SYNCOOKIE authentication problems

David Malone dwmalone at
Fri Jun 29 14:55:50 UTC 2007

On Wed, Jun 27, 2007 at 06:43:11PM -0700, Steve Kargl wrote:
> Any advice on how to isolate or avoid?
> Jun 27 18:31:19 node11 kernel: TCP: []:59661 to 
> []:63266 tcpflags 0x10<ACK>; syncache_expand: Segment failed
> SYNCOOKIE authentication, segment rejected (probably spoofed)

It looks like you tried to open a TCP connection to yourself, but
the connection failed. You could try leaving a tcpdump running:

	tcpdump -i whatever_interface -w /tmp/synfinrstdata -s 1500 'tcp[tcpflags] & (tcp-syn|tcp-fin|tcp-rst) != 0'

while your MPI app runs and then we can have a look at the packets
that caused the problem. The above should collect all TCP SYN, FIN
and RST packets, which would probably be enough to diagnose the


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