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Bug 437937 - udp packet duplication in localhost with multicast sendto()
udp packet duplication in localhost with multicast sendto()
Product: Red Hat Enterprise Linux 4
Classification: Red Hat
Component: kernel (Show other bugs)
x86_64 Linux
low Severity high
: rc
: ---
Assigned To: Neil Horman
Martin Jenner
Depends On:
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Reported: 2008-03-18 06:28 EDT by keisuke kuzukawa
Modified: 2009-03-23 07:11 EDT (History)
0 users

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Doc Type: Bug Fix
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Last Closed: 2009-03-23 07:11:20 EDT
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Description keisuke kuzukawa 2008-03-18 06:28:06 EDT
Description of problem:
UDP Packet duplication occurs when sendto() called within many process
at the same time. each processes are joined to different multicast addr,port.
ratio of duplication is around 0.6%-2.0% of all sent packet per 1 addr.
(verified by tcpdump)

Version-Release number of selected component (if applicable):
uname -a
Linux xxxxxxx 2.6.9-5.EL #1 Wed Jan 5 19:21:57 EST 2005 x86_64 x86_64 x86_64

How reproducible:
As the number of the processes increases, the packet repetition rate rises.

Steps to Reproduce:
1.send multicast packet with sendto().
2.capture any multicast group with tcpdump
Actual results:
when 20 process startup, each process sent 10000 udp packet.
captured 1 multicast addr with tcpdump, and received 10003packet. 
3 packets was the same one sent just before.

Expected results:

Additional info:
it never happen if sendto() called sequential.
Comment 1 Neil Horman 2008-05-12 14:29:36 EDT
I'm going to set up a system to reproduce this.  In the interim, if you have a
copy of the tcpdump that you captured for me to review, that would be helpful. 
Comment 2 Neil Horman 2008-08-07 08:48:15 EDT
ping, any word on that tcpdump?
Comment 3 Neil Horman 2009-03-23 07:11:20 EDT
closing, no response

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