Building a layer-3 topology is relatively easy because routers must be
explicitly aware of their neighbors in order to perform their basic function.
Therefore, standard routing information is adequate to capture
and represent layer-3 connectivity. Unfortunately, layer-3 topology
covers only a small fraction of the interrelationships in an IP
network, since it fails to capture the complex interconnections of
layer-2 network elements (e.g., switches and bridges) that comprise
each subnet. As more switches are deployed to provide
more bandwidth through subnet microsegmentation, the portions
of the network infrastructure that are invisible to a layer-3
mapping will continue to grow. Under such conditions, it is obvious
that the network manager’s ability to troubleshoot end-toend
connectivity or assess the potential impact of link or device
failures in switched networks will be severely impaired.
The lack of automated solutions for capturing physical (i.e.,
layer-2) topology information means that network managers are
routinely forced to manually input such information for each
management tool that they use. Given the dynamic nature and
the ever-increasing complexity of today’s IP networks, keeping
track of topology information manually is a daunting (if not impossible)
task. This situation clearly mandates the development
of effective, general-purpose algorithmic solutions for automatically
discovering the up-to-date physical topology of an IP network.
An additional challenge in the design of such algorithms
is dealing with the lack of established, industry-wide standards
on the topology information maintained locally at each element
and the diversity of elements and protocols present in today’s
multi-vendor IP networks. The combination of these factors implies
that any practical solution to the problem of discovering
physical IP topology needs to deal with three fundamental difficulties.
1. Limited local information.
2. Transparency of elements across protocol layers.
3. Heterogeneity of network elements.