SCTP seems to lose its socket state.

[David Laight <David.Laight@ACULAB.COM>]

I've been looking at an ethernet trace from one of our customers.
They seem to have got an SCTP socket into a rather confused state.

There seem to be a significant number of transmit ethernet frames
that don't read the far end.
This shouldn't cause a real problem, but we end up with the following:
This trace was taken on the linux system:

39964   0.304473        ->      SCTP    INIT
39965   0.292669        <-      SCTP    INIT  (I think this has an invalid checksum)
39968   0.467935        <-      SCTP    INIT
39969   0.000093        ->      SCTP    INIT_ACK
39970   0.003947        <-      SCTP    COOKIE_ECHO
39971   0.000072        ->      SCTP    COOKIE_ACK
39972   0.000337        ->      M3UA    ASPUP
39979   0.809659        <-      SCTP    COOKIE_ECHO
39980   0.000058        ->      SCTP    COOKIE_ACK
shutdown() called here - seems to be ignored
39983   0.949471        <-      SCTP    COOKIE_ECHO
39984   0.000053        ->      SCTP    COOKIE_ACK
39986   0.730072        ->      M3UA    ASPUP           Same TSN as above
40002   0.270589        ->      M3UA    ASPUP           Same TSN as above
40008   3.689088        <-      SCTP    HEARTBEAT
40009   0.000027        ->      SCTP    HEARTBEAT_ACK
40014   0.261152        <-      SCTP    HEARTBEAT
40015   0.000033        ->      SCTP    HEARTBEAT_ACK
40026   0.123048        <-      SCTP    HEARTBEAT
40027   0.000030        ->      SCTP    HEARTBEAT_ACK
40036   1.615048        ->      M3UA    ASPUP           Same TSN as above

There are no signs of any SACKs for the ASPUP, I think they have the
correct TSN (the same value as in the INIT_ACK).
No signs of any shutdowns or aborts from either system.

As seems to be typical for M3UA the source and destination ports are
the same. No additional IP addresses appear in the INIT (etc) messages.

Some 80 seconds after the start of the above the remote sends us another INIT.
This is responded to (with new verification tags from both ends), but only
SCTP heartbeats get sent/received (both ways).

The remote sends a few heartbeats with the old verification tag they are
ignored.

The application is repeatedly trying to connect() - but the requests fail
immediately (errno unknown).
I think the system is RHEL 6.4, kernel: 2.6.32-358.el6.x86_64.

Does this 'ring any bells' ?
I think I've asked a similar question before - and 2.6.32 was thought
to be a late enough kernel.
It is, of course, possible they are running RHEL 5 on this system.

I can't think of an easy way to repeat the above sequence to verify
on a much more recent kernel.

	David