Hi,
I'm trying to connect to some old banking code, which has a limited
TCP implementation. When trying to connect with stock 2.4 and 2.6
kernels it fails. I want to know if there is a way of working around
the problem that doesn't break anything.
The server doesn't reassemble fragments, so I need to send 311 bytes
of data on a TCP stream, in one fragment. Since the MSS is 1460
(Ethernet), this shouldn't be a problem. However, the server sets
it's window size to 536 (with a MSS of 1460). Again, I should be
able to do this, but I can't.
In net/ipv4/tcp_output.c there is a chunk of code:
/* Bound mss with half of window */
if (tp->max_window && mss_now > (tp->max_window>>1))
mss_now = max((tp->max_window>>1), 68U - tp->tcp_header_len);
which means the first packet is half of 536, or 268 bytes.
If I change it, I can connect.
Why /2? Why not run:
/* Bound mss with window */
if (tp->max_window && mss_now > (tp->max_window))
mss_now = max((tp->max_window), 68U - tp->tcp_header_len);
--
Regards,
Berend
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