SYNCOOKIE authentication problems

[David Malone]

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: [192.168.0.11]:59661 to 
> [192.168.0.11]: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
problem.

	David.