Re: strange tcp behavior

["Simon Arlott" <simon@fire.lp0.eu>]

On Thu, August 2, 2007 11:16, Evgeniy Polyakov wrote:
> On Thu, Aug 02, 2007 at 01:55:50PM +0400, Evgeniy Polyakov (johnpol@2ka.mipt.ru) wrote:
>> On Thu, Aug 02, 2007 at 09:19:06AM +0300, john@screen.lv (john@screen.lv) wrote:
>> > 1186035057.207629    127.0.0.1 -> 127.0.0.1    TCP 50000 > smtp [SYN]
>> > Seq=0 Len=0
>> > 1186035057.207632    127.0.0.1 -> 127.0.0.1    TCP smtp > 50000 [SYN, ACK]
>> > Seq=0 Ack=1 Win=32792 Len=0 MSS=16396
>> > 1186035057.207666    127.0.0.1 -> 127.0.0.1    TCP 50000 > smtp [ACK]
>> > Seq=1 Ack=1 Win=1500 Len=0
>> > 1186035057.207699    127.0.0.1 -> 127.0.0.1    SMTP Command: EHLO localhost
>> > 1186035057.207718    127.0.0.1 -> 127.0.0.1    TCP smtp > 50000 [ACK]
>> > Seq=1 Ack=17 Win=32792 Len=0
>> > 1186035057.207736    127.0.0.1 -> 127.0.0.1    TCP 50000 > smtp [RST]
>> > Seq=17 Len=0
>> > 1186035057.223934    127.0.0.1 -> 127.0.0.1    TCP 33787 > 50000 [RST,
>> > ACK] Seq=0 Ack=0 Win=32792 Len=0
>> >
>> > Can someone please comment as to why, tcp  stack sends rst packet from the
>> > wrong source port in this situation.
>>
>> Besides the fact, that test applications do not run if started not as
>> root, I got this:
>
> And it actually does not initializes a session, since tird line below
> shows RST, but not ack. The same with sendmail smtp server (i.e. 25 port
> like in your server) and unmodified client.
> Please provide application which can trigger the issue and I will help
> to debug this issue. If it will help you to debug client, I can run
> tcpdump on public server (say 194.85.82.65, please tell me your source
> address) to collect dumps. Current code does not trigger the issue on my
> machines (and works not like was intended by you). Ugh, and code really
> looks horrible...
>

I just got multiple RSTs instead of a connection too. The second RST looks
like it's from another connection - and a RST for a RST is wrong...

-- 
Simon Arlott