circular parent/child chain

[Andreas Ericsson]

On 11/17/2012 06:08 PM, Lucy Pelzer wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Hi List,
> 
> I am in charge for a big network infrastructure and at the moment we
> evaluate solutions for our nagios monitoring with configuration via
> monarch. I really would like to create the new solution with nagios and
> puppet. There is only one big problem. In our infrastructure there are a
> lot of switches connected together like this:
> 
>                ------------
>                | switch-1 |
>                ------------
>                  /       \
>                 /         \
>                /           \
>        ------------     ------------
>        | switch-2 |-----| switch-3 |
>        ------------     ------------
>             |                 |
>             |                 |
>        ------------     ------------
>        | switch-5 |-----| switch-4 |
>        ------------     ------------
> 
> All the time I try to configure this switch connections in nagios with
> more than one parent, where the hosts are at the same time parent and
> child, I get the following error:
> 
> ERROR: The host 'switch-2' is part of a circular parent/child chain!
> ...
> 
> I know by now that this is because nagios has to be hierarchically, but
> I do not understand why. Maybe somebody could tell me exactly why I
> can’t configure this in nagios or better could tell me how I can do it.
> I only found the explanation that this could conduct a deadlock. Maybe I
> am wrong, but is this not a likely network infrastructure? At last it is
> no problem to build something like this with STP running in your network.
> 

It is, but parent-child relations concern network data flows, and not
necessarily the cables connecting various pieces of equipment.

In your case switch5 should have switch2 as parent, switch4 should have
switch3 as parent, switch2 and switch3 should both have switch1 as
parent.

Think of how the traffic goes. It will never travel like this:
  switch1 -> switch2 -> switch3 -> switch4
but it will travel like this:
  switch1 -> switch3 -> switch4

(assuming you have a somewhat sane network, that is).

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

Considering the successes of the wars on alcohol, poverty, drugs and
terror, I think we should give some serious thought to declaring war
on peace.

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