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Re: [lwip-users] TCP keeps re-transmitting but no ACK packet after SYN,

From: Sergio R. Caprile
Subject: Re: [lwip-users] TCP keeps re-transmitting but no ACK packet after SYN, SYN+ACK
Date: Mon, 09 Mar 2015 10:56:28 -0300
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

There are 298 frames in your capture file.
Somewhere in the middle of it I see a sending a TCP SYN to
port 80 to
Judging by the amount of crap it is sending, and the fact that it is
opening the connection, I assume is your PC
Then, must be your "box", which is running git head code on
a X processor with a X port, configured for X (SYS or NO_SYS) which is
OK and tested good because ? And, your webserver is X from X, using API
X which is also OK and tested good because ?

The TCP three-way handshake for opening is
I can see the first two frames, but there is no clue of the third one.
Since it has to be sent by the opener in response to the SYN+ACK, which
I can see, then the opener is either not seeing this frame or not liking
itm or broken.
Enabling checksum validation in wireshark, I see the (supposed to be)
lwIP box sends correct checksums, but the PC does not. (?) This is
probably due to checksum offloading and you taking the capture on the
same machine.

Can you do a plain "telnet mybox 80" from a known-to-be-good machine on
a not so loaded (read "just the two boxes and all the extra crap
removed") network and ellaborate on all the Xs ?


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