Computer Information System

1

CSCI351 Assignment 4

Due by: 11:59PM on April 9, 2021 (Friday)

Instruction:

• Show your work (at least 50% penalty otherwise)

• Submit a single PDF document containing all your answers to the corresponding
assignment folder under D2L (at least 10% penalty otherwise)

• Make sure if you submitted the intended one. It is recommended that you
download what has been uploaded and double-check if the correct document has
been submitted.

• You can submit as many times as you want, but the last submission will only be
graded. If the last submission is made after the deadline, there will be a late
submission penalty.

• No plagiarism: Do not copy and paste any from textbooks and other resources to
answer questions (Zero points will be given otherwise).

• No resubmission/extension request will be accepted.

Problem 1. Firewall Configuration (30 pt.)

Suppose a home network with a network address of 129.100.5.* (i.e.,
129.100.5.0/24).The IP addresses of the Web server and email server are 129.100.5.1
and 129.100.5.2, respectively. Assume that the Web server’s port number is TCP/80 and
the email server’s port number is TCP/25. Configure the firewall table to implement the
following ruleset.

Ruleset:

1. Allow external users to access the internal web server.
2. Internal users can access external web servers (i.e., TCP/80).
3. Allow external users to send email in.
4. Internal users can access a specific external service with TCP port number 8080

(i.e., TCP/8080).
5. Allow UDP connections with destination port number 6700 to the internal network

(i.e., UDP/6700).
6. Everything not previously allowed is explicitly denied.

Rule Type Source
Address

Dest.
Address

Dest.
Port

Action

1

2

3

4

5

6

2

Problem 2. Intrusion Detection (20 pt.)

Suppose 10,000 events including 9,900 for benign (negative) and 100 for malignant
(positive). From the evaluation of a newly developed IDS system, the developer observed
that 10 (out of 9,900) benign events were incorrectly classified into malignant, while 3 (out
of 100) malignant events were wrongly classified into benign.

a. (10 pt.) Construct the confusion matrix (as shown in the slide of “Possible Alarm

Outcomes”).

Intrusion Attack No Intrusion Attack

Alarm
Sounded

No Alarm
Sounded

b. (5 pt.) Calculate accuracy using the formula given.

Accuracy = (TP+TN) / (TP+TN+FP+FN)

c. (5 pt.) Calculate false positive rate using the formula given.

False positive rate = FP / (TN+FP)