When you trunk two interfaces together, it creates a third virtual interface that is the “trunk interface”. This may also be called the “Link Aggregate Group” (LAG) interface.

Let’s say you need more bandwidth between two switches, and you already have a 1gig link between these switches.

It would be really expensive to have to replace both switches with ones that had 10gig links.

The intermediary solution is to group two 1gig connections together as a “trunk” and allow 2gigs of bandwidth to flow between the switches. This also provides redundancy so if one of the 1gig connections go down, you don’t lose all connectivity between the switches.

Different manufacturers call “trunking” by different names:

• Cisco calls theirs “EtherChannel”
• Avaya calls their “Multi-Link Trunking”
• Huawei calls theirs “EtherTrunk”

Historically, you could only trunk between the same manufacturer’s switches since the trunking protocols were proprietary. Eventually, standards were adopted so trunking can occur between different manufacturers. This virtual interface may or may not show any statistics, so the value in monitoring these interfaces is manufacturer specific. See if utilization or error counts exist on the interface to determine if there is any value to monitoring.

Additional details on Wikipedia:  https://en.wikipedia.org/wiki/Link_aggregation