Ring topology parent/child relation Nagios
Mihai Tanasescu
mihai.tanasescu at airbites.ro
Mon May 12 22:55:24 CEST 2008
>
> This problem should not exist.
Nagios --> Router A --> Router B uplink1+2 ring (and Router B is in a
ring topology which closes in it)
http://tinypic.com/view.php?pic=11uhx7a&s=3 (this is the logical layout)
Yes. But if you cut the 2 uplinks from Router B, then the Nagios machine
will see Router B as up but will not be able to reach any other router
from the ring and will thus alert that all other routers are down (which
is not true).
I mean having split the ring into the 2 halves you suggested that:
C has parent B, D has parent C, E has parent D
G has parent B, F has parent G
=> B up but B uplinks to C and G down -> alerts that C and G are down
although they aren't
Can this be eliminated ? (I'm sure the solution should be simple and
obvious but I'm not being as careful as I should to see it)
Am I right ?
P.S. Currently I am monitoring each link state (up/down) by using SNMP
interface queries (on Cisco routers) and the hosts themselves with
ping/icmp on loopback interfaces that are propagated throughout the
network for reachability(OSPF).
>
> Because if you cut the ring in 1 place all nodes can still be reached.
> So no router will go down. If you cut it in 2 places you loose part of
> the ring and only get alerts for the nodes directly on the other side of
> the cuts from your perspective.
>
> If you alert on unreachable as well then you get all the alerts you
> tried to get rid of by introducing the parent relation in the first
> place. So don't use them.
>
> You need an additional means of detecting your first cut in the ring as
> all routers can still be reached at that time and you will never know
> you had a problem unless you alert on the actual link conditions.
>
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