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2 CASE-BASED LEARNING IN
VNEL
VNEL uses a case-based approach, where students
are given a particular problem scenario to solve. They
then work through a sequence of scenarios and exer-
cises. Within each exercise are performance objec-
tives, activities, and feedback. Activities typically in-
clude a small problem, a topology, tasks, deliverables,
and self-assessments. Once students have completed
the exercises, they should be able to perform the ter-
minal activity: solving the case in the scenario.
Case-based learning was chosen as the instruc-
tional model because novices needed to learn how to
gain and refine their expertise at solving real-world
cybersecurity problems (Jonassen et al., 1999). In ef-
fective learning environments, that experience is scaf-
folded with expert case knowledge. A case serves
as a representation of real-world phenomena and is
a safe, yet meaningful environment in which students
can develop understanding of the complexity of net-
work engineering. Jonassen and Hernandez-Serrano
(Jonassen and Hernandez-Serrano, 2002) describe the
case-based reasoning cycle as the presentation of a
new problem-case to solve. Learners apply previ-
ous experiences and general knowledge to solve the
case, suggest solutions, test the solutions, revise their
suggestions, and confirm solutions. During the cycle,
learners retrieve, reuse, revise, and retain understand-
ing until expertise is gained from the problem-case.
For the case of a Firewalls course unit, task analy-
sis indicated that network engineers need to be able to
align a network topology with security requirements,
configure network access control, and protect infor-
mation through encryption and VPNs. Once students
have mastered each of the skills, they should be able
to address the case in the problem scenario.
2.1 Remote Device Access in VNEL
The VNEL is not a simulation or an emulated environ-
ment. Rather, students remotely manipulate real net-
works and receive real-world feedback when the net-
work works or does not work effectively. It is instruc-
tionally innovative in that it provides students with
remote but real-time access to equipment during net-
working experiments so that a a large number of stu-
dents can perform their experiments simultaneously
and at their convenience. It also provides a complete
instructional system including quizzes, automated as-
sessment of simple student submissions, and oppor-
tunities for students to work collaboratively on larger,
poorly structure or unstructured, case studies.
Figure 1 describes the architecture of the VNEL.
The facility is accessed through a single publicly vis-
ible server, the Web Access Exercise System (WAES).
Actual equipment is organized into pools that can
be assigned to exercises on-the-fly. The VNEL pro-
vides a set of network devices (switches, routers, or
firewalls) from a device pool and a set of hosts and
servers from a host pool. When students start an exer-
cise, the WAES brings in devices and hosts and con-
figures the network infrastructure accordingly. All de-
vices and hosts are connected through a virtual-LAN
capable switch infrastructure that can create whatever
connectivity is required by the exercises. This infras-
tructure cannot be seen by the students. Only the
connections established for the exercises are visible.
These connections are managed by the configuration
management component of the WAES.
The WAES provides five services:
Courseware Access and Management. This com-
ponent of the WAES provides access to traditional,
non-exercise related, course material. It provides stu-
dents with descriptions of case studies and links to
reference material. It also provides the courseware
framework for students to access the “hands-on” ex-
ercises. Finally, it also offers opportunities to author
quizzes and other assessment mechanisms.
Resource Configuration. Exercises are associated
with so-called resource sets, which define the network
devices and hosts needed for the particular exercise,
together with the interconnection topology as defined
by the exercise. Devices and hosts are selected from
their respective pools and are appropriately config-
ured when the student starts the exercise.
Resource Management. Since the resource sets
represent physical resources, and there are only lim-
ited numbers available thereof, students are encour-
aged to reserve the required resource sets in advance.
Students do this by scheduling a particular exercise
for a given time, and are therefore not aware of the
detailed reservation issues. Given that the VNEL is
used by multiple institutions, it is important to guar-
antee fair access to the available resources, both at
student level and at institution level. Individual stu-
dents, or groups of students at an institution, should
be flexible in how much time they want to spend on
some exercises. They should not be able, however, to
over-reserve resource sets at the expense of other stu-
dents or student groups at other institutions. We are
experimenting with hierarchical fair-share schedul-
ing algorithms to control over-allocation of resources.
Students and institutions are allocated a guaranteed
share of resources in number of reservation slots per
time period. Whenever the number of slots in share is
reached, no additional reservations are accepted until
the end of the period. For example, an institution may
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