ipSentry provides a method to set devices to be checked depending on the status of another device.  This feature is known as a dependency.

Say for instance that you are monitoring several web servers that reside on the other side of a critical router.  There may be no need to attempt access to the web servers if you know the router is non-functioning.  This presents us with an ideal case for a dependency structure where the web servers should not be checked if the router is down.

In this example, we will make a couple of assumptions.

• You have already configured three web server entries for the servers WEB_A, WEB_B, WEB_C

• You have configured a monitoring entry for ROUTER_A using simple ICMP-Ping.

• You have configured the alert functions of each.

The only task remaining is to tell ipSentry that WEB_A, WEB_B, and WEB_C should only be checked if ROUTER_A is accessible.

To accomplish this, the following steps provide the quickest solution.

1. From the ipSentry active display console, select Action, Edit Devices.
    

2. Drag WEB A device onto ROUTER A

3. Drag WEB B device onto ROUTER A

4. Drag WEB C device onto ROUTER A
    

The above will cause the following scenario to exist.

ROUTER_A is checked
If OK then WEB_A, WEB_B, and WEB_C are checked.
Otherwise, if ROUTER_A fails, the alerts are triggered and WEB_A, WEB_B, WEB_C are skipped due to ROUTER_A failure. 

This avoids having alerts generated on devices that can not be reached due to a failure in front of them in the network.

This can go even a step further such that ROUTER_A is dependent on yet another device - ROUTER_B. You can then simply drag ROUTER A onto ROUTER B. This would then cause the following scenario.

ROUTER_B is checked.
If OK - ROUTER_A is checked
If OK - WEB_A, WEB_B, and WEB_C are checked.

Notice that in the above case, WEB_A, WEB_B, WEB_C are only checked if BOTH ROUTER_B and ROUTER_A are accessible.

Note:  The limit of nesting level of dependencies is 50 devices but the number of devices that can be tied to a parent is not limited.