There have been multiple posts on this and looks like a feature request also (sorry new to Thwack).
The basic idea is a way to report and alert on bandwidth across two devices as an aggregate.
An example would be: two routers, A and B, each with one 50M circuit. It would be nice to monitor and alert based on the aggregate (100M) of the two circuits.
Alert me when the 100M aggregate reaches/exceeds 85%.
I did a search on Aggregate bandwidth, one is recent from me and here are a few others:
aggregate utilization feature request NPM
Aggregate Bandwidth Usage w/ Universal Device Poller
Aggregate Bandwidth Alerts
Thanks