TCP conection problems IBM VM -> FreeBSD
cswiger at mac.com
Fri Mar 23 17:30:27 UTC 2007
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
>> option corresponds. Looks to be a bug with the vm machine, the
>> 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).
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