TCP Free-BSD setup behaviour.

[Louis Mamakos]

On Jun 15, 2009, at 3:44 AM, saravana perumal wrote:

> Hi Louie ,
>
>
> Thanks for the Response on my Queries.
>
> For QUERY 3,
> ACTIVE open frm Free BSD end:
>
>        FREE BSD          APPLICATION
>                 Send ---------> syn
>                 Receive <-------- SYN
>
> Expect SYN & ACK-------------> Getting only ACK in this Scenario,
>
>  Now Expects FREE BSD to respond back with the SYN & ACK , but BSD  
> is sending only ACK message as the response.

There's no reason why the FreeBSD host would send another SYN;  
presumably the "APPLICATION" host received the SYN and responds back  
with SYN of it's own and ACK of the FreeBSD host's SYN.  Once the SYN  
has been ACK'd, there's no reason to resend it.  I suppose I wonder  
why you expect the FreeBSD system to retransmit it's SYN?

> 4    .When checking the State - TIME-WAIT    Sending FIN and  
> expecting the ACK ;Getting the ACK properly.   Sending Data Segment  
> and Expecting the RST signal not getting the RST ; Instead DUT is  
> sending the Last TCP packet. Issue seen only in Free BSD
>
>
> For this Issue mentioned above, Last TCP packet is jst a Testing  
> packet with the
> following Field set  in TIME-WAIT state ,
>
>
> TCP: ---- TCP Packet ----
> TCP:
> TCP: Source Port           = 16815 (16815)
> TCP: Destination Port      = 16816 (16816)
> TCP: Sequence Number       = 3865716731 (0xE66A27FB)
> TCP: Acknowledgment Number = 0 (0x00000000)
> TCP: Data Offset           = 5 (20 bytes)
> TCP: Reserved              = 0
> TCP: Control Bits          = 0x10
> TCP:  |543210
> TCP:  |0.....              = Urgent Pointer Isn't Significant
> TCP:  |.1....              = Acknowledgment Is Significant
> TCP:  |..0...              = No Push Function
> TCP:  |...0..              = No Reset Connection
> TCP:  |....0.              = No Synchronize Sequence Numbers
> TCP:  |.....0              = More Data From Sender
> TCP: Window                = 32752 bytes
> TCP: Checksum              = 0x41A0 (Correct)
> TCP: Urgent Pointer        = 0 (Not Significant)
> TCP:
> TCP: --- Trailing Data [12 bytes] ---
> TCP:  53 61 6D 70 6C 65 20 44 61 74 61 00               Sample Data.
> TCP: --- Trailing Data End ---
> From machine Sending  to the FREE BSD machine,
>
> This is to verify that Free BSD is in TIME-WAIT state.

Not sure what good this packet trace is; the only reason the TCP would  
respond with a RST segment is if the segment it receives is somehow  
bogus.  Perhaps that the send sequence is outside the window.  If the  
data is within the window, it might be considered an "old" segment  
that happens to arrive, perhaps out-of-order; why would the local TCP  
reset the connection for no good reason?

louie