[hobbit] Extension of bbmrtg.pl: check on link down

[W.J.M. Nelis]

>> Attached is the list of modifications in bbmrtg.pl.
>>     
>
> that's a good start, but it doesn't take a few things into
> consideration:
> 1.  what if snmp V3 is in use instead of snmp V2?
> 2.  What if each router uses a different snmp community string?
>   
In both cases, one can use the condition (input == 0 && output == small) 
as sufficient to signal an error condition, thus skipping the SNMP 
(double) check. In my experience, this gives hardly any false positives. 
In our network, about 300 connections are checked in this way, of which 
about 100 are configured without an SNMP check.

> 3.  how do you score it if there are more than one interfaces associated
> with a bb*host?
>   
We have collected all the inter-switch links (trunks) on one switch in 
one test, called "trunk". It shows one graph, including is status green, 
yellow or red,  per trunk on that switch. The failing trunks are shown 
at the top of the page. The status of the test <switch>.trunk becomes 
the worst status of all trunks on that page.

> I think you are going to need a bit more logic to make it generally
> useful.
>   
I am wondering what you mean which "generally". This modification is 
intended to be used in specific situations. In our case redundancy build 
in the network may mask the failure of one connection (trunk). The users 
won't notice the failure, but the network administrator should know 
about it. On the other hand, I think the extension to bbmrtg.pl is 
generally usable for those who have this specific need.

  Wim Nelis.
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