Why an IP layer?
The internetworking problem
Scaling to data-link technologies
Scaling to network size
Uncommon MAC address spaces
A layer-3 solution to internetworking
IP: Scaling to data-link technologies
IP: Scaling to network size
IP: Uncommon MAC address spaces
Directly connected IP hosts
Indirectly connected IP hosts
Encapsulation
Demultiplexing
Internet addresses and port numbers
IP software at end hosts
An example
IP Software at routers
Network programming
Basic socket calls for a client
Basic socket calls for a server

IP Software at routers

The software at routers is mainly used for routing and datagram forwarding. Each router is running at least a “routing protocol” to construct a routing (or forwarding) table. Each entry in a routing table consists of IP destination address and the next-hop’s IP address. Upon receiving a datagram, a router forwards it based on a set of forwarding rules and the routing table.