comp.protocols.tcp-ip
Affichage de l'article :
Re: Somthing wrong with the RST-ACK? Server/Client broken?

Date : Le 03 avril 2008
From : Barry Margolin
Sujet : Re: Somthing wrong with the RST-ACK? Server/Client broken?

In article ,
Markus Rehbach wrote:

> Hi all,
>
> in the follwing trace we see a quite pathological TCP session.
>
> What's broken? RST-ACK in packet 8 malformed? Telnet host defect? Client,
> too?

Where did you make this trace, on the client or the server? I assume
it's the server. Basically, it looks like the SYN-ACKs aren't getting
to the client for some reason. That's why the client resent the SYN in
packet 4. The server keeps resending the SYN-ACKs, doubling the
retransmit time each time.

After about 30 seconds, the client has given up and closed the
connection. When the server retransmits the SYN-ACK after that, it gets
a RST because the connection no longer exists.

What I don't understand is why the server is repeating its SYN-ACKs
after receiving the RST. This seems like a bug in the server's TCP
stack.

>
> 1 0.000000 10.1.14.2 -> 10.2.33.2 TCP 62 1201 > 23 [SYN] Seq=1181960481
> Win=64512 Len=0 MSS=1260
> 2 0.000828 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604381 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 3 2.919766 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604381 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 4 2.920221 10.1.14.2 -> 10.2.33.2 TCP 62 1201 > 23 [SYN] Seq=1181960481
> Win=64512 Len=0 MSS=1260
> 5 8.825826 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604381 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 6 20.645954 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604381 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 7 44.304512 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604381 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 8 44.305136 10.1.14.2 -> 10.2.33.2 TCP 60 1201 > 23 [RST, ACK]
> Seq=1181960483 Ack=1999604382 Win=65535 Len=0
> 9 44.305455 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604382 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 10 44.305773 10.1.14.2 -> 10.2.33.2 TCP 60 1201 > 23 [RST, ACK]
> Seq=1181960483 Ack=1999604383 Win=65535 Len=0
> 11 44.306152 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604383 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 12 44.306573 10.1.14.2 -> 10.2.33.2 TCP 60 1201 > 23 [RST, ACK]
> Seq=1181960483 Ack=1999604384 Win=65535 Len=0
> 13 44.306794 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604384 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 14 44.307531 10.1.14.2 -> 10.2.33.2 TCP 60 1201 > 23 [RST, ACK]
> Seq=1181960483 Ack=1999604385 Win=65535 Len=0
> 15 44.307834 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604385 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 16 44.308265 10.1.14.2 -> 10.2.33.2 TCP 60 1201 > 23 [RST, ACK]
> Seq=1181960483 Ack=1999604386 Win=65535 Len=0
> 17 44.308546 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604386 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 18 44.308911 10.1.14.2 -> 10.2.33.2 TCP 60 1201 > 23 [RST, ACK]
> Seq=1181960483 Ack=1999604387 Win=65535 Len=0
> 19 44.309190 10.2.33.2 -> 10.1.14.2 TCP 60 23 > 1201 [SYN, ACK]
> Seq=1999604387 Ack=1181960482 Win=65535 Len=0 MSS=1452
> 20 44.310401 10.1.14.2 -> 10.2.33.2 TCP 60 1201 > 23 [RST, ACK]
> Seq=1181960483 Ack=1999604388 Win=65535 Len=0
> following an endless SYN-ACK RST-ACK pingpong......
>
> Thank you
>
> Markus
>
> P.S.: Sorry for the length of the trace lines.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE don't copy me on replies, I'll read them in the group ***

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