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Re: [SCTP-Discussion] sctplib 1.0.4


Chronological Thread 
  • From: Michael Tuexen <Michael.Tuexen AT micmac.franken.de>
  • To: Andreas Fink <afink AT global-networks.ch>
  • Cc: "discussion (E-mail)" <discussion AT sctp.de>
  • Subject: Re: [SCTP-Discussion] sctplib 1.0.4
  • Date: Wed Sep 21 20:42:02 2005
  • List-id: SCTP Discussions <discussion.sctp.de>
Andreas,

see my comments in-line.

Best regards
Michael

On Sep 21, 2005, at 20:01 Uhr, Andreas Fink wrote:

2005-09-21 16:37:45 [10298] [2] DEBUG: SCTP[101] communication lost (status 1)
Error Info: 16:37:45.976 - sctp_send: addressed association does not exist
2005-09-21 16:37:45 [10298] [11] DEBUG: sctp_send: returns error -3 Assoc not found


Could it be that you have multiple instances of the SCTPlib running on a host.
This works only if you disable the OOTB handling.

No there is only one instance which owns the sctp raw port. There might have been a version running and unsafely quit leaving open ports on the remote side.
Hmm. Maybe running ethereal helps understanding that.


the association is re established by my application

2005-09-21 16:37:45 [10298] [11] DEBUG: SCTP[101] sctp instance [1] associated and opened [193.53.0.180:8002] -> [210.50.197.60:8002]. Assoc=[2]
Error Info: 16:37:46.362 - rxc_buffer instance not set !
2005-09-21 16:37:47 [10298] [2] DEBUG: SCTP[101] communication UP. Assoc=2 (status 2)
2005-09-21 16:37:47 [10298] [2] DEBUG: SCTP[101] network status change: path 0 is now ACTIVE

so far so good. I can now communicate and send M2PA packets back and forth and upper layers come up.
Maybe first attempt, other side was not ready or so (can easily be if you debug stuff with SCTPLib as the other side might not have noticed you having shut down or such).

now I break the IP link on purpose (the bug I'm hunting in my app is a non re-establishment of a M2PA link if the IP link in between gets interrupted for a few seconds). I wouldt expect to get a communication lost error after a few seconds or so. But I get nothing. When I force a packet being sent I simply get:

Error Info: 16:46:07.277 - AF_INET : sendto()=-1 !

When you plug out a cable the routing table is changed and it may happen
that you can not send a packet to a particular destination because you
have no route.

This is of course so. There is only one path and that one we broke up. But SCTP should detect the loss of connectivity and signal it to the upper layer (why else are there triggers for com-up and com-down?).
com-up is given to the upper layer after the four way is completed. com-down means that
SCTP has decided to close the association because en ABORT was received or some error
thresholds are reached.


For SCTP it does not matter. It will not receive an ACK...

Yes it wont receive ack. my application should be notified of this lack of communication but sctp lets me continue sending messages into the blue.
There should not me more than 10 retransmissions or so. Depends on the parameters. The
standard setting can take some minutes to detect it.
Do you get eventually the com-lost notification or not?


Am I running into a bug or did I do something wrong?
I didn't see those new error messages in sctplib1.0.3 (havn't tested the breaking of the link though).

There are not that much changes between 1.0.3 and 1.0.4...

Well I never had those errors in 1.0.3. That worries me.

Andreas Fink
Global Networks Schweiz AG

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