$4$A$)$ Write down the algorithm used to elect Designated Routers $($DR$)$ and Backup Designated Routers $($BDR$)$ in OSPF. $[9$ Marks$]4$B$)($i$)$ Explain the impact of LAN virtualization on your large local area network. $($ii$)$ What are the desirable features of VTP$?$ Explain the three modes of VTP operations $[8$ Marks$]4$C$)$ With the aid of a diagram explain how the Spanning Tree Algorithm is used to address frame looping problem in switch networks.