attempt to change the configuration. Atomicity is very
important to ensure a holistic and uniform view of the
network and to make sure that partial and incomplete
configurations do not negatively affect the functionality
of the network.
Another consideration with network controllers involves
auditing and managing the configuration drift of the
network elements. Configuration drift happens when the
configuration of a network device has changed from its
intended state, which means the configuration of the
device in the network controller is different from the
configuration of the device itself. This situation can easily
lead to inconsistencies and unexpected network
behavior. A good controller has built-in mechanisms to
address configuration drift; in some instances these
mechanisms go as far as limiting or even blocking device
configuration changes.
The main advantage provided by network controllers is
that the abstraction and central administration of
individual network devices eliminate the need for device-
by-device configuration, management, and monitoring,
as shown in Figure 15-1.