I would like to buy or d/l an application that will alert our sysadmin in the event of network failure, like via email and/or phone call. I've looked around the net before posting this question, but I have one main concern: if our network goes down, how can a network monitoring application send email to alert us that it's down? Doesn't this have to be an external application that looks at our network from outside?

Well anyway, I want to find something that will handle this for us - freeware if possible, sice we're not looking for heavy analysis - just simple alerts. Advice is appreciated.