I doubt it to be caused by McAfee antivirus. The Default Gateway the is IP address of your modem or router (it depends where your ethernet connection is plugged in).
You may also assign Default gateway:
For Windows 10, Go to: Network & Internet settings-> Ethernet->Change adapter settings->Find your ethernet adapter->Right click and find properties of it->Find Internet Protocol Version 4->Assign the static ip and put the ip of your router in the default gateway (if you're directly connected to the modem, instead of router's, put modem's ip).
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