This lecture brifly describe on Exterior Routing Protocols and Multicasting. Multicasting means sending message to multicast address. Multicast address refers to a group of hosts. Here also focus on the problems with Distance-Vector and Link-State Routing and Path Vector Routing. Finally explain Boarder Gateway Protocol, which allows routers (gateways) in different ASs to exchange routing information, Inter-Domain Routing Protocol (IDRP), Multicasting within LAN, Requirements for Multicasting and Internet Group Management Protocol.