checking internet connectivity

[nagios at mm.quex.org]

On Tue, Oct 26, 2004 at 12:38:18PM +0200, Moritz Both wrote:

> Please excuse me if this is a frequently discussed question; i have 
> searched but found it difficult to find good search terms:
> 
> How do folks check Internet connectivity?
> 
> - Do you simply ping www.google.com or something?
> 
> - Is pinging third party hosts considered unfriendly since we use their 
> bandwidth? (Do you ping hosts you dislike for this reason? :)
> 
> - Is there a best practice for that?
> 
> - Even Google can vanish, but in that case we still would like to check 
> our services.

Usually you'd use your default gateway.  If you're in a position
where you have multiple gateways with automagical failover, you
could either create a special check to test all of them and report
okay if any of them is up, or pick some other part of your network
provider's core infrastructure.  Some people do get annoyed at
having random hosts pinging them all the time, but most ISP's would
not have too much of an issue with their customers doing it.

For our network, I use our upstream provider's network core (which
all our traffic goes through), and then the external network IP
of the internet gateway at our locations in either cities.  If
there's a fault "somewhere on the internet", then we'll see it
as the gateway for a particular remote location being down (or
multiple remote locations, if it's a big fault).  We can then
investigate further ourselves to see exactly where the problem is.
If our provider implodes, we should see their core as being the failure
point (whether it's because it failed, or just our link to them failed).

Basically, just run a traceroute to the target and pick a hop that
looks important.  It's a good idea to do a few of these at different
times over the course of a week or so; you should pretty easily be
able to work out which ones are always there and which ones aren't.

Alternatively, you could ask your upstream to provide a suitable
host you can use to check your connectivity.


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