We have discussed the problems in network security. We have not discussed every vulnerability that exists in network security but have tried to group them, as most are similar. We have seen that some of these attacks can be mounted from an unprivileged mode. Having introduced Ethernet, we continued to illustrate some problems with its multiple access and broadcast system. We have provided this discussion both in theory and with illustrations of how these attacks can be mounted. In the next chapter, we show how the issues discussed in the last two chapters can be applied in real-life break-ins.