Warning, got duplicate tcp line – netstat error and solution

Posted on in Categories last updated June 28, 2006

Q. Whenever I run netstat command it bumps be back with an error, which read as follows:
tcp 0 0 ip-201-19-xxx-xxx.ip.s:http adsl-71-129-54-230.dsl:2249 TIME_WAIT
tcp 0 0 ip-201-19-xxx-xxx.ip.s:http ca-dstreet-cuda3-c6a-5:4380 TIME_WAIT
tcp 0 0 ip-201-19-xxx-xxx.ip.s:http ip72-199-249-17.sd.sd.:1845 TIME_WAIT
tcp 0 0 ip-201-19-xxx-xxx.ip.s:http cache-mtc-ad10.proxy.:59985 TIME_WAIT
warning, got duplicate tcp line
warning, got duplicate tcp line

Although, everything is working fine but I am little worried about this error. How do I fix this error and what does it mean?

A. This is quite uncommon. This error indicating that client/server connection are rapidly closing and reconnecting to ip ip-201-19-xxx-xxx.ip on same port 80.

To fix this problem, open /etc/sysctl.conf and

# vi /etc/sysctl.conf

Append or modify text as follows:

net.ipv4.tcp_tw_reuse = 0
net.ipv4.tcp_tw_recycle = 0

Save the file and reboot the system. If particular client IP addresses causing this problem, use the iptables to drop the client IP or block IP with null routes.

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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3 comment

  1. # Append or modify text as follows:

    # net.ipv4.tcp_tw_reuse = 0
    # net.ipv4.tcp_tw_recycle = 0

    I did like you said, but “warning, got duplicate tcp line” still happens. What does it mean actually. Where I can find more info about the matter?

    Reply Report comment

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