Re: Selective ACK ON / OFF does not have any impact ?

[Tal Bar-Or <tbaror () gmail com>]

hi
you should look into syn negation
if both support sack option
On 28/04/2011 11:20, "Andi Wijaya" <stev2711 () gmail com> wrote:
> Hi Guys,
> This is my first post, and it's so nice to be able to join this community
so please excuse me if I make any mistake.
> I'm doing a capture with SACK ON and with SACK OFF, my understanding is
with SACK OFF, the server will have to retransmit the packet from the point
of packet lost. However what I see is the server does not retransmit the
packet at all and just continuing with the rest of the data (please see the
TCP Trace screenshot attached). While for SACK ON, everything went well as
the theory.
> SACK OFF: (I removed some column for easier viewing)
>
> No  Source           Destination      Seq.#   Nxt.Seq.  Ack.#   Info
> 193 10.10.1.58       125.252.232.170    2286            112769  [TCP Dup
ACK 125#34] 1069 > 80 [ACK] Seq=2286 Ack=112769 Win=32768 Len=0
> 194 125.252.232.170  10.10.1.58       112769  114229      2286  [TCP
Retransmission] [TCP segment of a reassembled PDU]
> 195 10.10.1.58       125.252.232.170    2286            137589  1069 > 80
[ACK] Seq=2286 Ack=137589 Win=32768 Len=0
> 196 125.252.232.170  10.10.1.58       137589  139049   2286 [TCP
Retransmission] Continuation or non-HTTP traffic
> 197 10.10.1.58      125.252.232.170 2286 144889 1069 > 80 [ACK] Seq=2286
Ack=144889 Win=32768 Len=0
> My question is, packet no.193 is the Dup ACK and no.194 is the TCP
retransmission, but why no.195 does not do a TCP retransmission of 114229
(which is the next seq.) but go to 137589 (no 195)instead ?  Am I missing
something here ?  Thanks/
>
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