Recently I met very strange behavior from some Windows clients. Normally the MTU setting on windows is 1500 for ethernet and wlan interface. The client started sending jumbor TCP with even 22k bytes two weeks ago, no site of path MTU discovery works. I use mturoute to determine the MTU the next hop and see our WAN interface has MTU 1492 byte (default with PPPoE) and our home router have MTU 1500 byte.
Why is this happening?, the window client should follow their own mtu. If I try to change MTU of home router to lower than 1492, everything becomes normal.