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Old 07-22-2008, 12:15 PM   #1
Registered: Feb 2007
Location: /home
Distribution: Kubuntu and CentOS
Posts: 214

Rep: Reputation: 32
RESOLVED: netstat lists interface that is not present

Hi LQers,

I have been working with a RHEL5 box that some one else installed. They did not know what they were doing and so used the "kitchen sink install method", as I like to call it (i.e. if it can be installed, it was installed). Stuff like the xen kernel was installed (which I have no real experience with).

Now I am trying to troubleshoot why a network service we are developing isn't working correctly. netstat is displaying a connection which neither endpoint is part of the box. Any ideas why I might be seeing this? And how to fix it / make it go away?

The issue was apparently related to the network service. Grrrr.

Last edited by Hewson; 07-25-2008 at 12:06 PM. Reason: problem was resovled
Old 07-23-2008, 11:41 PM   #2
Registered: Sep 2007
Location: SF Bay Area, CA
Distribution: CentOS, SLES 10+, RHEL 3+, Debian Sarge
Posts: 159

Rep: Reputation: 32
Can you copy/paste the output of netstat here?

XEN installs about 10 VIFs and a bridge or two, but shouldn't affect networking for dom0 unless you customized it (e.g. turned on vlan tags or changed the interface of dom0). You can always just disable XEN and delete the VIFs/bridges.

Last edited by kenoshi; 07-23-2008 at 11:42 PM.
Old 07-25-2008, 12:19 PM   #3
Registered: Feb 2007
Location: /home
Distribution: Kubuntu and CentOS
Posts: 214

Original Poster
Rep: Reputation: 32
It wasn't XEN related. After further investigation I found out that netstat trims long IP addresses so that column layout stays intact. '-T' turns this off. It was a simple PEBKAC problem.

Instead of displaying the whole IP address it was displaying only 2 of the 3 digits of the last octet. A glance at this output from netstat and I started thinking that I had a phantom interface. I then saw the same issue on other machines (which also had the same first 3 IPV4 octets, as well as, the same first 2 digits of the last octect for their IPs). At this point I started thinking that the developers bound their service to some fictitious address so that different processes of the same service could communicate (which, of course, isn't a very good idea...). Finally I realized netstat was trimming the columns so they would look pretty and by co-incidence the other machine's addresses where close enough to mine that I only further confused myself.


netstat, xen

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