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Weird. I have some #FreeBSD jails that are using VNET to get access to the LAN. At least as far as I can tell, some TCP packets sent to it exceed the MTU by quite a bit.

Everything on the server is set up with a 1500 byte MTU but I see TCP packets with 2896 bytes in the packet trace. The jail doesn't ack them, and ~0.3 seconds later the first 1448 bytes get re-transmitted.

After a few 1448-byte packets, the remote end tries another 2896 which causes a 0.3s hiccup,... yielding about 16kB/s 👎