Date: Sun, 05 Mar 2000 18:30:50 +0100 From: Michael Hartung <hartung@zkom.de> To: freebsd-net@FreeBSD.ORG Subject: Re: Answer keep-alive requests Message-ID: <38C299CA.E3C47051@zkom.de> References: <38C23F61.853FEE66@zkom.de> <20000305161540.A22005@pingoo.ifn.fr>
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Rémi Guyomarch schrieb:
> On Sun, Mar 05, 2000 at 12:05:05PM +0100, Michael Hartung wrote:
> > Hi Folks,
> >
> > a customers hardware (fucking S7 CP from Siemens) loves to emit
> > keep-alive packets once a TCP-connection is established. No chance to
> > turn this off (Siemens doesn’t care about RFC1122). How can I force our
> > FreeBSD 3.4 system to answer these packets. Probably a switch in
> > /sys/netinet/tcp_timer.c...? Compile the kernel and everything is
> > fine...?
>
> If I read /usr/src/sys/netinet/tcp* correctly, you shouldn't have to do
> anything to answer keepalive messages. In fact keepalive messages are just 0
> bytes packets which repeat the last ack sent to the peer.
>
> There is a few sysctl variables which allow you to customize the rate your
> system *sends* those keepalive messages, but none to answer them, because
> the answer is part of the normal TCP processing.
>
> Am I right ? :-)
>
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Hi again,
sounds very reasonable. Are the following tcpdumped packets keep-alive packets
(Siemens says they are)? 10.64.60.100 – 103 are the Siemens S7 CPs, 10.64.60.104
is our FreeBSD 3.4 server.
After a couple of these packets, not replied by 10.64.60.104, the S7 CP resets
the connection.
The wrong packet length (for example 0028) is a result of ethernet frame
padding.
Michael Hartung
.
.
.
10:57:15.975984 10.64.60.103.callbook > 10.64.60.104.globe: . win 0
4500 0028 0194 0000 7806 b3ed 0a40 3c67
0a40 3c68 07d0 07d2 0291 2200 07fe 974e
5000 0000 4f16 0000 b6ff ffff 1011
10:57:16.078589 10.64.60.101.callbook > 10.64.60.104.globe: . win 0
4500 0028 02a3 0000 7806 b2e0 0a40 3c65
0a40 3c68 07d0 07d2 0291 21f1 07ff 303f
5000 0000 b635 0000 b6ff ffff 1011
10:57:16.080035 10.64.60.101.dc > 10.64.60.104.globe: . win 0
4500 0028 02a4 0000 7806 b2df 0a40 3c65
0a40 3c68 07d1 07d2 034b a5a8 07ff b1d0
5000 0000 b031 0000 b6ff ffff 1011
10:57:16.080885 10.64.60.100.globe > 10.64.60.104.globe: . win 0
4500 0028 03c3 0000 7806 b1c1 0a40 3c64
0a40 3c68 07d2 07d2 0428 e651 0800 8439
5000 0000 9c41 0000 b6ff ffff 1011
10:57:16.093227 10.64.60.102.callbook > 10.64.60.104.globe: . win 0
4500 0028 0196 0000 7806 b3ec 0a40 3c66
0a40 3c68 07d0 07d2 0291 2200 0801 74b3
5000 0000 71af 0000 b6ff ffff 1011
10:57:18.481166 10.64.60.100.callbook > 10.64.60.104.globe: .
337956829:337956833(4) win 0
4500 002c 03c4 0000 7806 b1bc 0a40 3c64
0a40 3c68 07d0 07d2 1424 cfdd 098e c49c
5000 0000 a9c6 0000 b6ff ffff 1011
10:57:18.482608 10.64.60.100.dc > 10.64.60.104.globe: . 357566179:357566183(4)
win 0
4500 002c 03c5 0000 7806 b1bb 0a40 3c64
0a40 3c68 07d1 07d2 1550 06e3 098f b75c
5000 0000 7ed3 0000 b6ff ffff 1011
10:57:34.778487 10.64.60.103.callbook > 10.64.60.104.globe: .
43065856:43065860(4) win 0
4500 002c 0195 0000 7806 b3e8 0a40 3c67
0a40 3c68 07d0 07d2 0291 2200 07fe 974e
5000 0000 9812 0000 b6ff ffff 1011
10:57:34.881053 10.64.60.101.callbook > 10.64.60.104.globe: .
43065841:43065845(4) win 0
4500 002c 02a5 0000 7806 b2da 0a40 3c65
0a40 3c68 07d0 07d2 0291 21f1 07ff 303f
5000 0000 ff31 0000 b6ff ffff 1011
10:57:34.882509 10.64.60.101.dc > 10.64.60.104.globe: . 55289256:55289260(4) win
0
4500 002c 02a6 0000 7806 b2d9 0a40 3c65
0a40 3c68 07d1 07d2 034b a5a8 07ff b1d0
5000 0000 f92d 0000 b6ff ffff 1011
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