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

[Gollakota, Srinivas]

I checked with the TCP flags set to 0 with my test and my test works same as to 
that of ACK flag set.So no objections with the fix. 

If you have the exact section in the RFC1122 that talks about the TCP flags in 
conjunction with keep alive timer please post it. I could only find about the 
sequence numbers nothing about flags.
-Srinivas.

-----Original Message-----
From: Frédéric Bernon [mailto:address@hidden 
Sent: Monday, June 11, 2007 9:36 AM
To: Kieran Mansley; Srinivas Gollakota; Oleg Tyshev; Frédéric Bernon; 
address@hidden
Subject: [bug #20075] A problem with keep-alive timer and TCP flags



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)); 
flag=10; setsockopt( sock, IPPROTO_TCP, TCP_KEEPIDLE, (char*)&flag, 
sizeof(flag)); flag=2; setsockopt( sock, IPPROTO_TCP, TCP_KEEPINTVL, 
(char*)&flag, sizeof(flag)); flag=10; 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
abort:

tcp_slowtmr: KEEPALIVE timeout. Aborting connection to 192.168.1.85.

I attach the network capture file for the first part of the test. Ethereal 
seems correctly "detect" keepalives packets. In this capture, 192.168.1.246 is 
my lwIP device (and 192.168.1.85 the PC).

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




(file #13012)
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Additional Item Attachment:

File name: KeepAlive.cap                  Size:1 KB


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