In certain unique situations the output of the netstat command may produce output similar to below:
tcp 0 0 X.X.X.X:80 X.X.X.X:1035 TIME_WAIT tcp 0 0 X.X.X.X:80 X.X.X.X:2028 TIME_WAIT warning, got duplicate tcp line warning, got duplicate tcp line
Another incarnation of the same issue is:
tcp 0 0 X.X.X.X:80 X.X.X.X:1035 TIME_WAIT tcp 0 0 X.X.X.X:80 X.X.X.X:2028 TIME_WAIT warning, got BOGUS tcp line warning, got BOGUS tcp line
It is likely an artifact of having tcp_tw_recycle and tcp_tw_reuse enabled in the sysctl settings. To check if you have these parameters set run the following commands:
sysctl net.ipv4.tcp_tw_recycle sysctl net.ipv4.tcp_tw_reuse
The output value of 1 means they are enabled. These kernel parameters can be disabled with the following entries in /etc/sysctl.conf:
net.ipv4.tcp_tw_reuse = 0 net.ipv4.tcp_tw_recycle = 0
Execute sysctl -p to make these new settings take effect.
Essentially the messages mean there are two identical recorded TCP connections. This can happen if a connection is rapidly closing and re-connecting on the same address/port tuple. This should not happen, however, having the settings above enables increases the chances.
These messages are harmless and have not been found to degrade performance in any way. Work is underway at the moment to suppress these messages in further releases of Red Hat Enterprise Linux but is not a high priority because of the messages' benign nature.
Note: This is the most common cause of the message. There maybe other causes. If this does not solve the problem, contact Red Hat Technical Support to troubleshoot the issue.