netdev - Re: Question on SCTP ABORT chunk is generated when the association_max

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Message-ID: <54C62912.3040401@gmail.com>
Date:	Mon, 26 Jan 2015 09:46:26 -0200
From:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:	Sun Paul <paulrbk@...il.com>, Daniel Borkmann <dborkman@...hat.com>
CC:	Michael Tuexen <tuexen@...muenster.de>,
	Vlad Yasevich <vyasevich@...il.com>,
	linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Question on SCTP ABORT chunk is generated when the association_max_retrans
 is reached

Hi,

On 25-01-2015 23:27, Sun Paul wrote:
> Hi
>
> sorry for the late reply. I am a bit confused. when side-A sends a
> request to side-B, and side-B return the response, but side-A keep
> re-transmit the same request to side-B, why side-B needed to send a
> ABORT to side-A?

That happens on data transfers. When A pushes data to B, A has to retry it 
until B finally acknowledges it and A receive this signal. If the ack from B 
gets dropped, A has no way to know if a) the ack was lost or b) its initial 
message never actually made it to A, thus it retransmits. If it reaches a 
limit, it gives up..

> If it is used in order to reestablish the connection, shoudn't it
> should be side-A to send ABORT instead?

Meant to reestablish it? Not really.. just to keep both sides in sync, as A 
has given up by then.

   Marcelo

> - PS
>
> On Sat, Jan 24, 2015 at 3:05 AM, Daniel Borkmann <dborkman@...hat.com> wrote:
>> On 01/23/2015 07:36 PM, Michael Tuexen wrote:
>> ...
>>>
>>> Yepp. It might not reach the peer or it might. If it does it helps
>>> to keep the states in sync. If it doesn't it sometimes helps in
>>> analysing tracefiles. In BSD, we also send it. It is not required,
>>> doesn't harm and is useful in some cases...
>>
>>
>> Ok, as the TCB is destroyed in any case, should be fine then.
>>
>> Thanks,
>> Daniel
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