Address the following issues that are related to replication and fault tolerance. 1. Explain the difference between the passive replication model and active replication model. 2. Explain the difference between the crash of a server and the Byzantine failure of a server. Assume the active replication and passive replication models are available for fault tolerance. 3. If s of s+1 servers crash, explain whether the passive or active model is still fault-tolerant. 4. If s of 2s+1 servers have byzantine faults, explain whether the passive or active model is still fault-tolerant. Question 2 Recall the internet Domain Name System (DNS), which is detailed in the Week 7 unit contents and practised by Week 8 and Week 9 lab tasks, and answer the following questions. 1. Explain the hierarchical structure/arrangement of the DNS servers. 2. If the Recursive Server-Controlled Navigation is used, explain the workflow when a client sends a name resolution request. 3. If you program/implement a DNS server in Java, what multi-threading strategy will you use? Justify your answer.