Network layer problems include any problem that involves a Layer 3 protocol,
including both routed and routing protocols.
This
module will focus primarily on IP routing protocols.
Problems at the
network layer can have the following affects on a network:
- Network failure
- Failure to perform optimally
Network failure is when the network is nearly or completely
nonfunctional, affecting all users and applications using the network. These
failures are usually noticed quickly by users and network administrators, and
are obviously critical to the productivity of a company.
Network
optimization problems can be more difficult to discover and sometimes harder to
diagnose. These problems usually involve a subset of users, applications,
destinations, or a particular type of traffic. Optimization issues in general
can be more difficult to detect and even harder to isolate and diagnose as they
usually involve multiple layers or even the host computer itself. Determining
that the problem is a network layer problem can take time. Aspects of network
optimization are discussed in more detail in the module "Layer 1–7
Troubleshooting".
Many of the problems discussed in this module can
apply to both network failures and optimization problems, depending upon the
scenario and configuration of the actual network.
Not all of the
information in this module has to do with troubleshooting routing problems.
This module also contains information regarding routing optimization, which
includes some additional information on how the routing table process operates.
Understanding the routing table process is helpful when troubleshooting certain
situations, so that the cause of the problem is understood, not just how to
solve it.