multiple IPs for a host?

[Peter J. Holzer]

On 2005-01-18 13:02:26 +0000, Andy Smith wrote:
> On Tue, Jan 18, 2005 at 11:39:35AM +0100, Peter J. Holzer wrote:
> > On 2005-01-17 16:08:44 +0000, Andy Smith wrote:
> > > So, what I would like to do is have nagios ping the production IP
> > > but do all the other service checks over the management IP.
> > 
> > Should those services be available only on the management network or
> > also on the production network? In the latter case you probably should
> > check them on the production network as well. Otherwise you won't notice
> > if a service goes down only on the production network.
> 
> The thinking here is that we don't want all the service checks going
> over the production network, so as long as the production network IP is
> reachable and the services are all available over the management IP
> then we would assume that the services are also available over the
> production IP.
> 
> Is this a reasonable assumption?

That depends on the services, and maybe the OS.

For example, if a server binds every interface explicitely (Bind does
this, and Apache in many configurations), it is entirely possbile that
it succeeds to bind to the management interface, but fails to open the
production interface (e.g., because the production interface was down
during a restart, or a hung process was still using it). Then you can
ping the production interface, and access the service at the management
interface, but still not access the service at the production
interface.

If the service binds to any interface (0.0.0.0), then I think your
assumption would be correct (but I'm still not 100% sure).

My rule of thumb is: If you want to know whether X works, try to test X
directly, instead of testing Y and Z and reasoning that if Y and Z work
then X must work, too. Of course I realize that this is not always
possible.

	hp


-- 
   _  | Peter J. Holzer      | If the code is old but the problem is new
|_|_) | Sysadmin WSR / LUGA  | then the code probably isn't the problem.
| |   | hjp at wsr.ac.at        |
__/   | http://www.hjp.at/   |     -- Tim Bunce on dbi-users, 2004-11-05
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