[CentOS] Multiple IP Address

Brett Serkez bserkez at gmail.com
Sat Sep 15 15:40:14 UTC 2007

> > > I have only assumed it is the address that matches it's
> > host name, which
> > > is why I always configure that in the /etc/hosts file.
> >
> > Right, one would think so, but this doesn't seem to effect
> > this behavior either.
> >
> > Shutting down and start up OpenVPN immediately effects the behavior,
> > indicating this behavior is dynamic.   I've been searching for a way
> > to effect this behavior, perhaps in a configuration file
> > (/etc/sysconfig... or /proc/...) with no luck so far.
> I should have asked this, but what do you mean by the default IP on
> a multi-homed host?

It is not multi-homed, as described in my initial post.  It has only
one ethernet card with a single IP address.  The problem comes in when
running OpenVPN which adds two virtual adapters, each with a unique IP
address (i.e., 10.55.5.x and 10.55.6.x).

When OpenVPN is stopped, all works fine, it is only with OpenVPN
running that the server starts using one of the IPs from the last
virtual adapter as its IP address, in some cases.

> I am unsure whether there is a default IP at all and the routing table
> decides which interface depending on the source and destination IP
> addresses used on the host.

OpenVPN does modify the routing table, but only for the specific
subnet routing, ie. and

The problem is that when a Windows desktop is OpenVPN connected to
another CentOS system on the same local network as the subject server
on an unrelated subnet ( i.e. it is given the subject
server's 10.55.6.x address vs. the ethernet 10.44.0.x address, which
would work perfectly.

So from a Windows workstation on the local subnet, if I ping
CentOServer I get 10.44.0.x, which is what I want.  If I am on the
Windows desktop VPN connected to the other CentOS server on subnet and I ping CentOSServer I get 10.55.6.x vs the 10.44.0.x
I would have expected.  There should be no relationship between the
originating Workstation's IP and the IP it is given for CentOServer,
but there is, I am trying to understand why if there is a way to
change this behavior.

Is this any clearer?


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