How much memory is consumed by the Linux kernel per TCP/IP network connection?

Question

How much memory on average is consumed by the Linux kernel (in kernel address space) per TCP/IP network connection?

Answer 1

It depends. On many many things.
I think an idle connection will take a few hundreds of bytes.
But if there's data in the transmit and/or receive data, then the consumption increases. The window size can roughly limit this consumption.
The extra consumption for data isn't just the bytes in the receive/transmit queue. There are overheads, so a segment with one byte might take something like 2K. TCP tries to reduce this, for example by merging segments into a single sk_buff, but it doesn't always succeed.