IP Routing | Network Layer Routing Logic Part 2

Network Layer Routing (Forwarding) Logic Our discussion is based on the way data travels from source to destination. During discussion, our focus will be on IP routing. In TCP/IP networking model, the main protocols at network layer are IPv4 and IPv6 and On of the main job of IP protocol is end-to-end delivery of the packets from source to destination However, IP is not responsible for physical transmission of packets. This is the responsibility of Lower layers to carry physical data. Host computer operating system has TCP/IP software. When users generate data and handover that data with the help of transport layer to the network layer, the network layer creates packets. The hosts use network layer software to decide where to send IP packet Host knows about hosts on the same network only. If the destination host is on the same network then packets are delivered using local media without router. If the host needs to communicate with a host outside his own local area network (LAN) then it contacts with a router available on his own network – called default router Appropriate frame format is used to send packet from host to the router. The gateway and the host should have IP address in the same local area network. If the host needs to communicate with a host outside his own Local Area Network. It contacts with a router available on his own network – called default router Appropriate layer-2 frame format is used to send packet from host to the router Data link layer at router check for error using FCS field, it discards it, if there are errors and process it, if there are no errors. Ethernet header has layer-2 address of router interface. All routers maintain a routing table. Routing Table is a database about the possible paths to reach IP destinations It combines IP addresses into IP subnets Looking at destination IP address, the router finds the interface to forward the packet to destination, this process is known as ROUTING If the destination network is not directly connected. Router forwards the packet out the interface serial 0 to router R1 with IP address 192.168. 2. 7 At R1, if the destination network is not directly connected. Router forwards the packet out the interface Fast Ethernet 0/0 to router R2 with IP address 192.168. 3. 1 If the destination network is directly connected, router forwards the packet out the interface Gigabit Ethernet 0/0 to destination MAC of PC2 Router learns the Layer-2 address by ARP protocol #IPRouting #NetworkLayerRouting