Chapter 12 makeup
IP routing, Static and connected routes
IP routing defines how an IP packet can be delivered from the host at which the packet is created to the destination host. Hosts and routers participate in the IP routing process. The list summarizes a host’s logic when forwarding a packet, assuming that the host is on an Ethernet / wireless LAN. When sending a packet, compare the destination IP address of the packet to the sending host’s perception of the range of addresses in the connected subnet, based on the host’s IP address and subnet mask. If the destination is in the same subnet as the host, send the packet directly to the destination host. ARP is needed to find the destination host’s MAC address. If the destination host is not in the same subnet as the host, send the packet directly to the host’s default gateway. ARP is needed to find the default gateway’s MAC address. Routers use the following steps: the packet must first be received, whereas the sending host begins with the IP packet in memory. For each received frame, use the data-link trailer frame check sequence (FCS) field to ensure that the frame had no errors; if errors occurred, discard the frame and don’t continue to the next step. Check the frame’s destination data link layer address, and process only if addressed to this router or to a broadcast/multicast address. Discard the incoming frame’s old data-link header and trailer, leaving the IP packet. Compare the packet’s destination IP address to the routing table, and find the route that matches the destination address. This route identifies the outgoing interface of the router, and possibly the next-hop router. Determine the destination data-link address used for forwarding packets to the next router or destination host as directed in the routing table. Encapsulate the IP packet inside a new data-link header and trailer, appropriate for the outgoing interface, and forward the frame out that interface. Brief summary of the...
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