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Outbound traffic spike every 30 minutes on my Linux server?

+3 votes

Since last two days one of my CentOS servers has been generating a small spike of outbound traffic every 30 minutes (X:00 and X:30). It's not enough traffic to really cause any notice except for the fact that it is a very regular pattern and it started abruptly at midnight Sunday.

I tried grepping through my firewall logs, but have been unable to find anything useful there either. I don't see any cron jobs that would generate network traffic. Any suggestions how I can go about tracking this down?

posted Dec 3, 2013 by Meenal Mishra

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Run rkhunter? Actually, if it's that regular, you could run tcpdump when you expect it.
Is inbound or outbound? What port? tcp or udp?
It is outbound from my server to the Internet. My traffic monitor does  not give me any more detailed information, just a nice sawtooth graph showing the regular spikes.

TCP or UDP and the port is part of what I am trying to determine.

1 Answer

0 votes

Actually, if it's that regular, you could run tcpdump when you expect it.

answer Dec 5, 2013 by Kumar Mitrasen
rkhunter complained about a few files, but "rpm --verify" doesn't flag any of them. Other than that, just a few insecure settings and out of date programs, which are not ideal, but do not indicate a problem on their own.

I could try running tcpdump or wireshark, but that's going to generate a lot of data and I'm not sure how to go about filtering it. I know the spike happens on the hour and half hour, but my traffic monitor does not give me enough detail to see exactly when it starts or exactly how long it lasts and I don't know what protocol or port I'm looking for.
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