I’m working on a networking exercise and need support to help me learn.

1. In this chapter we have described sequence numbers between a sender and receiver as a way to protect a communication stream against substitution and replay attacks. Describe a situation in which an attacker can substitute or replay in spite of sequence numbers. For which type of sequence numbering—one general stream of sequence numbers or a separate stream for each pair of communicators—is this attack effective?

4. You are designing a business in which you will host companies’ websites. What issues can you see as single points of failure? List the resources that could be involved. State ways to overcome each resource’s being a single point of failure.

6. How can hardware be designed for fault tolerance? Are these methods applicable to software? Why or why not?

9. The OSI model is inefficient; each layer must take the work of higher layers, add some result, and pass the work to lower layers. This process ends with the equivalent of a gift inside seven nested boxes, each one wrapped and sealed. Surely this wrapping (and unwrapping) is inefficient. (Proof of this slowness is that the protocols that implement the Internet—TCP, UDP, and IP—are represented by a four-layer architecture.) From reading earlier chapters of this book, cite a security advantage of the layered approach.