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I0OJJ > AX25 11.12.20 15:04l 84 Lines 3108 Bytes #999 (0) @ WW
BID : 2Z47_I0OJJ
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Subj: Re: SABM gets double UA response ? why ?
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>From i0ojj@i0ojj.ampr.org Fri Dec 11 13:54:01 2020
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>From: Gustavo Ponza <i0ojj@i0ojj.ampr.org>
References: <A08ZJ_VE4KLM@i0ojj.bbs>
Organization: SICD Rome
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Hi,
On 12/11/20 6:55 AM, ve4klm@ve4klm.#wpg.mb.can.noam wrote:
> I have stumbled across a problem where if I connect to a node that
> depends on
> the AX25 Linux stack it is now sending me 2 (TWO) UA frames in response to
> my opening SABM frame. I've never seen this happen until the past week ...
are you referring to a front-end node, or a particular kinda node?
However, as per my experience, the first problem may be caused
by a faulty linux kernel; there are several kernel series that
had the AX.25 stack corrupted/malformed; then also some AX.25
apps/tools/libs versions make their part on the play; then the
may add faults ... :)
So, I'm also convinced that non-official apps/tools/libs have
minor problems with respect to the official one.
> The first UA frame comes in and I move to a LAPB_CONNECTED state, but
> then almost instantly a second UA frame comes in. From what I can see, JNOS
> will see this as a reason to try and re-establish the link, and suddenly
> a firestorm
> is unleashed, effectively creating a DOS attack. It's quite unreal to
> watch on the logs (trace).
I experimented in the past when play with the ax(x) interfaces
by doing some intrepid setup; the result obtained was an infinite
flow of zeros; I used the ax.25 'listen' this avalanches ...
> My instant fix for this (and I confirm it works) is to ignore UA FRMR if
> we are
> in a LAPB_CONNECTED state, which probably should have been the case all
> along. But honestly in the 16+ years of xNOS, this is a first. I've
> never seen this
> before, ever ! I can fix it on my end no problem, but I want to find the
> cause.
No, no, the JNOS2 can not be touched to accomplish the external faults;
but, towards certain limits may be created a /dev/null mechanism or the
complete exclusion on the insidious: front-end, node, or other else.
> I can't find in the AX25 specs what a system should do it it receives a
> UA while
> in LAPB_CONNECTED, but I never saw this situation ever happen until now, so
> it was never a problem.
>
> The system I am connecting to is dependent on AX25 Linux Stack if I am not
> mistaken, so is anyone aware of an bug or issue in the AX25 utils or
> tools or
> whatever they are called (sorry, but I don't use the AX25 Linux Stack) that
> might be causing this ?
>
> Maiko / VE4KLM
You may refer to RMGATE:I0OJJ-3, 44.134.33.71, to compare the data
of any kinda mode, but no telnet connection is available :)
--
73 and ciao, gustavo i0ojj/ir0aab/ir0eq
non multa, sed multum
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