INT21CN Computer Networks

Tutorial #20

1. What are some of the standard security attacks which The Bad Guys can make against an Internet-connected computer system? What are the implications of "springboard" attacks for security of so-called "unimportant" systems?

2. What is meant by the term "packet filtering firewall"? Why would such a device be used? What are some of its limitations?

3. In the lecture, a diagram was presented showing a DMZ & Bastion Host firewall structure. Describe in detail how each of the two packet-filtering (firewall) routers would be configured in this structure.

4. The firewall examples given in the lecture all assumed a single point of connection between a business's internal network (or Intranet) and the outside Internet. How would the situation be complicated if there were multiple connections?

5. You have been asked to configure the Bendigo "gateway" router r-bgoatm34 to prohibit traffic from subnet 8 (ie, 149.144.8.0) from crossing the microwave link to Bundoora. Define an access list (address and mask pair) which will do this, using the syntax from the lecture.

6. The La Trobe "gateway" router blocks connections made to TCP port 80, except under certain conditions. What are these conditions?

7. The "Firewall and DMZ" configuration discussed in the lecture protects the "internal" hosts from most types of security attacks, but not all. For example, internal hosts could still be vulnerable to virus (various forms), worm and trojan horse attacks. Discuss these issues.

8. In the lecture, a minimal firewall structure was suggested whereby the "gateway router" (or host) for an organisation serves as in a similar function to a combined firewall and bastion host. This type of structure is sold by several vendors as an economical solution to Internet security. How would you expect the firewall/host system to be configured?

Discussion Questions

1. Imagine you are the network manager of a company which uses a DMZ/firewall configuration to secure its connection to the Internet. You discover that an employee has attached a modem to his office phone line so that he can dial in to his desktop computer to get access to his files so he can work at home.
   1. Is this a potential security risk for the company? Explain.
   2. What immediate action should you take in this situation?
   3. The employee has a legitimate need to work from home. How should you handle this? NB You're not expected to know the answer!

2. You are an honest student. One day you receive a letter from the University requiring you to see the IT manager about a serious security breakin which you appear to have been involved in. You've never done anything like this. What could be happening here, and how could you have become implicated?

3. (Philosophical Question) Discuss some of the legal and ethical questions alluded to in the last slide of today's lecture.