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[lwip-users] Establishing TCP Connection after power-up

From: farid mahini
Subject: [lwip-users] Establishing TCP Connection after power-up
Date: Mon, 21 Feb 2011 08:47:35 -0800 (PST)



I have lwIP 1.3.2 running on AVR32/FreeRTOS (MyServer). I have a TCP server that listens for client connections. If MyServer is powered up after being off (> 1 min), I can connect to it very quickly. Ethereal shows client does ARP for MyServer before sending SYN message. All makes sense. Client ARP cache has probably timedout and MyServer was bumped.


Now if I close client connection (from client app), cycle power to MyServer and I try to connect, it takes a little while (in version 1.3.0  I was getting a refusal so I upgraded to 1.3.2). Ethereal shows MyServer doing ARP for client after receiving the SYN message and does not ACK (ie dropping SYN message). 3 secs later client sends another SYN message which is ACK'd by MyServer.


Question:  Since the SYN message has both source and destination addresses (IP and MAC), why does MyServer request it? Wouldn't it get added to ARP table as the SYN message travels up the stack to TCP layer.


Thanx in advance,


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