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Slide 1

• Repetition: IP Forwarding • Definitions ▪ All nodes take forwarding decisions ▪ Only the destination IP address is considered traditionally ❖ Today, partially additional policies • Two general forwarding types ▪ Destination node is part of the same subnet ❖ Direct forwarding ▪ Destination nodes is reachable via Router/Gateway nodes only ❖ In-direct forwarding via multiple Routers ❖ Address packet to next Router on layer below IP

Slide 2

• What is a Router? • A device to couple networks on the network layer • Allows ▪ Communication of end systems via one or more subnetworks ▪ Routing, i.e., determining the “best” path to a certain destination ▪ Forwarding of packets based on unique, ideally hierarchical network addresses ▪ Segmentation and reassembly in IPv4 to support different PDU sizes of underlying MAC layer ▪ Security mechanisms to control the access to the network based on IP addresses (Firewalls)