[lwip-users] LWIP Accept Failures

[Neil Burton]

Hi all,

I'm working with a port of LWIP onto a Z80182 platform, which until now has
been very successful. However, recent testing has thrown up an unpredictable
problem whereby LWIP seems to accept (briefly) an incoming TCP connection,
and then almost immediately abort it. I TCPDUMP'd one such occasion on a
relevant gateway, with the following trace:

15:22:24.988891 192.168.1.5.1169 > 10.128.0.15.8082: S
3696301131:3696301131(0) win 64240 <mss 1460,nop,nop,sackOK> (DF)
15:22:27.259441 10.128.0.15.8082 > 192.168.1.5.1169: S 2214116:2214116(0)
ack 3696301132 win 1024 <mss 128> (DF)
15:22:27.295033 192.168.1.5.1169 > 10.128.0.15.8082: . ack 1 win 64256 (DF)
15:22:27.332945 192.168.1.5.1169 > 10.128.0.15.8082: P 1:4(3) ack 1 win
64256 (DF)
15:22:27.958011 10.128.0.15.8082 > 192.168.1.5.1169: R 2:2(0) ack 1 win 0
(DF)
15:22:28.003770 10.128.0.15.8082 > 192.168.1.5.1169: R 2:2(0) ack 4 win 0
(DF)
15:23:30.068880 192.168.1.5.1170 > 10.128.0.15.8082: S
3711228507:3711228507(0) win 64240 <mss 1460,nop,nop,sackOK> (DF)
15:23:33.261482 192.168.1.5.1170 > 10.128.0.15.8082: S
3711228507:3711228507(0) win 64240 <mss 1460,nop,nop,sackOK> (DF)
15:23:33.640154 10.128.0.15.8082 > 192.168.1.5.1170: S 2320082:2320082(0)
ack 3711228508 win 1024 <mss 128> (DF)
15:23:33.681788 192.168.1.5.1170 > 10.128.0.15.8082: . ack 1 win 64256 (DF)
15:23:33.704224 10.128.0.15.8082 > 192.168.1.5.1170: S 2426049:2426049(0)
ack 3711228508 win 1024 <mss 128> (DF)
15:23:33.717342 192.168.1.5.1170 > 10.128.0.15.8082: P 1:4(3) ack 4294861330
win 64256 (DF)
15:23:33.740220 192.168.1.5.1170 > 10.128.0.15.8082: . ack 4294861330 win
64256 (DF)
15:23:34.378489 10.128.0.15.8082 > 192.168.1.5.1170: R
4294861331:4294861331(0) ack 1 win 0 (DF)
15:23:34.424260 10.128.0.15.8082 > 192.168.1.5.1170: R
4294861331:4294861331(0) ack 4 win 0 (DF)
15:23:34.464386 10.128.0.15.8082 > 192.168.1.5.1170: R
4294861331:4294861331(0) ack 4 win 0 (DF)

192.168.1.5 is a Win2k server machine running one end of our application (a
Win32 gateway app), and 10.128.0.15 is the remote, Z80-based platform
running LWIP. At the Windows end, the connection is established, and then
immediately reports reset by peer. Linux telnet attempting to connect to the
LWIP platform shows the exact same symptoms. However, ICMP pings still work
fine to the LWIP platform, and connections *from* LWIP into the Win2k
gateway app also work fine. Only the LWIP listener has a problem.

Notably, none of the callbacks into my application are fired from LWIP
during this process. Whatever is happening, is happening entirely in the
LWIP system.

This is my first post to the list so apologies if the information is
incomplete, and I didn't actually write the port though I did integrate the
supplied code into my app. I'd appreciate any and all insight into the
nature of this problem while I'm digging around trying to solve it.

Thanks in advance,

Neil Burton