2014-05-18
I'm using 2013.4 SDK and created the example lwip 1.4.0 project with the echo server. The only change I made was to set the IP address of my board to 192.168.7.99 and the mask to 255.255.0.0. The TCP MSS is set to 1460 in the lwip driver.
When running an echo program from a Windows 7 machine, I see the following:
I'm sending 7,038 bytes, which the PC does in four 1460 bytes plus one 1198, but lwip responds in four 1446 bytes and one 1254 bytes. The counts are right, but why does lwip refuse to use the full 1460 byte segment? Note: MSS=1460 in both SYN packets.
I've tried this for other apps in both socket and raw mode and on two different boards. A google of "lwip len=1146" shows others have the issue.