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Performance problem with bidirectional nc

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Old 02-25-2011
Performance problem with bidirectional nc
Working on a simple, half duplex network diagnostic that will run anywhere using nc and dd. Performance is symmetrical with sink and source nc processes open as a server:

Code:
nc -vkl 5000 > /dev/null &
cat /dev/zero | nc -vkl 5001 &

With this on the client:

Code:
nc host0 5001 | dd of=/dev/null count=10000
5119384 bytes (5.1 MB) copied, 0.037134 seconds, 138 MB/s

dd if=/dev/zero count=10000| nc host0 5000
5120000 bytes (5.1 MB) copied, 0.036661 seconds, 140 MB/s

When I try to make the connection bi-directional on the same port, the write performance degrades:

Code:
cat /dev/zero | nc -vkl 5000 >/dev/null &

nc host0 5000 | dd of=/dev/null count=10000
5098656 bytes (5.1 MB) copied, 0.036657 seconds, 139 MB/s

dd if=/dev/zero count=10000| nc host0 5000
5120000 bytes (5.1 MB) copied, 11.6311 seconds, 440 kB/s

I'd like the diagnostic to use a single port, if possible. Any insights or suggestions would be greatly appreciated.

Thanks,

Tom
Last edited by pludi; 02-25-2011 at 05:16 AM.. Reason: code tags, please...
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