On 13.07.2011 12:37, Vladimir Budnev wrote:
Hello.
Iv faced some problem and seems don't realize the mechanincs why does it
occures.
First of all i'd like to notice that my freebsd knowledge and expirience is
limited, especially in such "strange" cases.
In details(code example ill be at the end):
System:
# uname -spr
FreeBSD 7.2-RELEASE amd64
We have simple TCP client and server.
Server is very casual, it listens on some port in while->select->accept
loop.
Client knocks on server port and sends some data and closes the port.
First it was designed for sending data 3-5/times per minute. But once during
test I'v noticed that if client sends data very fast (more precisely it
opens and closes socket to server very fast) there is
"54 - Connection reset by peer" error on call to "connect".(on client side
ofc)
Some illustration from tcpdump:
(test on localhost.server side is port 10002.i'v cuted other fields for
simplicity)
<...>
13:48:58.491229 IP 127.0.0.1.56677> 127.0.0.1.10002: S
13:48:58.491255 IP 127.0.0.1.10002> 127.0.0.1.56677: S ack
13:48:58.491266 IP 127.0.0.1.56677> 127.0.0.1.10002: . ack
13:48:58.491300 IP 127.0.0.1.56677> 127.0.0.1.10002: P
13:48:58.491346 IP 127.0.0.1.56677> 127.0.0.1.10002: F
13:48:58.491365 IP 127.0.0.1.10002> 127.0.0.1.56677: . ack
13:48:58.491466 IP 127.0.0.1.55238> 127.0.0.1.10002: S //
13:48:58.491490 IP 127.0.0.1.10002> 127.0.0.1.55238: S ack // handshake
13:48:58.491503 IP 127.0.0.1.55238> 127.0.0.1.10002: . ack //
13:48:58.491536 IP 127.0.0.1.55238> 127.0.0.1.10002: P<--data
13:48:58.491580 IP 127.0.0.1.55238> 127.0.0.1.10002: F<-- client
closes session
13:48:58.491599 IP 127.0.0.1.10002> 127.0.0.1.55238: . ack // OK
13:48:58.491701 IP 127.0.0.1.60212> 127.0.0.1.10002: S
13:48:58.491726 IP 127.0.0.1.10002> 127.0.0.1.60212: S ack
13:48:58.491738 IP 127.0.0.1.60212> 127.0.0.1.10002: . ack
13:48:58.491745 IP 127.0.0.1.10002> 127.0.0.1.60212: R<-- this is
strange answer.Why?
13:48:58.491887 IP 127.0.0.1.60804> 127.0.0.1.10002: S
13:48:58.491914 IP 127.0.0.1.10002> 127.0.0.1.60804: S ack
13:48:58.491924 IP 127.0.0.1.60804> 127.0.0.1.10002: . ack
13:48:58.491931 IP 127.0.0.1.10002> 127.0.0.1.60804: R
<...>
Some connections were OK but then server application begin to send RST right
after handshake.
Tuning listen backlog parameter doesn't help much, BUT what really solves
the "problem" is increasing time interval between client
requests.egusleep(10000) solves the "problem" at all.
Iv maned for some tuning like syncache and syncookies but nothing usefull,
or i missed something.But here they are:
# sysctl -a | grep syncache
net.inet.tcp.syncache.rst_on_sock_fail: 1
net.inet.tcp.syncache.rexmtlimit: 3
net.inet.tcp.syncache.hashsize: 512
net.inet.tcp.syncache.count: 0
net.inet.tcp.syncache.cachelimit: 15360
net.inet.tcp.syncache.bucketlimit: 30
ipfw rules allows any from any, nothing special.
QUESTION:
So the question is why such thing happening?Is this is some freebsd defense
from syn flood?(to be honest don't think so because seems there is no fixed
"ALLOWED syn/syn-ack/ack per seconds"). It more looks like some queue
overflow,but I don't know what queue and how it can be enlarged.
If i can provide some more info to clear some aspects I will!
When you enable "net.inet.tcp.log_debug=1" it will tell you at LOG_DEBUG
level what went wrong and why it sent the RST.
--
Andre
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