While complete data-link layer failures are relatively easy to identify and
rectify, it is much more difficult to isolate problems caused by suboptimal
Layer 2 operations. The fact that some, or all, frames do actually reach their
destination can make it difficult to determine the boundary of the problem and
focus on the devices or link causing the problem. There are two distinct types
of suboptimal Layer 2 operation that can occur in a network:
- Frames take an illogical path to their destination, but do arrive.

- Some frames are dropped.
Although these are different problems that can be caused by Layer 2 or
Layer 1 faults, or design issues, they share some similar symptom:
- Network delays.
- Lack of throughput.
- Poor network application performance.
It is important to remember that the loss of some frames can be
tolerated by many applications, since TCP will retransmit the lost segment. For
delay sensitive traffic such as voice, video, or SNA (IBM developed networking
environment), suboptimal levels of performance can actually bring the
application to a halt.
An example of a problem which would cause frames
to take an suboptimal path through the network would be a poorly designed Layer
2 spanning-tree topology. In this case, the network might experience high
bandwidth utilization on links that should not have that level of traffic.
Problems that cause frames to actually be dropped can be identified through
error counter statistics and console error messages that appear on the switch
or router. In an Ethernet environment, an extended or continuous ping will also
reveal if any frames are being dropped.
