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[lwip-devel] [bug #20075] A problem with keep-alive timer and TCP flags

From: Frédéric Bernon
Subject: [lwip-devel] [bug #20075] A problem with keep-alive timer and TCP flags
Date: Mon, 11 Jun 2007 13:35:57 +0000
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; fr; rv: Gecko/20070515 Firefox/

Follow-up Comment #4, bug #20075 (project lwip):

I have set in tcp_keepalive a TCPH_FLAGS_SET(tcphdr, 0);

I have test with a pseudo telnet server with lwip with these parameters:

int flag=1;
setsockopt( sock, SOL_SOCKET, SO_KEEPALIVE, (char*)&flag, sizeof(flag));
setsockopt( sock, IPPROTO_TCP, TCP_KEEPIDLE, (char*)&flag, sizeof(flag));
setsockopt( sock, IPPROTO_TCP, TCP_KEEPINTVL, (char*)&flag, sizeof(flag));
setsockopt( sock, IPPROTO_TCP, TCP_KEEPCNT, (char*)&flag, sizeof(flag));

Like this, when my client (the Windows 2000 Telnet client) connect, and wait
forever, I see the keepalive exchange. All seems ok, the TCP connection is
maintained. But, if I cut the network between lwip and my pc, after 10sec,
keepalive exchange become faster, and after 10 retry, the TCP connection is

tcp_slowtmr: KEEPALIVE timeout. Aborting connection to

I attach the network capture file for the first part of the test. Ethereal
seems correctly "detect" keepalives packets. In this capture,
is my lwIP device (and the PC).

So, if no objects about that, I will check in with 0 in TCP flags for

(file #13012)

Additional Item Attachment:

File name: KeepAlive.cap                  Size:1 KB


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