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Date: Sun, 7 Nov 2010 23:38:15 +1100 (EST)
From: Ian Smith <smithi@nimnet.asn.au>
To: Alexander Frolkin <avf@eldamar.org.uk>
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Cc: freebsd-questions@freebsd.org
Subject: Re: How to disable syncookies & syncache
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In freebsd-questions Digest, Vol 335, Issue 14, Message: 2
On Sun, 7 Nov 2010 12:09:26 +0100 Alexander Frolkin <avf@eldamar.org.uk> wrote:
 > Hi,
 > 
 > I spent all day yesterday trying to get my FreeBSD box (8.1-RELEASE,
 > amd64) to talk to a Qlogic 4010 iSCSI card.
 > 
 > The problem is that when the Qlogic card tries to make a connection,
 > FreeBSD resets it (SYN, SYN|ACK, ACK, RST).
 > 
 > If I turn on net.inet.tcp.log_in_vain, I can see a message similar to
 > 
 >   TCP: [172.16.25.2]:30557 to [172.16.25.1]:3260 tcpflags 0x10<ACK>;
 >   syncache_expand: TSECR 0 != TS 267223, segment rejected
 > 
 > for each connection attempt.
 > 
 > I've tried fiddling around with the net.inet.tcp.syn* sysctls, but all
 > I've managed to to is change the message to
 > 
 >   TCP: [172.16.25.2]:29387 to [172.16.25.1]:3260 tcpflags 0x10<ACK>;
 >   syncache_expand: Segment failed SYNCOOKIE authentication, segment
 >   rejected (probably spoofed)
 > 
 > (this was with net.inet.tcp.syncookies_only=1, I believe) --- the
 > connection still gets reset, as before.
 > 
 > The only "solution" I've found so far is to comment out the bit of code
 > in sys/netinet/tcp_syncache.c that checks if TSECR == TS, but needless
 > to say, this is horrible, and will probably create other problems.
 > 
 > Now, I know what you're probably going to say --- the Qlogic card has a
 > broken TCP implementation.  While that may well be true, this is the
 > card I have and I'm stuck with it, so there's not much I can about that.
 > 
 > Any suggestions welcome. :-)

Only that if I had such an issue I'd head for net@freebsd.org and post 
the above there, where the syncache cookie monsters tend to hang out :)

cheers, Ian