Date: Fri, 23 Mar 2007 10:30:23 -0700 From: Chuck Swiger <cswiger@mac.com> To: Torbjorn Granlund <tg@swox.com> Cc: freebsd-questions@freebsd.org Subject: Re: TCP conection problems IBM VM -> FreeBSD Message-ID: <A6AC4F24-6D1D-4D54-8DDE-9EE531FADB79@mac.com> In-Reply-To: <861wjfev78.fsf@king.swox.se> References: <868xdqnnzd.fsf@king.swox.se> <E2D691F7-FF70-4D6E-95D7-357B5815C419@mac.com> <86odmlhzn8.fsf@king.swox.se> <4A2495E9-3060-4D05-A7B4-7CCC019AFEB8@mac.com> <861wjfev78.fsf@king.swox.se>
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On Mar 23, 2007, at 10:16 AM, Torbjorn Granlund wrote: >>> These are the ones the correspond. They come in bursts like >>> that. If >>> I let it run a little longer, I get output like this: >>> >>> 19:45:56.939958 IP vm.se.lsoft.com.58679 > bang.swox.se.smtp: S >>> 678305700:678305700(0) win 8192 <mss 1420,wscale >>> 0,nop,nop,nop,timestamp 2317060084 0> >>> 19:45:56.940154 IP bang.swox.se.smtp > vm.se.lsoft.com.58679: S >>> 3183232720:3183232720(0) ack 678305701 win 57344 <mss >>> 1460,nop,wscale 0,nop,nop,timestamp 24588210 2317060084> >> >> Notice the ACK from vm.se.lsoft.com is off by one, but the >> timestamp >> option corresponds. Looks to be a bug with the vm machine, the >> bang >> machine is behaving properly per the TCP requirements. > > Now you're confusing me. It's not intentional. I might be confusing us both. :-) > (1) There is no ACK sent from vm.se.lsoft.com. The only ACKs sent > are i the other directions, as per the tcpdumps above. Uh, yes. I meant this packet: bang.swox.se.smtp > vm.se.lsoft.com.58679: S 3183232720:3183232720 (0) ack 678305701 > (2) The ACKs are not off by one, or if you prefer, ACKs on TCP are > always off by one. They are one higher than one would expect. You're right-- the SYN+ACK reply to a connection open (bare SYN) should reply with SEQ = ISS + 1 to acknowledge the SYN (which counts as a byte). -- -Chuck
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