Even if end-to-end connectivity at the transport layer is
verified, there can still be issues on the network that
cause connections to applications to fail. These issues are
usually rather difficult to discover and troubleshoot and
are related to data traffic load and network delay. The
difficulty with these issues comes from the fact that they
are difficult to reproduce and can be temporary in
nature, caused by short spikes in network traffic.
Networking tools such as iperf can be used to
dynamically generate traffic and perform load stress on
the network to ensure that large amounts of data can be
transported between the source and destination.
Implementing quality of service (QoS) throughout the
network can help with these problems. With QoS, traffic
is categorized in different buckets, and each bucket gets
separate network treatment. For example, you can
classify traffic such as voice and video as real-time traffic
by changing QoS header fields in the Layer 2 data frames
and Layer 3 packets so that when switches and routers
process this type of traffic, they give it a higher priority
and guaranteed bandwidth, if necessary.
At the application layer, network tools such as tcpdump
can be used to capture actual data traffic received on any
of the network interfaces of either the source device or
the destination device. Comparing between sent and
received data can help in troubleshooting connectivity
issues and determining the root cause of a problem. Slow
or no responses at the application layer could indicate an
overloaded backend database, misconfigured load
balancer, or faulty code introduced through new
application features.
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