packet Undeliverable (Packet too large) message in each case. The message is sent by the PC, not by the Pi via the PC. I ran netsh interface ipv4 show subinterfaces and found that the Ethernet interface is set to MTU size 1300, while the WiFi interface is set to 1500. So I ran netsh interface ipv4 set subinterface "Local Area Connection" mtu=1500 store=persistent which corrected the problem. However, when I restarted the PC, the MTU size had reset back to 1300. From reading the documentation about the netsh command, that's not supposed to happen. I have to assume that something else is resetting the size on reboot, but I haven't been able to track down the culprit. I also have not found any way to prevent the size from being changed, by, e.g. setting an access control on the key value. (For that I'd have to know where to find the key value.) The Ethernet NIC is a REALTEK PCIe FE Family Controller, and I've updated the driver to the latest on the Realtek site. I've noticed that others have asked about store=persistent settings getting lost on reboot, as far back as 2010. I'm hoping that this question might finally get answered.

As far as I know, the realtek cards support large MTU configuration in the advanced properties of the NIC driver. Try to configure them there; it might be the driver overwrites the Windows settings when loaded. the required setting usually is caleld 'Jumbo frames' or 'Jumbo Packets'. There are some screenshots on this blog on how to configure this! MCP/MCSA/MCTS/MCITP